Malaysia Transmission System Reliability Standards

Transmission System Reliability Standards Effective January 1, 2006

Version 2.0 Edition 1.0

© TENAGA NASIONAL BERHAD, 2006

Contents TRANSMISSION SYSTEM RELIABILITY STANDARDS ........................................1 CONTENTS........................................................................................................................1 CHAPTER 1: INTRODUCTION.....................................................................................4 1.1 1.2 1.3

GENERAL ..............................................................................................................4 APPLICATIONS AND OBJECTIVES OF THE STANDARDS ...........................................5 SCOPE ...................................................................................................................6

CHAPTER 2: GENERATION RELIABILITY STANDARD ......................................8 2.1 GENERATION PLANNING SECURITY CRITERIA ......................................................8 2.2 REQUIREMENTS ASSOCIATED WITH LOSS OF POWER INFEED ................................8 2.3 GENERATION CONNECTION CRITERIA...................................................................9 2.3.1 General Generation Connection Requirements...............................................9 2.3.2 Planning Criteria for Generation Connections .............................................10 2.3.3 Operational Criteria for Generation Connections ........................................13 CHAPTER 3: TRANSMISSION RELIABILITY STANDARD.................................14 3.1 GENERAL ............................................................................................................14 3.2 TRANSMISSION ADEQUACY AND SECURITY CRITERIA ........................................15 3.2.1 Planning Criteria ...........................................................................................15 3.3.2 Operational Criteria ......................................................................................18 3.2.3 Mitigating Unsecured Contingency Events ...................................................21 3.3 DEMAND CONNECTİON CRİTERİA .......................................................................23 3.3.1 General ..........................................................................................................23 3.3.2 Planning Criteria ...........................................................................................23 3.3.3 Operational Criteria ......................................................................................24 CHAPTER 4: PERFORMANCE CRITERIA AND LIMITS .....................................25 4.1 INTRODUCTION ...................................................................................................25 4.2 VOLTAGE ............................................................................................................25 4.3 VOLTAGE PERFORMANCE MARGİN .....................................................................28 4.4 FREQUENCY LİMİTS ............................................................................................29 4.5 STABİLİTY LİMİTS ...............................................................................................29 4.6 FAULT CLEARİNG TİMES .....................................................................................30 4.7 SHORT-CIRCUIT LIMITS ......................................................................................30 4.8 BASİC INSULATİON LEVEL ..................................................................................31 4.9 CRİTERİA FOR EVALUATİNG UNSECURED CONTİNGENCİES ................................32 4.10 THERMAL LOADİNG LİMİTS OF TRANSMİSSİON COMPONENTS ............................33 4.11 SUMMARY OF TRANSMISSION SYSTEM REQUIREMENTS – NORMAL AND EMERGENCY CONDITIONS...............................................................................................33

Transmission System Reliability Standards

Contents

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TRANSMISSION SYSTEM POWER QUALITY STANDARDS ..............................36 CONTENTS......................................................................................................................37 CHAPTER 1: INTRODUCTION...................................................................................38 1.1 1.2

POWER QUALITY DEFINITION AND REQUIREMENTS ............................................38 SCOPE .................................................................................................................40

CHAPTER 2: TRANSMISSION POWER QUALITY STANDARDS.......................41 2.1 2.2 2.3 2.4 2.5 2.6

VOLTAGE SAG OR VOLTAGE DIP ........................................................................41 VOLTAGE STEP CHANGE .....................................................................................42 VOLTAGE FLUCTUATİONS AND FLİCKER .............................................................42 HARMONICS ........................................................................................................44 PHASE UNBALANCE AND TRACTION LOAD .........................................................46 STEP CHANGES OF POWER ..................................................................................49


Contents

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GLOSSARY AND DEFINITIONS FOR TRANSMISSION SYSTEM RELIABILITY STANDARDS AND TRANSMISSION SYSTEM POWER QUALITY STANDARDS ...............................................................................................50 APPENDIX A – BACKGROUND TO THE STANDARDS ........................................66 A1 PURPOSE ...................................................................................................................67 A2 STANDARDS FOR BULK GENERATION, TRANSMISSION AND DELIVERY .....................70 A3 STANDARDS FOR DISTRIBUTION ................................................................................71 A4 PROCESSES AND PROCEDURES ..................................................................................72 A5 SUMMARY .................................................................................................................77 APPENDIX B FOR TRANSMISSION SYSTEM RELIABILITY STANDARDS – GUIDANCE ON ECONOMIC JUSTIFICATION OF GENERATION AND TRANSMISSION CONNECTIONS..............................................................................79 B1 GENERAL PRINCIPLES ................................................................................................80 B2 GUİDELİNES ...............................................................................................................80 APPENDIX C FOR TRANSMISSION SYSTEM RELIABILITY STANDARDS – GUIDANCE ON SUBSTATION CONFIGURATIONS AND SWITCHING ARRANGEMENTS .........................................................................................................82 C1 GENERAL GUİDANCE .................................................................................................83 C2 GENERATİON POİNT OF CONNECTİON SUBSTATİONS .................................................84 C3 MARSHALLİNG SUBSTATİONS....................................................................................84 C4 GRİD SUPPLY POİNT SUBSTATİONS ...........................................................................84 C5(1) TYPICAL TNB SUBSTATION LAYOUT AND SWITCHING ARRANGEMENTS .............86 C5(2) TYPICAL TNB SUBSTATION LAYOUT AND SWITCHING ARRANGEMENTS – CONT’D ........................................................................................................................................87 APPENDIX D FOR TRANSMISSION SYSTEM RELIABILITY STANDARDS – ADDITIONAL CRITERIA TO LIMIT THE COMPLEXITY OF TRANSMISSION CIRCUITS ........................................................................................................................88 D1 GENERAL PRINCIPLES ...............................................................................................89 D2 REQUİREMENTS/RESTRİCTİONS .................................................................................89


Contents

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Chapter 1: Introduction

1.1

General

1.1.1

In large interconnected Electric Power Systems its Reliability is of utmost importance as electricity is an essential commodity, which underpins the economic activity of a country. The Transmission Function of an Electric Power System is pivotal to the objectives of: a) Developing and maintaining an efficient, coordinated and economical Transmission System for bulk delivery of electrical energy; b) Ensuring continuous availability of sufficient electrical energy supply for all consumers, with an adequate margin between supply and demand.

1.1.2

The distinct processes and their related Standards are paramount in ensuring Reliability in planning the development of an Electric Power System, and in ensuring its Secure and Robust operation: 1) The Generation Reliability Standard which relates to provision of sufficient firm Generation Capacity to meet the Demand with a sufficient margin with allowance for Plant maintenance, Plant breakdown and Plant Unavailability, i.e., scheduled and unscheduled generating Plant outages, to meet the annual and daily electric energy demand without the need to disconnect customers at critical periods or cause interruptions in supply. This is used by Tenaga Nasional Berhad (TNB) to determine additional generation investment requirements on an annual basis. 2) Transmission Reliability Standard which relates to provision of sufficient Transmission Capacity, operational facilities, maintenance activity and coordination with generation and Distribution Functions to enable continued supply of electric energy to the distribution systems and Directly Connected Customers. This Standard is used by TNB to determine the investment requirements for the Transmission System and transmission operational facilities and implement the necessary measures. The development and maintenance of Transmission System Reliability Standards is the duty of TNB Transmission Division under the provisions of the TNB Licence that includes Generation Reliability Standards. These Standards are also termed as License Standards.


Chapter 1:Introduction

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1.1.3

This Standard contains technical terms and phrases specific to Transmission Systems and the Malaysian Electricity Supply Industry. The meanings of some terms or phrases in this Standard may also differ from those commonly used elsewhere. For this reason a ‘Glossary and Definitions’ has been included as a separate document but attached to these Standards. All defined terms have been identified in the text by the use of capitalised words.

1.1.4

Appendix A provides a background the Standards as well as general principles of its applications.

1.2

Applications and Objectives of the Standards

1.2.1

The electric power Transmission System needs to be planned, operated and maintained according to a set of Transmission System Reliability Standards. The development of these Standards determines the investment requirements for capital Plant and operational facilities; operation and maintenance practices; as well as provision of Supplementary Services. The provision of levels of Transmission System performance in accordance with these Standards is the duty of TNB Transmission Division as specified in TNB License Conditions.

1.2.2

The transmission planning process involves the application of the Transmission System Reliability Standard and the Transmission System Power Quality Standard (as the second Standard within this combined document), together with strategic, environmental and economic analysis, to determine the planned development of the Transmission System to meet the forecast future demand.

1.2.3

The operational processes involve application of these Standards in operational planning, maintenance and actual operation of the Electric Power System under the Prevailing System Conditions on the actual operational day. Whilst the System operational conditions are carefully planned at the operational planning stage, in the months, weeks and days ahead, the operation of the System on the day is dictated by the actual prevailing climatic conditions, planned outages as well as the unplanned events that occur on the day, such as unscheduled generation breakdown, unplanned transmission outages due to faults and exceptional demand.

1.2.4

The Standards also provide the limits and permissible excursions of key System parameters enabling secure implementation of operational measures.



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1.2.5

The above-mentioned transmission Standards therefore determine a defined level of Reliability for electric power that is delivered at the bulk demand supply points at the interface between the Main Interconnected Transmission System (MITS) and the 132kV and 66kV Systems, as well as other parts of the Transmission System and the Distribution Systems at 33kV and below.

1.3

Scope

1.3.1

This document only covers the Transmission System Reliability Standards, which are the responsibility of TNB Transmission Division. Amendments or changes to these Standards can only be made with the concurrence of the Energy Commission (EC) as provided for in the TNB License.

1.3.2

This document is solely concerned with the Standards for the Transmission System, which includes the Main Interconnected Transmission System (MITS) and its interface with the Generation Systems as well as the other parts of the Transmission System which have voltages at 132kV and 66kV. These Standards are applicable to bulk generation, transmission and delivery of electric power. These Standards are also reflected in the Malaysian Grid Code which contains all the technical requirements governing the planning, the development, connection to, and operation of, the Generation and Transmission System as a whole known as the Grid System.

1.3.3

Figure 1.1 indicates the contents of the Standards and the subject coverage in terms of the generation, transmission and distribution Security and Reliability.



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TOTAL POWER SYSTEMS

G

G Generation Reliability Standards

Sufficient generation capacity and connections to deliver full generation output for normal and Specific contingencies


Sufficient transmission capacity to meet demand for specified contingencies Meeting standards performance limits

Transmission Reliability Standards

Criteria for planning, designing and operating of transmission system to meet reliability and power quality standards

Transmission

Transmission radial network and demand points

Transmission Power Quality Standards

Sufficient transformer capacity to meet demand Power quality limits at interfaces

DG

Distribution System

Distribution Supply Security and Power Quality Standards

DG

Distribution

Embedded Distribution

Customers

STANDARDS

Criteria for planning, designing and operating of distribution system to meet supply security and power quality standards

CODES

DISTRIBUTION CODE

Main Interconnected Transmission System

GRID CODE

Generation

Figure 1.1: The outline contents of the Transmission System Reliability Standards and its relationship with the systems and codes



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Chapter 2: Generation Reliability Standard

2.1

Generation Planning Security Criteria

2.1.1 The Generation Security Standard for the Peninsular Malaysia Electric Power System shall be the Reliability Index of Loss of Load Probability (LOLP). LOLP is defined as the proportion of days per 365 days in a year when insufficient generating capacity is available to serve the daily peak Loads. Alternatively, the standard can also be defined in term of Loss of Load Expectation (LOLE) which is a measure of the time duration in a year when insufficient generating capacity is available to serve the daily peak Loads. Normally, this is expressed in number of days per year. For the Peninsular Malaysia Grid System the LOLE is normally set at one (1) day per year, which translates to a LOLP of 0.0274 (ratio of LOLE to number of days in a year).

2.2

Requirements Associated with Loss of Power Infeed

2.2.1

The Transmission System shall be designed to be secure for the instantaneous Loss of Power Infeed represented by the output of a single Generating Unit, CCGT Module, imports of power from External Systems or DC Link Monopole as a result of a Secured Contingency Event. Following such an event the System Frequency shall return to its Normal Operational Limits defined in the Transmission System Power Quality Standard within sixty (60) seconds and the System shall operate within normal voltage and Frequency limits, in a stable manner both transiently and in the Steady State. There shall be: (1) no loss of demand; (2) no overloading of any transmission equipment; (3) no operation outside post contingency voltage limits; and (4) no excessive degradation of Voltage Performance Margins.

2.2.2

The Largest Loss of Power Infeed Risk for the Peninsular Malaysian Power System is defined as the largest single generating unit or a CCGT module or a DC Link Monopole or power import whichever is the largest. In order to ensure the System is secure after such an event, TNB facilitates the provisions of sufficient Spinning Reserve and Reactive Power Reserve to avoid deviation of Frequency and voltage beyond Normal Operational Limits defined in the Transmission System Power Quality Standard for more than sixty (60) seconds.


Chapter 2:Generation Reliability Standard

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2.2.3

The instantaneous Loss of Power Infeed may exceed that of the Largest Loss of Power Infeed Risk on very rare occasions which may occur for the loss of a complete Power Station for contingencies outside the planning or operational Criteria. This is termed an Infrequent Loss of Power Infeed Risk and is defined as the loss of the largest single power station. For an Infrequent Loss of Power Infeed Risk, planning and operational limits may be violated but the Transmission System shall be planned and operated so that while controlled load loss is allowed, the integrity of the Transmission System is maintained.

2.3

Generation Connection Criteria

2.3.1 General Generation Connection Requirements 2.3.1.1 This Section of Chapter 2 includes the planning and operational Criteria for the direct connection of one or more Power Stations to the Transmission System. The connection Criteria will also apply to the connections from a Demand Supply Point to the Transmission System by which Power Stations embedded within the Distribution System or within a User’s Network that are connected to the Transmission System. 2.3.1.2 In planning the Generation Connections, this Standard will be considered as met if the connection design either: (1) satisfies the minimum deterministic Criteria detailed in paragraphs 2.3.2.1 to 2.3.2.13 below; or (2) varies from the design necessary to meet item (1) so as to meet a higher Standard than those set out in paragraphs 2.3.2.1 to 2.3.2.13 below if the higher Standards can be economically justified or if they are specifically requested by an external party connecting to the Transmission System, to ensure a higher level of connection Security and Reliability, which will then be subject to appropriate commercial negotiation and contract. Guidance on the economic justification of generation connections is given in Appendix B. 2.3.1.3 The overarching principle in this Standard applicable to the generation connections is that the transfer capacity of the connection facilities for the following conditions: (1) normal System operation; (2) (n-1) contingencies; shall provide full export capability for the generation facility into the Transmission System by satisfying the following Criteria: (a) the continuous transfer capacity shall be at least equal to the Facility Contractual Available Capacity (in MW), and Transmission System Reliability Standards


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(b) the connection facilities and the Power Station shall not cause any reduction in the power quality delivered at the Bulk Supply Points to the Distribution System and/or to a User’s Network.

2.3.2 Planning Criteria for Generation Connections 2.3.2.1 The connection configurations for Generating Units need to be planned to minimise the effect of coincident Fault Outage(s) of generation and Transmission Circuits and for the risk of losing multiple Generating Units within a Power Station. 2.3.2.2 In this respect the Generating Unit connections define the magnitude of the largest generation loss risk for which dynamic Spinning Reserve will be provided to contain the Frequency deviation and restore the System Frequency to within limits defined by the Transmission System Power Quality Standard. Therefore, there is a requirement to provide sufficient switching facilities and sufficient connection capability to ensure adequate operational flexibility, and compliance with the Criteria defined below. 2.3.2.3 Generation connections shall be planned such that starting with an Intact System the consequences of System contingency events and design of generation connections to the Transmission System shall be as follows: (1) following a Fault Outage of any single Transmission Circuit, no Loss of Power Infeed shall occur; (2) following the arranged outage of any single section Busbar, the Loss of Power Infeed shall not exceed the Largest Loss of Power Infeed Risk; (3) following a Fault Outage of any single Generation Circuit or a single section of Busbar, the instantaneous Loss of Power Infeed shall not exceed the Largest Loss of Power Infeed Risk; (4) following the Fault Outage of any single Transmission Circuit, single section of Busbar, during the arranged outage of any other single Transmission Circuit or single section of Busbar, the Loss of Power Infeed shall not exceed the Largest Loss of Power Infeed Risk; (5) following the Fault Outage of any single Busbar coupler circuit breaker or Busbar section circuit breaker or mesh circuit breaker, during the arranged outage of any single section of Busbar or mesh corner, the Loss of Power Infeed shall not exceed the Largest Loss of Power Infeed Risk.



