Auxiliary grounding/ earthing for Isolators in substation. 1

[IndianTechEngg1001]

One of my friend asked me this question where he was wondering if a separate earthing design is done for isolators 220kV. These grounding/earthing are then connected to main grid. If it is done what practices are followed? He was calling this earthing as auxiliary grounding/ earthing.

If anyone practiced this kindly help

 

[Marmite]

Normally the operating handle has an earth mat buried beneath where the operator would stand. Is that what you mean?
Regards
Marmite

 

[IndianTechEngg1001]

Yes it is the one where operator will stand. He is telling me that normally he saw following for grounding/earthing

Normally For 400kV Switch Yard- Mesh Formed is LxW :: 1500mmX 1500mm spacing of rod @300mm this was beneath the isolator

Normally For 220kV Switch Yard Mesh Formed is LxW :: 1200mmX 1200mm spacing of rod @300mm which is beneath the isolator

If it is OK then what codes they might have followed?

 

[jghrist]

There are no codes/standards in the USA that address the size of the grounding platform. I don't know about IEC. I see no reason for the size of the platform to be voltage dependent. It need to be big enough to stand on comfortably to operate the switch. A 400 kV switch operating handle is no larger than a 220 kV switch operating handle.

 

[bacon4life]

We also use a 1200mm x 1200 underground mesh for 115 and 230 kV switches.

The operators do more than just stand ;-) Staying strictly on that size can be hard if the switch isn't well maintained or if it is ice covered.

 

[IndianTechEngg1001]

Any idea from where this size 1200x1200 with conductor spacing 300 came from? OR it is just a practice everybody following up?

 

[potteryshard]

Having additonal conductors buried beneath the finished grade will help reduce step potential for the operator, but do nothing to reduce the voltage difference due to ohmic resistance of the grounding lead between the connection to the switch handle and where the operator stands.

I prefer to install a galvanized steel platform which rests on top of the finished grade and which is bonded not directly to the ground grid, but instead to the point where the ground grid connects to the switch lever ground strap. This ensures that the operators hands and feet are tied to the same electrical potential and can no longer be part of a shunt path.

 

[IndianTechEngg1001]

I add all into following....please check

1. Auxiliary ground Grid should be bonded to Ground Grid where Grid connects the switch lever ground strap.

2. The purpose of this auxiliary ground is to keep potential of handle lever and ground at persons atep at same level.

3. Size 1200mmx 1200mm with 300 mm horizontal conductor spacing is just a standard practice and as it is connected to main grounding its size and conductor spacing normally dosen't vary with soil resistivities.

4. Also Size 1500mmx 1500mm with 300 mm horizontal conductor spacing is used at many places to take care of safe working space around equipment.

Please correct me if I am wrong in analysis anywhere.