TRANSMISSION ENGINEERING STANDARD
TES-P-122.01, Rev. 0
TABLE OF CONTENTS
1.0
PURPOSE
2.0
SCOPE
3.0
CODES, STANDARDS & REFERENCES
4.0
ORDER OF PRECEDENCE
5.0
SYSTEM PARAMETERS 5.1 5.2
Frequency Voltage
6.0
INSULATION LEVELS
7.0
SYSTEM CONVENTIONS 7.1 7.2 7.3
Circuit Configuration Phase Designation Phasing Sequence
8.0
SHORT CIRCUIT RATING
9.0
STRUCTURAL SUPPORTS
10.0
INSULATORS 10.1 10.2 10.3
Creepage Distance Insulators in the Coastal Zone Insulators in the Inland Area
TEP122.01R0/MAA
Date of Approval: October 17, 2006
PAGE NO. 2 OF 20
TRANSMISSION ENGINEERING STANDARD
11.0
HARDWARE
12.0
ENVIRONMENTAL CONSIDERATIONS 12.1 12.2 12.3
Appearance Public Safety Polluted Environment
13.0
WEATHER CONDITIONS
14.0
DESIGN INFORMATION 14.1 14.2
15.0
Wind Velocities Soil Conditions
OBSTRUCTION MARKING AND LIGHTING 15.1 15.2
Spherical Markers Warning Lights
16.0
TRANSPOSITION
17.0
LINE IDENTIFICATION 17.1 17.2 17.3 17.4 17.5
18.0
Circuit Designation Voltage Level Designation Structure Numbering Structure Identification Phase Identification
LIGHTNING PERFORMANCE 18.1 18.2
19.0
TES-P-122.01, Rev. 0
Outage Rate Due To Lightning Overhead Ground Wires
BIBLIOGRAPHY
TEP122.01R0/MAA
Date of Approval: October 17, 2006
PAGE NO. 3 OF 20
TRANSMISSION ENGINEERING STANDARD
1.0
TES-P-122.01, Rev. 0
PURPOSE The purpose of this standard is to clearly define design philosophy and practices adopted by SEC to enable the design engineer to develop cost effective designs of SEC Transmission Lines. This standard is intended to serve as a reference and to give guidelines to SEC engineers for engineering, design, construction, operation and maintenance of Transmission Lines in SEC system. It is understood that consulting engineers, designers, manufacturers, lump sum turnkey contractors and such other agencies that do business with SEC in various capacities shall use this standard.
2.0
SCOPE This standard: 2.1
Covers transmission lines for 69 kV, 110kV, 115 kV, 132kV, 230 kV and 380 kV systems.
2.2
Generally deals with the design philosophy and design practices as adopted by SEC based on management directives, policy guidelines and the operation and maintenance experience gained by SEC over a period of time particularly in the onerous environmental conditions experienced in SEC franchise area.
2.3
Lays down the system parameters and tolerance limits as have been enunciated by SEC and indicates the design criteria for various systems such as wood poles, lattice structures, steel poles etc., which have been adopted by SEC as a result of studies conducted from time to time.
2.4
Indicates ratings for various equipment and hardware, which have so far been standardized by SEC.
2.5
Gives certain basic concepts of design, engineering, general assumptions and guidelines, methods of calculations, typical examples for transmission lines to be designed for various voltage levels for SEC network.
2.6
Intends to minimize the frequent references by the design engineers to various international standards, other texts or technical papers and intends to furnish the minimum needed information at one place, for particular use in SEC system.
2.7
Does not intend to replace the international or national standards or other reference documents.
2.8
Does not specify the material standard specifications for various materials and equipment, which are covered separately under SEC Transmission Materials Standard Specifications (TMSSs).
TEP122.01R0/MAA
Date of Approval: October 17, 2006
PAGE NO. 4 OF 20
TRANSMISSION ENGINEERING STANDARD
3.0
4.0
TES-P-122.01, Rev. 0
2.9
Assumes that all materials and equipment that are used in the transmission line meet the requirements specified in the respective TMSS.