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2.3.2.4 The connection of a particular Power Station shall meet the following planning Criteria set out in paragraphs 2.3.2.5 to 2.3.2.8 under the following background conditions: (1) the Active Power output of the Power Station and individual Generating Units shall be set equal to their respective rated power output, and to the corresponding full leading or lagging Reactive Power output; and (2) conditions on the Transmission System shall be set to those which ought reasonably to be expected to arise in the course of a year of operation. Such conditions shall include forecast demand cycles, typical Power Station operating regimes and typical arranged transmission equipment outage patterns modified where appropriate by the provisions of paragraph 2.3.2.5. 2.3.2.5 The Transmission Capacity for the connection of a Power Station shall be planned such that, for the background conditions described in paragraph 2.3.2.4, prior to any fault there shall not be any: (1) equipment loadings exceeding their continuous rating; (2) voltages outside the Pre-Disturbance Planning Voltage Limits or Insufficient Voltage Performance Margins; or (3) System Instability. The above performance requirements are summarised in Table 4.12, in section 4.11, under system condition classified as Category A – No contingencies. 2.3.2.6 The Transmission Capacity for the connection of a Power Station shall also be planned such that for the background conditions described in paragraph 2.3.2.4 and for the Secured Event of either an Outage of any of the following: (1) a single Transmission Circuit or element, a reactive compensator or other Reactive Power resource; there shall not be any: a) Loss of Supply Capacity; b) Unacceptable Overloading of any Primary Transmission Equipment; c) Unacceptable Voltage Conditions or Insufficient Voltage Performance Margins; or d) System Instability. The above performance requirements, contingencies and impacts are summarised in Table 4.12, in section 4.11, under system condition classified as Category B – Events resulting in loss of a single element. 2.3.2.7 The Transmission Capacity for the connection of a Power Station shall also be planned such that for the background conditions described in paragraph 2.3.2.4 and for the Secured Event of a Fault Outage of any of the following:



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(1) a Double Circuit Overhead Line (with the exception of 500kV and radial 275kV lines), or (2) a single Transmission Circuit with the prior outage of another Transmission Circuit (with the exception of 500kV and radial 275kV lines); (3) a section of Busbar; or (4) a single Transmission Circuit with the prior outage of a Generating Unit, a reactive compensator or other Reactive Power resource; there shall not be: (a) cascade tripping; and (b) System Instability. Under the conditions described above, it is however acceptable for planned/controlled loss of load to occur. The above performance requirements, contingencies and impacts are summarised in Table 4.12, in section 4.11, under system condition classified as Category C – Events resulting in loss of two or more elements. 2.3.2.8 Under maintenance conditions it shall be assumed that the prior circuit outage(s) specified in paragraphs 2.3.2.7(1) and 2.3.2.7(4) reasonably form part of the typical outage pattern referred to in paragraph 2.2.2.4(2) rather than in addition to that typical outage pattern i.e., only a reasonable typical outage pattern will be assumed without any double counting or excessive and unrealistic outages being included. 2.3.2.9 In the event of a contingency more severe than those described in 2.3.2.3, 2.3.2.6 and 2.3.2.7 of this chapter which results in a total generation infeed loss up to the Infrequent Infeed Loss Risk the Frequency shall not fall below 47.5Hz, with all defence measures inplace and operational. System performance requirements, contingencies and expected impacts following more severe or extreme contingencies than those described in 2.3.2.3, 2.3.2.6 and 2.3.2.7 are summarised in Table 4.12, in section 4.11, under system condition classified as Category D – Extreme events resulting in two or more elements removed or cascading out of service. 2.3.2.10 Guidance on typical substation configurations and switching arrangements are described in Appendix C. However, other configurations and switching arrangements which meet those Criteria are also acceptable. 2.3.2.11 Variations, arising from a generation customer’s request, to the generation connection design necessary to meet the requirements of paragraphs 2.2.1 to 2.2.3 shall also satisfy the requirements of this Standard provided that the varied design satisfies the conditions set out in paragraph 2.3.2.12(1) to (3). For example, such a Transmission System Reliability Standards


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generation connection design variation may be used to take account of the particular characteristics of a Power Station. 2.3.2.12 Any generation connection design variation must not, other than in respect of the generation customer requesting the variation, either immediately or in the foreseeable future: (1) reduce the Security of the Transmission System to below the minimum planning Criteria specified in Chapter 3; or (2) result in additional investment or operational costs to any particular customer or overall, or a reduction in the Security and quality of supply of the affected customers’ connections to below the planning Criteria in this chapter or in the Transmission System Power Quality Standards, unless specific agreements are reached with affected customers; or (3) compromise TNB’s ability to meet other statutory obligations or licence obligations. 2.3.2.13 Should System conditions subsequently change, for example due to the proposed connection of a new customer, such that either immediately or in the foreseeable future, the conditions set out in paragraph 2.3.2.12(1) to (3) are no longer satisfied, then alternative arrangements and/or agreements must be put in place such that this Standard continues to be satisfied. 2.3.2.14 The additional operational costs referred to in paragraph 2.3.2.12(2) and/or any potential Reliability implications shall be calculated by simulating the expected operation of the Transmission System in accordance with the operational Criteria set out in Chapters 3 and 4 of this Standard. Guidance on economic justification is given in Appendix B.

2.3.3 Operational Criteria for Generation Connections 2.3.3.1 The operational Criteria for generation connections are the same as the operational Transmission System criteria which are set out in Chapter 3 of this Standard.



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Chapter 3: Transmission Reliability Standard

3.1

General

3.1.1

The Transmission System is and shall continue to be planned and developed such that, under both normal System operational conditions or following a Secured Contingency Event, there will be sufficient Transmission Capacity and capability available to enable the System to return to normal operation. Normal operation of the System in this respect means operation of the System within thermal, voltage, Frequency and stability limits.

3.1.2

In rare circumstances, disturbed System operating conditions involving multiple outages and/or equipment failures beyond the Secured Contingency conditions can occur. Usually the occurrence of such events, will result in a controlled or planned loss of load.

3.1.3

In some rare and extreme cases, Unsecured Contingency Events could also lead to partial or full disruption of the whole System and affect supplies to consumers. Under such adverse operating conditions, and as part of the special Protection and defence measures, some generation and/or demand disconnection is permitted to ensure stable operation of the remaining System in the post-contingency period.

3.1.4

This Chapter 3 includes: (1) the Transmission Adequacy and Security Criteria which ensures adequate Transmission Capacity so that the Security and integrity of the power System is maintained for a set of defined Secured Contingency Events; (2) the planning and operational measures that shall be applied towards mitigating the impact of rare events with multiple outages and/or equipment failures beyond the Secured Contingency conditions termed as Unsecured Contingency Events; and (3) the Demand Connection Criteria which ensures Adequacy of interface connection capacity to meet demand.

3.1.5

This Chapter 3 also presents the planning and operational Criteria for ensuring Reliability of the Transmission System. These Criteria apply throughout the Transmission System and must be met by TNB in planning and operating the Transmission System. In addition, in those parts of the Transmission System where the Criteria of Chapter 2 also apply, those Criteria must be met.


Chapter 3:Transmission Reliability Standard

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3.2

Transmission Adequacy and Security Criteria

3.2.1 Planning Criteria 3.2.1.1 The following System background conditions will be used to set up the base case for the planning studies to determine the adequate Transmission Capacity requirements for the Transmission System: (1) For the Intact System, the base case power flows shall be set to those arising from the Planned Transfer Condition prior to application of any fault or outage; (2) Conditions on the Transmission System shall be set to those which ought reasonably to be foreseen to arise in the course of a year of operation. Such conditions shall include forecast demand cycles, typical Power Station operating regimes and consideration on arranged transmission equipment outage. Rearrangement of transmission outages and appropriate reselection of Generating Units, from those expected to be available may be considered in order to satisfy the adequate Security Criteria provided that maintenance access for each Transmission Circuit can be achieved and provided that such measures are economically justified. Guidance on economic justification is given in Appendix B; (3) The expected Availability of generation reactive capability shall be set to that which ought reasonably to be expected to arise. This shall take into account the variation of reactive capability with the Active Power output as defined in the machine performance chart. Any long term reactive capability limitations and exemptions or derogations issued by the Energy Commission will be taken into account. The target reactive output of generators, at this stage, shall be set as close as possible to 50% of the expected available reactive capability; (4) The Planned Transfer Condition is defined as the condition arising from scaling the Registered Capacities of each directly connected Power Station and embedded Large Power Station such that the total of the scaled capacities is equal to the Peak Demand plus dynamic spinning reserve for Frequency control and minus imports from External Systems. This scaling shall be achieved by ranking all directly connected Power Stations and embedded Large Power Stations in order of likelihood of operation at times of Peak Demand. Those Power Stations considered least likely to operate at peak are progressively removed and treated as non-contributory until an Operational Plant Margin of 10% or just fractionally below is achieved. This is regarded as sufficient to meet the demand on the day with sufficient Plant to cater for unscheduled outages and Plant breakdown; Transmission System Reliability Standards


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(5) The output of contributing Power Stations will include its operating reserve which is calculated in accordance with their ability to provide dynamic spinning response based on the characteristics of the Plant at that Power Station; (a) for thermal units, a typical dynamic response of about 8%, if the actual response is not available; (b) for GT units, a typical dynamic response of 10%, if the actual response is not available; (c) for hydro units, equally proportionally part loaded to balance the demand, plus losses, plus interconnection infeed; (d) power imports from External Systems (e.g., Thailand and/or Singapore) shall be assumed to be at their typical values as indicated by reciprocal agreements for the base case Planned Transfer Condition; (e) a Load power factor of 0.9 or better shall be maintained, if the measured power factor is not avilable, at the 132kV side of the 132/33kV and 132/11kV transformers; and (f) for the Planned Transfer Conditions on the Transmission System there shall not be: (i) equipment loadings exceeding the pre-fault rating; (ii) voltages outside the Pre-fault Planning Voltage Limits or Insufficient Voltage Performance Margins; or (iii) system Instability, otherwise remedial planning measures to remove any violations will be considered. 3.2.1.2 The minimum Transmission Capacity of the Main Interconnected Transmission System shall be planned such that, for the background conditions described in paragraph 3.2.1.1, prior to any fault there shall not be: (1) equipment loadings exceeding the continuous current rating; (2) equipment Three-Phase Short-Circuit currents exceeding 90% of their ShortTime Current Ratings; (3) voltages outside the Pre-fault Planning Voltage Limits or Insufficient Voltage Performance Margins; or (4) System Instability. The above performance requirements are summarised in Table 4.12, in section 4.11, under system condition classified as Category A – No contingencies.



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3.2.1.3 The minimum Transmission Capacity of the Main Interconnected Transmission System shall also be planned such that for the background conditions described in paragraph 3.2.1.1 and for the Secured Contingency Event of a Fault Outage of a single Transmission Circuit or Element, a reactive compensator or other Reactive Power resource there shall not be any of the following: (1) Loss of Supply Capacity (except as permitted by the Demand Connection Criteria detailed later in this Chapter 3); (2) Unacceptable Overloading of any Primary Transmission Equipment; (3) Unacceptable Voltage Conditions or Insufficient Voltage Performance Margins; or (4) System Instability. The above performance requirements, contingencies and impacts are summarised in Table 4.12, in section 4.11, under system condition classified as Category B – Events resulting in loss of a single element. 3.2.1.4 The minimum Transmission Capacity of the Main Interconnected Transmission System shall also be planned such that for the background conditions described in paragraph 3.2.1.1 and for the Contingency Event of a Fault Outage of any of the following: (1) a Double Circuit Overhead Line (with the exception of 500kV and radial 275kV lines), or (2) a single Transmission Circuit with the prior outage of another Transmission Circuit (with the exception of 500kV and radial 275kV lines); (3) a section of Busbar or mesh corner; or (4) any single Transmission Circuit with the prior outage of another Transmission Circuit, Generating Unit, reactive compensator or other Reactive Power resource, there shall not be: (a) cascade tripping; and (b) System Instability. Under the conditions described above, it is however acceptable for planned/controlled loss of load to occur. The above performance requirements, contingencies and impacts are summarised in Table 4.12, in section 4.11, under system condition classified as Category C – Events resulting in loss of two or more elements. 3.2.1.5 In addition to the requirements set out in paragraphs 3.2.1.3 and 3.2.1.4, for the background conditions described in paragraph 3.2.1.1, the System shall also be planned such that operational switching of any component or part of the Main Interconnected Transmission System shall not cause: (1) Unacceptable Overloading of any Primary Transmission Equipment; Transmission System Reliability Standards


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(2) Unacceptable Voltage Conditions or Insufficient Voltage Performance Margins; (3) Any switchgear with duty exceeding 90% of its Short Circuit Break or Make capacity;or (4) System Instability. 3.2.1.6 Circuits comprising the Main Interconnected Transmission System shall not exceed the circuit complexity limit defined in Appendix D. 3.2.1.7 Guidance on substation configurations and switching arrangements are described in Appendix C. These guidelines provide an acceptable way towards meeting the Criteria of this Chapter 3. However, other configurations and switching arrangements which meet the Criteria are also acceptable.

3.2.2 Operational Criteria 3.2.2.1 The Main Interconnected Transmission System shall be operated under Prevailing System Conditions so that for the Secured Contingency Event of a Fault Outage of a single Transmission Circuit or Element, a reactive compensator or other Reactive Power provider there shall not be any of the following: (1) a Loss of Supply Capacity (except that under certain maintenance outage conditions, should an unplanned outage occur, some loss of Load can be accepted, and except as permitted in paragraph 3.2.2.3); (2) Unacceptably High or Low Frequency Conditions; (3) Unacceptable Overloading of any Primary Transmission Equipment; (4) Unacceptable Voltage Conditions; or (5) System Instability. The above performance requirements, contingencies and impacts are summarised in Table 4.12, in section 4.11, under system condition classified as Category B – Events resulting in loss of a single element. 3.2.2.2 The Main Interconnected Transmission System shall be operated under Prevailing System Conditions so that for Contingency Event of any of the following: (1) a Double Circuit Overhead Line (with the exception of 500kV and radial 275kV lines); or (2) a single Transmission Circuit with the prior outage of another Transmission Circuit (with the exception of 500kV and radial 275kV lines); or (3) a section of Busbar or mesh corner; or



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(4) any single Transmission Circuit with the prior outage of another Transmission Circuit, Generating Unit, reactive compensator or other Reactive Power resource, or (5) the most onerous Loss of Power Infeed there shall not be: (a) cascade tripping; and (b) System Instability. Under the conditions described above, it is however acceptable for planned/controlled loss of load to occur. The above performance requirements, contingencies and impacts are summarised in Table 4.12, in section 4.11, under system condition classified as Category C – Events resulting in loss of two or more elements. 3.2.2.3 The operational Criteria above are subject to the following exceptions: (1) Provided that it is in accordance with the appropriate requirements of the demand connections criteria in part 3.3 of this Chapter 3, there may be an associated Loss of Supply Capacity due to a Secured Contingency Event, for example by virtue of the design of the generation connections and/or the designed switching arrangements at the substations concerned. Typical examples of this could be: (a) at mesh substations where the loss of a Double Circuit Overhead Line would result in the consequential loss of mesh corner Demand Supply Point transformers; (b) Demand Supply Point transformers which are teed off circuits that form part of the Main Interconnected Transmission System and which would become disconnected following the loss of these circuits. (2) During periods of Severe Weather conditions or other high System risk periods, TNB Transmission Division may implement measures to mitigate the consequences of this risk. Such measures may include reducing output at certain Power Stations. 3.2.2.4 For the purposes of paragraph 3.2.2.2, it is acceptable to utilise short term post fault actions to avoid Unacceptable Overloading of Primary Transmission Equipment which may include a requirement for demand reduction; however this will not be used as a method of increasing reserve to cover abnormal post fault generation reduction. Where possible these post fault actions shall be notified to the appropriate Users. Normally the provisions of the Grid Code, in respect of Emergency Manual Demand Disconnection will be applied. Additional post fault actions beyond the Grid Code provisions may be applied, but only where they have been agreed in advance with the appropriate Users.



