|Definition:|| a) of two-winding transformers (for the principal tapping):|
the active power absorbed at rated frequency when rated current is flowing through the line terminal(s) of one of the windings, the terminals of the other winding being short-circuited, and any winding fitted with tappings being connected on its principal tapping
b) of multi-winding transformers, related to a certain pair of windings (for the principal tapping):
the active power absorbed at rated frequency when a current flows through the line terminal(s) of one of the windings of the pair, corresponding to the smaller of the rated power values of both windings of that pair, the terminals of the other winding of the same pair being short-circuited, any winding of the pair fitted with tappings being connected on its principal tapping and the remaining winding(s) being open-circuited
NOTE 1 – The load loss can also be considered for tappings other than the principal tapping. The reference current of two-winding transformers is, for any tapping, equal to the tapping current. For multi-winding transformers, the reference current or reference power are related to a specified loading combination.
NOTE 2 – The load loss is normally related to the appropriate reference temperature.