2.10
Does not cover the construction requirements of the transmission line, which are covered under SEC Transmission Construction Standards (TCSs).
CODES, STANDARDS AND REFERENCES 3.1
Applicable codes, standards and other reference materials have been indicated in each chapter of this "Transmission Line Design Standards (TES-P-122)".
3.2
Items not specifically covered in this standard (TES-P-122) shall be in accordance with the latest revisions of the referenced Industry Codes and Standards.
3.3
It shall be the responsibility of the design engineer preparing the base design or detailed design to be or become knowledgeable of the requirements of the latest Industry Codes and Standards referred in TES-P-122. He shall bring to the attention of SEC, any latest revisions of these Codes and Standards, which may have an impact on the technical requirements of TES-P-122.
3.4
Whenever equivalent Codes and Standards are used SEC approval to the same shall be obtained before proceeding with the design. The equivalent Codes and Standards shall be equal to or better than those specified in TES-P-122. Copy of the equivalent Codes and Standards and the comparison with the specified Codes and Standards shall be provided to SEC for review and acceptance. ,
ORDER OF PRECEDENCE In case of any conflict between various documents and standards or specifications, the order of precedence shall be as follows: 4.1
The Scope of Work and Technical Specifications (SOW/TS) for any project
4.2
SEC Transmission Materials Standard Specifications (TMSSs)
4.3
The Transmission Line Construction Standard TCS-P-122
4.4
This Transmission Line Design Standards (TES-P-122) If there is any conflict between different chapters of TES-P-122, and/or TCSP-122 then the applicable chapter shall have the precedence over the other chapters
4.5
Other applicable SEC Engineering Standards (TESs)
4.6
Applicable Industry Codes and Standards
TEP122.01R0/MAA
Date of Approval: October 17, 2006
PAGE NO. 5 OF 20
TRANSMISSION ENGINEERING STANDARD
5.0
TES-P-122.01, Rev. 0
SYSTEM PARAMETERS 5.1
Frequency The nominal frequency for SEC system is 60 Hz and the permissible operating frequency range is between 59.9 Hz and 60.1 Hz. The transient frequency variations shall be between 58.5 Hz and 61.5 Hz.
5.2
Voltage The standard nominal system voltages adopted by SEC are listed in Table 01-1. The permissible operating voltage range is ± 5% under normal operating conditions and ± 10%, for 30 minutes, under emergency operating conditions. These are detailed in Table 01-1. Table 01-1: Permissible Operating Voltage Ranges
6.0
Nominal System Voltage (kVrms)
Voltage Range (Normal Operating Condition), kVrms
Voltage Range (Emergency Operating Condition for 30 minutes), kVrms
69
65.6-72.5
62.1-75.9
110
104.5-115.5
99-121
115
109.3-121
103.5-126.5
132
125.4-138.6
118.8-145.2
230
219-241.5
207-253
380
361-399
342-418
INSULATION LEVELS The insulation levels for all equipment shall not be less than the values specified in Table 01-2. For installations at an altitude higher than 1000 m, the insulation requirements shall be calculated by multiplying the insulation value indicated in the Table 01-2 below by the altitude correction factor as specified in IEC 60694 & IEC 60071-1. Basic lightning impulse insulation levels (BIL) are specified with respect to a standard 1.2/50 μs wave shape and the basic switching impulse insulation level (BSL) is specified for a 250/2500 μs impulse.
TEP122.01R0/MAA
Date of Approval: October 17, 2006
PAGE NO. 6 OF 20
TRANSMISSION ENGINEERING STANDARD
TES-P-122.01, Rev. 0
Table 01-2: Insulation Levels
Nominal System Voltage (kVrms)
Basic Insulation Level (BIL), kVPeak
Power Frequency Withstand Votage *Dry/Wet, (kVrms)
Basic Switching Impulse Level (BSL), kVrms
69
350
160/140
-
110
650
275/275
115
650
275/275
-
132
750
325/325
-
230
1050
460/460
-
380
1425
620/620
1050
*Dry for 1 minute, wet for 10 seconds
7.0
SYSTEM CONVENTIONS 7.1
Circuit Configuration Three-phase three wire (3φ-3W) circuit configuration shall be used throughout SEC system for all voltage levels from 380 kV down to 69 kV.
