Abstract: An electric power distribution system having a number of automatic protection breakers distributed on various levels is disclosed herein. Each protection breaker includes an electronic protection unit to open the breaker, which is controlled based on the amount of current flowing through the breaker and its derivative. Each of the breakers is preferably connected in order to exchange information concerning their respective status. Also disclosed herein is method for controlling the intervention sequence of the mutually interlocked breakers, in which a breaker reports a detected fault condition to its next higher level breaker.

Abstract: A safety system for electronic devices having multiple power inputs includes dedicating a different power detector to each power input and includes disabling all of the power inputs upon detection that one input has been disabled. Each of the power inputs is typically a power cord that provides electrical energy to a discrete electrical circuit. Thus, the safety system permits the electronic device to use a different power supply for each electrical circuit, while ensuring that there is no erroneous assumption that disconnecting one of the power cords will de-energize the entire electronic device. In the preferred embodiment, the paths to the power supplies are disabled by opening relay switches, with the switches that are specific to a power cord being in a logical AND arrangement.

Abstract: Power supplied from a battery via a power-supply line is distributed via switching means to load drive lines, connected to loads, respectively. Memory means stores the data of current-breaking time characteristics providing the breaking time which corresponds to the amount of each excessive current and the capacity of each load. When any of the current detection means has detected an excessive current flowing through any of the load drive lines, control means breaks power supplied via the load drive line to the load, by opening the switching means immediately after the corresponding breaking time has elapsed.

Abstract: Both fault location and fault resistance of a fault are calculated by the present method and system. The method and system takes into account the effects of fault resistance and load flow, thereby calculating fault resistance by taking into consideration the current flowing through the distribution network as well as the effect of fault impedance. A direct method calculates fault location and fault resistance directly while an iterative fashion method utilizes simpler calculations in an iterative fashion which first assumes that the phase angle of the current distribution factor D.sub.s is zero, calculates an estimate of fault location utilizing this assumption, and then iteratively calculates a new value of the phase angle .beta..sub.s of the current distribution factor D.sub.s and fault location m until a sufficiently accurate determination of fault location is ascertained. Fault resistance is then calculated based upon the calculated fault location.

Abstract: An integrated protection system for an electrical distribution system including a panelboard for receiving power from a utility source and distributing the power to a plurality of branch circuits each having line and neutral conductors for delivering the power to a load. The integrated protection system comprises a plurality of arcing fault detectors and line interrupters attached to positions in the panelboard. The arcing fault detectors detect the occurrence of an arcing fault in either of the branch circuits, while the line interrupters disconnect the load from the power source in response to the detection of an arcing fault in either of the branch circuits. The line interrupters and arcing fault detectors may comprise separate modules, each being connected to one of the positions in panelboard or being attached externally to the other module.

Abstract: An electric power distribution system is shown where even if supply of electric power is interrupted, other normal electric part systems can be operated. A number of electric power distribution portions are supplied with electric power through at least two systems of electric power lines. The amounts of electric currents in the two systems of the trunk lines respectively are detected and monitored by a sensor and each current detection portion. Moreover, a controller controls a switch corresponding to a sensor which has detected an abnormal value among output values from a number of current detection portions to make non-conductive the trunk line from which the abnormal value has been detected. If a fault takes place in, for example, the trunk line between the electric power distribution portions, the two ends of the trunk line respectively are disconnected by the switch.

Abstract: A current limiter arrangement particularly adapted to be positioned at a substation of an electrical power system for limiting the fault current for a predetermined period of time to permit protective devices positioned downstream in the network to clear the fault. If the fault is not cleared and the fault persists for a predetermined period of time the current limiting arrangement acts as a circuit breaker to open the load circuit. The arrangement includes an SCR bridge having a superconducting coil connected across two nodes. A novel gate pulse firing circuit generates two pulses per ac cycle for application to the gates of the SCR's of the bridge at 90.degree. and 270.degree. of each 360.degree. cycle and is ON at all times to provide for prompt dc charging of the super conducting coil with no ac load current and non-fault conduction of ac current at less than the maximum current limit.

Abstract: Negative sequence, positive sequence and zero sequence quantities are determined from voltage and current values for a power signal on a radial distribution feeder line. Negative sequence quantities are evaluated against selected threshold standards; the negative sequence impedance is also determined, which is then evaluated to determine fault direction (if a fault is indicated). If a reverse fault is declared, the trip output of overcurrent elements in the protective relay for the feeder is blocked for a selected period of time. The same evaluation process is carried out for zero sequence quantities. A selection process determines whether the negative sequence or the zero sequence element is to be enabled. Further, voltages and currents of all three phases of the power signal are evaluated to determine relative change over a period of one cycle. If within the one cycle there is a decrease of both voltage and current in all three phases of approximately 10%, the overcurrent elements are also blocked.

