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Lusail Particular Specification

Section 38

Part 25

Earthing system and lightning protection

Page 1

25.0

25.1 25.2 25.3

EARTHING SYSTEM AND LIGHTNING PROTECTION 2

General Scope of Works Description

25.3.1 25.3.2 Earthing System Lightning Protection (if applicable) Electrical Parameters for Earthing Calculation: Earthing system materials Lightning Protection Material

2 2 2

2 6

25.4 25.5

Main Technical Data

25.4.1 25.5.1 25.5.2

6

6

Equipment Requirements

7

7 9

25.6 25.7 25.8 25.9 25.10 25.11 25.12

Performance Guarantees Inspection and Tests Special Equipment and Tools Spare Parts Packaging, Shipping and Transport Training Documentation

25.12.1 25.12.2 Documentation with Tender Documentation after Award of Contract

9 9 9 10 10 10 10

10 10

Lusail City

Revision 0

Issue Date: April 2010

Lusail Particular Specification

Section 38

Part 25

Earthing system and lightning protection

Page 2

25.0

25.1

EARTHING PROTECTION

GENERAL

SYSTEM

AND

LIGHTNING

This Specification covers the ratings, design, equipment requirements, erection, inspection and testing of complete earthing system and lightning protection system. This is basically a performance specification and covers only those aspects that are required to define a minimum standard of quality and performance. All materials and equipment shall be provided as required to make a complete, properly, functioning installation and shall conform to the highest standards of engineering design and workmanship. The Contractor shall at an early stage of the Project and before the Site works commence, undertake a survey of the ground all over the site in order to establish general characteristics and ascertain values of soil resistivity at various depths to a minimum of 20 meters. A report of the resistivity values measured, the effective ground resistivity and the expected resistance of the proposed grid shall be submitted to CLIENT for approval. Based on the above survey the Contractor shall prepare a detail design of the earthing system and lightning protection system for approval by CLIENT. Thereafter the Contractor shall supply, excavate, install, erect, backfill and test the installation to the satisfaction of CLIENT. The design and installation of the earthing and lighting protection systems shall be based on the following standards: IEEE 80 IEEE 81 IEC 60364-5-54 NFPA 78 BS 6651 Guide for safety in AC Substation Grounding Guide for Measuring Earth Resistivity, Ground Impedance and Earth Surface potentials for Ground system Earthing arrangements and protective conductors for indoor installations up to 1000 V a.c. and 1500 V d.c. Lightning Protection Code Protection of Structures against Lightning The electrical equipment shall be in accordance with the requirements of IEC recommendations.

25.2

SCOPE OF WORKS

The supply and services to be performed by the Contractor shall comprise the design, manufacture, shop testing, packing, transport, insurance, unloading, storage on Site, construction works and erection, corrosion protection, site testing, submission of documentation, commissioning, training of CLIENT's personnel and warranty of the works. The Contractor is bound to provide complete works, even if the equipment or services to be provided are not specifically mentioned in the specification.

25.3

25.3.1

DESCRIPTION

Earthing System

The earthing system shall mainly comprise a meshed earthing grid directly buried in the ground and a set of spur connections to all electrical equipment

Lusail City

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Issue Date: April 2010

Lusail Particular Specification

Section 38

Part 25

Earthing system and lightning protection

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and all metallic frames to form an equi-potential bonding system capable of carrying the fault currents resulting from short circuits. The earthing system shall fulfill the following requirements: · Maintain a low overall resistance of the earth mass to limit the potential rise with respect to true earth and ensure protective relay operation in the event of an external fault. Provide ground connections to all electrical apparatus enclosures and structural steelworks adequate to carry prospective ground faults without excessive heating or fire risk. Limit potential differences within the substation site in the event of earth current, originating from within or outside the station. Ensure the safety of personnel by limiting step and touch voltages within and immediately outside the substation to values well within acceptable levels and eliminate interference or damage to sensitive electronic circuits.

·

· ·

The Contractor shall be entirely responsible for the earthing system and connections to cover the whole area and for ensuring that all apparatus and metallic structures are securely and safely connected to this system. The earthing system of the substation shall be common for: · · · · Protective earthing of the equipment at all voltage levels, Transformer neutral point earthing, Equipment equi-potential bonding and earthing Lightning protection system earthing etc.

