The Phase Angle of Current Transformers

A method of testing the phase angle of current transformers by comparing readings obtained on a wattmeter whose current circuit is first connected to receive a part of the primary current (the remainder of the primary current passing in shunt through resistance) and then connected to the secondary circuit; the potential circuit is supplied from the primary voltage, and capacity or inductance is used to give the effect of a low power factor in the wattmeter. Corrections are applied for the error of phase of the part of the primary current which passes through the wattmeter, and separately for the error of phase in the primary caused by the fact that the primary current is not exactly in phase with the voltage used to supply the wattmeter. A second method of connection is suggested which avoids the latter correction, and other methods including the use of a three-phase circuit are discussed. Results of tests are given, and also check obtained by the use of an a-c. potentiometer. The method requires only portable instruments.