Abstract: Phase comparison relaying apparatus associated with the local and remote end terminals of a protected line section wherein the phase comparison is performed at one terminal by unsupervised circuitry to generate an echo trip signal which is employed to effect breaker tripping at the other terminal. Additional circuitry supervises the generation of a breaker trip signal for use at the terminal where the echo trip signal is generated without preventing generation and transmission of the echo trip signal.The use of such circuitry is described in the operating context of phase comparison relaying apparatus adapted to utilize offset keying. Also described is the effectiveness of such circuitry during open breaker or zero-feed conditions.

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.

Abstract: A phase comparison relaying network wherein a transmitter keying threshold is set at a predetermined value of the current wave at the transmitter end which is offset from the effective zero axis of the current wave. This yields a signal which, when phase compared with the current wave at the receiver end of the protected line section, permits a tripping response in the presence of "outfeed" current at the "weak feed" end of the protected line section which might occur during an internal fault.

Abstract: This disclosure relates to a segregated phase comparison relaying system which is of the type wherein the current at each end of each of the conductors of a protected section of a three-phase transmission network is phase compared over a communication network for determining whether the fault of the faulted conductor is located within or external to the protected section of the transmission network. Under certain conditions it is desirable to transmit a breaker opening signal from one end (transmitting end) of the protected section to the other end (receiving end) thereof to provide a direct transfer-trip at the receiving end in response to the detection at the transmitting end of a fault which might not cause the breaker at the receiving end to open when using the segregated phase comparing system.