7.2
Phase Designation The phases shall be designated as R (Red), Y (Yellow) and B (Blue) for untransposed lines, when viewed from East to West, from North to South, and Top to Bottom. For transmission lines with delta configuration same phase designation shall be applied when viewed from top to inner and inner to outer phases. This convention shall be applied from the source substation.
7.3
Phasing Sequence All 230 kV (vertical and delta configuration) and 380 kV (vertical configuration) double circuit transmission lines shall have phase arrangement of RYB-BYR i.e., the phases on the two circuits shall be located in a completely reversed order to reduce line unbalance and induced ground wire currents.
TEP122.01R0/MAA
Date of Approval: October 17, 2006
PAGE NO. 7 OF 20
TRANSMISSION ENGINEERING STANDARD
8.0
TES-P-122.01, Rev. 0
SHORT CIRCUIT RATING The 3φ symmetrical interrupting (short circuit) current ratings of the various transmission line equipment shall be as specified in Table 01-3. Table 01-3: 3φ Symmetrical Interrupting Short Circuit Current Ratings for Various Transmission Line Equipment Transmission Line Nominal Voltage Rating, kV
3φ Symmetrical Interrupting Current, kArms
380
50/63*
230
50/63*
132
40
115
40
110
40
69
31.5/40*
*
9.0
The design engineer shall select and specify in the SOW/TS the appropriate value of short circuit rating applicable for the area/location of the transmission line.
STRUCTURAL SUPPORTS In SEC system wood poles are used for 69kV and 115kV system, steel monopoles for 69kV, to 230kV and lattice structures for 69kV to 380kV system.
10.0
INSULATORS Cap and pin disc type porcelain/glass insulators (fog/aero form), Long Rod type porcelain (aero form) and Composite insulators are used in the SEC system. The type of insulators to be used for a particular project shall be specified in the relevant SOW/TS. 10.1
Creepage Distance All suspension and tension strings with porcelain or glass insulators shall have a minimum leakage (creepage) distance of 50mm/kV (line to line nominal system voltage) for transmission lines located in the Coastal Area (the area located within a distance of 100 km and 50km from the sea coast line for Consolidtaed Transmission Area and Developing Transmission Area respectively).
TEP122.01R0/MAA
Date of Approval: October 17, 2006
PAGE NO. 8 OF 20
TRANSMISSION ENGINEERING STANDARD
TES-P-122.01, Rev. 0
All suspension and tension strings with porcelain or glass insulators shall have a minimum leakage (creepage) distance of 40mm/kV (line to line nominal system voltage) for transmission lines located in the Inland Area (the area located beyond the above specified limits). For the existing transmission lines in the Inland Area (SEC Central Operating Area and SEC Southern Operating Area) where a creepage distance of 31mm/kV has been used and no problems have been encountered due to this, the same creepage distance may be adopted for future transmission lines. When Composite insulators are used, the creepage distance shall be kept as 40mm/kV both for suspension and tension strings. These types of insulators may be used for transmission lines located in the Coastal Areas. 10.2
Insulators in the Coastal Area When using fog type cap and pin disc insulators on transmission lines located in the coastal zone, the number of units in each string (suspension and tension) shall be as follows: Table 01-4:
Line Voltage (kV) 69
110
115
132
230
380
TEP122.01R0/MAA
Fog Type Cap and Pin Disc Insulators in the Coastal Area (Based on 50 mm/kV Creepage Distance)
String Configuration
Number of Insulators
Insulator String Length (mm)