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3.2.2.5 Post-fault Restoration of System Security - Following the occurrence of a Secured Contingency Event measures shall be taken to re-secure the System to the above operational Criteria as soon as reasonably practicable. To this end it is permissible to put operational measures in place to facilitate the speedy restoration of System Security. 3.2.2.6 Authorised Variations From the Operational Criteria - The principles of these operational Criteria shall be applied at all times except in special circumstances where TNB, following consultation with the appropriate Network Operator, Generator or Directly Connected Customer, may need to give instructions to the contrary to preserve overall System integrity.



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3.2.3 Mitigating Unsecured Contingency Events 3.2.3.1 In rare circumstances, disturbed System operating conditions, with multiple outages and/or equipment failures beyond the Secured Contingency conditions can occur on the Transmission System. Such events can lead to partial or full disruption of the whole System and affect the Security and Adequacy of supplies to consumers. Reasonably predicting the full extent and nature of such events and hence putting sufficient investment in preventive measures is not fully possible even when excessively large capital investment is available. These types of events are therefore termed as Unsecured Contingency Events. 3.2.3.2 In practice however, TNB Transmission Division shall evaluate and install special protective measures and defence mechanisms such that the impact of the Unsecured Contingency Events is contained such that only part of the System may be affected with some generation and demand loss. 3.2.3.3 The Transmission System is and shall continue to be planned and developed such that special protective measures and defence mechanisms are included not only to prevent a total System shutdown but also to facilitate rapid recovery to normal System operation in the case of Unsecured Contingency Events. Under such adverse operating conditions and as part of the special Protection and defence measures loss of some generation and/or demand is permitted to ensure stable operation of the remaining System in the post-contingency period. 3.2.3.4 Planning Requirements - As part of the System planning process, based upon the System background conditions in paragraph 3.2.1.1 (used to set up the base case for the planning studies to determine the adequate Transmission Capacity requirements for the Transmission System), TNB shall study the impact of and the sensitivity of the System to Unsecured Contingency Events relating to multiple and very severe but rare System contingency events well beyond the Secured Contingency Events. 3.2.3.5 For the impact assessment at the System planning stage the following types of Unsecured Contingency Events will be considered and fully evaluated. Consideration and full evaluation of events will not be restricted to those events listed below but an assessment of reported events occurring in other power Systems and a full consideration of such events as relevant to the Transmission System. The types of Unsecured Contingency Events include: (1) Loss of a bus section; (2) Stuck breaker; Transmission System Reliability Standards


21

(3) Loss of the transmission towers in a Right of Way (involving loss of two or more double circuit lines); (4) Loss of a substation; and (5) Loss of a complete Power Station. In making the assessment, system performance requirements, contingencies and expected impacts following Unsecured Contingency Events or extreme contingencies summarised in Table 4.12, in section 4.11, under system condition classified as Category D - Extreme events resulting in two or more elements removed or cascading out of service - shall be considered. 3.2.3.6 Operational Requirements - The Main Interconnected Transmission System shall be operated with all the special Protection and defence measures in a fully operational state. If any one or more of these measures are out of service or on maintenance then specific Operational Planning studies shall be carried out well in advance to put in place appropriate operating regimes and alternative measures with a target of reducing the risk.



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3.3

Demand Connection Criteria

3.3.1 General 3.3.1.1 The Demand Connection Criteria relate to the planning of demand connections and provision of sufficient transformer capacity and/or demand transfer facilities to avoid undue Loss of Supply Capacity for Secured Contingency Outages included in the Transmission Reliability Standard. These Criteria enable TNB Transmission Division and the Distributors, Network Operators or Directly Connected Customers to make necessary investments ensuring the planning, development and operation of the Transmission and Distribution Systems within the provisions of Transmission System Reliability and Power Quality Standards, and the Grid Code both under normal and Secured Contingency Outage conditions. 3.3.1.2 This section of Chapter 3 presents the planning and operational Criteria for the connection of demand to the Transmission System. In those parts of the Transmission System where the Criteria of Chapter 2 of this Standard also apply, those Criteria must also be met.

3.3.2 Planning Criteria 3.3.2.1 The objective of planning is to ensure there are sufficient connections from the Transmission System at the Demand Supply Point such that the demand can be fully met under secured contingency conditions. 3.3.2.2 The supply of demand shall also be planned such that for the background conditions described in paragraph 3.2.1.1 and for the Secured Contingency Event of a Fault Outage of a single Transmission Circuit, a reactive compensator or other Reactive Power resource, or a step down transformer supplying demand whose high voltage side is connected to the Transmission System, there shall not be any loss of demand. The performance requirements, contingencies and impacts for the demand connection are summarised in Table 4.12, in section 4.11, under system condition classified as Category B – Events resulting in loss of a single element. 3.3.2.3 The above requirements shall not preclude the Customer/demand to be provided with higher or lower security of supply level as stated in appropriate Agreement.



23

3.3.2.4 It is permissable to secure demand against the contingencies outlined in section 3.3.2.2 by demand transfer or other methods at distribution voltages levels.

3.3.3 Operational Criteria 3.3.3.1 In the case of a planned outage of a single Transmission Circuit, a reactive compensator or other Reactive Power resource, or a step down transformer supplying demand whose high voltage side is connected to the Transmission System, full demand may not be met for a subsequent forced outage.



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Chapter 4: Performance Criteria and Limits

4.1

Introduction

4.1.1

This Chapter 4 presents performance criteria and limits used in this Standard for planning and operation. performance criteria and limits specified in this Chapter are: (1) Voltage; (2) Voltage Performance Margin; (3) Frequency Limits; (4) Stability Limits; (5) Fault Clearing Times; (6) Short Circuit Limits; (7) Basic Insulation Levels; (8) Criteria for Evaluating Unsecured Contingencies; and (9) Thermal Loading Limits of Transmission Components.

4.1.2

The specified criteria and limits in this Chapter shall be complied with for planning and operation of the Grid as outlined in Chapter 2 and Chapter 3.

4.2

Voltage

4.2.1

The Transmission System is planned, maintained and operated in accordance with the Standards included in Chapters 2 and 3. Pre-Fault Planning Voltage Limits and Unacceptable Voltage Conditions are defined as follows. The operation of the System is planned in Operational Planning timescales for operation within the Pre-Fault Planning Voltage Limits and operated under the Prevailing System Conditions so that for the Secured Contingency Event of a Fault Outage, any Unacceptable Voltage Conditions will not be experienced. Under rare Unsecured Contingency Events some parts of the System may experience Unacceptable Voltage Conditions and some parts of the voltage may experience total loss of the supply voltage.


Chapter 4:Performance Criteria and Limits

25

4.2.2

The voltage limits applicable in planning studies for the pre-disturbance/pre-fault state of the Transmission System are (see table 4.1): Table 4.1: Pre-disturbance voltage limits for planning studies Nominal Voltages Maximum Minimum (Note 2) 500kV

525kV (+5%)

500kV (-0.0%)

275kV

289kV (+5%)

275kV (-0.0%)

132kV

139kV (+5%)

132kV (-0.0%) (Note 1)

Lower Voltages

1.05 p.u. (+5%)

1.0 p.u. (-0.0%) (Note 1)

Note 1 There is no minimum planning voltage provided that, at the Busbar of the same nominal voltage at the Demand Supply Point from which it is derived, it is possible (for example by tap changing) to achieve at least 105% of nominal voltage. Note 2 It is assumed that at the planning stage the load power factor at the 132kV bus is no lower than 0.9 .

4.2.3

In both planning and operational timescales the voltage is unacceptable if outside the limits set out in table 4.2. Table 4.2: Unacceptable voltage limits in planning and operation Planning Timescales

Nominal Voltage

Note 1 Maximum

Minimum

Operational Timescales Maximum

Minimum

525kV (+5.0%)

475kV (-5.0%)

525kV (+5.0%)

450kV (-10.0%)

Note 2

Note 3

Note 6

275kV

289kV (+5.0%)

248kV (-10.0%)

303kV (+10.0%)

248kV (-10.0%)

132kV

139kV (+5.0%)

145kV (+10%)

119kV (-10%)

(+6.0%)

(-6.0%)

500kV

Less than 132kV Note1

Note 2 Note 3

Note 4

Note 5 Note 6

(+5.0%)

Note 4 Note 5

These voltages to be achieved without widespread post-fault generation transformer re-tapping or postfault adjustment of reactive compensation equipment reference voltage set points to increase the Reactive Power output or to avoid exceeding the available reactive capability of generation or reactive compensation equipment. It is permissible to relax this to 550kV (+10%) if lasting for no longer than 15 minutes (or longer if the equipment permits). It is permissible to relax this to 450kV (-10%) if: the affected substations are on the same radially fed spur post-fault; there is no lower voltage interconnection from these substations to other Main Interconnected System Substations; and no auxiliaries of Large Power Stations are derived from them. It shall be possible to operate the lower voltage Busbar of a Demand Supply Point up to 100% of nominal voltage unless the Secured Contingency Event includes the simultaneous loss of a 500/275kV transformer. The target operational voltages at Demand Supply Point should be as agreed with relevant Users. It is permissible to relax this to 550kV (+10%) if lasting for no longer than 15 minutes (or longer if the equipment permits).



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4.2.4

Under System operational conditions elements of the Transmission System need to be switched to optimise the operation of the System, to facilitate maintenance and to isolate faulty equipment for repair. Under such operational activities switching of any element or equipment shall not cause unacceptable Voltage Step Changes. The voltage change is deemed unacceptable if it changes by more than the limits set out in table 4.3. Table 4.3: Unacceptable voltage step changes in planning and operation System Condition

Planning Timescales Note 1 Voltage Rise

Voltage Fall

Operational Timescales Note 3 Voltage Rise

Voltage Fall

+10%

-2.5% for 500kV -5% for others Note 2

+10%

-2.5% for 500kV -5% for others Note 4

Following operational switching less frequent than specified in ER P28

+3%

-3%

+3%

-3%

Otherwise

According to ER P28

Following Secured Contingency Events

Note 1 These limits apply at all demand conditions and only to the interfaces between the Transmission System and customers, and must be applied with the Load response to voltage change taken into account. Note 2 This is relaxed to -12% if the fault involves the loss of a section of Busbar, or a mesh corner, or a Secured Contingency Event which also includes the simultaneous loss of a 500/275kV transformer (Applicable to voltage other than 500kV). Note 3 Following Voltage Step Change within these limits, it must be possible to restore the Steady State voltage to 95% of nominal at Demand Supply Points following any manual and/or automatic facilities available, including switching in or out of relevant Apparatus. Note 4 This is relaxed to -12% if the fault involves the loss of a Double Circuit Overhead Line, a section of Busbar, or mesh corner (Applicable to voltage other than 500kV).



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4.2.5

Limits of voltage changes due to frequent and infrequent operational switching of Load both by TNB and the User are defined as follows (see table 4.4), provided that this does not constitute a risk to the Transmission System. Table 4.4: Voltage limits on switching of load Load Switching Limit of Voltage Change Infrequent single switching or disconnection of Load (e.g., twice a day) 3% Including capacitor banks and reactors Frequent switching and/or disconnection 1% of Load (e.g., Many times in a day)

4.2.6

Immediately following a fault clearance and removal of the faulted item of equipment from the Transmission System, and, prior to reaching Steady State conditions whose limits are described in Sections 4.2.3 and 4.2.4 above, the voltage at any point on the Main Interconnected Transmission System is unacceptable if outside the limits set out in the table 4.5. Table 4.5: Dynamic voltage excursion limits Low voltage 0.7 p.u. for not more than 400ms

High voltage

1.2 p.u. for not more than 30s

4.3

Voltage Performance Margin

4.3.1

At the planning stage power transfer within the System and at each specific demand point shall be limited such that there is a margin of 15% to the maximum possible transmitted power, under the base case conditions described in Section 3.2.1.1 of this Standard.

4.3.2

At the planning stage power transfer within the System and at each specific demand point shall be limited such that there is a margin of 7.5% to the maximum possible transmitted power, under the contingency conditions described in Section 3.2.1.4 of this Standard.

4.3.3

During operation, power transfer within the System and at each specific demand point shall be limited such that there is a margin of 5% to the maximum possible transmitted power, under the contingency conditions described in Section 3.2.2.1 of this Standard.

4.3.4

These voltage margin Criteria are in additon to any other voltage Criteria requirements.



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4.4

Frequency Limits

4.4.1

During normal steady-state operational conditions the Frequency is to be maintained to within ±1% of the nominal, that is, between 49.5 and 50.5Hz.

4.4.2

The System Frequency could rise to 52Hz or fall to 47Hz in extremely rare and exceptional circumstances. Therefore the design of both TNB and User's Plant and Apparatus must enable operation of that Plant and Apparatus within that range in accordance with table 4.6. Table 4.6: Frequency excursion limits Frequency Range Requirement 47.5Hz - 52Hz*

Continuous operation is required

47Hz - 47.5Hz

Operation for a period of at least 10 seconds is required each time the Frequency is below 47.5Hz * This value may be lowered to 51.5Hz if substantive evidence can be provided to show that the operation of the generating unit beyond 51.5Hz will affect the safety of the plant.

4.5

Stability Limits

4.5.1

The relative rotor angle of any two Generating Units in the System must not exceed 180 degrees at any time.

4.5.2

Following any disturbance the Damping Ratio of power, angle or voltage oscillation must not be less than 5%.



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4.6

Fault Clearing Times

4.6.1

The following maximum fault clearance times (see table 4.7) are normally expected from the Main Protection equipment installed in the Transmission System. Table 4.7: Maximum Fault Clearing Times System Voltage (kV) Fault Location 500 and 275 132

Fault Clearance Time (ms)

Substation

100

Overhead Line/Cable

100

Substation

150

Overhead Line/Cable

150

4.6.2

For planning studies: (1) a 100ms fault clearance time shall be used for system at nominal voltage of 500kV and 275kV; (2) a 150ms fault clearance time shall be used for system at nominal voltage of 132kV. Fault clearance time is defined as the time between fault inception and complete disconnection of the faulted item of equipment from the Transmission System.

4.6.3

For operational studies the Protection times in 4.6.2 shall also be used. However, where the used of fault clearing times in 4.6.2 is found to be limited, the actual fault clearing times may be used.

4.7

Short-Circuit Limits

4.7.1

The Transmission System shall be planned such that the maximum sub-transient three phase symmetrical short circuit fault levels are not greater than 90% of the switching equipment short-circuit ratings, the breaking and making capacities of switching equipment shall not be exceeded under maximum system short circuit condition.

4.7.2

For three-phase or single-phase-to-earth faults, the planned maximum subtransient short circuit fault levels shall not be greater than that indicated in the table 4.8.



