Earthing Design 1

[jamie79]

Hello, I'm read this forum all the time but have a question so decided to join up.

I'll give you some background first. I am working on an installation which has a 22KV supply, feeding 4 22KV to 400V transformers via a HV panel. The Panel is fed by 95mm single core per phase cable, and the TX each fed by 95mm single core XLPE per phase also. The incoming supply is run with a 120mm earth cable. I was proposing to therefore run a 120mm to each TX.

I have been advised that I need run only 1 120mm earth to the TX room (which houses all 4 TX'S)to an earth bar, then earth each tx with 120mm cable to the earth bar.

I'm looking to back up this advice some how, but can't really find anything relevent in the Australian Standards.

There is a British standard I used to use in UK, BS7430 code of practice for earthing, is there an AS equivalent or IEC?

Any help would be appreciated

 

[Kiribanda]

jamie79,
I agree & support your proposal of running four seperate individual earthing wires from the panel to each transformer.Always the intention should be to reduce the zero seq impedance looking from the fault.So if we install four seperate wires it will reduce the zero seq. impedance rather than having longer loops as per the alternate proposal.
IEC60364 depicts TNS earthing method which is widely used in industrial installations.It is identical to your method of earthing.Otherwise I donot think any IEC std will show you how to ground the transformers.I have no idea about AS stds.It is designer's choice based on best engg practices and codes.