Insulator Rating, Leakage Distance, and Spacing (kN, mm, mm)
Suspension
FI-8
1168
111, 432, 146
Tension
FH-8
1248
160, 432, 156
Suspension
FI-13
1898
111, 432, 146
Tension
FH-13
2028
160, 432, 156
Suspension
FI-14
2044
111, 432, 146
Tension
FH-14
2184
160, 432, 156
Suspension
FI-16
2336
111, 432, 146
Tension
FH-16
2496
160, 432, 156
Suspension
FI-22
3212
111, 545, 146
Tension
FH-22
3422
160, 545, 156
Suspension
FI/FV-35
5460
160, 545, 156
Tension
FH-35
5950
222, 545, 170
Date of Approval: October 17, 2006
PAGE NO. 9 OF 20
TRANSMISSION ENGINEERING STANDARD
TES-P-122.01, Rev. 0
When using Long Rod type insulators on transmission lines located in the coastal zone, the insulators in the suspension and tension strings shall have the ratings as follows: Table 01-5:
Nominal System Voltage (kV) 69 110 115 132 230 380 380
Long Rod Type Insulators in the Coastal Area (Based on 50 mm/kV Creepage Distance) Creepage Distance (mm) 3450 5500 5750 6600 11500 19000 19000
Specified Mechanical Failing Load (SFL) Suspension (kN)
Tension (kN)
120 120 120 120 120 160 160
160 160 160 160 160 210 330
Note: 1. While replacing insulators on the existing transmission lines adequate conductor clearances to structure/ground must be maintained. 2. A detailed study must be carried out to determine the proper insulation requirements before insulation level is increased on the existing 115 kV transmission lines in the coastal area, where no surge arresters are installed at the substation entrance. 10.3
Insulators in the Inland Area Transmission lines located in the inland area shall have Fog type insulators or Aero-Form type insulators or Long Rod type insulators. When using aero form type insulators on the existing structure designs adequate conductor clearances to structure/ground must be ensured. A detailed techno-economic study must be carried out when aero form type insulators are to be used for new transmission lines employing new structure designs. Long Rod type insulators on transmission lines located in the Inland Area shall have the ratings as follows:
TEP122.01R0/MAA
Date of Approval: October 17, 2006
PAGE NO. 10 OF 20
TRANSMISSION ENGINEERING STANDARD
Table 01-6:
TES-P-122.01, Rev. 0
Long Rod Type Insulators in the Inland Area (Based on 40 mm/kV Creepage Distance)
Nominal System Voltage (kV) 69 110 115 132 230 380 380
Creepage Distance (mm) 2760 4400 4600 5280 9200 15200 15200
Specified Mechanical Failing Load (SFL) Suspension (kN)
Tension (kN)
120 120 120 120 120 160 160
160 160 160 160 160 210 330
Number of Fog Type insulators in each string (suspension and tension) s hall be as follows: Table 01-7:
Line Voltage (kV) 69 110 115 132 230 380
TEP122.01R0/MAA
Fog Type Cap and Pin Disc Insulators in the Inland Area (Based on 40 mm/kV Creepage Distance)
String Configuration
Number of Insulators
Insulator String Length (mm)
Insulator Rating, Leakage Distance, and Spacing (kN, mm, mm)
Suspension
FI-7
1022
111, 432, 146
Tension
FH-7
1092
160, 432, 156
Suspension
FI-11
1606
111, 432, 146
Tension
FH-11
1716
160, 432, 156
Suspension
FI-11
1606
111, 432, 146
Tension
FH-11
1716
160, 432, 156
Suspension
FI-13
1898
111, 432, 146
Tension
FH-13
2028
160, 432, 156
Suspension
FI-22
3212
111, 432, 146
Tension
FH-22
3422
160, 432, 156
Suspension
FI/FV-28
4368
160, 545, 156
Tension
FH-28
4760
222, 545, 170
Date of Approval: October 17, 2006
PAGE NO. 11 OF 20
TRANSMISSION ENGINEERING STANDARD
Table 01-8:
Line Voltage (kV) 69 110 115 132 230 380
Table 01-9:
Line Voltage (kV) 69 110 115 132 230 380
TEP122.01R0/MAA
TES-P-122.01, Rev. 0
Aero Form Type Cap and Pin Disc Insulators in the Inland Area (Based on 40 mm/kV Creepage Distance)
