What is the definition of zero-sequence impedance for a three-phase winding of a transformer
The impedance, expressed in ohms per phase at rated frequency, between the line terminals of a three-phase star-connected or zigzag-connected winding, connected together, and its neutral terminal
NOTE 1 The zero-sequence impedance may have several values because it depends on how the terminals of the other winding or windings are connected and loaded.
NOTE 2 The zero-sequence impedance may be dependent on the value of the current and the temperature, particularly in transformers without any delta-connected winding.
NOTE 3 The zero-sequence impedance may also be expressed as a relative value in the same way as the short-circuit impedance
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