Abstract: A detection circuit for remote release apparatus is disclosed which monitors a circuit carrying high-voltage between two connection points A and B and disconnects the circuit from the rest of a high-voltage network by automatically opening two power switches when a short circuit is detected. The ground fault protection system includes a pair of power switches for disconnecting points A and B from the remainder of a high-voltage network when a fault is detected in the high-voltage carrying circuit. A different one of a pair of detection circuits are associated with each point A and B. Each detection circuit causes both power switches to open when a fault is detected. The fault detection circuit associated with point A detects faults occurring in the high-voltage carrying circuit at any location extending from point A to at least one-half a distance to point B.

Abstract: The method of protecting power transmission lines is, accpording to the invention, based on a comparison between the actual quantities of current and/or voltage at the beginning of the protected section of a power transmission line and the same quantities of current and/or voltage calculated by means of current and voltage parameters at the end of the protected section providing there are no faults in this section. In apparatuses for realization of this method the voltage and current at the end of the protected section are multiplied in symmetrical components multipliers by respective coefficients of an equivalent four-terminal network substituting for the protected section and summed up. If there are no faults in this section, this calculated sum is equal to the respective electrical quantity at the beginning of the protected section.

Abstract: In a protective relaying system wherein a carrier wave frequency modulated by an electric quantity is transmitted to a receiving station for operating a relay and an abnormal condition of the transmitted signal is detected by detecting the frequency variation of the carrier wave, there is provided an abnormal condition detector which compares the lengths of contiguous or closely adjacent periods, or functions thereof, of the received carrier wave.

Abstract: An improved in-band signal-to-noise ratio monitor is used in conjunction with the receiver of an FSK relaying system. The improved monitor measures the signal-to-noise ratio both prior to and after the receiver input signal is filtered by a narrow bandpass filter. The magnitudes of the measured ratios are compared and, if all signal-to-noise ratio permissives are not satisfied, the tripping function of the relaying system at the receiver or local station is blocked or inhibited.

Abstract: In a static protective relay device utilizing a converter including a bandpass filter which causes time delay during transients, there are provided a detector responsive to the output from the converter, and means for preventing misoperation of the detector due to an attenuating oscillation of the output caused by the transient phenomenon of the converter which occurs during attenuation of the output.

Abstract: Phase comparison relaying apparatus wherein the keying threshold levels at the local and remote ends of a protected power line section are each offset by a different value from the effective zero axis of the current waveform. One of the keying threshold values is set at a magnitude which will cause a trip response in the presence of low or medium magnitudes of outfeed current. The other keying threshold level is set at a magnitude which will cause a trip response in the presence of maximum magnitudes of expected outfeed current. The upper and lower current margin threshold levels are set to appropriately reflect the keying threshold level with which they are respectively associated. In addition, the transmmitter having the higher keying threshold level is located at that end of the protected line section where outfeed is expected.