String Configuration
Number of Insulators
Insulator String Length (mm)
Insulator Rating, Leakage Distance, and Spacing (kN, mm, mm)
Suspension
AI-9
1314
111, 335, 146
Tension
AH-9
1404
160, 335, 156
Suspension
AI-14
2044
111, 335, 146
Tension
AH-14
2184
160, 335, 156
Suspension
AI-14
2044
111, 335, 146
Tension
AH-14
2184
160, 335, 156
Suspension
AI-16
2336
111, 335, 146
Tension
AH-16
2496
160, 335, 156
Suspension
AI-28
4088
111, 335, 146
Tension
AH-28
4368
160, 335, 156
Suspension
AI/AV-46
7176
160, 335, 156
Tension
AH-46
7820
222, 335, 170
Aero Form Type Cap and Pin Disc Insulators in the Inland Area (Based on 31 mm/kV Creepage Distance)
String Configuration
Number of Insulators
Insulator String Length (mm)
Insulator Rating, Leakage Distance, and Spacing (kN, mm, mm)
Suspension
AI-7
1022
111, 335, 146
Tension
AH-7
1092
160, 335, 156
Suspension
AI-11
1606
111, 335, 146
Tension
AH-11
1716
160, 335, 156
Suspension
AI-11
1606
111, 335, 146
Tension
AH-11
1716
160, 335, 156
Suspension
AI-13
1898
111, 335, 146
Tension
AH-13
2028
160, 335, 156
Suspension
AI-22
3212
111, 335, 146
Tension
AH-22
3432
160, 335, 156
Suspension
AI/AV-36
5616
160, 335, 156
Tension
AH-36
6120
222, 335, 170
Date of Approval: October 17, 2006
PAGE NO. 12 OF 20
TRANSMISSION ENGINEERING STANDARD
TES-P-122.01, Rev. 0
Where:
11.0
12.0
FI
=
Suspension Insulator string in vertical position (fog type insulators)
FV
=
Suspension Insulator string in diagonal position (fog type insulators)
FH
=
Suspension Insulator string in horizontal position (fog type insulators)
AI
=
Suspension Insulator string in vertical position (aero form type insulators)
AV
=
Suspension Insulator string in diagonal position (aero form type insulators)
AH
=
Suspension Insulator string in horizontal position (aero form type insulators)
HARDWARE 11.1
The ratings of line hardware shall equal or exceed the Mechanical and Electrical strength ratings of the insulator or the ultimate load it shall support and as specified in the relevant TES/TCS and SOW/TS. The range of hardware fitting used in SEC transmission system shall be as per relevant TMSS.
11.2
The line hardware on suspension and tension strings shall be suitable for removal and/or replacement of insulators and fittings by tools designed for hotline/live-line working/maintenance operations. On double insulator strings for both suspension and tension, yoke plate must have the same shape and thickness so that the same tool can be used for maintenance.
ENVIRONMENTAL CONSIDERATIONS 12.1
Appearance 12.1.1
TEP122.01R0/MAA
Load growth has brought the need to transmit bulk power to areas of thick population resulting in the increasing contact with these transmission lines. Therefore transmission lines are to be designed taking into account impact of electromagnetic fields, aesthetic design and impact of physical location.
Date of Approval: October 17, 2006
PAGE NO. 13 OF 20
TRANSMISSION ENGINEERING STANDARD
12.2
12.3
13.0
TES-P-122.01, Rev. 0
12.1.2
The insulation of line, air gap, and insulator strings shall be designed to withstand switching surges, fault initiated over voltages and lightning impulses. Tower dimensions are affected by the number of insulators, type of string for insulators, type of insulator and clearances.
12.1.3
Transmission line shall consider nearby airports and aeronautic corridors (if any), as they are usually restricted on the maximum height.
12.1.4
Transmission lines shall be designed taking into consideration acceptable level of radio noise, television interference, audible noise and ozone generation. Proper considerations shall be given to conductor diameter.
