ESB-Earthing and Lightning Protection

Section 5.11 Technical Specification Protection

–

Earthing

and

Lightning

Alba Line 6 Expansion, Power Distribution Distribution System

Document No.: P000206-TP01-0014

Date: January 2016

ESB International, Stephen Court, 18/21 St Stephen’s Green, Dublin 2, I reland. Phone +353

(0)1 703 8000

ww w .esbi.ie

Copyright © ESB International Limited, all rights reserved.

Technical Specification – 5.14 Earthing and Lightning Protection Client Recipient:

/ Aluminium Bahrain (ALBA)

Project Title:

Power Station 5: Alba Line 6 Expansion, Power Distribution System

Doc Title:

Technical Specification 5.14 – Earthing and Lightning

Doc. No.:

P000206-TP01-0014

Volume:

1

Prepared by:

B. Perry

Date:

Title:

Consultant

January 22 2016

Verified by:

M. O’Leary

Date:

Title:

Consultant

January 22 2016

Approved by:

D. de Beer

Date:

Title:

PDS Project Manager

January 22 2016

nd

nd

nd

Copyright © ESB International Limited All rights reserved. No part of this work may be modified, reproduced or copied in any form or by any means - graphic, electronic or mechanical, including photocopying, recording, taping or used for any purpose other than its designated purpose, without the written permission of ESB International Limited.

Change History of Report Date

New Revision

Author

Summary of Change

22/01/2015

0

B. Perry

Released for Draft Issue

29/01/2016

1

S. Byrne

Issued for Tender

Alba Line 6 Expansion, Power Distribution System

Page 2 of 13

Technical Specification – 5.14 Earthing and Lightning Protection

Contents 5.11

Technical Specification – Earthing & Lightning Protection

4

5.11.1

Scope of Supply

4

5.11.2

General

4

5.11.3

Specification Codes and Standards

5

5.11.4

Service Conditions

6

5.11.5

Network Parameters

6

5.11.6

Earthing System

6

5.11.6.1

Earthing System Works

6

5.11.6.2

Soil Resistivity Survey and Earthing Design

6

5.11.6.3

Fault Current and Duration

7

5.11.6.4

Earth Electrodes

7

5.11.6.5

Above Ground Earthing System

8

5.11.7

Electrical Equipment Connections to Earth

9

5.11.8

Earth Connections to Non-Electrical Equipment & Structural Steelwork

10

5.11.9

Joints

11

5.11.10

Fixings

11

5.11.11

Bonding and Earthing of Cables

12

5.11.12

Equipotential Bonding

12

5.11.13

Earthing Instrument Cables

12

5.11.14

Lightning Protection

12


Page 3 of 13


5.11 Technical Specification – Earthing & Lightning Protection 5.11.1

Scope of Supply

1.

This specification covers the Employer’s requirement for design, supply and installation of the substation earthing and lightning protection systems. The scope of supply shall include all equipment and auxiliaries necessary to ensure safe, efficient and reliable design of the installation.

2.

The earthing system shall consist of a grid of horizontally buried conductors, supplemented by a number of vertical earth rods connected to the horizontally buried conductors. The earthing system shall limit the potential rise under fault conditions, and also limit the potential differences (touch and step voltages) on the site and adjacent to the site to ensure safety to people and animals. It shall also help prevent damage to substation equipment under fault conditions.

3.

The earthing of gas insulated switchgear (GIS) installations shall be subject to special considerations regarding step and touch potentials and HF transient voltages across enclosures (or Transient Enclosure Voltages (TEVs)) in accordance with the applicable standards. Switchgear manufacturer’s recommendations in this respect shall also be duly taken into consideration. TEVs shall be limited to protect 1. Secondary wiring of the GIS (BIL as per IEC) and 2. Cable sheath of HV cables connected to the GIS (BIL of approximately 3 kV but shall be confirmed with HV cable manufacturer).

4.

