Grounding and Lightning Protection for Substations

This is about requirements for lightning protection for buildings, Substation Earthing Layout, lightning protection system, transformer lightning protection, grounding and lightning protection for substations, Buildings and structures. This article is mainly based on lEC Standards and is created by ANSI/IEEE based.  Main keywords for this article are Lightning Protection for Buildings, Substation Earthing Layout, Lightning Protection System , transformer lightning protection, Grounding and Lightning protection for Substations, Buildings and Structures.

References

International Electrotechnical Commission (IEC)
IEC 60079 Electrical apparatus for explosive gas atmospheres
IEC 60364 Low-voltage electrical installations / Electrical installations of buildings
IEC 60479 Effects of current on human beings and livestock
IEC 61000 Electromagnetic compatibility (EMC)
IEC 62305 Protection against lightning

Grounding and Lightning Protection for Substations, Buildings and Structures

• All grounding and bonding materials shall be in strict compliance with IEC 60364 and  shall have approvals/certifications from reputable independent laboratories/institutions.
• All lightning protection air terminals shall be in strict compliance with IEC 62305, and shall have approvals/certifications from reputable independent laboratories or institutions.

Plant Ground Loop Requirements

• Grounding shall be installed in accordance with IEC 60364.
• A ground loop shall be installed around equipment and structures in the operating  areas of the plant.
• The ground loop shall have a maximum ground resistance of one ohm.
• Grounding conductors extended above grade and exposed to possible damage shall  be protected with schedule 40 PVC conduit.
• Grounding conductors shall not be looped between structures, buildings, substations or  equipment, but shall be connected directly to ground rods, grounding connection buses, or the main ground conductors.
• For buildings and structures located 30 m or more from the main ground loop, a supplemental 70-mm² green insulated (TW) loop connected to the main loop shall be utilized. Connection to the main loop shall be minimum from two separate points.  
• Remote Locations
  • Isolated equipment, remote from process area, shall be grounded by using a  local 70 mm² ground loop attached to ground rods.
  • Buildings and structures remote from the ground loop around grouped  equipment or structures shall have a maximum ground resistance of five ohms.
• Above details is related to Grounding and Lightning protection for Substations, Buildings and Structures.

Main and Unit Substations

Substation Earthing Layout / Substation Ground Grid

• The Substation Earthing Layout shall be grounded by means of a grid system consisting of  conductors supplemented by ground rods.
• The ground grid shall be of a size in accordance with IEC 60364 to limit the step potential, touch potential, and transfer potential to less than the corresponding maximum allowable potentials based on a person weighing 50kg.
• The resistance to ground shall not exceed one Ohm.
• The ground grid shall not be limited by the size of the HV switchgear or GIS  building. The area around the S/S building shall also be included based on allowable potential calculations.
• The soil resistivity shall be determined before the ground grid design is finalized. If a mass excavation or build-up technique is to be used for construction, the resistivity of the backfill or fill material must be recognized in the design.
• Grid conductors should be bare and in direct contact with the soil if they are intended to control potentials on the earth surface and serve as the grounding electrode.
• Ground rods shall be used in conjunction with a ground grid to lower the grid resistance.
• The required spacing between the grid conductors shall be determined using the procedures outlined in IEC 60364.
• Preliminary grid conductor size shall be a minimum of 95 mm². The final grid conductor size shall be determined by calculations. Ground wires bonding electrical equipment shall be sized in accordance with IEC 60364.  
• The grid conductors shall be laid out in a square pattern of Substation Earthing Layout.
• The grid should be installed throughout the substation area.
• The type of underground conductors for use in highly corrosive soils should also be chosen for their corrosion resistance.
• Ground buses shall be provided in the vicinity of electrical equipment and shall be sized to carry the total ground fault current. The ground bus shall be bonded to the grid conductors at several locations. Equipment grounding conductors are connected to the ground bus rather than directly to the grid conductor unless the equipment is isolated from other equipment.
• Ground buses shall be mounted inside the building for grounding the equipment. Each ground bus shall be connected to the substation ground loop at two or more locations.
• Overhead transmission line static and ground conductors shall be bonded to the substation grid.
• The overall plant ground loop shall be bonded to other existing grounding grid at two or more locations.
• The grounding shall take into account the future additions with Substation Earthing Layout.
• For more details, you can check standard international about Substation Earthing Layout.

https://www.youtube.com/watch?v=KlhI9GTJ2B8

Lightning Protection System

1. The substation shall be protected from direct lightning strokes by shielding designed in accordance with IEC 62305.
2. The substation building shall be protected from lightning according to IEC 62305.
3. Each air terminal shall have at least two paths to ground.  
4. The air terminal ground wires shall be connected to lightning ground rods,  which shall be connected to the substation ground grid.
5. The essential generator and transformers shall be grounded to the ground  loop, minimum from two points.
6. Check this article Lightning Protection System more with our website.

Buildings and Structures

1. Structures and buildings shall be protected from lightning in accordance with the requirements and recommendations of IEC 62305.
2. Reinforced concrete buildings and structures should be treated as nonmetallic structures.
3. Buildings and structures shall have adequate grounding.
4. A minimum size of 6-mm² copper wire or larger is satisfactory for bonding where there  is no danger of mechanical injury; otherwise 25-mm² wire is required.
5. The connection to the main ground grid shall be 70 mm2 copper wire or larger. The  stranded wire shall be corrosion protected.
6. The following items shall be connected to the grounding system either directly or  through bonding:
   a. Structural columns of buildings  
   b. Bus structures, towers, platforms, etc.
   c. Tanks, vessels, stacks, exchangers and similar equipment.
   d. Floating roofs on tanks when they are non-inherently bonded.
   e. Exposed conductive materials enclosing electrical conductors, such as metallic conduit, electrical metallic tubing, metallic sheaths and shields, cable trough trays and racks, wire ways, bus ways and raceways.

