In circuitry for generating tripping and blocking signals for the protection of electrical power supply network components as a result of the occurrence of faults, the blocking signals are selected from each phase of the electrical power supply network to prevent tripping in each phase for faults occurring behind the protected component. A sequence detector includes a partial detector for each phase of the electrical power supply network and includes logic circuitry responsive to respective tripping and blocking signals generated for each phase of the electrical power supply network in dependence on whether the fault lies ahead or behind the protected electrical component, respectively. Each logic circuit includes a gate and a delay circuit responsive to the output of the gate. The output of the delay circuit in the tripping logic circuit is input to the gate in the blocking logic circuit and vice-versa. Each blocking logic circuit includes an additional gate for receiving a blocking input from another protection circuit which is common to all the partial detectors for passing blocking signals and blocking tripping signals.

Multiphase blocking circuitry for electrical power supply networks

A system and method for measuring phase-angle in electrical power systems includes inputting a reference signal into a receiving terminal of a communication system at a reference station and then sending the reference signal through the communication system. The reference signal is received at a substation and shaped as a quasi-reference signal. A phase difference β between the quasi-reference signal and a tested signal at the substation is then measured. Phase delay of the reference signal caused by the communication system, including phase delay produced from sending means, receiving means, relaying units, and communication channels, is calculated. A phase difference α is then calculated between the reference signal and the tested signal according to the phase difference β between the quasi-reference signal and the tested signal and the phase delay of the reference signal caused by the communication system.

Phase angle measurement method and system in electric power systems

The square wave phase comparison signals generated for each phase of a power distribution system by phase comparison relays at each end of a protected three phase transmission line segment are combined to generate a single, multi-level signal with discrete values for each instantaneous combination of square wave signals. The single, multi-level signal is used to modulate a carrier signal which is transmitted over a single channel of a two-way communications link to the other terminal where the carrier signal is demodulated to reproduce the multi-level signal. The reproduced multi-level signal is then decoded to generate remote square wave signals which are compared with the phase of locally generated square wave signals to generate trip signals for circuit breakers at the respective terminals. Square waves representative of priority functions, such as direct transfer trips, can be integrated into the single, multi-level signal transmitted to the other terminal.

Phase comparison relaying system with single channel communications link

Protective relay apparatus which performs a segregated phase current comparison of a three-phase protected line section, with a single relay at each end thereof for making the phase current comparison The single relay includes a rectifier arrangement which provides a signal responsive to the largest phase current of a predetermined polarity, at any instant In response to a fault detection, it successively phase compares the signals from its rectifier with the signals of the corresponding phases from the rectifier in the relay at the other line end

Protective relay apparatus

A method and apparatus is disclosed herein for protecting a power circuit within a first cycle after power up using a current transformer to sense current and an electronic trip unit having a first trip threshold value at power up and a second trip threshold value for the reference value at about the first half cycle of the first cycle after power up. The first and second trip threshold values are threshold values used to determine an over-current condition at different preselected times after powering up is initiated.

Current transformer initial condition correction

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.

Offset keying technique for segregated phase comparison relaying

MODIFIED OFFSET KEYING APPARATUS FOR PHASE COMPARISON RELAYING ABSTRACT OF THE DISCLOSURE 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 transmitter having the higher keying threshold level is located at that end of the pro-tected line section where outfeed is expected.

Russell W. Gonnam

Papers

Offset keying technique for segregated phase comparison relaying

Modified offset keying apparatus for phase comparison relaying

Phase comparison relay device

Schutzrelaiseinrichtung fuer kraftstrom-uebertragungsleitung