Abstract: Teed circuit protection is provided by a master unit at one terminal and slave units at the other terminals with broad band communication links between the master unit and the slave units. All units include line current transformers to the master unit signals derived from the current transformers to the master unit and circuit breakers controlled by operating signals sent from the master unit. The master unit has a logic decision-making facility which takes measurements of the amount by which a differential quantity proportional to the sum of the measurement signals exceeds a bias quantity proportional to the difference between the measurement signals proportional to the sum of the measurement signal exceeds slave units. The facility sends operating signals when that amount exceeds a threshold value. To prevent spurious operation of the circuit breakers a sequence of consecutive measurements may be taken all of which must exceed the threshold value.

Abstract: It is desirable to provide remote digital protection of distribution transformers. This specification discloses a protection system able to measure and compare increases in both negative and positive phase reference currents on a distribution cable feeding a transformer and to trigger a circuit breaker to isolate the cable only if the negative sequence current increase exceeds a predetermined proportion of any simultaneous positive sequence current increase. Consequently, engergizing with a 12.5% unbalance current has been found possible without false tripping.

Abstract: A method and a device in connection with digital distance relays for obtaining a backup function in the event of faults in the digital signal processing and/or in the event of faults detected during automatic testing. The method comprises testing the distance relay continuously, in case of a faultless network, with respect to the digital signal processing by means of a central control unit. In case of a characteristic fault on the network, the distance relay is switched over from testing to protective function involving measurement by means of measurement signal units included in the distance relay. In case of a fault on the network and a simultaneous fault in the digital signal processing, fault signals from the measurement signal units, via time delay circuits and logical elements, bring about tripping of the line section subjected to the fault. When a fault is detected in the digital signal processing, an alarm function is triggered.

Abstract: A method and device for range limitation and direct tripping for protection in the event of a fault on an electrical power line extending between two stations (P, Q) involves employing a travelling wave model in one of the stations (P) which, with the aid of measured currents and voltages in that station, to calculate the voltage distribution at a number of control points along the line. The range of the protection device is indicated as the distance between the measuring station and that control point for which a voltage difference (.delta.u) becomes equal to zero. The voltage difference consists of the difference between the absolute value of a voltage differene between the absolute value of a voltage difference (.DELTA.u), formed as the sum of a voltage value (U") calculated with the travelling wave model for the control point at a certain time, and the corresponding voltage value (U') one half-period earlier and the absolute value of the latter voltage value.

Abstract: A distance relay, for indicating single phase to ground faults on a polyphase electric power transmission system, having guard zone comparators (17,18,19) generating a first guard zone quadrilateral characteristic (21,23,25,27) in respect of each phase of the system and additional comparators (43,45,47) cooperating with the guard zone comparators (17,18,19) for generating a second main quadrilateral characteristic (23,25,27,49) in respect of each phase of the system, and a logic circuit arrangement (31 to 41) whereby the relay indicates the presence of a fault on a single phase to ground within the reach of the main characteristic relating to the relevant phase only if the corresponding guard zone characteristic, and no other, indicates a fault. The slope of the reactance line (21) of each guard zone characteristic is arranged to change its slope under two-phase phase to earth fault conditions by a lesser amount than the reactance line (49) of the corresponding main characteristic.

Abstract: A protective system for protecting elements (for example D) of an electric power system allocates a protection zone to each element. The protection zones are defined by switching points (for example 19', . . . , 24') which isolate the associated element (for example D) from the power system. Each of these switching points is associated with a transmitter/actuator unit (for example 19, . . . , 24). The transmitter/actuator units (for example 19, . . . , 24) produce "open" commands for their associated switching points (for example 19', . . . , 24') if it is determined that a fault has occurred inside the associated protection zone. The "open" commands for the switching points (for example 19', . . . , 24') are formed locally within the vicinity of each of the switching points.

Abstract: A safety mechanism is described which is used in an electrical distributing system with a bus-bar and of branches emanating from the bus-bar and has safety relays which turn off the malfunctioning part of the system in case of error. In this safety mechanism, redundancy is increased with respect to a malfunctioning of any one of the relays while the number of safety relays remains the same. This is achieved by the fact that each of the safety relays responds to a measurement of currents and voltages of two branches and acts upon both branches via the switches separating them from the mains.

Abstract: A protective relay for detecting power arcing faults on a three-phase electrical power spot network. A phase-to-phase power arc on a spot network produces harmonics on the phase-to-phase voltages, and the phase currents; a phase-to-ground arc produces harmonics on the phase-to-neutral voltages. The protective relay of the present invention monitors one or more of the three phase-to-phase voltages, the three phase-to-neutral voltages, or the three phase currents and indicates a fault based on the harmonic content of those signals.

