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Transformer Impedance

Derek Eccles

Transformer Impedance. I am trying to calculate the Ze part of Zs. I have the impedance of the phase conductor and the CPC, all I need now is the impedance of the supply authorities secondary transformer winding. The transformer is a pole mounted 100kVA, 11kV / 400v. Is there such a thing as typical impedances for such transformers ?

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    IEC 60076-5 recognises a minimum short-circuit impedance of 4.0% for 25-630kVA and 5.0% for 631-1250kVA for two-winding transformers at nominal tap, with a +/-10% tolerance

    Actual impedance specified by DNOs may vary, and the upstream network fault level is sometimes signifcant.

    However I think what you really want is table F5 of the IET book Calculations for Electricians and Designers

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    IEC 60076-5 recognises a minimum short-circuit impedance of 4.0% for 25-630kVA and 5.0% for 631-1250kVA for two-winding transformers at nominal tap, with a +/-10% tolerance

    Actual impedance specified by DNOs may vary, and the upstream network fault level is sometimes signifcant.

    However I think what you really want is table F5 of the IET book Calculations for Electricians and Designers

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