Lightning monopoles and/or lightning spikes with down conductors on buildings shall be provided to connect to the substation earthing system for lightning protection of substation control buildings, switchgear, transformers and any other outdoor equipment within the substation compound.

5.

The Contractor shall design the earthing and lightning protection systems independent of the other systems on site, for example, the new PS5 power station and existing earthing systems and lightning protection coverage close or adjacent to the substation site. After construction and testing, this contract shall include the interconnections to the other systems and be to the approval of the Engineer. These interconnections shall include inspection pits with test links to allow for future resistance measurements.

5.11.2

General

1. The Contractor shall supply a risk assessment of the proposed earthing and lightning protection systems stating the hazards presented to persons involved in the installation, commissioning, inspection, testing and maintenance of the installations. The overall risk presented by the hazards shall be evaluated based on the recommended inspection and maintenance intervals. Measures to ease the severity of the risk or elimination of the hazard shall be considered in the risk assessment. All necessary safety precautions to be observed by personnel involved in the activities above shall be detailed in the risk assessment.


Page 4 of 13

Technical Specification – 5.14 Earthing and Lightning Protection 2.

The final approval of the earthing and lightning protection designs by the Employer is subject to completion of a satisfactory safety risk assessment by the Employer. All design approvals must be regarded as provisional pending the results of this risk assessment.

5.11.3

Specification Codes and Standards

The Earthing and Lightning Systems shall comply with this Specification and with the latest editions of the following standards, Codes and normative references: IEEE 80

IEEE Guide for Safety in AC Substation Grounding

IEEE 81

IEEE Guide for Measuring Earth Resistivity, Ground Impedance and Earth Surface Potential of a Grounding System

IEEE 142

Recommended Practice for Grounding of Industrial and Commercial Power Systems.

IEEE 367

Recommended Practice for Determining the Electric Power Station Ground Potential Rise and Induced Voltage from a Power Fault

IEC 60227

Specification for PVC insulation and sheath of electric cables

IEC 60228

Specification for conductors in insulated cables and cords

IEC 60364

Electrical Installation of Buildings.

IEC 60502

Specification for XLPE or EPR insulated cables

IEC 62305

Protection against lightning

BS EN 50164/IEC1024 Lightning Protection Components (LPC) BS 1432

Specification for copper for electrical purposes: high conductivity copper rectangular conductors withdrawn or rolled edges.

BS 1433

Specification for copper for electrical purposes. Rod and bars

BS 2871

Specification for copper and copper alloys. Tubes

BS 2874

Specification for copper and copper alloy rods and sections (other than forging stock).

BS 6651

Code of practice for protection of structures against lightning

BS 7430

Code of practice for earthing

BS 7671

IEE wiring regulations

DIN VDE 0141

Earthing systems for special power installations with nominal voltages above 1 kV


Page 5 of 13

Technical Specification – 5.14 Earthing and Lightning Protection International Telecommunication Union ITU-T Directives Volume VI Technical Specification 5.17 other than Wire

5.11.4

Hot dip galvanising of Iron and Steel Articles

Service Conditions

The earthing and lightning protection systems shall be designed and installed as required by this specification under the service conditions outlined in the Technical Specification 5.0 General Technical Requirements Clause 5.7.1.

5.11.5

Network Parameters

For Network Parameters including nominal voltage, rated voltage, short circuit level, rated insulation levels, neutral earthing arrangements etc. see Technical Specification 5.0 General Technical Requirements Clause 5.7.1.

5.11.6

Earthing System

5.11.6.1

Earthing System Works

The work for the earthing system shall comprise of a site survey (including soil resistivity survey), design, supply, installation (including excavation, backfilling and reinstatement) and connections to electrical and metallic equipment at each substation.