Abstract: A method and apparatus for receiving, monitoring and characterizing network power information in real time through the use of a specialized display system. A processor receives three phase current and voltage information from a network power relay, converts and scales that data into a two-dimensional vector having coordinates that are represented by, and displayed as, a single pixel on a display screen. The repeated monitoring provides a Feature Map (FM) of the network system that can be easily read and understood by operating personnel.

Abstract: When a trouble occurs in a cable, a feeding pass for another cable is ensured. In a feeding pass switching circuit, optical fibers are respectively connected to the terminals A, B and C. When a negative current is applied to the system in a state where a BRANCH2 is put in an open circuit and a TRUNK is grounded, a relay K1 is activated, and then a relay K2 is activated. Successively, when a positive current is supplied from the TRUNK, a cable connected to the TRUNK and a BRANCH1 is fed from both terminals. When the positive current is supplied from the BRANCH1 in a state where the TRUNK is put in a open circuit and the BRANCH2 is grounded, a relay K3 is activated. Successively, when the negative current is supplied to the BRANCH2, a relay K5 is activated. In such a manner, the power is fed to each feeding pass from one terminal.

Abstract: A differential current protective device for a transformer arranged in a multi-phase power supply system and having at least one star-connected winding arrangement with a grounded star point. The differential current protective device receives currents proportional to the system currents via current transformers provided on the high and low voltage sides of the transformer. A computing circuit of the protective device determines a differential phase-related current from the currents measured, taking into account a current parameter that corresponds to the zero system current based on the phase and whose intensity is monitored. The differential current protective device includes an auxiliary current transformer having its primary winding in the connection between the star point and ground. The computing circuit processes the secondary current of the auxiliary current transformer as the current parameter corresponding to the zero system current.

Abstract: An improved ground fault protection system is provided for protecting an electrical power distribution system having multiple sources and multiple grounds. In accordance with a preferred embodiment, an electrical power distribution circuit having a primary electrical circuit for distributing electrical power from a plurality of sources to a plurality of loads is provided with a ground fault protection circuit magnetically coupled to the primary circuit. The primary electrical circuit includes conventional main and tie buses for distributing power to the loads and switches or circuit breakers for interrupting power from flowing in the buses. The ground fault protection circuit includes current sensors, tripping functions or ground fault relays associated with each circuit breaker and a novel use of an auxiliary transformer. When a ground fault occurs, the ground fault protection circuit is capable of sensing and determining the specific bus in which a ground fault condition exists.

Abstract: Coordination of the overcurrent/time trip characteristics of a hierarchy of overcurrent protection devices is accomplished through a central tester which establishes a pattern of test currents for the individual overcurrent protection devices which simulates a fault at a specified location in the power system. The individual assigned test currents are transmitted over a communications link to the separate overcurrent protection devices where they are stored in memory. The central tester then broadcasts a test signal which simultaneously initiates testing of all of the overcurrent protection devices using the assigned test currents stored in memory. The trip times are recorded and reported back to the central tester for analysis.

Abstract: A circuit protecting device for an automotive wiring harness designed to make the dimensions of wires downstream from fuses smaller and minimize the number of circuits which will be brought into an inoperative state upon blowout of a fuse resulting from a short circuit which occurs in a wire by supplying protecting circuits for supplying power from a power source to loads with fuses provided in the circuits connected in one-to-one relationship with the loads so that, upon blowout of one fuse, only a power supply to the load connected with this fuse is cut off. The fuses are formed by a flat fuse 20 including a plurality of conductive fusible elements 21 arranged at specified intervals on the surface of an insulating plate 22.

Abstract: A plurality of solid-state switches are provided in parallel with a main circuit switch. A main circuit current is detected by a first current detecting device. A current flowing in each of the plurality of solid-state switches is detected by a second current detecting device. Based on the detected currents of the first and second current detecting devices, the main circuit switch is commanded to open and each solid-state switch is commanded to close by a control circuit, when a fault is detected by a fault detecting circuit. At this point of the process when the main circuit switch is opened, when a commutation anomaly is detected by a commutation detecting circuit, the conducting status of each solid-state switch is maintained. When the commutation achieves a normal status, each solid-state switch is interrupted and circuit breaking, at the point the capability of each solid-state switch is exceeded, is prevented.