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Table 4.8: Short-circuit limits System Voltage (kV) 500 275 132

Circuit Breaker Short Circuit Rating Break Capacity

50kA, 1s • 40kA, 3s for bulk substation • 50kA, 1s for Power Station and 275kV within 500kV substation • •

31.5kA, 3s 40kA, 3s for Power Station and 132kV within a 500/275kV substation

33

25kA, 3s

22, 11, 6.6

20kA, 3s

0.415 and 0.240 31.5kA, 3s Note: Typically closing-and-latching (momentary) capability of a circuit breaker as an rms current is not more than 1.6K times Symmetrical Short Circuit Rating or as an instantaneous peak current is not more than 2.7K times Symmetrical Short Circuit Rating. For most circuit breakers, K is equal to one.

4.8

Basic Insulation Level

4.8.1

Typical Basic Impulse Insulation Levels (BIL) of the Transmission and Distribution Systems are as given in the following table. The User’s Plant and Apparatus is required to match these insulation levels. These may vary under specific circumstances. Table 4.9: Basic insulation level (BIL) System Voltage (kV) BIL (kV) 500

1550

275

1050

132

650

33

170

22

125

11 and 6.6

75



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4.9

Criteria for Evaluating Unsecured Contingencies

4.9.1

For the purposes of determining the types of special Protection and defence measures the following contingencies which will be considered together with the appropriate Fault Outage Criteria to be considered are listed in table 4.10 and also as described under Category D of Table 4.12, in section 4.11,. In all these cases special Protection and/or defence measures shall be put in place such that whilst some demand and generation loss may be experienced a total System shutdown will be avoided. Table 4.10: Unsecured contingencies to be evaluated Unsecured Fault Outage Criteria Contingency Note 1 Event

Outage of System Elements

Bus Section Fault

Single-phase-to-ground fault cleared in 250 ms followed by the loss of the entire bus section through tripping of all circuit breakers connected to that section of Busbar

All Transmission Circuits and any transformers and/or reactive compensation equipment connected

Stuck Breaker Fault – Single Phase Fault Initiation

Single-phase-to-ground fault being cleared in 250 ms by the tripping of the circuit breakers of transmission elements in the immediate proximity to clear the fault which could not be normally cleared due to the stuck breaker

All Transmission Circuits and any transformers and/or reactive compensation equipment in the immediate proximity

Stuck Breaker Fault – Three Phase Fault Initiation

Three-phase fault cleared in normal clearing time followed by a single line to ground fault cleared in delayed time. Typical delay time is assumed at 250ms.

All Transmission Circuits and any transformer and/or reactive compensation equipment in the immediate proximity

Loss of one Bipole of the HVDC Interconnector

Blocking of one Bipole through its control equipment reducing the current flow to zero and the resumption of current flow

Outage of some elements of the HVDC link

Loss of Right of Way

Three-phase fault cleared in 150ms or 100ms followed by the loss of circuits on the Right of Way


Loss of all circuits on the Right of Way


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Unsecured Contingency Event

Fault Outage Criteria Note 1

Outage of System Elements

Loss of substation (one transmission voltage level plus associated transformers) i.e., loss of a Busbar Loss of a complete Power Station

Three-phase fault cleared in 150ms or 100ms followed by the loss of circuits connected to the busbar

Loss of all circuits connected to the busbar

Three-phase fault cleared in 150ms or Loss of all Generating Units 100ms followed by the loss of all at the Power Station Generating Units at the Power Station Note 1: Normal clearing time - Three-phase fault duration for 500kV and 275kV is 100ms and for and 132kV is 150ms

4.10 Thermal Loading Limits of Transmission Components 4.10.1 The thermal loading limits of equipment in planning and operational timescales are defined in table 4.11. Table 4.11: Thermal loading limits on transmission components Equipment Planning Operation Lines

No thermal overloading allowed

Underground cables

Strict observation of equipment continuous rating

Transformers

No thermal overloading allowed

Switching and Isolation Equipment

Strict observation of equipment continuous rating

130% for not more than thirty (30) minutes or an applicable time dependent emergency limit 125% for not more than thirty (30) minutes or an applicable time dependent emergency limit 130% for not more than thirty (30) minutes or an applicable time dependent emergency limit Applicable time dependent emergency limit

4.11 Summary of Transmission System Requirements – Normal and Emergency Conditions 4.11.1 Table 4.12 summarises the required and/or expected performance of the transmission system under four (4) categories of contingencies and for each category: (1) the initiating events and contingency elements; and (2) system performance requirements and expected impacts are specified.



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Table 4.12: Summary of System Performance Requirements Following Events Involving Loss of Single or More Grid System Elements under Both Normal and Emergency Conditions Category

A No Contingencies B Event resulting in the loss of a single element

C Event(s) resulting in the loss of two or more (multiple) elements

Contingencies Initiating Event(s) and Contingency Element(s)

System Limits or Impacts System Stable Loss of Cascading & both Thermal Demand Outages and Voltage or Limits within Curtailed Applicable Firm Rating Note (a) Transfers

All Facilities in Service Single Line Ground (SLG) or 3Phase (3Ø) Fault with Normal Clearing (Note (e)): 1. Generator 2. Transmission Circuit 3. Transformer Loss of an Element without a Fault Single Pole Block, Normal Clearing (Note (e)): 4. Single Pole (dc) Line SLG Fault, with Normal Clearing (Note (e)): 1. Bus Section 2. Breaker (failure or internal fault)

Yes

No

No

Yes Yes Yes Yes

No No No No Note (b)

No No No No

Yes

No Note (b)

No

Yes

Planned/ Controlled Planned/ Controlled Note (c)

No

Yes

Planned/ Controlled Note (c)

No

Yes

Planned/ Controlled

No

Yes

Planned/ Controlled Note (c)

No

Yes

SLG or 3Ø Fault, with Normal Clearing (Note (e)). Manual System Adjustment, followed by another SLG or 3Ø Fault, with Normal Clearing (Note (e)): 3. Category B (B1, B2, B3 or B4) contingency, manual system adjustments, followed by another Category B(B1, B2, B3 or B4) contingency Bipolar Block with Normal Clearing (Note (e)): 4. Bipolar (dc) Line Fault (non 3Ø) with Normal Clearing (Note (e)) 5. Any two circuits of a multiple circuit tower (Note (f)). SLG Fault, with Delayed Clearing (stuck breaker or protection system failure) (Note (e)): 6. Generator

No

Note (c) Yes

7. Transformer

Yes

8. Transmission Circuit

Yes

9. Bus Section

Yes


Planned/ Controlled Planned/ Controlled Planned/ Controlled Planned/ Controlled

No No No No


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Category

D Extreme event resulting in two or more (multiple) elements removed or Cascading out of service Note (d)

Contingencies Initiating Event(s) and Contingency Element(s)

System Limits or Impacts System Stable Loss of Cascading & both Thermal Demand Outages and Voltage or Limits within Curtailed Applicable Firm Rating Note (a) Transfers 3Ø Fault with Delayed Clearing (stuck breaker or protection system Elevate for risks and failure) (Note (e)): consequences: 1. 2. 3. 4.

Generator Transmission (Circuit) Transformer Bus Section

3Ø Fault with Normal Clearing (Note (e)) : 5. Breaker (failure or internal Fault) 6. Loss of tower with three or more circuits 7. Loss of all transmission lines on a common right-of way 8. Loss of a substation (one voltage level plus transformers) 9. Loss of a switching station (one voltage level plus transformers) 10. Loss of all generating units at a station. 11. Loss of large Load or major Load center 12. Failure of a fully redundant Special Protection System to operate when required 13. Operation, partial operation, or misoperation of a fully redundant Special Protection System in response to an event or abnormal system condition for which it was not intended to operate 14. Impact of severe power swings or oscillation from Disturbances in another Interconnected Systems

• May involve substantial loss of customer Demand and generation in a widespread area or areas • Portions or all of the interconnection systems may or may not achieve a new, stable operating point. • Evaluation of these events may require joint studies with neighboring systems.

Notes: (a) Applicable rating refers to the applicable Normal and Emergency facility thermal Rating (see table 4.11) or system voltage limit as determined and consistently applied specified in section 4.1 of this Standard. Applicable Ratings may include Emergency Ratings applicable for short durations as required to permit operating steps necessary to maintain system control. (b) Planned or controlled interruption of electric supply to radial customers or some local Network customers connected to or supplied by the Faulted element or by the affected area, may occur in certain areas without impacting the overall reliability of the interconnected transmission systems. To prepare for the next contingency, system adjustments are permitted, including curtailments of contracted firm power transfers. (c) Depending on system design and expected system impacts, the controlled interruption of electric supply to customers (load shedding), the planned removal from service of certain generation, and/or the curtailment of contracted firm power transfers maybe necessary to maintain the overall reliability of the interconnected transmission systems. (d) A number of extreme contingencies that are listed under Category D and judged to be critical will be selected for evaluation. It is not expected that all possible facility outages under each listed contingency of Category D will be evaluated. (e) Normal clearing is when the protection system operates as designed and the Fault is cleared in the time normally expected with proper functioning of the installed protection systems (see table 4.7). Delayed clearing of a Fault is due to failure of any protection system component such as a relay, circuit breaker, or current transformer, and not because of an intentional design delay. Three phase delayed clearing is when a three phase fault is cleared in normal clearing time followed by a SLG fault cleared after a delay time (to represent the single pole of a stuck breaker or protection system failure). Typical delay times are 250 milliseconds (f) System assessment may exclude these events where multiple circuit lowers are used over short distances (e.g. substation entrance, river crossings).



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Transmission System Power Quality Standards Effective January 1, 2006

Version 2.0 Edition 1.0

© TENAGA NASIONAL BERHAD, 2006 Transmission System Power Quality Standards

Contents

36

Contents TRANSMISSION SYSTEM POWER QUALITY STANDARDS ..............................36 CONTENTS......................................................................................................................37 CHAPTER 1: INTRODUCTION...................................................................................38 1.1 1.2

POWER QUALITY DEFINITION AND REQUIREMENTS ............................................38 SCOPE .................................................................................................................40

CHAPTER 2: TRANSMISSION POWER QUALITY STANDARDS.......................41 2.1 2.2 2.3 2.4 2.5 2.6

VOLTAGE SAG OR VOLTAGE DIP ........................................................................41 VOLTAGE STEP CHANGE .....................................................................................42 VOLTAGE FLUCTUATİONS AND FLİCKER .............................................................42 HARMONICS ........................................................................................................44 PHASE UNBALANCE AND TRACTION LOAD .........................................................46 STEP CHANGES OF POWER ..................................................................................49

Transmission System Power Quality Standards

Contents

37

Chapter 1: Introduction

1.1

Power Quality Definition and Requirements

1.1.1

In this Standard, Power Quality is defined as the degree to which the Voltage at the point of connection to the User of the Transmission System is maintained to be Sinusoidal at declared rated Voltage and Frequency within the stipulated limits.

1.1.2

Major Power Quality Problems that are associated with the Transmission System is Voltage Sag or Voltage Dip. Voltage sag would occur in the System during the short-circuit fault. The most severe Voltage Sag would occur at the fault location and the Voltage Sag effects would be propagated throughout the Systems with the magnitude of the Voltage Dip attenuated.

1.1.3

Voltage Sag could also be caused by short circuit faults in User’s System and propagated to other Users’ Systems through the Transmission Systems or through the Distribution System as the case may be. Majority of problems associated with harmonics are caused by non-linear loads that draw non-sinusoidal current from the system and thus causing the supply voltage to be distorted. Frequent switching of large load such as motors is also another source of power quality problems that result in voltage flicker to be experienced by other Users.

1.1.4

The approaches to resolving power quality problems depend on the types of the power quality problems. Both utility and Customers have their individual roles and responsibilities in resolving power quality problems. Individual Customer shall ensure that any non-linear load to be connected to the Transmission System does not produce harmonic currents that would result in voltage at Point of Common Coupling to be distorted beyond the limits as set out in section 2.4 of this Standard. Likewise the utility shall continue to monitor and ensure that Harmonic limits as specified in section 2.4 are complied with.

1.1.5

Voltage sag could affect sensitive loads usually connected at low voltage network of the Customer’s installation. Not withstanding the presence of several voltage transformations from transmission voltage to low voltage, voltage sag caused by Transmission faults can affect Customers voltage sensitive loads and the effect is more pronounced during severe three-phase faults on the Transmission System. It shall be the responsibility of the utility to provide appropriate information on voltage sag and for the individual customer to ensure sufficient ride-through capability of the voltage sensitive equipment.


Chapter 1: Introducton

38

1.1.6

The Standards contained in this document specify the Power Quality requirements of the bulk supply point that delivers electricity supply to the Distribution System and other bulk supply Users in terms of stable voltage and frequency within specific limits so that Generator, TNB Transmission equipment or Consumer’s equipment directly connected to the Transmission System can operate safely within its design performance without suffering undue damage or breakdown.

1.1.7

The requirements and limits specified in this Standard shall also be complied with by all Users connected or intending to be connected to the Transmission System.

1.1.8

Consequently these Standards also determine the investment required in provision and/or procurement of Supplementary Services such as Reactive Power, Active Power response, hot standby generation, fast start generation, demand control and black start by TNB Transmission. They also indicate the investment required both in the Transmission and Distribution Systems for containing harmonics, voltage unbalance as well as the permitted types and levels of special Loads adversely affecting the power quality and requirements for compensation plant to limit their adverse effects. Compliance with these Standards is the responsibility of TNB Transmission, Generators, Distributors, Network Operators and Non-Embedded Customers.

1.1.9

In order to achieve the required Transmission Power Quality these Standards will be used by TNB Transmission in planning, developing, maintaining and operating the Transmission System as well as in connecting generation and demand to the System. In turn the equipment utilised by the Generators, TNB Transmission, Distributors and Customers also need to comply with the provisions of this Standard. Compliance with these Standards is therefore not optional and where a connecting party’s plant or equipment is likely to be non-compliant at the planning stage then such plant and/or equipment will not be energised until appropriate remedial measures are put in place and are fully functional. In addition, TNB Transmission shall put in place appropriate monitoring facilities to ensure compliance with the provisions of this Standard as part of its Licence.

1.1.10 In cases where, the nature and operation of the new types of plant and equipment to be connected to the Transmission System is perceived to be likely to cause problems to other customers and user’s of the System, but not fully covered by this Standard, appropriate remedial measures shall be put in place based on expert advice within a mutually agreed time period.



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1.2

Scope

1.2.1

This Standard covers most of the power quality related phenomena generated by various types of plant and equipment connected to the Transmission System. In each particular case the Transmission Power Quality that should be maintained is indicated together with the remedial approach and responsibilities of parties.



40

Chapter 2: Transmission Power Quality Standards

2.1

Voltage Sag or Voltage Dip

2.1.1

Voltage “sag”, “dip” or “swell” is the transient phenomena which can affect the voltage level and is usually experienced during System faults and the subsequent recovery period. These phenomena can adversely affect some customer equipment that are sensitive to such changes. This Standard does not specifically cover voltage “sag”, “dip” or “swell”.

2.1.2

The voltage sags are caused by faults on the Transmission System due to short circuits incidents which are cleared by System Protection. The nature and technical detail of such events is a function of the location of the connection point on the System, the distance of the short circuit from the connection point and the short-circuit level at the connection point, the severity (magnitude and duration) of the short circuit. Voltage Sag may also be caused by short-circuit fault in one User’s System and propagated to other Users’ Systems through the Transmission System.

2.1.3

In most cases, the Transmission System faults were cleared within the primary protection fault clearing time. Statistics of monitored events of voltage sags indicates that not all faults on the Transmission System affect voltage sensitive customer demand. However for certain severe fault, the voltage sag may be felt by voltage sensitive customer up to (three hundred) 300km away from the fault location.

2.1.4

There is no single Standard for voltage sag but statistical information is available from TNB Transmission in terms of past records of voltage sag events. If Users or prospective Users have equipment which are sensitive to voltage sags, they can request such statistical information from TNB at the application stage to enable compatibility assessment to be carried out, if necessary. Whenever necessary, remedial actions may be rendered by TNB and/or the affected Customer through appropriate Agreement.



