Primary ZIg Zag

[vreijb]

What's the advantage of using auxiliary transformers ZNyn11 over Dyn11 (750KVA 11x.4KV)

Thanks

 

[RRaghunath]

vreijb,
Z-winding is specified if neutral is not available for system grounding. This could be with auxiliary Y- winding or without. The zero sequence reactance of Z-winding is important for system grounding.
Hope it is helpful.

 

[pwrtran]

several reasons go with Zig Zag primary:
a) need a grounded neutral on primary
b) need phase angle shift
c) apply reduced the primary insulation on primary
d) apply OLTC on primary at a lower vs on delta

 

[vreijb]

We have separate Z Transformer for neutral earthing. The client is asking ZNyn11 Transformer to reduce the gorund fault on low voltage side

 

[RRaghunath]

vreijb,
I must say it is a bad application to use zigzag primary just to reduce the ground fault current magnitude in 400V system. This can more simply done by adding a low ohmic resistor in the 400V neutral-to-ground circuit.
It is true that the Zigzag winding on primary will mean the zero sequence reactance for faults in 400V system would be of the order of 50%, reducing the ground fault current magnitude to just about 50% of the transformer rated current.

 

[slavag]

Hi,
Im second with Raghun.
It seems a very strange, use this type of trafo for reduce the ground fault :-(.
More, I never see this type of trafo ZnYn11, once, for the distribution was used D(Y)zn... trafo.
Best Regards.
Slava