5.11.6.2

Soil Resistivity Survey and Earthing Design

1. A preliminary earthing system design shall be carried out upon award of Contract based on typical values of earth resistivity. 2. Not later than one month after the site has been handed over to the Contractor for mobilisation, the Contractor shall carry out a soil resistivity survey of the site. The methodology for the soil resistivity survey shall be submitted to the Employer for approval before the survey takes place. Once the survey has been completed the contractor shall report in writing to the Employer. The report shall detail the methods and instruments used during the survey and the results of the surveys. Based on the results, the Contractor shall include in the report the proposed resistivities to be used in the design of the earthing system. 3. The Contractor shall complete the final design of the earthing system only after approval of the report by the Employer is received. The final design shall include calculation of step, touch and mesh potentials which shall be within the allowable limits of the standards quoted in this specification. 4. The minimum main earth conductor and safety earth conductor sizes for equipment shall be calculated in accordance with IEEE Standards or other equivalent or better standard and subject to the Employer’s approval. The earthing system shall be designed to the latest edition of IEEE 80. 5. The earthing system design shall also include the following: A. Width and depth of all trenchs for buried conductors B. Diameter and depth of all holes for buried earth rods C. Details of back-fill material to be used around electrodes Alba Line 6 Expansion, Power Distribution System

Page 6 of 13

Technical Specification – 5.14 Earthing and Lightning Protection D. Details of different layers of back-fill and materials to be used E. Type of material to be used for top layer i.e. crushed rock or tarmacadam F. Resistivity of top layer material 5. The final design, including calculations of step, touch and mesh potentials, accompanied by full installation design drawings and material requirement schedules, shall be submitted to the Employer for approval before materials procurement or installation commences.. A means of verification shall be submitted for comment, but it should be done on the basis of injecting a high current (> 50 A) and furthermore, a verification test for touch and step voltages shall carried out on site after installation is completed. The design shall be such that the Rise of Earth Potential (ROEP) should not exceed 650 V beyond the perimeter fence during earth faults. 6. The earthing design shall also ensure that TEVs shall be limited to protect 1. Secondary wiring of the GIS (BIL = as per IEC) and 2. Cable sheath of HV cables connected to the GIS (BIL of approximately 3 kV but shall be confirmed with HV cable manufacturer).

5.11.6.3

Fault Current and Duration

1. The design of the earthing system shall be based on total earth fault current as specified in Technical Specification 5.0 General Technical Requirements clause 5.5.2. The earthing system shall be capable of carrying the total earth fault current for it’s maximum duration. The maximum duration of the earth fault current shall be three seconds.

5.11.6.4

Earth Electrodes

1. Earth electrodes (i.e. earth grid conductors and earth rods) shall consist of a network of horizontally buried conductors with vertically buried earth rods connected to the horizontal conductors at intervals of 20 m. The main electrode system (i.e. the earth grid) shall be buried to a depth of not less than 1 m. 2. The buried conductors shall be made from hard drawn high conductivity copper. The rating of the conductors shall be compatible with the fault current after allowing for parallel paths, with a minimum size of 150 mm 2 in the vicinity of the substation (final size to be finalised based on study). 3. The earth rods shall be made from solid copper or copper alloy having equivalent corrosion resistance and are subject to approval by the Engineer. Earth rods shall have a diameter of not less than 16 mm 2 and a length not less than 3 m. 4. Where separate electrode systems exist, they shall be connected together at not less than two points. Minor remote electrode systems may rely on cable armouring for connecting to the main electrode system provided that earth loop impedance and resistance to earth of the circuit meet the requirements of BS7430.


Page 7 of 13

Technical Specification – 5.14 Earthing and Lightning Protection 5. The electrode system shall be designed to have a resistance to general mass of earth not exceeding 0.5 ohm. Any deviation from this design figure shall be to the approval of the Employer. 6. In areas subject to ground fill operations the resulting disturbance may alter site conditions for earthing. Under these circumstances deep driving of earth rods may be necessary to reach soil layers of reasonable resistivity. 7. The resistance of the complete earthing system shall be measured by the Contractor with an approved form of earth resistance tester. The method of measurement shall be as defined in ANSI / IEEE Std 81. Any deviation shall be to the approval of the Employer. The measured value of electrode resistance shall be submitted to the Employer for acceptance. 8. The Contractor shall include a facility to isolate major sections of the buried earth electrode system via inspection pits with test links such that the earth resistance of each section can be measured at any time in the future. 9. Prior to the connection of earthing conductors, the Contractor shall ensure that connection surfaces are clean and free from contamination.