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2.2

Voltage Step Change

2.2.1

Under System operational conditions, elements of the Transmission System need to be switched to optimise the operation of the System, to facilitate maintenance and to isolate faulty equipment for repair. Under such operational activities, switching of any element or equipment shall not cause unacceptable Voltage Step Changes. The voltage change is deemed unacceptable if it changes by more than the limits set out in Sectıon 4.2.4 of the Transmission System Reliability Standards.

2.2.2

Limits of voltage changes due to Load, frequent and infrequent operational switching of Load both by TNB and the User are defined in Sectıon 4.2.5 of the Transmission System Reliability Standards.

2.3

Voltage Fluctuations and Flicker

2.3.1

The limits of Flicker that are acceptable on the Transmission System are in accordance with the “Engineering Recommendation P28, Issued by The Electricity Council of UK in 1989 entitled Planning Limits for Voltage Fluctuation Caused by Industrial, Commercial and Domestic Equipment in the United Kingdom” (ER P28). TNB Transmission Division uses the procedures contained in this document to plan the connection of Fluctuating Loads and applies the limits therein in measuring and monitoring the levels of Flicker at such points of connection.

2.3.2

In accordance with ER P28, voltage fluctuations at a Point of Common Coupling with a fluctuating Load directly connected to the Transmission System shall not exceed: (1) 1% of the voltage level for step changes, which may occur repetitively. Any large voltage excursions other than step changes or less frequent step changes may be allowed up to a level of 3% provided that this does not constitute a risk to the Transmission System or, in TNB’s view, any other party connected to the System. (2) The planning limits for the Short and Long Term Flicker Severity applicable for Fluctuating Loads connected to the Transmission System are as set out in the table below (see table 2.1).



42

Table 2.1: Maximum allowable flicker severity Transmission System Absolute Short Voltage Level at which the Term Flicker Fluctuating Load is Severity (Pst) Connected 500, 275 and 132kV Less than 132kV

0.8 1.0

Absolute Long Term Flicker Severity (Plt) 0.6 0.8

2.3.3

In connecting a Fluctuating Load at a particular point or Point of Common Coupling it is necessary to assess the total Flicker due to the Fluctuating Load itself and the background Flicker measured at that point. In assessing the total Flicker TNB shall use the so called “RSS Rule”. This assessment is carried out by the RSS Rule by obtaining the sum of the squares of the Flicker from the Fluctuating Load and the background Flicker, with the square root of this sum yielding the total assessed Flicker at that Point of Common Coupling due to the specific Fluctuating Load and the background Flicker at that point.

2.3.4

Connection of more than one Fluctuating Load at the same Point of Common Coupling or addition of further Fluctuating Load at the same location is carried out on a “first come first served” basis on the Transmission System. This means that whilst the first Fluctuating Load may be within the allowable Flicker limits and not require any Flicker mitigation or compensation equipment, the second Fluctuating Load which may cause violation of Flicker limits will be obliged to invest in appropriate Flicker mitigation or compensation equipment. At the planning stage, in carrying out the assessment of the total Flicker due to more than one Fluctuating Load connecting at a particular Points of Common Coupling TNB shall use the methodology described in P28.

2.3.5

In assessing level of Flicker due to a Fluctuating Load at the planning stage the assessment will be carried out at a realistic Weak System operating condition giving the minimum number of connections with which that point on the System can be operated within normal voltage limits with maintenance outages or following Secured Contingency Events. This condition shall be considered as representative of the type of System conditions under which the Flicker due to a Fluctuating Load will be at its highest value as the voltage fluctuations due to the Fluctuating Load will be at their highest level under such conditions.

2.3.6

If under the operating conditions described in 2.3.5 the Flicker due to a Fluctuating Load exceeds the limits then Flicker compensation which will reduce the Flicker to an acceptable level shall be installed. For the avoidance of doubt the acceptance Criteria for Flicker is the 95% values of Short and Long Term Flicker Severity i.e., Pst and Plt will be below the limits specified in the above table. Here the 95% values mean the 95th percentile of the cumulative probability function of



43

the values of Flicker Severity measured and observed during the total observation period. The System overall performance yardstick for the level of Flicker reduction to be achieved shall be based upon enabling connection of other similar Fluctuating Load and/or permitting for future extension and development of the location with further Fluctuating Load installations. The Flicker compensation method and equipment to be used shall be of a type that does not cause resonance problems with the existing and intended future developments of the Transmission System. 2.3.7

If the permissible Flicker limits cannot be met even with installation of Flicker compensation at a particular Points of Common Coupling at a particular System voltage level then connection of the Fluctuating Load at a higher voltage level or elsewhere in the System shall be considered. The connection point of choice will need to have to experience lower voltage fluctuations than the first connection point considered under the operational conditions in 2.3.5.

2.4

Harmonics

2.4.1

The limits of Harmonics that are acceptable on the Transmission System are in accordance with the IEC Standard 61000-3-6 “Assessment of emission limits for distorting loads in MV and HV power systems”. TNB Transmission uses the procedures contained in this document to plan the connection of Loads producing Harmonics and applies the limits therein in measuring and monitoring the levels of harmonics at such points of connection.

2.4.2

All plant and equipment connected to the Transmission System, and that part of the Transmission System at each connection site, should be capable of withstanding the following distortions of the voltage waveform in respect of harmonic content. The maximum total levels of Harmonic Distortion at any connection point on the Transmission System from all sources under both planned outage and Secured Contingency Event conditions, unless abnormal conditions prevail, shall not exceed: (1) at 500kV, 275kV and 132kV, a maximum planning limit for Total Harmonic Distortion of 3% with no individual Harmonic Voltage greater than that shown in the table 2.2; (2) infrequent short duration peaks may be permitted by TNB to exceed the above levels for harmonic distortion; (3) TNB will make an assessment for the connection of each Load to the Transmission System, which may result in harmonic emission limits being specified for these Loads in the relevant Agreement. The assessment will take



44

into account the position of existing and prospective Users’ Plant and Apparatus in relation to harmonic emissions. Users must ensure that connection of distorting Loads to their User Systems do not cause any harmonic emission limits specified in the Connection Agreement to be exceeded; and (4) Users shall ensure that the Immunity Level of their plant and Apparatus is compatible with the electromagnetic disturbances present on the System including harmonics. 2.4.3

In assessing level of Harmonic Distortion and Individual Harmonic Levels at the planning stage the assessment will be carried out at a realistic Weak System operating condition giving the minimum number of connections with which that point on the System can be operated within normal voltage limits with maintenance outages or following Secured Contingency Events. This condition shall be considered as representative of the type of System conditions under which the Harmonic Distortion and Individual Harmonic Levels will be at their highest value.

2.4.4

If under the operating conditions described in 2.4.3 the Harmonic Distortion and Individual Harmonic Level due to the Load exceed the limits then harmonic filters which will reduce the harmonics to an acceptable level shall be installed to bring the levels within the limits. The System overall performance yardstick for the level of harmonic reduction to be achieved shall be based upon enabling connection of other similar harmonic producing Load and/or permitting for future extension and development of the location with further harmonic producing Load installations. The harmonic filters to be installed shall be of a type that does not cause resonance problems with the existing and intended future developments of the Transmission System.



45

Table 2.2: Indicative Values of Planning Levels for Harmonic Voltage in HV (35 < kV < 230) and EHV (kV >230) Odd Harmonics Odd Harmonics Even Harmonics (Non-multiple of 3) (Multiple of 3) Order Harmonic Order “h” Voltage (%) “h” 3 2.0 5 9 2.0 7 15 1.5 11 21 1.5 13 >21 1.0 17 1.0 19 0.7 23 0.7 25 0.2+0.5(25/h) >25 The total harmonic distortion level is 3%

Harmonic Voltage (%) 2.0 1.0 0.3 0.2 0.2

Order “h” 2 4 6 8 10 12 >12

Harmonic Voltage (%) 1.5 1.0 0.5 0.4 0.4 0.2 0.2

2.5

Phase Unbalance and Traction Load

2.5.1

In planning the limits on voltage unbalance, TNB makes reference to “Engineering Recommendation (E/R) P24, issued by the Electricity Council of UK in 1984 entitled “AC Traction Supplies to British Rail” and its successor document P 29 issued in 1990 entitled “Planning Limits for Voltage unbalance in the United Kingdom”.

2.5.2

In all power Systems including the Transmission System, the impedances of each phase of the transmission lines are unequal due to differences in their physical geometry, and therefore create a voltage unbalance at the termination points of the lines. As a general rule, the longer the line the higher this unbalance will be. In addition the demands connected to each phase at a Demand Supply Point are not precisely equal as customers connected to individual phases utilise their equipment at varying times. Also there are large single-phase connected demands such as railway traction Loads connected at various points. Together these factors create a level of unbalance between the phases of the transmission lines within the Transmission System causing the so called negative phase sequence currents to circulate in the Transmission System which can be harmful to plant equipment if they exceed certain levels.

2.5.3

To prevent the circulation of excessive negative sequence currents conductor transpositions are applied over the length of line to reduce the level of inequality between the phase impedances of the transmission lines in the Transmission



46

System. This process requires a change in the physical position of each phase conductor over the length of the line. Thus a full transposition would involve each phase conductor to physically occupy a different position at each third of the line length. This undertaking by itself is sometimes not sufficient to reduce the circulating negative phase sequence currents due to the connected single-phase and unbalanced three-phase Loads. In such cases it is necessary to install compensation equipment at the point of connection of the specific Load to achieve balanced voltages within specified limits given below. 2.5.4

All plant and equipment connected to the Transmission System, and that part of the Transmission System at each connection site, should be capable of withstanding the following distortions of the voltage waveform in respect of Phase Unbalance at the planning stage. 1) Under planned outage conditions, the maximum negative phase sequence component of the phase voltage on the Transmission System should remain below 1% unless abnormal conditions prevail (P29 limit is not exceeding 2% for 1 minute). 2) Under the planned outage conditions, infrequent short duration peaks with a maximum value of 2% are permitted for Phase Unbalance, subject to the prior agreement of TNB under the connection agreement. TNB will only agree following a specific assessment of the impact of these levels on TNB and other Users’ plant and equipment with which it is satisfied. 3) At the terminals of a User’s installation or specific Load the unbalance voltage shall not exceed 1% for 5 occasions within any thirty (30) minute time period. 4) In terms of traction Loads connected to the Transmission System the acceptable limits of unbalance are in accordance with “Engineering Recommendation (E/R) P24, issued by the Electricity Council of UK in 1984 entitled “AC Traction Supplies to British Rail” and its successor document P 29 issued in 1990 “Planning Limits for Voltage unbalance in the United Kingdom”. TNB Transmission uses the procedures contained in this document to plan the connection of Loads producing Unbalance and applies the limits therein in measuring and monitoring the levels of unbalance at such points of connection.

2.5.5

In assessing level of Unbalance at the planning stage the assessment will be carried out at a realistic Weak System operating condition giving the minimum number of connections with which that point on the System can be operated within normal voltage limits with maintenance outages or following Secured Contingency Events. This condition shall be considered as representative of the type of System conditions under which the Unbalance will be at its highest value.



47

2.5.6

If under the operating conditions described in 2.5.4 the Unbalance due to the Load exceeds the limits then balancing compensation equipment which will reduce the unbalance to an acceptable level shall be installed to bring the levels within the limits. The System overall performance yardstick for the level of unbalance reduction to be achieved shall be based upon enabling connection of other similar unbalance producing Load and/or permitting for future extension and development of the location with further unbalance producing Load installations. The balancing compensation equipment to be installed shall be of a type that does not cause resonance problems with the existing and intended future developments of the Transmission System.

2.5.7

Current TNB practice requires that 500kV overhead line with more than fifty (50) km in length to be fully transposed.



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2.6

Step Changes of Power

2.6.1

The magnitude of the step power constraint shall be as follows: (1) The magnitude of step power for a single Load variation is limited to 50MW or 50% of the full capacity whichever is the lower. (2) In view of the technical difficulties of fulfilling the requirement in (1) above, special approval shall be sought from TNB in deciding a suitable quantum of step Load at the initial supply application stage. (3) The magnitude of the step power shall be maintained for sixty (60) seconds before any other step power may be applied.

2.6.2

In the case of an arc furnace installation the following restrictions will apply: (1) No initial arcing is to be carried out simultaneously for any combination of arcing Loads that lead to a step power magnitude greater than that described in Section 2.6.1 (1) of this Standard. (2) Suitable interlocking Systems shall be provided to ensure compliance with (1) above.



49

Glossary and Definitions for Transmission System Reliability Standards and Transmission System Power Quality Standards


50

TERM Active Power

DEFINITION The product of voltage and the in-phase component of alternating current measured in units of watts and standard multiples thereof, i.e.: 1000 Watts = 1 kW 1000 kW = 1 MW 1000 MW = 1 GW 1000 GW = 1 TW

Adequacy

Adequacy of an electrical System is the ability of the System to supply each customer’s electrical demand and energy requirement at all times with due consideration to scheduled and credible unscheduled outages of elements of that System.

Apparatus

All types of equipment in which electrical conductors are used, supported or of which they may form a part or High Voltage electrical circuits forming part of a System on which safety precautions may be applied to allow work and/or testing to be carried out.

Apparent Power

The product of voltage and of alternating current measured in units of voltamperes and standard multiples thereof, i.e.: 1000 VA = 1 kVA 1000 kVA = 1 MVA

Availability

A measure of the time a Generating Unit, transmission line, or other facility is capable of providing service, whether or not it actually is in service. Typically, this measure is expressed as a percentage of Availability of the item for the period under consideration.

Available Transfer Capacity Bulk Supply Points

Power transfer capacity available as defined in the appropriate Interconnection Agreement with an External System.

Busbar

The common connection point of two or more Transmission Circuits.

Connection Agreements

Technical Agreements or Technical Sections of Power Purchase Agreements between TNB and all Generators, Distributors, Non-

For the purpose of defining the boundaries between the Main Interconnected Transmission System and Bulk Supply Point transformer circuits, the Bulk Supply Point is taken to be the connection point between the User System and the Transmission System.

Glossary and Defintions for Transmission System Reliability Standards and Transmission System Power Quality Standards

51

TERM

DEFINITION Embedded Customers and Network Operators Transmission System excluding External Systems.

connected

to

Criteria/ Criterion

A defined set of conditions under which, a power System is judged to be operating or capable of operating, without violating its design and operational Standards.

Damping Ratio

A term used to describe the rate at which the amplitude of a Power System oscillation frequency, represented by a complex pair of eigenvalues (σ±jω), will decay as given by the expression:

ς(%) =

−σ 2

σ +ω

2

×100

where Η is termed as the Damping Ratio. DC Link Monopole

An HVDC system comprising rectifier and inverter and uses one conductor for connection with metallic or ground return.

Demand Connection Criteria

The Criteria which ensure Adequacy of transformer capacity to meet the Distribution Systems or Network Operators or Non-Embedded Customers demand connected at Demand Connection Points and Demand Supply Points across the System.

Demand Connection Point

The high voltage side of a Demand Supply Point.

Demand Supply Point

A point of supply from the Transmission System to Distribution Networks, Network Operators or Non-Embedded Customers.

Directly Connected Customers

Users connected directly to the Transmission System without any connection through and intermediate Distribution System

Distribution Reliability Standard

Distribution Reliability Standard or Distribution Security Standard, which relates to provision of sufficient Distribution Capacity, operational facilities, maintenance activity and co-ordination with transmission and embedded generation functions to enable continued supply of electric


52

TERM

DEFINITION energy to the customers connected to the Distribution System.

Distribution Code

A set of technical rules setting the Criteria and Standards to be complied with in planning the development of, connection to and operation of a Distribution System, receiving bulk power from the Main Interconnected Transmission System and which may also contain generation plant, with legal status.

Distribution Function

The particular functional unit of a person or company or User who distributes electricity under a licence granted by the Energy Commission under the Electricity Act 1990 acting in its capacity as a distributor in Peninsular Malaysia.

