Electronic Load-Angle Measurement with Unusually Fast Response

A dc output voltage proportional to the phase angle between any two accessible points in an ac system is generated by the circuitry described in this paper. The transient response of the output voltage involves delays of less than one ac cycle, which represents an advance upon established techniques, and the linearity is of the order of 1 percent. The device has been used for alternator load-angle measurement and in sensing for control of excitation of an alternator in response to load-angle changes. Essentially, a flip-flop is turned on by one of the ac input waveforms and is turned off again by the waveform derived from the other point in the system with respect to which the phase angle is to be measured. To achieve the fast transient response there are six such flip-flops and thus six output pulses per ac cycle, which are then passed through a T-section m-derived filter with band rejection at six times the basic ac frequency. Discrete transistors have been used and their number has been kept to a minimum by the use of circuits with three and six stable states.