Grounding for a spare transformer

[KnicksJets]

We are procuring a 607MVA transformer (345 KV to 22 KV) which we are storing as spare. As for the grounding requirements, while the transformer stays de-energized as spare, we were provided with three #4 gauge wires. We want to know if there is a spec (IEEE or ANSI) on such requirements particularly for Transformers that stay deenergized, except for the cooling bank that might be operational every 6 months through 480V circuit for routine checks. If any case would #4 gauge (3 phase) wire be adequate?

 

[PHovnanian]

By 'spare', do you mean it will be placd into service in its current location? Or moved into place prior to energizing?

If its the former, I'd size the grounding for operations. Its one less thing to worry about come the panic when the primary unit goes T.U. and people are scrambling around getting it hooked up. Someone may see temporary grounds and assume they are OK for operation.

If this unit will have to me moved, ground to suit the 480V system and to ensure poper lightning protection. I'm assuming that LAs will be installed (or grounds) on bushings to protect the stored unit so as not to discover damage only after dragging the spare out in an emergency.

 

[waross]

Grounding size for energizing from a 480 Volt source will be dependent on the size of the breaker feeding the 480 Volts. Check the NEC for the appropriate size of an equipment grounding conductor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[KnicksJets]

Thanks for the response.
I am more worried about the size of the wires for grounding to protect the transformer from lightning. This transformer will be stored as a Spare until we have a need to use it. That means it will remain in the storing pad for years, without any lightning arrestors or anything else. What should be the size of the wire to protect a deenergized transformer from lightning?

 

[PHovnanian]

What should be the size of the wire to protect a deenergized transformer from lightning?

6 AWG is the smallest size allowed by the NEC for surge arrester conductor (2008 NEC 280.23). I'd go with that as a start. Or whatever meets the 480V circuit requirements. And I'd ground the bushings as well if there won't be any arresters connected while in storage.

 

[racookpe1978]

I don't know transformers - since I'm usually on the piping, oil, and turbine side of the plants - but is there any potential for trouble from a lightening strike/near miss/hit on the on-service transformers nearby if he doesn't ground both sides of the insulated transformer cores?

That is: for long-term outdoor storage, wouldn't you have to ground the frame or casing itself, the input power leads, and the output power leads?