The main parts of this common earthing system are: · · · · · Main earthing electrode (a buried grid) Connections from outdoor equipment and structures to the main grid Indoor earthing sub-system in buildings GIS switchgear earthing Lightning protection system.

25.3.1.1

Outdoor Earthing System

Underneath the substation site a meshed earthing grid shall be installed in the form the main earth electrode for the substation and provide a common network for the connection of equipment and structures. The mesh conductors shall be spaced is to prevent the occurrence of excessive step potentials and touch potentials on conducting parts of the installation which are not part of the main electrical circuits and form The meshed earthing grids consist of: · Earth ring electrodes around each individual building in the substation area,

Issue Date: April 2010

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Lusail Particular Specification

Section 38

Part 25

Earthing system and lightning protection

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· · · · ·

Reinforcing steel mesh of GIS foundation, Earth electrodes for outdoor lighting pole earthing (if applicable), Substation fence earth electrodes (if applicable), All interconnections, Vertically driven rods, etc.

Lead-sheathed stranded copper conductor shall be generally used for mesh conductors in the ground and spur conductors to the equipment. The earth electrodes buried directly in the ground shall be arranged so as to utilize fully the available site area. A continuous conductor shall be laid outside the periphery of substation site typically at a distance of 1.5m to 2m from the boundary fence, and at a depth of 0.5 metres below the surface. The exact positioning of the perimeter conductor and the depth of burial shall be determined by the contractor during the design process taking into account external step and touch potentials. The substation wall reinforcing shall be connected to the main earth system at a minimum of once per wall panel section. Where overhead lines enter the substation passing over the wall additional earthing shall be provided to ensure an effective earth path. A meshed earthing grid shall be formed by interconnection of various points of the earth electrode perimeter. The spacing between conductors forming the mesh system shall be such as to limit the maximum mesh potential to a value not greater than the maximum tolerable contact potential, assuming a fault clearance time equal to that of the back up protective gear being provided. In the GIS substation, extra attention should be paid to the possibility of unwanted circulation of induced currents. Where appropriate, the earth system shall be designed so as to include all overhead line terminal towers, which shall be earthed by extending the system so as to envelope all towers within the earth system. If the event of the substation resistance obtained with the foregoing installation being of a magnitude unacceptable to CLIENT, then where practicable, the ground area enclosed by the earth system may have to be increased by installing directly in the ground earth electrodes in the form of a ring outside the site at a significant distance from the substation boundary. Alternatively, earth rods may be approved if the earth resistivity survey indicates that their use is warranted. In all cases the contractor shall demonstrate by calculation that extensions of the grid outside the substation perimeter do not create a hazard for humans or animals under all conditions of operation. Items of equipment and structures which are most likely to contribute high earth fault currents, such as AIS switchgear, instrument transformers, power transformers, GIS frames, towers, arrester pads etc. shall always be connected to the grid with a minimum of two fully rated spur connections. The spur connections shall preferably run in opposite directions to eliminate common mode failure. The location of the grounding grids shall be such as to enable all items of equipment to be connected to the earth system via the shortest practicable route. The lighting poles of the outdoor lighting system are to be connected with separate earth electrodes at the meshed earthing grids (if applicable). Two interconnections between each of the building earthing sub-systems and the main earthing electrode shall be provided each having an accessible isolating point to enable measurement of the earthing resistance.

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Lusail Particular Specification

Section 38

Part 25

Earthing system and lightning protection

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The lightning installations for all the buildings, structures, etc., must also be connected to the main earthing electrode. The effects of lightning strikes on the control and monitoring systems vary from faulty pulses in control and measurement to the destruction of electronic sub-assemblies and cables and must therefore be prevented by the earthing of screens. To this end the screens of the control cables leading from the signal transmitters, actuators etc. must be taken to the dedicated earthing points and from there to the indoor earthing installation. They must be insulated and terminated via the screen bars in subsidiary distribution boxes, intermediate terminal boxes, marshalling racks, control cabinets and DC main distribution boards.