Distribution Power Quality Standards

These Standards specify the quality of the supply to be delivered at the connection point of the consumer to the Distribution System, in terms of stable voltage and frequency within specific limits so that consumer equipment connected to the System can operate safely within its design performance without suffering undue damage or breakdown. These Standards also indicate the investment required both in the Distribution System for containing harmonics, voltage unbalance as well as the permitted types and levels of special equipment and Loads adversely affecting the power quality and requirements for compensation plant to limit their adverse effects.

Distribution System

The System consisting (wholly or mainly) of electric lines which are owned or operated by a Distribution Company and used for the distribution of electricity from Bulk Supply Points or Generating Units or other connections to External Systems to the point of delivery to Customers, or other Users, and includes any Plant and Apparatus and meters owned or operated by the Distribution Company in connection with the distribution of electricity, but does not include any part of the Transmission System.

Distributors

A person or company who distributes electricity under a licence granted by the Energy Commission under the Electricity Act 1990 acting in its capacity as a distributor in Peninsular Malaysia.

Double Circuit Overhead Line

A transmission line which consists of two circuits sharing the same towers for at least one span or more.


53

TERM

DEFINITION

Electric Power System

All the elements encompassing the production, transmission, distribution, and delivery electric power to Users.

External Interconnections

Apparatus for the transmission of electricity to or from the Transmission System or a Distribution System into or out of an External System. For the avoidance of doubt, a single External Interconnection may comprise several circuits operating in parallel.

Facility Contractual Available Capacity (in MW)

The available capacity of a generating in MW as agreed in the Power Purchase Agreement (PPA) between the Generator and TNB as the Single Buyer and precisely defined in individual PPA.

Fault Outage(s)

An outage due to an event occuring on electric system such as a short circuit, a broken wire or intermittent correction.

Flicker

Flicker is the sensation experienced by the human visual system when subjected to changes occurring in the illumination intensity of light sources. Persistently and rapidly varying illumination due to the System voltage changes caused by rapidly varying Loads such as arc furnaces can cause annoyance and adverse effects.

Flicker Severity (Long Term)

A value derived from 12 successive measurements of Flicker Severity (Short Term) (over a two hour period) and a calculation of the cube root of the mean sum of the cubes of 12 individual measurements, as further set out in Engineering Recommendation P28.

Flicker Severity (Short Term)

A measure of the visual severity of Flicker derived from the time series output of a Flicker meter over a ten (10) minute period and as such provides an indication of the risk of customer complaints.

Fluctuating Load

These are the types of non-linear Loads connected to Electric Power Systems causing rapid voltage fluctuations due to rapid variations in their active and reactive requirements dictated by the nature of the associated process or the process control requirements. Typical examples of such Loads are resistance welding machines, rolling mills, arc furnaces, arc welders, saw/woodchip mills, rock crushers and large scale lasers.


54

TERM

DEFINITION

Frequency

The number of alternating current cycles per second (expressed in Hertz) at which the Transmission System is running.

Generating Unit

Any Apparatus which produces electricity.

Generation Adequacy or Generation Security Standard

Generation Adequacy or Generation Security Standard relates to provision of sufficient firm Generation Capacity to meet the Total System Demand with a sufficient margin with allowance for plant maintenance, Plant breakdown and Plant Unavailability, i.e., scheduled and unscheduled generating Plant outages, to meet the annual and daily electric energy demand without the need to disconnect customers at critical periods or cause interruptions in supply.

Generation Capacity

The sum of the rated outputs of Generating Units connected to the Transmission System including allowances for reduction in the rating of units.

Generation Capacity Requirements

The total installed Generation Capacity required to meet the peak System demand during a specific period (normally a year) without violating the requirements specified in the Generation Reliability Standard.

Generation Reliability Standards

Standards relating to generation Reliability. See definition of Generation Adequacy and Security Standard.

Generation Circuit

The sole electrical connection between one or more Generating Units and the Main Interconnected Transmission System, i.e. a radial circuit which if removed would disconnect the Generating Units.

Generation Point A point at which a Generating Unit or a CCGT module, as the case may be, which is directly connected to the Transmission System, connects to of Connection the TNB Transmission System. For the purpose of defining the boundaries between the Main Interconnected Transmission System and Generation Circuits, the Generation Point of Connection is taken to be at point between the HV bushing and circuit breaker as per the Agreement


55

TERM Generator

DEFINITION A person or company who generates electricity under a licence granted by the Energy Commission under the Electricity Act 1990 acting in its capacity as a Generator in Peninsular Malaysia.

Grid Code

A document that sets out the principles governing the relationship between the GSO, Energy Commission, Single Buyer and all Users of the Grid System.

Infrequent Infeed Loss Risk

This is the Infrequent Infeed Loss Risk which is secured by TNB by long term provision of sufficient dynamic spinning reserve, Reactive Power reserve, and defence measures such as under Frequency Load and/or under voltage shedding, to avoid deviation of Frequency beyond the extremely rare limits, and voltage outside the unacceptable limits, defined in Chapter 4 of the Transmission System Reliability Standard. The Infrequent Infeed Loss Risk for the Peninsular Malaysian Power System is defined as 2100MW and will remain at that value until review of this Standard.

Insufficient Voltage Performance Margins

Insufficient Voltage Performance Margin occurs when the margin to the maximum possible transmitted power is less than that defined in Section 2 of Chapter 4 of the Transmission System Relibaility Standard.

Intact System

This is the Transmission System with no Outage i.e. with no arranged outages (e.g. for maintenance) and no unplanned outages (e.g. fault).

Largest Loss of Power Infeed Risk

This is the Largest of Loss of Power Infeed risk which is secured by TNB by long term provision of sufficient dynamic spinning reserve and Reactive Power reserve to avoid deviation of Frequency and voltage beyond normal operational limits defined in Chapter 4 of the Transmission System Reliability Standard for more than sixty (60) seconds. The Largest Loss of Power Infeed Risk for the Peninsular Malaysian Power System is defined as 700MW and will remain at that value until review of this Standard.

Large Power Stations

A Power Station with a Registered Capacity of 100MW or more.

Load

The Active, Reactive or Apparent Power, drawn by the particular


56

TERM

DEFINITION installation or equipment connected to the Transmission System.

Loss of Load Expectation

Refer to Loss of Load Probability

Loss of Load Probability

A reliability index that indicates the probability that some portion of the peak demand will not be satisfied by the available generating capacity as defined in these standards. It may also be expressed as an expected duration in a year for which the peak demand is not being met, in which case it is referred as Loss of Load Expectation (LOLE).

Loss of Power Infeed

The output of a Generating Unit or a group of Generating Units or the import from External Systems disconnected from the System by a Secured Contingency Event, less the demand disconnected from the System by the same Secured Contingency Event. For the avoidance of doubt if, following such a Secured Contingency Event, demand associated with the normal operation of the affected Generating Unit(s) is automatically transferred to a supply point which is not disconnected from the System, e.g. the station board, then this shall not be deducted from the total Loss of Power Infeed to the System. For the purpose of the operational Criteria, the Loss of Power Infeed, includes the output of a single Generating Unit, CCGT Module, boiler, or one pole of DC Link loss as a result of an event.

Loss of Supply Capacity

This is the reduction in the supply capacity at a Grid Supply Point as a result of TNB’s failure to maintain the potential to provide the supply capacity in full. For the avoidance of doubt, where TNB does maintain the potential to provide a supply but, following an outage, demand is lost because of circuit configurations not under the control of TNB, that lost supply does not constitute Loss of Supply Capacity.


Main Interconnected Transmission System (MITS) comprises all the 500kV and 275kV elements of the Transmission System but excludes Generation Circuits, transformer connections to lower voltage Systems and External Interconnections between the Transmission System and External Systems.

Main Protection

Protection equipment or system expected to have priority in initiating either a fault clearance or an action to terminate an abnormal condition in


57

TERM

DEFINITION an Electrical Power System.

Malaysian Electricity Supply Industry

All the parties associated with the generation, transmission, distribution and use of electrical energy and the institutions related to the governance thereof in Peninsular Malaysia.

Marshalling Substations

A substation which connects circuits from more than two line routes.

Network Operator

A person with a System directly connected to the Transmission System to which customers and/or Power Stations (not forming part of that System) are connected, acting in its capacity as an operator of that System, but shall not include a person who operates an External System.

Non-Embedded Customer

A customer in Peninsular Malaysia, except for a Network Operator acting in its capacity as such, receiving electricity direct from the Transmission System irrespective of from whom it is supplied.

Normal Operational Limits

Limits are those parameters defined in the Standards to indicate the performance of the System. The System is said to operating under Normal Operational Limits when all those limits defined in the Standards are met.

Peninsular Malaysian Electric Power System

The Electric Power System in Peninsular Malaysia supplying the demand, consisting of generation, transmission and distribution assets of TNB, Independent Power Producers, Distributors, Network Operators, Non-Embedded Customers and associated Networks.

Performance Requirements and Limits

These are the Performance Requirements and Limits derived from the Standard which describe the performance Criteria and limits applicable in the planning, operational planning and actual operation of the System which should be complied with in ensuring Security of the System together with the required quality of supply.

Phase Unbalance The inequality between the magnitudes of the three phase voltages at a specific point on the Transmission System where there is an appreciable difference due to either the inequalities between the Load connected to each phase and/or the inequalities of transmission line impedances in each Glossary and Defintions for Transmission System Reliability Standards and Transmission System Power Quality Standards

58

TERM

DEFINITION phase due to their geometry.

Planned Transfer Condition

The Planned Transfer Condition is defined as the condition arising from scaling the Registered Capacities of each directly connected Power Station and embedded Large Power Station such that the total of the scaled capacities is equal to the Peak Demand plus dynamic spinning reserve for Frequency control and minus imports from External Systems.

Plant

Fixed and movable items used in the generation and/or supply and/or transmission of electricity, other than Apparatus.

Point of Common Coupling

This is a point of connection of Fluctuating Loads to the TNB Electric Power System where other customers which may be adversely affected by such Loads are also connected.

Power Purchase Agreement

A commercial agreement between TNB and a Generator for the purpose of purchasing the power output of a particular generation Plant owned and operated by the Generator. This agreement also contains technical clauses relating to the connection and operation of the generation Plant.

Power Station

An installation comprising one or more Generating Units (even where sited separately) owned and/or controlled by the same Generator, which may reasonably be considered as being managed as one Power Station.

Pre-Fault Planning Voltage Limits Prevailing System Conditions

The voltage limits applicable in planning studies are as defined in Section 4.2 of the Transmission System Reliability Standard

Primary Transmission Equipment

Any equipment installed on the Transmission System to enable bulk transfer of power. This will include Transmission Circuits, Busbars, and switchgear.

Protection

The provisions for detecting abnormal conditions on a System and initiating fault clearance or actuating signals or indications.

These are conditions on the Transmission System prevailing at any given time and will therefore normally include arranged outages (e.g. for maintenance) and unplanned outages (e.g. fault).


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TERM Reactive Power

DEFINITION The product of voltage and current and the sine of the phase angle between them measured in units of voltamperes reactive and standard multiples thereof, i.e.: 1000 VAr = 1 kVAr 1000 kVAr = 1 MVAr

Reactive Power Reserve

The quantum of additonal reactive power from the Generating Units and/or additional output from both static and dynamic reactive compensation equipment to reach maximum reactive power output.

Registered Capacity

In the case of a Generating Unit other than that forming part of a CCGT Module, the normal full load capacity of a Generating Unit as declared by the Generator, less the MW consumed by the Generating Unit through the Generating Unit's unit transformer when producing the same (the resultant figure being expressed in whole MW.) In the case of a CCGT Module, the normal full load capacity of a CCGT Module as declared by the Generator, being the Active Power declared by the Generator as being deliverable by the CCGT Module at the Grid Entry Point (or in the case of an Embedded CCGT Module, at the User System Entry Point), expressed in whole MW.

Reliability

Reliability of an Electric Power System is defined as “The degree of performance of the elements of the bulk electric System that results in electricity being delivered to customers within accepted Standards and in the amount desired”. The level of “Reliability” may be measured by the frequency, duration, and magnitude of adverse effects on the electricity supply. A reliable Electric Power System is one that can cater for customer's electrical requirement with very few supply interruptions. It can be addressed by considering two basic and functional aspects of electric System i.e. Adequacy and Security.

Robustness

The ability of the System to contain the extent of a disturbance resulting from Unsecured Contingency Event into a wide scale outage or collapse.

RSS Rule

A rule used to assess at the planning stage, the resultant Flicker due to a Fluctuating Load connecting at a particular Point of Common Coupling and the background Flicker at that point. The assessment is carried out by obtaining the sum of the square of Flicker from the Fluctuating Load and


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TERM

DEFINITION the background Flicker and the square root of this sum will yield the total assessed Flicker at that Point of Common Coupling due to the specific Fluctuating Load and the background Flicker at that point in accordance with the procedure defined in P28.

Secured Contingency Event

A contingency which would be considered for the purposes of assessing System Security and which must not result in the losss of supply/demand and cause the remaining Transmission System to be in breach of the Security Criteria with respect to performance limit.

Security

The ability of the Electric Power System to withstand pre-defined specific types of sudden disturbances such as electric short circuits or unanticipated loss of System facilities.

Spinning Reserve

Unloaded generation that is synchronized and ready to serve additional demand.

Standard

A complete description of the required • nominal and limit values of particular system variable(s) • under normal and defined contingency conditions. • Standards are: – Obligatory; – Measurable; – Monitored; and require strict universal and unconditional compliance by all entities connected to the Transmission System. Standard as singular may also refer to a particular document containing several Standards defined above. ‘Standard’ as singular carries a meaning of a document as in ‘this Standard’. Standards as plural mean list of criteria, principles, measures etc.

Steady State

A condition of a power System in which all automatic and manual corrective actions have taken place and all of the operating quantities that characterise it can be considered constant for the purpose of analysis.

Supplementary Services

Services such as black start, MW response and reserve for Frequency control, AGC, Reactive Power, reactive energy, stand-by reserve and demand control.


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TERM

DEFINITION

System

Any User System and/or the Transmission System, as the case may be.

System Instability

System Instability means inability of electrical system to maintain a state of equilibrium during normal and abnormal condition or distrubances. This can take the form of the following: (i) poor damping - where electromechanical oscillations of Generating Units are such that the resultant peak deviations in machine rotor angle and/or speed at the end of a twenty (20) second period remain in excess of 15% of the peak deviations at the outset (i.e. the time constant of the slowest mode of oscillation exceeds twelve seconds); (ii) pole slipping - where one or more synchronous Generating Units lose synchronism with the remainder of the System; or (iii) voltage collapse - where progressive, fast or slow, voltage decrease or increase develops such that it can lead to partial or total System blackout.

Total System Demand

The total electrical demand that must be supplied through the Transmission System from generation and infeed through interconnectors, and includes directly connected demand, demand at Bulk Supply Points, exports through interconnectors and losses in the Transmission System.

Tenaga Nasional Berhad (TNB)

The registered incorporated company with separate generation, transmission and distribution divisions licenced to undertake generation, transmission and distribution activities under Electricity Act 1990 by the Electricity Commission, owner operator of the Main Interconnected Transmission System responsible for Security and integrity of the Peninsular Malaysian Electric Power System.

Thermal Rating

The maximum amount of electric current that a transmission line or electrical facility can conduct over a specific time period before it sustains permanent damage by overheating or before it sags to a point that it violate public safety requirement.

TNB Distribution

Distribution Division of Tenaga Nasional Berhad(TNB).


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TERM TNB Transmission

DEFINITION Transmission Division of Tenaga Nasional Berhad(TNB).

Transmission Adequacy or Transmission Security Standard

Transmission Adequacy or Transmission Security Standard relates to provision of sufficient Transmission Capacity, operational facilities, maintenance activity and co-ordination with generation and Distribution Functions to enable continued supply of electric energy to the distribution companies and Directly Connected Customers.

Transmission Capacity

The ability of a network or a connection to transmit electricity.