5.11.6.5

Above Ground Earthing System

1. The above ground earthing system shall comprise the following components: A. The conductors between the buried electrode system and the main earth connection to / earth bar for the earthed equipment. B. The main earth connection / earth bar of the earthed equipment. C. The conductors between the main earth connection / earth bar and the metallic frames, enclosures or supports of the earthed electrical equipment. D. The conductors between the main earth connection / earth bar and the structural metalwork of non-electrical earthed equipment. 2. All main and subsidiary earth connections shall consist of appropriately sized copper strip or stranded copper conductor. Their size shall be such so as to safely carry the appropriate fault current for the necessary length of time. Where appropriate, sections of the main or subsidiary plant earthing shall be carried out in single core, stranded copper, PVC insulated, green/yellow cable. 3. Connections to equipment main earth connection / earth bar, transformer neutrals, etc. shall be made direct to the buried electrode system. Other apparatus earth connections shall be made directly to the equipment main earth connection / earth bar or alternatively directly to the buried electrode system. 4. The main columns of steel structures shall be earthed using continuous conductors connected directly to the buried electrode system. Foundation bolts shall not be used for connection to the earthing system. 5. The installation shall ensure that earthing conductors shall not be damaged or broken while in-service by rubbing off hard sharp edges of concrete or equipment or by movement, bending or flexing over time. Earthing conductors may not be cast directly in concrete but may be run through concrete using Alba Line 6 Expansion, Power Distribution System

Page 8 of 13

Technical Specification – 5.14 Earthing and Lightning Protection appropriate PVC ducting. Where earthing conductors are exposed to mechanical damage sheet steel guards shall be provided for protection.

5.11.7

Electrical Equipment Connections to Earth

1. Connections between: (a) all HV electrical equipment and (b) LV electrical equipment comprising substantial multi-cubicle switchboards to the buried electrode system shall be duplicated (one connection at either end of earth bars). The bare copper conductor size shall be adequate for the applicable fault currents but not be less than 95 mm 2. 2. All substation equipment, including switchgear, transformer, surge arresters, current and voltage transformers etc. shall all be connected to the buried electrode system in accordance with the manufacturer’s recommendations. All equipment supporting steelwork and GIS operational access and maintenance platforms shall also be connected to the earth grid. The size of the copper conductor used shall be not less than 95 mm 2. 3. Buildings containing electrical equipment shall be provided, at each level, with a ring of earthing conductors. Each ring of earthing conductors shall be connected to the earth grid outside the building at least 4 points suitably spread around the perimeter of the building. The frames or earth bars of all control and relay panels other electrical equipment and exposed structural metalwork shall be connected by branches to a ring. The ring and branch conductors shall be appropriately sized copper strip or stranded copper conductor. Strip run within buildings, inside cable trenches or above ground level on apparatus shall be neatly supported in non-ferrous clamps. 4. Where GIS equipment is installed indoors an earthing net shall be provided cast in the floor under the GIS. This earthing net is required to mitigate against TEVs. The net shall be formed from a minimum of 95 mm 2 stranded copper conductors which shall be laid in an 3 m X 3 m mesh interconnected at all crossing nodes by suitable clamps. The net shall extend throughout the GIS room and shall be connected to the earthing ring at that level at several locations. At least 2 tails/connections to the earth net per GIS bay shall be provided for earthing of the GIS. The reinforcing steel in concrete floors shall not be used to provide the earth net. In any case, TEVs shall be limited to protect 1. Secondary wiring of the GIS (BIL = as per IEC) and 2. Cable sheath of HV cables connected to the GIS (BIL of approximately 3 kV but shall be confirmed with HV cable manufacturer). 5. Surge Voltage Limiters (SVLs) shall be connected between the HV cable termination box on the GIS and the HV cable screen to dissipate fast acting transients at this location during switching. For details please refer to clause 5.2.16.1 of Technical Specification 5.2 – Gas Insulated Switchgear. 6. Separate earth wires shall be run to all lighting fittings and small power circuits. Conduit is not considered to be a sufficient earth connection. 7. The neutral of instrument transformers and/or relays shall be earthed only at one location, as close to the transformers or relays as possible.


