losses by using a Zig-zag transformer

[HamidEle]

We are providing power to 25KV line through Step up transformer (4.16kv/25kv). The utility specified Delta(25Kv) Wye(4.16KV), and later on they asked us to add Zig-zag transformer to avoid the potential over voltage issues. We were asked to assess the losses as a result of using Delta-Wye+ zig-zag transformer.

one loss I can think of is, the failure of the additional equipment-Zig-zag trnasformer would cause some loss over the years.

Are there any loss difference between Delta-wye+ Zig-zag and Wye-wye?

Any inputs would be appreciated.

 

[RRaghunath]

As it seems the network will have Delta/Wye + Zigzag trafo combination in place of Wye/Wye trafo, that is two trafos in place of one.
The utility wants to know a comparison of Watt losses between the two options.
What I guess is there will not be much difference in terms of watt losses between the two options. Additional loss in Zigzag trafo (only no-load loss need to be considered during normal operation) will be compensated by the less copper losses in Delta/Wye trafo (when compared to Wye/Wye trafo).
For numbers, a manufacturer will be in a better position to advise.

 

[prc]

raghun,in a transformer whether deta or star connected,copper losses will be the same as long as current density adopted is same.In delta connection resistance will be 3 times more than star winding,but current will be one by root3 times lower than star connection.

 

[waross]

In non fault operation the zig-zag transformer will have only no-load losses.

Bill
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