the ratio Ud/ UN (tapping factor) or 100 Ud/ UN (tapping factor expressed as a percentage)
where:
UN is the rated voltage of the winding
Ud is the voltage which would be developed at no-load at the terminals of the winding, connected on the tapping concerned, by applying rated voltage to an untapped winding
NOTE – The tapping factor expresses the relative value of the "effective number of turns" of the tapped winding at the relevant tapping, the basis 1 being the effective number of turns of this winding at the principal tapping.
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