Page 9 of 13

Technical Specification – 5.14 Earthing and Lightning Protection 8. Special care is required for cables that cross the site boundary as they may require insulating joints and surge suppression devices. 9. Earthing of equipment such as transformers, reactors, etc t hat are located within the existing power plant (e.g TIB91x and TIB95B transformers) shall be to the existing earthing networks at connection points to be agreed. Earth cables installed with the HV cables to this equipment may have to be connected at these existing locations, subject to detailed engineering

5.11.8

Earth Connections to Non-Electrical Equipment & Structural Steelwork

1. All metalwork within the scope of the buried electrode system which does not form part of the electrical equipment shall be bonded to the buried electrode system except where otherwise specified. This shall include but not be limited to bonding of all pipes, cable trays, conduits, steel structures, etc. The bonding conductor size shall be not less than 95 mm 2. Cable trays shall be connected to earth with copper bonding jumpers at 20 metre intervals or in at least two places for shorter runs. 2. Bare earthing conductors shall not be run on metallic cable trays, ladders, racks, etc. 3. Individual components of non-electrical metallic structures shall be bonded to adjacent components to form an electrically continuous metallic path to the bonding conductor. 4. All crane rails shall be connected to the earthing system in at least two places. All metal doors shall be connected to the earthing system. 5. All fences shall be connected to the earthing system with earth jumpers connected to fence gates. Boundary fences should also have an underground earth electrode run in parallel with the fence at a separate distance of about 1 m from the fence on the outside and the same on the inside. 6. Reinforcing Bars: A. The Contractor shall where required for his earthing design ensures that the structure reinforcing bars in any concrete work are electrically continuous from the top to the bottom of the structure. B. The normal lapping and wiring together of the reinforcing is considered adequate for electrical continuity, provided that each successive level of rebar is wired to the lower level at each junction. C. As soon as erection of the structure reinforcing is started, the Contractor will make permanent electrical earthing connections to earth risers furnished in place next to the structure foundations. D. No connections shall be made to reinforcing bars and other steelwork which do not form part of the earthing system and are completely encased in concrete.


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5.11.9

Joints

1. Permanent joints shall be made by exothermic welding below ground, or crimping for above ground connections. 2. Detachable joints shall be bolted and stranded conductors at bolted joints shall be terminated in exothermically welded lugs below ground or a crimped cable socket above ground. The diameter of any holes drilled in strip conductors shall not be greater than half the width of the strip. 3. Connections to electrical equipment shall be detachable and made at the earthing studs or bolts provided on the equipment by the manufacturer. When an earthing point is not provided, the point and method of connection shall be agreed with the Employer. 4. Bolted connections shall use the NEMA “two-hole” or “four-hole” pattern. 5. Connections to metallic structures for earthing conductors and bonding conductors between electrically separate parts of a structure shall be either by direct exothermic welding or by bolting using a stud welded to the structure. Drilling of a structural member for a directly bolted connection shall only be carried out to the approval of the Employer. 6. Bolted joints in metallic structures, including pipework, and which do not provide direct metallic contact, shall either be bridged by a bonding conductor or both sides of the joint shall be separately bonded to earth, unless the joint is intended to be an insulated joint for cathodic protection or other purposes. 7. Where the reinforcing in concrete is to be connected to the earthing system, the fittings used to provide a connection point at the surface of the concrete shall be exothermically welded to a reinforcing bar. This fitting shall be provided with a bolted connection for an earthing conductor. The main bars in the reinforcing shall be welded together at intervals to ensure electrical continuity throughout the reinforcing. 8. No connections shall be made to reinforcing bars and other steelwork which do not form part of the earthing system and are completely encased in concrete.