25.3.1.2

Indoor Earthing System

Flat bare copper flat sized to carry the fault current shall be installed to form one ring inside the building on the walls of each storey. From the ring conductor the connections to the GIS main ground bus, cable trays, conduits, doors, steelworks, buried floor screens etc., shall be made using PVC sheathed copper stranded conductor or bare copper tape. Connection to panels and other sensitive electrical apparatus shall be made independently to the indoor ring to minimize conducted interference. All of the electrical equipment, frames and mechanical apparatus shall be provided with designated earthing points. An earth ring connected to the main earth grid at two or more points shall surround each item of large plant situated in the buildings. Provision shall be made for the connection of power cable sheath bonding systems and cable accessories to the indoor earthing sub-system. Copper conductors shall be laid and fixed at the cable trays. Where this is not possible earthing conductor supports shall be provided fixed in concrete or masonry. The bare copper tape shall be also fixed and supported on walls. Care shall be taken to avoid the creation of tripping hazards due to surface mounted earthing conductors. Cable trays and vertical runs are to be connected to earth at least 20 meter intervals. At maximum intervals of 20m, the earthing ring inside buildings shall be connected to the outdoor earthing system using lead-sheathed single 2 core copper conductor of size 300mm .

25.3.1.3

GIS Bonding and Earthing

The manufacturer of the GIS shall give particular attention to the bonding of the metallic enclosures of the GIS assembly to ensure that these enclosures carry induced currents, which can be of significant magnitude, via specifically designed paths. The points of connection of the bonding system to the earthing sub-system shall be defined, be sufficient in number and located to minimize hazardous touch and step voltages within the GIS area. Additional measures including the use of conductive platforms (earth mats) connected to GIS structures and earthing may be applied. Any integral access platforms provided for operation or servicing shall be integrated into the GIS earthing system. A conductor or system of conductors (main earth bus) shall be provided for connecting all designated metallic components of the GIS to station earthing system. In this respect, earthing recommendations of the GIS manufacturer shall be strictly observed. A continuous steel reinforced concrete slab should be used both as an auxiliary earthing device and for seismic reasons. The steel reinforcing mesh of the continuous floor slab shall be provided with electrical contact points brought out to convenient locations and connected to the building earthing

Lusail City

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Lusail Particular Specification

Section 38

Part 25

Earthing system and lightning protection

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sub-system so that both the GIS enclosures and the structural steel in and above the foundation will be at approximately the same potential level.

25.3.1.4

Cable Trenches

A lead sheathed copper main earthing conductor shall be provided for each cable route within substation to which all steelworks shall be bonded.

25.3.1.5

Pipelines

Where pipelines enter the site (fence / boundaries) they shall be fitted with a length of electrical insulation over the pipe on each side of the wall, and an insulating flange at the boundary. This prevents dangerous potentials occurring between the pipe and earth, both within and outside the site.

25.3.1.6

Communication Circuits

If it is not possible to limit the rise of station earth potential to the maximum of 650 V rms typically required by communication authorities, isolating devices shall be applied to the incoming lines as part of the communications installation.

25.3.2

Lightning Protection (if applicable)

Lightning protection shall be provided for all buildings and shall be in accordance with BS 6651. The main components of a lightning protection system are as follows: · · · · Air terminations, Down conductors, Earth terminations, Joints, bonds, test joints, etc.

The buildings have large flat roof. Air termination network mesh of approximately 10 m x 20 m shall be used. Down conductors, one for each 20 m of the building perimeter shall be used. Each down conductor should be provided with a test joint. The ring around a building installed as a part of main earth electrode system shall be used for air termination network. Nuts and bolts at the test joint or other joints, which are to remain detachable, shall be made of copper-nickel-silicon-bronze. Down conductors are to be connected to the earthing ring around the buildings. The connection points should be stripped of the lead sheath. The connection points are to be bitumen protected against corrosion.

25.4

MAIN TECHNICAL DATA

The 220, 132 and 66 kV System Neutrals are solidly earthed. The 11kV System neutral is earthed via earthing transformers each designed to limit the earth fault contribution to 750A.

