Sizing zig-zag transformers

[bozic77]

I would like to know a proper guide to size grounding transformer for a wind farm (ohms and MVA rating, continuous rating for 10 sec and short time rating for 3 seconds).

Following is assumed data: 34.5kV bus (line to line voltage at a switchgear bus), like to ground fault current given as I = 3000A. Charging current on the a 34.5kV feeder where zig-zag is to be installed is 120A.

thank you.

bozz

 

[waross]

If you are going to solidly ground the zig-zag transformer it will need to be able to withstand 3000 Amps for 10 Seconds.
If you are going to limit the fault current then the transformer may be a lot smaller.
If you cannot find published specs for zig-zag transformers then call a manufacturer with your requirements.

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

 

[HamidEle]

In some systems, you may want to consider the unbalance current

 

[waross]

Further to Hamid's post;
If there are phase to neutral connected loads, then:
A/ The zig-zag transformer must be solidly grounded by many codes.
B/ It must be capable of carrying the neutral load continuously.
C/ It must be capable of carrying the short circuit current until the circuit is disconnected.
But this probably does not apply in your case.

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