Public Safety 12.2.1
Transmission lines shall be safe for people who have occasion to be near them.
12.2.2
Primary means of ensuring public safety is by providing anticlimbing device approximately 4 meters above ground, wherever transmission lines are accessible to public or within one (1) km of residential or public areas. Steel monopoles shall also require anticlimbing devices.
12.2.3
Appropriate warning signs shall be provided on transmission line supports per relevant TCS. Whenever necessary crash barriers shall also be provided for safety of the supports.
Polluted Environment 12.3.1
The areas through which SEC transmission lines run are characterized by extreme atmospheric pollution with various degrees of sand, dust and salt. Due to low rainfall in the area, the natural washing of insulators is insufficient to control insulator contamination, accumulation and flash over may occur.
12.3.2
The insulators specified in 15-TMSS-02 to 15-TMSS-05 standards are intended to withstand an ESDD (Equivalent Salt Deposit Density) of at least 0.3 mg/cm² in inland area and 0.55 mg/cm² in coastal area.
WEATHER CONDITIONS The environment in Saudi Arabia can best be characterized by intense summer heat and frequent strong winds. However, heavy rains and sand storms occasionally occur in this desert climate. The atmosphere is highly corrosive, particularly near the coastal line.
TEP122.01R0/MAA
Date of Approval: October 17, 2006
PAGE NO. 14 OF 20
TRANSMISSION ENGINEERING STANDARD
TES-P-122.01, Rev. 0
All transmission line equipment/materials shall be suitable for operation at their standard ratings under the usual service conditions in the inland desert or coastal areas environment of Saudi Arabia as specified in 01-TMSS-01.
14.0
DESIGN INFORMATION The transmission line shall be designed taking into consideration the basic parameters such as the size of conductor, conductor configuration, length of line, nominal voltage, fault current, load requirement and transposition. 14.1
Wind Velocities Conductors, structures and all poles are to be designed for a wind velocity of 150km/hr. Funneling of winds may occur where there is a natural flow of air from an unrestricted area through a restricted area, such as a mountain pass and the wind velocity may gets accelerated. The design engineer shall study the effect of wind funneling in such areas and take into account, the increased loadings, if the wind velocity is greater than that specified above.
14.2
14.3
Soil Conditions 14.2.1
Surface conditions include salt flats (sabkhah), marl, aeolian sand and rock. Sabkhah areas shall be avoided as far as possible.
14.2.2
Ground water table varies from near surface in the coastal zone to several meters below grade in inland areas.
14.2.3
Areas of sand and marl presents the problem of shifting of the over burden due to wind action. This problem can be alleviated to some extent by elevating the soil surface at each foundation and stabilizing the elevated surface with crude oil. This practice tends to prevent the depositing of windborne sand at the foundation. This practice prevents surface sand moving away from the foundation.
Conductor Clearances Transmission lines shall be designed based on phase to phase, phase to ground and other clearances as specified in the Engineering Standard TES-P-122.09.
15.0
OBSTRUCTION MARKING AND LIGHTING Transmission lines located near the ends of the airport runways shall require warning lights and sphere marking to warn pilots of potential collision with the structures and conductors. The design engineer responsible for the detailed design shall arrange to contact the aviation authorities to determine the requirements and ensure compliance to the same.
TEP122.01R0/MAA
Date of Approval: October 17, 2006
PAGE NO. 15 OF 20
TRANSMISSION ENGINEERING STANDARD
15.1
15.2
TES-P-122.01, Rev. 0
Spherical Markers 15.1.1
Daylight spherical markers shall be installed on the shield wire per 12-TMSS-03. The color of spherical markers shall be aviation Orange. The spherical marker shall be equally spaced along the span conforming to the requirements of the aviation authorities.
15.1.2
The markers shall be recognizable in clear weather from a distance of 1219m (4000 ft) for an object to be viewed from the air and 305 m (1000 ft) for an object to be viewed from the ground in all directions in which an aircraft is likely to approach.
