Potential transformer testing: Note on the effect of the resistance of the detector circuit, in determining the ratio of two alternating voltages, and the phase angle between them, by the balance method

In the use of the balance method of determining the ratio of the primary and secondary voltages of potential transformers, certain variations in the result were noted which appeared to be dependent on the relation of the resistance of the detector (RD in Fig. 1) to the balance resistance R1 and R2. A short theoretical investigation and a few tests were made to determine the cause and the order of magnitude of the errors involved, and to ascertain safe limits of operation. As the measurement of the detector voltage has frequently been suggested as a means of determining phase angle between voltages, the relation of the detector resistance to this measurement was also considered.