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Equivalent circuit of Zero Sequence Impedance of Transformers

Equivalent circuit of Zero Sequence Impedance of Transformers

RE: Equivalent circuit of Zero Sequence Impedance of Transformers

Your attachment shows how the transformers are represented in the zero sequence network. I think you have to review a power analysis book if you don't understand this. I don't think you understand the topic enough to ask a real question.

RE: Equivalent circuit of Zero Sequence Impedance of Transformers

The zero sequence diagrams will probably make more sense if you think about how you would perform the tests to measure the impedance.

A zero sequence voltage source is simply a single phase voltage. If you connect three leads to that source, you have a zero sequence voltage source that can be connected to any three phase transformer connection.

Consider a delta wye-grounded transformer connection. If I connect my zero sequence voltage source to the delta side, you’ll get no current flow because each corner of the delta will have the same voltage. This results in an open circuit as viewed from the delta side.

If I now take my zero sequence voltage source and connect the three leads to each leg of the wye and the grounded end of the source to the neutral end of the wye connection, you will have a complete circuit on each leg consisting of the leakage impedance of the transformer. Since the currents on the wye side are all in phase, this results in a circulating current in the delta winding, but no line current on the delta side.

In view of this, does the third diagram make more sense to you now?

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