15.1.3
To retain the general definition of the object being marked, markers shall be displayed in conspicuous positions, i.e. shall be spaced equally along the wire at an interval of not more 61 m (200 ft). This interval in critical areas near airport runway end shall be in the range of 10 to 15 m.
15.1.4
Spherical markers shall be placed on the highest wire and where there are two wires at the same height; they may be installed alternately along each overhead ground wire only and not on composite optical fiber ground wire (OPGW) to facilitae easy maintenance of OPGW. The distance between the adjacent markers shall be maintained as above. This method shall allow the weight and wind loading to be distributed.
15.1.5
In order to protect the damage of conductor/shield wire strands at sphere clamp due to aeolian vibrations, each spherical marker shall be equipped with at least one Stockbridge type vibration damper, the placement distance to be determined by the damper manufacturer through analytical vibration damping study. Preformed aluminum alloy armor rods shall be installed on the shield wire before installing the spherical markers to protect the strands from any damage.
Warning Lights 15.2.1
Conductor Warning Lights Nighttime warning lights shall be installed on the phases of overhead lines per 12-TMSS-03. The complete light assembly when installed on the conductor shall not be affected by the vibrations transmitted by the conductor. To eliminate the risk of deterioration, each phase conductor light assembly shall be equipped with two Stockbridge vibration dampers, the placement of which shall be determined by the damper manufacturer through analytical vibration damping study.
TEP122.01R0/MAA
Date of Approval: October 17, 2006
PAGE NO. 16 OF 20
TRANSMISSION ENGINEERING STANDARD
15.2.2
TES-P-122.01, Rev. 0
Tower Warning Lights (Beacons) Nighttime warning lights shall be required on the towers per 12TMSS-03. The power requirement for beacon light shall be decided in consultation with SEC. Self-illuminated spherical marker may also be used (if practicable) in place of tower beacon lights. The diameter of marker shall be in the range of 510 mm to 610 mm. The power source for these markers shall be the magnetic field surrounding the phase conductors.
16.0
TRANSMISSION LINE UNBALANCE AND TRANSPOSITION The degree of unbalance over a set of three-phase transmission line is produced by asymmetrical placement of line conductors above ground plane. This unbalanced condition leads to generation of negative and zero sequence voltage and currents, which may have adverse effect sufficient to require line transposition. Line transposition shall be made for the purpose of reducing the electrostatic and electromagnetic unbalance among the phases, which can result in unequal voltages for long lines. Line transposition is changing the position of phase conductors so that within a specified length of a line, each conductor occupies the position of all the three phase conductors for the same length. All 230 kV and 380 kV transmission lines greater than 90 km in length shall be transposed, whereas, transmission lines less than 90 km in length may not require any transposition. The transposition shall be done at equal intervals along the line at points having L/3 distance (L being the length of transmission line between two terminal stations). After transposition, the relative phasing sequence on double circuit lines shall be kept in a reversed order as described in Clause 7.3. In case of inductance interference with parallel communication lines due to untransposed line, system interference can be prevented by transposition of telephone line or installing buried telephone much more economically and it is always necessary to transpose a power line only.
17.0
LINE IDENTIFICATION 17.1
Circuit Designation 17.1.1
TEP122.01R0/MAA
On single circuit wood pole or latticed steel structures; circuit designation plates “A” or “B” shall be installed on all structures facing the tap off point or source. These plates shall be mounted on the transverse faces of the structure approximately three (3) meters above the ground level.
Date of Approval: October 17, 2006
PAGE NO. 17 OF 20
TRANSMISSION ENGINEERING STANDARD
17.1.2
17.2
TES-P-122.01, Rev. 0
On double circuit tower structures, an “A” or “B” shall be installed on the respective side of the tower to correctly identify which side of the tower carries which line.
Voltage Level Designation Transmission system voltage level shall be shown on the structure identification plates.
17.3
17.4
Structure Numbering 17.3.1
On all radial feeders and tap lines, the structure numbering shall begin at the line origin and shall increase toward line destination. The line name designation shall be determined by the destination of the line rather than the name of the main lines.