25.4.1

Electrical Parameters for Earthing Calculation:

Parameter for Fault current (kA) 220kV 40 132kV 40 66kV 31.5 11kV 40

Lusail City

Revision 0

Issue Date: April 2010

Lusail Particular Specification

Section 38

Part 25

Earthing system and lightning protection 220kV 1 50 132kV 1 50 1 0.5 10

Page 7

Parameter for Duration of fault current (s) Frequency (Hz)

66kV 1 50 1 0.5 10

11kV 3 50 3 0.5 -----

Duration fault current for earthing 1 conductor sizing (s) Duration of shock for body current (s) Ratio X/R 0.5 10

To ensure the lowest possible resistance to earth and to lower the surge impedance for lightning protection, buried electrodes shall be provided to bring the overall resistance to earth to less than 0.25 ohms.

25.5

25.5.1 25.5.1.1

EQUIPMENT REQUIREMENTS

Earthing system materials Earth Electrodes

Lead-sheathed stranded copper conductor not less than 240mm² shall be used for earth electrodes (grid conductors) laying in the soil and spur connections. The lead sheath shall be at least 2 mm thick. The cross-section of earth electrode conductors shall be confirmed by calculation in accordance with the main technical data, but shall be not less than 400mm² for the spur connections and 240mm² for the branch connections shall be chosen. The size of lead-sheathed stranded copper conductors shall be uniform throughout the area under the Contract. The current density for lead sheathed stranded copper conductor shall not be greater than 140 A/mm² for 1 sec. duration.

25.5.1.2

Earthing Conductors

Bare copper tape shall be used for the ring inside the building on the walls at each operational level. The cross-sectional area shall be a minimum 150mm2 ( 30mm x 5mm); the size required is to be confirmed by the contractor. PVC sheathed stranded copper conductor or bare copper tape shall be used for connection of the equipment to the ring inside building. Lead-sheathed stranded copper conductor not less than 240 mm² crosssectional area shall be used for all connections of the ring inside the building to outdoor earth electrode system. Each connection between the equipment and the earthing system (spur connection) shall carry the total fault current, but the cross-section area of branch connections may be reduced to 60 percent of corresponding single conductor to provide for the current distribution in two or more conductors. The current density for copper earthing conductors shall not be greater than 190 A/mm² for 1 sec. duration.

25.5.1.3

Earthing Connections

All equipment within the station area shall be connected to the main grid including but not limited to the following: steel structures, hoist and motors, 66kV switchgear, transformers neutral points, transformer tanks, fences,

Lusail City

Revision 0

Issue Date: April 2010

Lusail Particular Specification

Section 38

Part 25

Earthing system and lightning protection

Page 8

cables armour, cable trays and conduits, AC switchboards, DC switchboards, control panels, control desks, relay panels, motor frames, lighting fixtures, lighting poles, housing of small equipment, ladders, steel reinforcing bars where it is applicable or where it is used in ground slabs for equi-potential grading, etc. Branch connections of the non-current carrying metal parts of equipment shall have a minimum size as follows: Relay and control panels, AC and DC switchboards, distribution boards, etc. From metallic enclosure of LV electrical equipment having a supply cable above 35 mm² From metallic enclosure of LV electrical equipment having a supply cable with a size between 6 mm² and 35 mm² From metallic enclosure of LV electrical equipment having a supply cable size below 6 mm² To structures and to plant equipment and other non-electrical equipment 70 mm² 70 mm²

25 mm²

6 mm²

6/25/70 mm²

The above conductor sizes are minimum. Each conductor shall be designed to carry maximum earth fault current for the fault clearance time or 1 sec. whichever is the longer time. All branch connections shall be made by means of compression type devices or exothermic welding (typically Cadweld) methods, approved by KAHRAMAA may be applied. All joints and connection welding shall be of by exothermic welding (Cadweld). All bare parts of underground earthing conductors shall be suitably protected against direct contact with the soil to prevent electrolytic corrosion of plant equipment. The Contractor shall record the route of all earth conductors with dimensions marked on the drawings to adequately define the position of the runs. The earthing systems will not be accepted as complete until the recorded information has been provided to the satisfaction of CLIENT. Earth bonds shall be used to bond all steel platforms operating floors, ladders, hand rails, cable tray, structural steel work, etc. which does not have a solidly welded path to the main structure/or earthing grid. Particular attention shall be paid to the effectiveness of bonds onto frames of electrical equipment, and at all points where the earth conductor is bolted. Whenever dissimilar materials are to be joined the necessary bi-metallic plates shall be inserted as required to ensure that electrolytic action is avoided. All electrical equipment shall be equipped with earthing hooks of sufficient size and shall be earthed at the earth system by means of heavy-duty tinned copper compression lugs.

