The Remote Measurement of Phase Angle

Abstract

In the distribution of electricity, it is necessary to link the outputs of substations, which may be many miles apart. In order to prevent an excessive surge of current in the connecting link, the connection between a pair of substations should not be made until the phase angle between their voltages is small, There has been, for many years, a need for the measurement of this phase angle, with the results displayed in the distribution Control Room, A direct measurement may be significantly in error, due to the time delay in transmission of the measurement signals from substation to Control Room. This error is avoided inthe measurement system described. A test signal, superimposed on the phase measurement signal, repetitively measures the transmission path delay, and applies a suitable correction to the phase angle indication, The system may be used either with pilot lines or a radio link between substations and Control Room, An advantage is that the route of a pilot line may be changed without affecting the accuracy, thus allowing the use of public telephone lines, if necessary. A pilot line system has been installed in the Birmingham Area of the Midlands Electricity Board: the maximum length of pilot line used is 12 miles, and the measurement error does not exceed a small fraction of one degree. The equipment has been designed to possess a high degree of reliability. Although primarily designed for operation at 50 Hz, the system could readily be adapted for use at higher frequencies.