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Hazardous Areas

• Electrical grounding and bonding installation methods shall comply with IEC 60079 in buildings and structures where handling of solids, liquids, and gases can result in the creation of dangerous static charges.
• Where static protection of piping or ductwork is required, each section and each fitting shall have no more than 100 ohms resistance to grounded building steel.
• Where piping is subject to either direct or induced lightning effects, the maximum allowable resistance to ground is 10 ohms in hazardous (classified) area and nonhazardous area.
• If measured resistance exceeds the appropriate value, then the high resistance joints shall be located and suitable bonding jumpers shall be installed. 
• All bonding connections, except those consisting of a permanent metal-to-metal contact accomplished by welding or brazing, shall be made with compression connectors, clamps, or other approved means. Connection devices or fittings that depend solely on solder shall not be used as per IEC 60364.  
• At loading stations a 35-mm2 cable (single conductor stranded copper welding cable with neoprene jacket) with battery type clip cramped to the end shall be provided for grounding the metallic frame of the tank trucks.  Grounding and bonding in hazardous areas shall conform to IEC 60079.
• Tanks containing flammable materials shall be grounded and have flameproof vents. Tanks with metal roofs and metal sides made of metal 4.76 mm² thick or greater according to IEC 62305 and IEC 60079 shall be considered self protected from lightning. Tanks with lesser metal thickness shall require lightning protection.

Lightning Protection for Buildings

• Metal objects on the top or sides of a structure shall be bonded to the lightning protection system. lightning protection for buildings.
• Sharp bends shall not be made in lightning protection for buildings conductors. Bends shall not have an included angle of more than 90 degrees and shall have a minimum radius of 200 mm.  
• A minimum of 2 down conductors shall be installed for each structure of lightning protection for buildings. For structures having a perimeter greater than 76 m, an additional down conductor shall be installed for every 30 m of perimeter.
• Each down-comer conductor must terminate at a ground rod dedicated to lightning protection.
• The lightning protection ground loop shall be bonded to the electrical system grounding.
• Grounding for static and lightning protection shall be kept independent of the electrical equipment and system grounding unless the grounding systems are installed in close proximity to each other.
• More information you can see about Lightning Protection for Buildings.

Instrument Grounding

Grounding of electronic equipment shall comply with IEC 61000 and Instrument specificationsand requirements. Refer also to relevant Control and Instrument standards.

Transformer Lightning Protection

1. For 208/120VAC transformer secondary, the transformer neutral shall have both a grounded (neutral) conductor and a grounding conductor that are brought out and connected to the downstream panel board. In the panel board the grounded (neutral) conductor shall be connected to the neutral ground bus bar and the grounding conductor shall be connected to the ground bus bar. At the panel board, the neutral bus bar and the ground bus bar shall be bonded together and connected to the ground loop.
2. For 480 V AC transformer secondary, the transformer neutral shall have a grounded (neutral) conductor connected to the line side of the high resistance package. The groundside of the high resistance ground package shall have a conductor connected to the corresponding low voltage switchgear ground bus and to the ground grid. This requirement is valid for high resistance grounded system when specified.
3. For 4.16 kV, 13.8 kV and 34.5 kV transformer secondary, the transformer neutral shall have a grounded (neutral) conductor connected to the line side of the low resistance ground package. Refer IEC-E11-S01 for details. The groundside of the low resistance ground package shall have a conductor connected to the corresponding switchgear ground bus immediately downstream and to the ground grid.
4. For HV transformer primaries, the transformer neutral shall have a grounded (neutral) conductor connected to the gas insulated switchgear (GIS) ground bus sized to carry full fault current for the rated time of the GIS switchgear not just the expected duration of the relay operation. The transformer neutral shall also be connected to the ground grid.
5. For dry type transformers, the transformer case shall be grounded to the ground grid with at least one conductor with the minimum size of 25 mm².
6. For oil filled transformer, the transformer case shall be grounded to the ground grid with at least two conductors with each connected to the ground pad located on opposite sides of the transformer. The size of the grounding conductor shall be the same as the size of the ground grid.  
7. For more information about transformer lightning protection check vendor recommendation.
8. The minimum grounding conductor size for transformer neutrals shall be in accordance with calculations but not less than 25 mm².

 

https://www.youtube.com/watch?v=ZQgRzATOn6k&list=PLQQzLbTYBcJW1C_T2Jo4oczp9DCT0Au3L&index=14&t=0s

 

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Lightning Static and Stray Protection

• Tall or isolated metallic structures, stacks, and columns shall be grounded for lightning protection.
• The lightning protection system shall consist of lightning masts; structure mounted lightning rods of varying lengths and the lightning system conductors.
• A direct connection to the plant main ground loop (grid) shall be provided for each lightning system conductor from lightning masts, lightning rods and above grade lightning protection interconnection conductors.
• Lightning protection installations shall be in accordance with NFPA 780.
• Tank trucks, tank cars, portable drums, storage tanks, and agitators shall be protected  against static electricity, lightening and stray currents. See API RP 2003 and NFPA 77 for details. Generally, all elevated or isolated, or both, metallic objects, for example columns, stacks, and structures shall be grounded for lightening protection.