Transmission Circuit

Part of the Transmission System between two or more circuit-breakers which includes,for example, transformers, reactors, cables and overhead lines but excludes Busbars and Generation Circuits.

Transmission Equipment Outage

The loss of any element of the Transmission System due to a planned action or fault occurance.

Transmission Function

Transmission Function of an electric power utility is the function which owns and operates the Transmission System.

Transmission Investment Plan

TNB’s investment plans in developments of the Transmission System.

Transmission Power Quality

The quality of the bulk supply to be delivered to the Distribution System, at the bulk Demand Supply Points where the Distribution System is connected to the Transmission System, in terms of voltage and Frequency within specific limits so that Generator or consumer equipment directly connected to the Transmission System can operate safely within its design performance without suffering undue damage or breakdown.


The Standards, which specify the quality of the bulk supply to be delivered to the Distribution System, at the bulk Demand Supply Points where the Distribution System is connected to the Transmission System, in terms of voltage and Frequency within specific limits so that Generator or consumer equipment directly connected to the


63

TERM

DEFINITION Transmission System can operate safely within its design performance without suffering undue damage or breakdown.

Transmission System Reliability Standard

The Standards, determining the investment requirements for capital Plant and operational facilities; operation and maintenance practices; as well as provision of services to ensure levels of Transmission System performance in accordance with these Standards in the Peninsular Malaysian Transmission System or Transmission System.

Transmission Security Standard

See Transmission Adequacy and Transmission Security Standard.

Transmission System

The TNB Transmission System which comprises all the 500kV, 275kV, 132kV and 66kV elements but excludes Generation Circuits, transformer connections to lower voltage Systems and External Interconnections between the Transmission System and External Systems.

Unacceptably High or Low Frequency Conditions

These are conditions where: (i) the Steady State Frequency falls outside the statutory limits of 49.5Hz to 50.5Hz; or (ii) a transient Frequency deviation on the Main Interconnected Transmission System for Secured Contingency Event persists outside the above statutory limits and does not recover to within 49.5Hz to 50.5Hz within sixty (60) seconds.

Unacceptable Overloading

The overloading of any Primary Transmission Equipment beyond its Thermal Rating.

Unacceptable Voltage Conditions

For Steady State Voltages, the voltage is unacceptable if it is outside the limits set out in Section 4.2.3 of the Transmission System Reliability Standard. For Voltage Step Changes, the voltage is unacceptable if it changes by more than the limits set out Section 4.2.4 of the Transmission System Reliability Standard

Unavailability

A measure of the time a generating unit, transmission line, or other facility which is not capable of providing service, whether or not it actually is in service. Typically, this measure is expressed as a percentage of Unavailability of the item for the period under consideration.


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TERM

DEFINITION

Unsecured Contingency Events

A set of rare unplanned simultaneous or multiple contingencies which would be considered for the purposes of assessing System Security and Robustness, which could cause disruption to parts of the System and cause loss of customer demand against which special Protection and defence measures are incorporated in planning and operating the Transmission System. These type of contingency event are listed in category C and D of Table 4.12.

User

Persons connected to and using the Transmission System.

Users’ Plant and Apparatus

Plant and Apparatus owned and operated by a User.

User System

Any System owned or operated by a User comprising Generating Units and/or Systems consisting (wholly or mainly) of electric lines used for the distribution of electricity from Demand Supply Points.

Weak System

A system condition at minimum generation excluding short outages of transmission lines.


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APPENDIX A – Background to the Standards


66

Appendix A BACKGROUND TO THE STANDARDS

A1 Purpose A1.1 The purpose and the objective of this appendix is to provide the background to development and application of the Transmission System Reliability Standards and Transmission System Power Quality Standards and their relationship to other documents, technical codes and regulations governing the generation, transmission, bulk delivery, distribution of electric power to all Users. A1.2 The functions of Peninsular Malaysia Electric Power System, a comparison of Peninsular Malaysia Standards with international standards, and the outline contents of the Peninsular Malaysia Standards are shown in Figures A1 to A3. Generation

G

G

Generation Circuit

Bulk Production

Generation Point of Connection


Bulk Transport

Transmission

Demand Point of Connection

1. Transmission System Reliability Standards 2. Transmission System Power Quality Standards

Transmission radial network and demand points Bulk Delivery

Demand Supply Point DG

Distribution System DG

Distribution Embedded Distribution

Distribution


Customers

Fig A1: The functions of the Peninsular Malaysian Interconnected Transmission System and Outline of Associated Standards Appendix A – Background to the Standards

67

Generation

G

Generation Security Standard

G

Generation Circuit

Generation Connection Criteria

Generation Point of Connection

Main Interconnected Transmission System Transmission




Transmission Planning & Design Criteria



Demand Connection Criteria Quality of Supply Standard (Bulk Supply)

Demand Supply Point

Distribution Security Standards

DG


Customers

Transmission System Power Quality Standard


Distribution Power Quality Standards


Distribution


Typical International Standards

Peninsular Malaysia Standards

Fig A2: The Reliability and Power Quality Standards applicable to the Peninsular Malaysian Interconnected Transmission System shown in comparison with International Security and Quality of Supply Standards

Appendix A – Background to the Standards

68

G

Generation Circuit Generation Point of Connection




Transmission



Transmission System Power Quality Standard

Demand Supply Point


DG



Distribution

Peninsular Malaysia Standards

Customers

Sufficient transmission and transformer capacity to meet the demand for specified contingencies with limits set in the Transmission System Power Quality Standards Criteria for planning & designing the Transmission System that will deliver the Transmission system Reliability and Power quality Standards

GRID CODE

G


Sufficient transformer capacity in accordance with the size of demand Limits of voltage, frequency, harmonics, Flicker etc. variations for specified contingencies

Sufficient distribution capacity to meet the demand for specified contingencies within the Power Quality Limits

Fundamental Contents of the Standards

DISTRIBUTION CODE

Generation

Sufficient generation capacity and connections to deliver full generation output for normal and specific Contingencies

Fig A3: The outline contents of Reliability/Security and Power Quality of Supply Standards


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A2 Standards for Bulk Generation, Transmission and Delivery A2.1 In large interconnected electric power Systems the Reliability and power quality are of utmost importance as electricity is an essential commodity, which underpins the economic activity. The Transmission Function of an electric power System is pivotal to the objectives of: (1) Developing and maintaining an efficient, coordinated and economical Transmission System for bulk delivery of electricity supply; (2) Ensuring continuous availability of sufficient energy supply for all consumers with an adequate margin to ensure continuity of supply catering for equipment maintenance and breakdown; and (3) Ensuring defined levels of power quality which enables purchase, connection and safe operation of equipment. A2.2 In order to achieve the above objectives, the electric power Transmission System needs to be planned, operated and maintained according to a set of Transmission System Reliability and Power Quality Standards. The application of these Standards determines the investment requirements for capital Plant and operational facilities; operation and maintenance practices; as well as provision of services for the Transmission System. The Transmission System Reliability Standards include Generation Reliability Standards and Transmission Reliability Standards which ensure Adequacy and secure planning and operation of generation and transmission facilities. A2.3 The transmission planning and development process involves the application of: (1) Generation Reliability Standards; (2) Transmission Reliability Standards; and (3) Transmission System Power Quality Standards. together with strategic, environmental and economic analysis, to determine the planned development of the Transmission System to meet the forecast future demand. The operational processes also involve application of these Standards in operational planning, maintenance and actual operation of the power System under the Prevailing System Conditions on the actual operational day. Whilst the System operational conditions are carefully planned at the operational planning stage, in the months, weeks and days ahead, the operation of the System on the day is dictated by the prevailing actual climatic conditions, planned outages as well as the unplanned events that occur on the day, such as unscheduled generation breakdown, unplanned transmission outages due to faults and exceptional demand. The Standards provide the limits and permissible excursions of key System parameters in the form of Performance Requirements and Limits. Appendix A – Background to the Standards

70

Compliance with these limits enables secure and safe operation of the System within the capability of the equipment constituting the System as well as connected equipment. A2.4 The Transmission System Reliability Standards and Transmission System Power Quality Standards mentioned above therefore determine a defined level of Reliability and quality for electric power that is delivered at the bulk Demand Supply Points where the Distribution System is connected to the Transmission System as well as the points where Users are directly connected. A2.5 The provision of levels of Transmission System performance in accordance with these Standards is the duty of Transmission Function of Tenaga Nasional Berhad (TNB) under Condition 13 of the TNB Licence granted under the Electricity Supply Act, 1990 on 1st September 1990.

A3 Standards for Distribution A3.1 In large electric power Systems the Distribution Systems are pivotal to achieving the objectives of: (1) Developing and maintaining an efficient, coordinated and economical Distribution System for delivery of electricity supply from Bulk Supply Points to consumers; (2) Ensuring defined levels of power quality which enables purchase, connection and safe operation of consumer equipment. A3.2 In order to meet the objectives listed in paragraph A3.1, the electric power Distribution System also needs to be planned, operated and maintained according to a set of Distribution Supply Security and Power Quality Standards. The development of these Standards, determine the investment requirements for capital Plant and operational facilities; operation and maintenance practices; as well as provision of services to ensure levels of Distribution System performance in accordance with these Standards is the duty of the Distribution Function of Tenaga Nasional Berhad (TNB) under Condition 14 of the TNB Licence granted under the Electricity Supply Act, 1990 on 1st September 1990 and other Users with their own Distribution Functions which are similarly licenced. There is also the distribution planning process that involves the application of Distribution Supply Security and Power Quality Standards, together with strategic, environmental and economic analysis, to determine the planned development of the Distribution System to meet the forecast future demand. The operational processes involve application of these Standards in operational planning, maintenance and actual Appendix A – Background to the Standards

71

operation of the Distribution System under the Prevailing System Conditions on the actual operational day.

A4 Processes and Procedures A4.1 This Appendix A (and the main document) is solely concerned with the Transmission System Reliability Standards and Transmission System Power Quality Standards which are the Standards applicable to bulk generation, transmission and delivery of electric power. These Standards are also reflected in the Grid Code which contains all the technical and operational codes governing the planning, development, connection to and operation of the generation and bulk Transmission System. The Distribution Supply Security and Power Quality Standards are contained in a separate document and are reflected in the Distribution Code which contains all the technical and operational codes governing the planning, development, connection to and operation of the Distribution System. A4.2 The following distinct processes and their related Standards are recognised by international best practice as paramount in ensuring Reliability, Security and quality of supply in planning the development of an electric power System, namely: (1) Generation Security Standard which relates to provision of sufficient firm Generation Capacity to meet the Demand with a sufficient margin with allowance for Plant maintenance, Plant breakdown and Plant Unavailability, i.e., scheduled and unscheduled generating Plant outages, to meet the annual and daily electric energy demand without the need to disconnect customers at critical periods or cause interruptions in supply. This Standard will be used by TNB Transmission Division to forecast additional generation investment requirements on an annual basis. The EC is responsible for implementation of policies ensuring generation Adequacy. (2) Transmission Security Standard which relates to provision of sufficient Transmission Capacity, operational facilities, maintenance activity and coordination with generation and distribution functions to enable continued supply of electric energy to the distribution companies and Directly Connected Customers. This Standard is used by TNB Transmission Division to determine the investment requirements for the Transmission System and transmission operational facilities and implement the necessary measures. (3) In the case of the Peninsular Malaysian Electric Power System the Generation Security and Transmission Security requirements are combined and recognised as the Transmission System Reliability Standards.


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(4) This Standard includes the Transmission System Power Quality Standards, which specify the quality of the bulk supply to be delivered to the Distribution System, at the bulk Demand Supply Points where the Distribution System is connected to the Transmission System, and to Directly Connected Customers to the Transmission System, in terms of voltage and Frequency within specific limits so that Generator or consumer equipment directly connected to the Transmission System can operate safely within its design performance without suffering undue damage or breakdown. Consequently these Standards also determine the investment required in provision of Supplementary Services such as Reactive Power, Active Power response, Automatic Generation Control (AGC), hot standby generation, fast start generation, demand control and black start by TNB Transmission. They also indicate the investment required both in the Transmission System and Distribution Systems for containing harmonics, voltage unbalance as well as the permitted types and levels of special Loads adversely affecting the power quality and requirements for compensation Plant to limit their adverse effects. Compliance with these Standards is the responsibility of TNB Transmission Division and the interfacing Generating Companies, Distributors, Network Operators and Directly Connected Customers. Ensuring compliance of all parties with these Standards is the responsibility of TNB Transmission Division. A4.3 These Standards only covers the Transmission System Reliability Standards and Transmission System Power Quality Standards, which are the responsibility of TNB Transmission Division. Discussion of proposals to amend or change these Standards is ensured through Energy Commission (EC) by TNB. The compatibility between the Standards contained in this document and Distribution Supply Security and Power Quality Standards is ensured through the Energy Commission (EC) by TNB. A4.4 The Transmission System Reliability Standards and Transmission System Power Quality Standards included in this document have been derived from previous documents reflecting the Reliability and power quality practices developed and adopted through the years and against which investments have already been made to ensure compliance. These documents include: (1) TNB Operation Planning Standards July 1998 (2) Guidelines of Power Quality Control for Connection to the Grid System (Issue 2 July 1998 and Revision 2004) (3) Generation Planning Criteria and Methodology (Rev1/2002, November 2002) (4) TNB Transmission Network Planning Manual (April 1998) (5) Planning Criteria, Study Assumptions and Methodology – 1998 (6) Voltage Control Policy – 2000 Appendix A – Background to the Standards

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(7) Interconnection Agreements with Singapore and Thailand (8) TNB Licence (1 September 1990) A4.5 The aim of the Transmission System Reliability Standards, Transmission System Power Quality Standards, Distribution Supply Security and Power Quality Standards is to ensure sufficient investments in generation, transmission and Distribution Systems and operational facilities. This means that if the facilities to meet the above Standards are provided then the Reliability and power quality of supply will be ensured within the defined Standards at both the transmission bulk delivery point and the consumer terminals. In this respect, it is important to note that the primary objective of the Criteria within these Standards is maintaining the integrity of the electric power System under a set of defined System contingencies, representing the most common, frequent and probable contingencies that occur from time to time, related to Plant breakdown, adverse weather or adverse operational conditions. This ensures that the power System is planned and developed in a co-ordinated, economic and efficient manner without making unnecessary investments to cater for events, which may very rarely or never occur. It follows therefore that if the electric power System experiences disturbances beyond those defined within the Criteria then it is likely that some loss of supply will occur. Provision of System investments and operational facilities to eliminate such rare System contingencies may be prohibitive. The implementation of any proposed changes to the existing Criteria within the Standards will therefore need to be examined in terms of the costs and the benefits of the proposed changes. A4.6 In certain cases it may be desirable to provide additional Reliability, Security and power quality for certain Loads over and above that designated within the above Standards. In such cases, the additional capital investment requirements will need to be met by the party or parties seeking provision of the enhanced Reliability and quality. As part of its Licence obligation it is the duty of TNB Transmission Division to make appropriate investments to provide a connection and supply in line with these Standards. Provision of a connection and supply with higher Reliability and power quality is subject to commercial negotiation. A4.7 Additional detailed technical Criteria, related to quality of supply and coordination of System Protection facilities, are included in the Grid Code and the Distribution Code. These Criteria together with the basic planning criteria referred to in the Transmission System Reliability Standard ensure development of all the Transmission System and facilities connected to it in a compatible manner. The application of the above Standards in operational planning and on the day operation, ensures day to day operation of the System compatible with the Appendix A – Background to the Standards