5.11.10

Fixings

1. Clips for supporting strip conductors not buried in the ground shall be of the direct contact type and clips for circular conductors shall be of the cable saddle type. The clips shall support the conductors clear of the structure. 2. Conductors shall be connected to earth rods by a bolted clamp to facilitate removal of the conductor for testing the rod. 3. All conductor fittings shall be manufactured from high strength copper alloys with phosphor bronze nuts, bolts, washers and screws. Binary brass copper alloys will not be acceptable. All fittings shall be designed for the specific application and shall not be permanently deformed when correctly installed. 4. Sheathed conductor support fittings may be of silicon aluminium, glass-filled nylon or other tough non-hygroscopic material for indoor installations.


Page 11 of 13

Technical Specification – 5.14 Earthing and Lightning Protection 5. Fittings not in direct contact with bare or sheathed conductors may be of hot-dip galvanised steel. Bimetallic connectors shall be used between conductors of dissimilar materials and insulating material shall be interposed between metallic fittings and structures of dissimilar materials to prevent corrosion.

5.11.11

Bonding and Earthing of Cables

1. All cables, except single core cable carrying alternating currents, shall have their armour bonded to earth at both ends. 2. Single core cables carrying alternating currents shall be bonded and earthed using one of the following techniques: A. All cables forming a circuit shall have their metallic sheaths or armour bonded together and earthed at both ends of the circuit. The cable shall be de-rated accordingly. B. All cables forming a circuit shall have their metallic sheaths or armour bonded together and earthed at the supply end of the cable only. Sheath voltage limiters (SVL) shall be installed as necessary at all unearthed terminations. The metallic sheath or armour shall be insulated or guarded in such a manner that personnel cannot touch the cable and receive a fatal shock from the voltages induced therein. C. The Contractor shall indicate any other proposed installation practices which help reduce EMI.

5.11.12

Equipotential Bonding

1. During an earth fault dangerous voltage levels may develop on exposed metalwork such as metallic cable trays, metallic trunking, false floor/ceiling frames, copper water pipes etc. giving rise to a risk of electric shock. This risk shall be minimised by bonding simultaneously accessible steelwork. 2. The equipotential bonding conductor shall have a cross sectional area not less than half the cross sectional area required for the earthing conductor of the installation and not less than 6 mm 2. The cross sectional area need not exceed 25 mm2 stranded copper.

5.11.13

Earthing Instrument Cables

Control cables which incorporate metallic screens shall have the screen earthed at the control room and / or at the nearest point to the control room. Earth connections are to be made to a “clean instrument only” earth.

5.11.14

Lightning Protection

1. Lightning protection shall be provided for the two new GIS buildings and all other new structures including cable gantries. 2. Structures are to be provided with a comprehensive and coordinated lightning protection & equipotential bonding SPD system in strict accordance with IEC 62305. The finished lightning protection installation must be such that the risk to the structure is within the “Rt” or tolerable risk, determined by a prepared complete and comprehensive IEC 62305-2 Risk Assessment. Enhanced Service Alba Line 6 Expansion, Power Distribution System

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Technical Specification – 5.14 Earthing and Lightning Protection Entry SPDs and coordinated SPDs must therefore form an integral part of the installation proposal and must be in keeping with the determined LPL protection level and risk assessed kA ratings. 3. All lightning protection components used should be pre-certified by one manufacturer, to EN 50164-1:2008 and EN 50164-2:2008. 4. All Lightning conductors to be HC 25 mm X 3 mm flat conductor (75 sq. mm) and conductive oxide inhibiting compound must be used on all connections. 5. All buildings and high structures shall be fitted with lightning air terminals in accordance with the relevant standard. 6. All lightning protection systems shall be strongly interlinked with the earthing system at a minimum of two points.


Page 13 of 13

ESB-Earthing and Lightning Protection

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