Lusail City

Revision 0

Issue Date: April 2010

Lusail Particular Specification

Section 38

Part 25

Earthing system and lightning protection

Page 9

All earthing copper conductors for indoor installation shall be PVC sheathed colored green and yellow. Lead sheathed copper earthing conductor emerging from the ground shall be protected against mechanical damage by steel pipes up to 150 mm above grade level. The pipes shall be sealed with a non-setting non-flammable compound.

25.5.1.4

Earth Pits and Earth Rods

Earth electrodes shall be 15 mm diameter extendible type of stainless steel copper clad driven directly into the ground to a minimum depth of 2.0 meters into the summer water table without excavation or drilling. The connections from earth electrodes to the earthing electrode ring cable shall be made in a concrete inspection pit with cover, using bolted clamps.

25.5.2

Lightning Protection Material

The following lightning protection material shall be used: lead sheathed copper tape at least 50 mm² for roof conductor and down conductor, stainless steel copper clad earth rod.

25.6

PERFORMANCE GUARANTEES

Where corrosion due to atmospheric, chemical, electrolytic or other causes is likely to impair any part of the earthing system and lightning protection system, suitable precautions shall be taken to prevent: · · Electrolytic corrosion between dissimilar metals, Chemical corrosion of copper.

Fittings and joints shall be resistant to the corrosive agents or otherwise suitably protected with bitumen or embedded in plastic compound according to the local conditions.

25.7

INSPECTION AND TESTS

Tests shall be carried out in order to determine whether the material and equipment comply with the required properties. All tests on material and equipment shall be made in accordance with IEC Standards if not otherwise specified. The testing of earthing installation shall be in accordance with IEEE 81. Upon completion of earthing system, the following measurement shall be effected: 1. 2. 3. 4. Measurement of resistance to earth, Measurement of contact voltage inside and outside perimeter fence Measurement of step voltage inside and outside perimeter fence, Determination of Grid Potential Rise.

25.8

SPECIAL EQUIPMENT AND TOOLS

Works to be done under this section include the delivery of special equipment and tools for erection, installation, maintenance, setting to work and other purposes. Requirements for special equipment and tools are described in Section General Technical Requirements and quantities in Schedule of Prices.

Lusail City

Revision 0

Issue Date: April 2010

Lusail Particular Specification

Section 38

Part 25

Earthing system and lightning protection

Page 10

Specified special equipment and tools to be delivered by the Contractor are listed in Schedule of Prices. Any additional special equipment and tools recommended by the Tenderer shall be listed and priced in Schedule of Prices.

25.9

SPARE PARTS

Works to be done under this section include the delivery of spare parts. Requirements for spare parts are described in Section General Technical Requirements and quantities in Schedule of Prices. Specified spare parts to be delivered by the Contractor are listed in Schedule of Prices. Any additional spare parts recommended by the Tenderer shall be listed and priced in Schedule of Prices.

25.10

PACKAGING, SHIPPING AND TRANSPORT

Packing, shipping and transport shall be arranged according to the requirements in Section General Technical Requirements.

25.11

TRAINING

Works to be done under this section include training of CLIENT's personnel to operate and maintain equipment efficiently and safely. The main requirements for training are described in Section General Technical Requirements. There shall be no constraints on the number and category of CLIENT's personnel to be trained.

25.12

DOCUMENTATION

The Contractor shall provide all necessary drawings, design specifications, design details, operation and maintenance manuals and other information in accordance with Section General Technical Requirements.

25.12.1

Documentation with Tender

The Tender shall contain at least the following information and documents: 1. General arrangement drawings of the main earthing equipment items; 2. Manufacturing specification of the proposed earthing equipment; 3. Catalogues, literature and reference lists of proposed equipment; 4. Quality Management System Manual and ISO Certificate of the equipment manufacturer.

25.12.2

Documentation after Award of Contract

All documents required for CLIENT's approval shall be submitted by the Contractor in accordance with Section General Requirements. END OF PART

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