74

Generation, Transmission and Distribution Systems available on the day to meet the demand under prevailing System and System contingency conditions. A4.8 Any Transmission Investment Plan proposed for adoption under these Criteria must ultimately be justifiable taking account of economic, financial, strategic and environmental considerations in accordance with the economic and environmental policy documents established under the terms of the TNB Licence. A4.9 Under the provisions of TNB Licence the Transmission and Distribution Functions of TNB are charged with the duties of preparing annual: (1) investment plans to develop an efficient, co-ordinated and economical Transmission System and international interconnections with neighbouring countries Transmission Systems; and (2) projections of Generation Capacity requirements, based on demand forecasts prepared by its own Distribution Function and other distribution companies. A4.10 The Transmission Investment Plans and Generation Capacity Requirements are subject to the scrutiny of EC in accordance with the Conditions 7 and 12 of the TNB Licence. Under Condition 10 of its Licence, TNB is obliged to furnish EC with details of “updated plans and capital programme, expenditure programme, covering generation, transmission and distribution for the next ten (10) years before the end of each financial year itemising details of major projects details of all assumptions and a reconciliation between planned and actual expenditure in the preceding financial year together with explanation of significant variations”. Under Condition 4 of the TNB Licence, TNB is prohibited from undue preference and discrimination towards consumers wishing to connect to its System. Finally, under Condition 8 of the TNB Licence and other Conditions such as 7, 10 and 12 TNB provides sufficient information to EC about the status of the electricity supply Reliability and power quality both at the point of connection to the Transmission System and to the Distribution System. A4.11 Clearly the development plans for generation, transmission and distribution need to be consistent and compatible with each other and extend to cover a mediumterm planning horizons of at least ten (10) years. The responsibility for the consistency of plans and developments rests with the EC as stated in the Electricity Supply Act 1990. The plans are prepared to achieve the levels of investment leading to full compliance with the Transmission System Reliability Standards, Transmission System Power Quality Standards, Distribution Supply Security and Power Quality Standards taking into account existing provisions to meet these Standards. These Standards will also be reflected in the terms offered by TNB to parties wishing to connect to the Transmission and Distribution Appendix A – Background to the Standards

75

Systems. Therefore, in order to ensure satisfactory development of the Peninsular Malaysian Electric Power System, these Standards and the additional detailed technical Criteria related to quality of supply and coordination of System Protection facilities included in the Grid Code and the Distribution Code, must be complied with by all parties connected to the Peninsular Malaysian Electric Power System as part of their Licence Conditions. A4.12 The adequate and secure development of the Transmission System as well as the generation and Distribution Systems connected to it delivering defined levels of power quality at both the bulk power delivery points and consumer terminals will be conditional on: (1) Remedial investments to remove inadequacies and shortfalls from the specified Standards in Generation, Transmission and Distribution Systems will be approved and made; (2) All Plant connected to the System will be operated in accordance with the technical parameters set in the Grid Code and the relevant Agreements; (3) All control Systems will be set as expected in the Grid Code and appropriate Agreements to meet power System operational requirements and will be normally kept in service unless otherwise requested by the Grid System Operator; (4) In the absence of any prior notice for non-compliance by any User, TNB cannot be considered responsible for System events where non-compliant Plant has had significant contributory or sole factor role or where the noncompliance is exposed by a System event; (5) External Interconnections will be operated in accordance with the Available Transfer Capacity and appropriate Interconnection agreements; (6) TNB cannot be responsible for erroneous or invalid data submitted by other parties; (7) TNB Transmission Division and TNB Distribution Division are the sole responsible respective parties for demonstrating the need for and the economics of Transmission and Distribution System development. A4.13 Design and operation of External Interconnections between the Peninsular Malaysian and other power Systems such as Singapore and Thailand are covered by other agreements which are consistent with this Standard. This Standard may therefore be referenced in the relevant agreements and shall apply to the extent of that specific reference. A4.14 In the course of verifying compliance with this Standard, TNB Transmission Division may identify cases of non-compliance with this Standard due to inadequate capability of equipment or Systems not owned or operated by TNB Appendix A – Background to the Standards

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(for example, the overloading of lower voltage connections). In such cases TNB will notify the affected parties. Reinforcement or alternative operation of the Transmission System to alleviate inadequacies of equipment or Systems not owned or operated by TNB would be undertaken where it is agreed by both TNB and the affected parties. A4.15 Given the continuous development of the power System, while it is a requirement for TNB to provide sufficient Transmission Capacity to meet the planning Criteria contained within these Standards, it does not follow that the Transmission Capacity should be reduced so that it only meets the minimum requirement of those Criteria. For example, it may not be beneficial to reduce the ratings of lines to reflect lower loading levels which have arisen due to changes in the generation or demand patterns. A4.16 All parties connected to the Transmission System and/or to the Main Interconnected Transmission System in Peninsular Malaysia shall comply with the provisions of this Standard in planning, developing, maintaining and operating their individual Systems as related to their specific connections and Plant. Compliance is an essential part of ensuring secure and robust operation of the Peninsular Malaysia Electric Power System and is therefore not optional as these Standards represent the minimum requirements necessary to achieve the appropriate Adequacy, Security and Robustness.

A5 Summary A5.1 As described above and illustrated in Figures A1 to A3 of this Appendix A and Figure 1.1 of the Transmission System Reliability Standards, there will be many parts of the TNB Transmission System where more than one set of Criteria apply. In such places the requirements of all relevant Criteria must be met. A5.2 In each of Chapters 2 and 3 of the Transmission System Reliability Standard, planning is the first to be set out, followed by operational Criteria. The planning Criteria set out the requirements for the Transmission Capacity for the TNB Transmission System. The planning Criteria also require consideration to be given to the operation and maintenance and so refer to the associated operational Criteria. The operational Criteria are used in real time and in the development of plans for using the Transmission System to permit satisfactory operation. A5.3

In the course of verifying compliance with the Standards, TNB Transmission Division may identify cases of non-compliance with the Standards due to


77

inadequate capability of equipment or Systems not owned or operated by TNB (for example, the overloading of lower voltage connections). In such cases, TNB will notify the affected parties. Reinforcement or alternative operation of the Transmission System to alleviate inadequacies of equipment or Systems not owned or operated by TNB would be undertaken where it is agreed by both TNB and the affected parties. A5.4

Finally, by giving a clear understanding of the Reliability and power quality Criteria used in the design and operation of the System in this Standard a clear distinction is drawn between the planned Security and Robustness measures included in the System. The concepts of planned Security and Robustness are illustrated in Figure A4. In this respect “planned Security” refers to “design and operational measures put in place to ensure that the power System continues to operate normally after the occurrence of the specific pre-defined sudden disturbances such as electric short circuits or unanticipated loss of System facilities designated in the Security Criteria”. On the other hand “planned Robustness” refers to “design and operational measures put in place to ensure that the power System quickly recovers from disturbances developing to beyond those specified in the Security Criteria, the performance benchmark being the avoidance of total blackout”.

LEVEL 1

LEVEL 2

LEVEL 3

LEVEL 4

OPERATIONAL SECURITY MANAGEMENT SYSTEMS

AUTOMATIC VOLTAGE AND FREQUENCY REGULATION EQ.

DUPLICATE MAIN PROTECTION TRIPLE GRADING

UNDER FREQUENCY LOAD SHEDDING

BACK-UP PROTECTION FAIL-SAFE FAULT REMOVAL

EMERGENCY AUXILIARY SUPPLIES

FAST RECLOSURE FOR FAST RESTORATION

ISLANDING AND HOUSE LOAD OPERATION

MANUAL AND UNDER VOLTAGE LOAD SHEDDING

EMERGENCY FAST START GENERATION

AUTOMATIC FAST ACTIVE & REACTIVE POWER RESERVES

PERFORMANCE MONITORING AND FAULT IDENTIFICATION

OPERATIONAL SECURITY MANAGEMENT SYSTEMS AND PLANNED AUTOMATIC RESERVES FOR FIRST CONTINGENCY LEVEL LAYERS OF PROTECTION TO RAPIDLY REMOVE THE FAULT TO PREVENT TOTAL SYSTEM BLACKOUT IN MULTIPLE CONTINGENCIES TO ENSURE FAST RECOVERY FROM SEVERE CONTINGENCIES

Figure A4: Planned Security – Levels of Designed Operational Measures


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APPENDIX B for Transmission System Reliability Standards – Guidance on Economic Justification of Generation and Transmission Connections

© TENAGA NASIONAL BERHAD, 2006 79

Appendix B GUIDANCE ON THE ECONOMIC JUSTIFICATION OF GENERATION AND TRANSMISSION CONNECTIONS B1 General Principles B1.1

These guidelines may be used to assist in the: i) economic justification of investment in transmission equipment and/or provision of Supplementary Services such as Reactive Power in addition to that required to meet the planning Criteria of the Transmission System Reliability Standards and the Transmission System Power Quality Standards; ii) evaluation of any expected additional operational costs or investments resulting from a proposed variation in connection design under the provisions of paragraphs 2.3.2.10 to 2.3.2.12 of Chapter 2 Transmission System Reliability Standards and/or paragraphs 2.3.3 to 2.3.7 of Chapter 2 of the Transmission System Power Quality Standards.

B2 Guidelines B2.1

The following are the guidelines: i) additional investment in transmission equipment and/or the provision of supplementary services would normally be justified if the net present value (NPV) of the additional investment cost are less than the net present value of the expected operational or unreliability cost that would otherwise arise. ii) the assessment of expected operational costs and the potential Reliability implications shall normally require simulation of the expected operation of the Transmission System in accordance with the operational criteria set out in Chapters 2, and 3 of the Transmission System Relaibility Standards and criteria set out in Chapter 2 of the Transmission System Power Quality Standards. iii) the operational costs to be considered shall normally include those arising from: • transmission power losses; • Frequency response; • reserve; • Reactive Power requirements; and • System constraints, and may also include costs arising from:

Appendix B for Transmission System Reliability Standards – Guidance on Economic Justification of Generation and Transmission Connections

80

• rearrangement of transmission maintenance times; or • modified or additional contracts for other services. iv) all costs should take account of future uncertainties v) the evaluation of unreliability costs expected from operation of the Transmission System shall normally take account of the number and type of customers affected by supply interruptions and use appropriate information available to facilitate a reasonable assessment of the economic consequences of such interruptions.

Appendix B for Transmission System Reliability Standards – Guidance on Economic Justification of Generation and Transmission Connections

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APPENDIX C for Transmission System Reliability Standards – Guidance on Substation Configurations and Switching Arrangements


Appendix C GUIDANCE ON SUBSTATION CONFIGURATIONS AND SWITCHING ARRANGEMENTS C1 General Guidance C1.1 The key factors which must be considered when planning a substation include: i) Security and Quality of Supply Relevant Criteria are presented in Chapters 2, and 3 of the Transmission System Reliability Standards and Chapter 2 of the Transmission System Power Quality Standards. ii) Extendibility The design should allow for the forecast need for future extensions. iii) Maintainability The design must take account of the practicalities of maintaining the substation and associated circuits. iv) Operational Flexibility The physical layout of individual circuits and groups of circuits must permit the required power flow control. v) Protection Arrangements The design must allow for adequate protection of each System element. vi) Short Circuit Limitations In order to contain short circuit currents to acceptable levels, Busbar arrangements with sectioning facilities may be required to allow the System to be split or re-connected through a fault current limiting reactor. vii) Land Area The low availability and/or high cost of land particularly in densely populated areas may place a restriction on the size and consequent layout of the substation. viii) Cost C1.2 Accordingly the design of a substation is a function of prevailing circumstances and future requirements as perceived in the planning time phase. This appendix is intended as a functional guidance for substation layout design and switchgear arrangements. Variations away from this guidance are permissible provided that such variations comply with the requirements of the Criteria set out in the main text of the Transmission System Reliability Standard.

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C2 Generation Point of Connection Substations C2.1 In accordance with the planning Criteria for generation connection set out in Chapter 2 of the Transmission System Reliability Standards, Generation Point of Connection substations should: a. have a double Busbar design (i.e. with main and reserve Busbars such that Generation Circuits and Transmission Circuits may be selected to either); b. have sufficient Busbar sections to permit the requirements of paragraph 2.3.2.3 of the Transmission System Reliability Standards to be met without splitting the substation during maintenance of Busbar sections; c. have sufficient Busbar coupler and/or Busbar section circuit breakers so that each section of the main and reserve Busbar may be energised using either a Busbar coupler or Busbar section circuit breaker; d. have Generation Circuits and Transmission Circuits disposed between Busbar sections such that the main Busbar may be operated split for fault level control purposes; and e. have sufficient facilities to permit the transfer of Generation Circuits andTransmission Circuits from one section of the main Busbar to another.

C3 Marshalling Substations C3.1 Marshalling Substations should:i) have a double Busbar design (i.e. with main and reserve Busbars such that Transmission Circuits may be selected to either); ii) have sufficient Busbar sections to permit the requirements of paragraphs 2.3.2.3 and 3.2.2.2 of the Transmission System Relaibility Standards to be met; iii) have Transmission Circuits disposed between Busbar sections such that the main Busbar may be operated split for fault level control purposes; and iv) have sufficient facilities to permit the transfer of Transmission Circuits from one section of the main Busbar to another.

C4 Grid Supply Point Substations C4.1 In accordance with the planning Criteria for demand connection set out in Chapter 3 of the Transmission System Relaibility Standards, Demand Supply Point substations configurations range from a single transformer feed into a Transmission Circuit to a four switched mesh substation or a double Busbar substation. The choice and need Appendix C for Transmission System Reliability Standards – Guidance on Substation Configurations and Switching Arrangements

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for the extendability will depend on the circumstances as perceived in the planning time phase.


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C5(1) Typical TNB Substation Layout and Switching Arrangements

275kV

TNB Transmission

User

G

G

Generation Spur

275kV/132kV

Generation Loop-in Loop-out

TNB Transmission

User G G

LV


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C5(2) Typical TNB Substation Layout and Switching Arrangements – cont’d

132kV

Network Connection

132kV

TNB Transmission

132kV

Main Intake Substation

Switching Station

11kV User

North Busbar

275kV

South Busbar 500/275kV Transformers 750MVA

One and Half Breaker Arrangement

North Busbar

500kV

South Busbar


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APPENDIX D for Transmission System Reliability Standards – Additional Criteria to Limit the Complexity of Transmission Circuits


Appendix D ADDITIONAL CRITERIA TO LIMIT THE COMPLEXITY OF TRANSMISSION CIRCUITS D1 General Principles D1.1 This appendix defines three restrictions to be applied by TNB Transmission when Transmission Circuits are designed, constructed or extended. These restrictions are intended to ensure that the time required to isolate and earth circuits in preparation for maintenance work is kept to a minimum and is not disproportionate to the time required to carry out maintenance work. The restrictions also limit the potential for human error.

D2 Requirements/Restrictions D2.1 The three restrictions to be applied to Transmission Circuits are as follows. i) The facilities, for the isolation and earthing of Transmission Circuits and Transmission Equipment, shall not be located at more than three individual sites; ii) The normal operational procedure, for the isolation and earthing of Transmission Circuits and Transmission Equipment, shall not require the operation of more than six (6) circuit-breakers; and iii) No more than three (3) transformers shall be connected together and controlled by the same circuit breaker. D2.2 A site, in this context, is defined as being where the points of isolation at one end of a Transmission Circuit are within the same substation such that only one authorised person is required, at the site, to enable the efficient and effective release and restoration of the circuit. D2.3 If the design of a substation is such that two circuit-breakers of the same voltage are used to control a circuit (e.g. in a mesh type of substation), for the purposes of the above restrictions the two circuit-breakers are to be considered as a single circuitbreaker. This also applies where duplicate circuit-breakers control a circuit including those used for Busbar selection. D2.4 Switch disconnecters are not rated for fault breaking duty and should not be included in the design of new Transmission Circuits and substations. Where the Appendix D for Transmission System Reliability Standards – Additional Ciriteria to Limit the Complexity of Transmisison Cicuits

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extension of an existing Transmission Circuit includes an existing switch disconnecter, that switch disconnecter can be considered for use in planned switching procedures only. D2.5 For the purposes of restriction in D2.1(iii) of this Appendix D, a transformer which includes two low voltage windings in its construction shall be considered as single transformer.

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Malaysia Transmission System Reliability Standards

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