zigzag transformer?
zigzag transformer?
(OP)
why do we use zigzag transformer to craete earthing for big plants?
for example:
4 frame 6 gtg 42mw
4 delta /star transformer 50mva
short circuit 23 ka
max load 100mw
bus rating 2500A 3 SECEND
for example:
4 frame 6 gtg 42mw
4 delta /star transformer 50mva
short circuit 23 ka
max load 100mw
bus rating 2500A 3 SECEND






RE: zigzag transformer?
But briefly, a zigzag transformer creates an artificial ground on a delta system. (Thus, a zigzag transformer is connected on the delta side of a transformer) Sometimes a combined auxiliary and zigzag transformer are used, the zigzag transformer for a grounding point, and the auxiliary transformer as the substation supply. (Local supply for lights, plugs, battery charger, etc in the sub)
RE: zigzag transformer?
The zig-zag unit is wound such that normal phase voltage sees a very high impedance, while zero sequence voltage sees a very low impedance.
Actually, there is nothing "artificial" about the ground established by a grounding transformer. It's real and it's got the iron in the transformer to prove it if you ground one of your phase conductors.
RE: zigzag transformer?
What I actually meant with "artificial" is that fact that you have to add a piece of equipment (in this case the zigzag trsf) to obtain a grounding point/method. I totaly agree with your statement that the grounding point is real.
A zigzag transformer is also called an interconnected-star earthing transformer or a Neutral-earthing coupler (NEC) In South Africa there is still a lot in use and they are easily obtainable.
Regards
Ralph
RE: zigzag transformer?
It's interesting that these transformers still seem to be popular everywhere except the US. I had to specifiy one for a client a few years back and all the major transformer suppliers here just laughed at me. They weren't interested. There are still a few small "custom" transformer shops such as Uptegraff that will make them.
I generally just recommend the use of a standard delta-wye transformer because they are so much easier to get and end up being cheaper.
RE: zigzag transformer?
Auxiliary/ZIgzag transformers are widely used in Sultanate of Oman, where I worked for about 3years.
There the 132/33kV transformers are Yd connected with auxliaray / zigzag transformers providing the neutral point for 33kV system and also power supplies for the substation (precisely the way you explained).
Just to share.