Check Synchronizing Equipment

The paper describes the development of a new form of check synchronizing unit, for use during the paralleling of an a.c. machine on to live busbars, to ensure that the circuit breaker controlling the incoming machine is closed only when the correct degree of voltage, phase and frequency matching has been attained. For its action it depends essentially on the production of a series of unidirectional voltage pulses of rectangular waveform and constant amplitude, whose duration is determined jointly by the phase and frequency of the incoming machine relative to those of the busbars. The duration, and therefore the mean value, of the pulse voltage, is used as the criterion by which the correctness of phase and frequency matching is assessed; separate provision is made for ensuring that the magnitudes of the two voltages are sufficiently closely matched. As soon as correct conditions have been attained in all respects, the check synchronizer operates automatically to close the circuit breaker and connect the machine to the busbars. Features of interest, in the unit here described, are that since the settings of the majority of the relays are far from critical, they can conveniently be of the standard telephone type, their time delays, when required, being provided by simple combinations of resistance and capacitance connected in the relay operating-coil circuit. The check on frequency and phase matching is performed separately from that on voltage matching, and, over a wide range, is independent of variations in voltage magnitude.