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Zig Zag Earthing Transformer

Zig Zag Earthing Transformer

Zig Zag Earthing Transformer

(OP)
How would you test operation to earth faults on a site, rather than at a test facility

RE: Zig Zag Earthing Transformer

Rodmcm:

What is the voltage of the NEC (zig-zag) trsf? 11kV?
How is it been earthed? Solidly (normally an old system) or through  resistors? (newer system)
What is your intention with the test? To see if the NEC  is fine? To see if your NEC is connected sufficiently to ground?(It is giving a good grounding point) Or just for relaying purposes?

Ralph

RE: Zig Zag Earthing Transformer

(OP)
Voltage is 11kV, earthed through a resistor. All protection checked by secondary/primary injection. Client wants to see that the TX/resistor 'works'. Ideally he would like to induce an 11kV earth fault on his system, but not prepared to take the risk on a working industrial site, so wants another 'real' test method. See the problem?

RE: Zig Zag Earthing Transformer

If the protections are electronic and settable to completely different settings, try connecting a temporary 110V supply (backed up by a GFCI) and simulate the fault.

RE: Zig Zag Earthing Transformer


From one zigzag phase through its neutral to the resistor-ground terminal would need 6½kV · 400A ˜ 2.6MW, if only for a short time.
  

RE: Zig Zag Earthing Transformer

I think primary and secondary injection for relaying puposes is enough. But if the client still insists on a "real" test, use 380V or a variac. With the ratio you can determine the current, measure it with a clamp-on over the neutral or through the neutral CT while you simulate the fault, and confirm. NEC's are designed to carry fault current usually for 10sec, (sometimes up to 30sec) so a 11kV fault simulation can be done, but do not exceed the time on the nameplate.

Ralph

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