17.3.2
On other transmission lines, the structure numbering shall begin with structure one from south to north or west to east. This geographical direction is dependent on the location from transmission line to transmission line and not the direction of the line at any point. The line name designation shall be according to the station name at each end of the line with the first name listed dependent on the same geographical directions listed above; i.e., the Abqaiq-Qurayyah line shall be designated by AB-QU.
17.3.3
Re-numbering of transmission line structures for re-routing or introduction of additional structures shall begin at the origin and shall increase towards line destination. Approval of SEC Lines Maintenance shall be obtained if the affected nearest structure is used.
Structure Identification 17.4.1
All structures shall have their respective structure numbers on them but the aerial line identification plates shall be insta lled on every tenth structure, the first structure, the last structure and on both structures adjacent to a crossing highway, rail road and access road.
17.4.2
Structure identification plates for aerial inspection shall be installed on top transverse face of the structure. Two plates shall be installed per structure one on ahead of the line and one on the back.
17.4.3
Physical layout of the markings on structure identification plates for aerial inspection shall include Voltage Level, Source Substation Name, Ending Substation Name and Structure Number.
17.4.4
Structure identification plates for ground inspection shall be installed on the transverse face of every structure three (3) meters above the ground level when viewed in the direction of increasing structure numbers. However, if structure identification plates installed in the
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Date of Approval: October 17, 2006
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normal position will not be readily visible from the access road, they shall be installed on the structure faces best exposed to view from the access roads. 17.4.5
17.5
18.0
Physical layout of the markings on structure identification plates for ground inspection shall include Circuit Designation, Voltage Level, Source Substation Name, Ending Substation Name and Structure Number.
Phase Identification 17.5.1
All transmission lines in the SEC power system, which do not require transposition, shall have the phases identified per clause 7.2.
17.5.2
In transposed lines, the correct phasing shall be indicated on transposition structures whenever the conductor phasing changes and shall be marked “TRANSPOSED LINE”.
17.5.3
Phase identification plates shall be installed next to the structure identification plates and phasing shall be indicated wherever the phasing configuration changes.
17.5.4
The structures requiring phase marking shall be indicated on the Plan and Profile drawings by the symbol “φ“ and shall be marked “TRANSPOSED” next to the structure numbers.
LIGHTNING PERFORMANCE 18.1
Outage Rate Due To Lightning Overhead ground wires are provided in transmission lines as shielding protection against lightning. The outage due to lightning is based upon the number of strokes terminating on the overhead ground wires; which result in structure flashovers and mid span overhead ground wire flashover. The outage rate due to lightning shall not be more than 0.62 per 100 km per year for an isokeraunic level as specified in 01-TMSS-01.
18.2
Overhead Ground Wires 18.2.1
TEP122.01R0/MAA
The overhead ground wire requirements on transmission lines are specified below: a.
On all wood pole transmission lines, overhead ground wires shall be provided, unless otherwise specified in the Project Technical Specifications.
b.
Due to the higher conductor elevation of all latticed and steel monopole transmission lines, continuous overhead ground wires Date of Approval: October 17, 2006
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of sufficient strength shall be provided to shield the line conductors from direct lightning strokes. c.
18.2.2
Overhead ground wires shall be adequately bonded to each steel structure or wood pole structure grounding. Whenever there are two overhead ground wires on a wood pole structure, they shall be tied together at the top of each structure to reduce the impedance to ground.
Shield Angle For 380kV transmission lines, the shielding angle shall be 20 degrees or less whereas for all other transmission lines (69 kV to 230 kV) the shielding angle may be kept up to 30 degrees maximum. However, in each case the outage rate due to lightning shall not exceed the maximum value specified in Clause 18.1 above.
19.0
BIBLIOGRAPHY 19.1
Electric Transmission and Distribution Reference Book, Westinghouse.
19.2
Design Manual for High Voltage Transmission Lines, Rural Electrification Administration (US Department of Agriculture).
19.3
Transmission Line Reference Book 345 kV and Above, Electric Power Research Institute.
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Date of Approval: October 17, 2006
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