Abstract: The invention comprises a method and a device for locating, isolating and by-passing a defective electrical device in an electrical circuit, and comprising sensing current and voltage at a first point in such circuit, on one side of such device, whereby the current and voltage are not significantly altered by the sensing process, sensing current and voltage at a second point in such circuit, on the other side of such device, whereby the current and voltage are not significantly altered by the sensing process, comparing such currents and voltages as between such two points, creating a control signal responsive to such compared currents and voltages, and, isolating such device from such circuit, and thereafter re-establishing such circuit whereby to by-pass such device, in response to a control signal of predetermined characteristics.

Abstract: A switching device is provided for alternating current parallel remote feed for the automatic disconnection of a faulty section and connection of a fault-free section of a remote feed field. The switching apparatus enables safe continued operation in case of a field fault. To this end, the switching apparatus contains switches for disconnecting the remote feed current paths and for connecting a d.c. voltage source to the section of the remote field facing away from the alternating voltage source. The switches are controllable by the direct current emitted by the d.c. voltage source and by the alternating currents flowing in the remote feed current paths.

Abstract: For the protection of electrical networks in the event of power transients, a surge arrester is employed which, independently of the value of the impedance at any time, continuously monitors and evaluates the change over time either of the measured impedance of the network or of the voltage multiplied by the cosine of the phase shift between current and voltage. Two parallel connected latch circuits store signals related to the current and voltage in the network. The difference between the signals stored in the two latch circuits is fed to a trigger circuit that controls a counter to emit a logic signal at the output terminal of the surge arrester only when the trigger circuit emits a logic signal twice in succession within a predetermined time. With this protection the electrical network is adequately protected against incorrect shutdown in the event of power transients in cooperation with any kind of short-circuit protective relay.

Abstract: Automatic voltage reduction is provided by a voltage regulator by monitoring utility load currents and comparing the load currents to a predetermined current value. When the predetermined current value is exceeded, the voltage input to the voltage regulator control is increased by a fixed predetermined amount causing the voltage regulator output to decrease. One embodiment of the automatic voltage reduction control circuit utilizes a current transformer for receiving a signal from a utility line in proportion to the amount of line load current. The current signal is compared to a predetermined current value by means of a differential amplifier to determine when the predetermined current is exceeded. The differential amplifier output then operates a relay to connect an auxiliary voltage source in series with the sensing transformer within the voltage regulator control unit.

Abstract: In a protective relaying device comprising first and second potential transformer circuits for transforming voltages of an electric power system, first and second relaying elements are further provided for receiving the output voltages of the first and second potential transformer circuits, respectively so that each of the relaying elements delivers an output of a particular logic state when it operates. When the outputs of the first and second relaying elements coincide with each other, a logic circuit receiving the outputs delivers a tripping signal to a circuit breaker.

Abstract: A system for electronically metering an A.C. electrical power system to derive performance parameters such as real and reactive power useful in revenue metering and fault protection applications. Voltage and current sensors associated with the power system provide isolated output signals proportional to the voltage and current in the system. From these signals finite-duration impulse-response filters periodically determine Walsh function correlation coefficients by integrating the voltage and current signals at least once during each period of the power system and periodically sampling and holding the integrated signal in sequence with the integration.

Abstract: A network protector relay produces a close signal entirely from sequence components based on the magnitude and phase relationships between the positive sequence component of the phase-to-ground voltages on the network side of the protector and the positive sequence component of the phasing voltages. The close signal may be inhibited by either the presence of the negative sequence component of the phase-to-ground voltages on the network side of the protector or if a trip contact is closed. The trip contact will be closed under certain specified conditions which make it advantageous to prevent manual closing of the contacts.

Abstract: Circuitry for generating tripping and blocking signals for the protection of electrical components included in electrical power supply networks as a result of the occurrence of faults therein provides multiphase pole tripping in the event that, after a single pole tripping has been executed, a new single phase fault occurs in any of the remaining phases of the electrical power supply network. Respective tripping and blocking signals are generated for each phase of the electrical power supply network in dependence on whether the fault lies ahead or behind the electrical component to be protected, respectively, in response to measurement of the voltae and current associated with transient waves generated by faults associated with each electrical power supply network phase.

Abstract: A power breaker system comprises a main breaker having a short timing delay function which is connected to a power source; a current limiting circuit for limiting fault current which is connected to the main breaker; and a plurality of branch load circuits consisting of each feeder breaker and each load which are connected to the current limiting circuit.

Abstract: A dynamo-electric machine is provided with a protective circuit arrangement whereby the machine is caused to be switched off if a short circuit current flowing in the machine exceeds a predetermined level.False operation of the protective circuit is avoided by incorporating a discriminating circuit which is able to distinguish the phase angle between the current and the voltage. This causes the protective circuit to trip for an over load current where the phase angle difference is small and the power factor near unity, which occurs with resistive fault situations; and not to trip where the phase angle difference is high, and thus there is a low power factor indicating a reactive condition, which occurs on start-up of the machine. A machine is able to run more safely as a result.