Abstract: A system and method of protection against the passive loss of differential current fault protection is provided for an electric power generating system (EPGS). The EPGS utilizes a bus power control unit (BPCU) to control and protect bus configuration, and a generator control unit to control each of the generators. This system and method protection protects against perpetuation of a bus fault on a left air vehicle distribution bus, a right air vehicle distribution bus, or a air vehicle tie bus during passive loss of normal differential current fault protection within the BPCU, and comprises circuitry for monitoring parameters of the generator output power, circuitry responsive to these parameters for detecting a high generator current condition for generating an output overload signal when the parameters indicate the presence of a bus fault.

Abstract: A communication power distribution system including a single power regulator which feeds a plurality of transmission lines current limited by corresponding active current limiters.

Abstract: The present invention relates to an apparatus and method for distributing electrical power from power substation circuits. The apparatus of the present invention is responsive to overcurrent conditions and selectively actuates a switching network so as to restore power to at least a portion of the users connected to the faulty circuit of the power distribution system.

Abstract: A power controller (10) for supplying power to a power distribution network (N) in which power from a polyphase source (G) is routed to using equipment (E) connected to the network through the power controller. A plurality of solid-state power devices (82) switch each separate phase of the polyphase power to the equipment. A firing circuit (14) controls gating of the switches to route the power. Fuses (F) are connected between the switches and the using equipment to interrupt power flow to the equipment if excessive current begins to be drawn. A con, roller (20) controls a shutdown sequence employed by the controller to eliminate current spiking at shutdown. The various components are housed in an enclosure (22) which includes a mounting structure (56) for mounting the aforesaid components. A cooling system (26) employs a fan (88) for directing air flow through the mounting structure to cool the components.

Abstract: A non-ferrous current sensor is used to continuously measure the charging current magnitude in step-graded foil and paper insulation systems and capacitive insulation systems used on high voltage measurement and control apparatus such as instrument transformers and on the condenser bushings of power transformers and circuit breakers. The low voltage measured signal is conditioned by an electronic circuit that modulates a DC signal in a system current control loop to provide continuous remote monitoring and alarm functions. Remote power is supplied to the sensor and conversion circuits through the current loop. The sensor detects changes in the charging current through the insulation ground conductor, indicating the degradation of the dielectric properties between the foil layers. The sensor and associated electronic circuitry are enclosed in a housing adaptable to be used with a capacitance tap common to high voltage measurement and control apparatus.

Abstract: Substation for the distribution of electrical energy, and protected against arcing faults, characterized by the fact that Hall-effect sensors and additional optical fiber conductors are provided as sensors, whereby the Hall-effect sensors are logically AND linked with the optical fiber conductors.

Abstract: In a reverse-charge prevention apparatus (24) including a 1st breaker (25) for connecting or disconnecting an electric power system (A) to or from a distributed electric power apparatus (11), in which the 1st breaker (25) is switched off when the distributed electric power apparatus (11) is disconnected from the electric power system (A) by switching off a 2nd breaker (F) disposed in the electric power system (A) so that reverse-charge from the distributed electric power apparatus (11) to the electric power system (A) is prevented, the reverse-charge prevention apparatus (24) further includes a disturbance generator (20) for slightly varying electric power outputted by the distributed electric power apparatus (11) regularly with a given period; a variable period extraction circuit and a filter (26, 27) for extracting a variable period same in period to the given period, the variable period existing in a period of an alternating-current voltage outputted by the distributed electric power apparatus (11); and a

Abstract: The reliability of transformer differential relays is enhanced by providing a method and apparatus which enable improved discrimination between transformer current differentials due to transformer inrush current and current differentials due the occurrence of an internal fault. This improvement in discrimination is provided by generating a first signal representative of currents flowing in at least two windings of the transformer, a second signal representative of a positive portion of the first signal, and a third signal representative of a negative portions of the first signal. A first output signal is generated when the magnitude of the second signal exceeds a first predetermined value, and a second output signal is generated when the magnitude of the third signal exceeds a second predetermined value. A trip signal is generated upon coincidence of the first and second output signals.

Abstract: A protective device for an electric distribution system capable of providing an easy inspection and confirmation of the setting for the operation characteristics of the device. The device includes an input unit for entering a setting of an operation characteristic of the protective device; a calculation unit for determining the operation characteristic of the protective device according to the setting entered by the input unit; and a display unit for displaying the operation characteristic determined by the calculation unit.

Abstract: A power supply system includes load circuits connected to a power source circuit through respective power lines. Each of the power lines is provided with a breaker element such as a FET that connects and disconnects the power line to and from the load circuit, and an overcurrent detection resistor for detecting an overcurrent in the load circuit. If an overcurrent is detected according to a signal from the overcurrent detection resistor, a short-circuit protection controller opens the breaker element to cut off the power line from the load circuit. A voltage monitor circuit monitors the voltage of the load circuit, and a control circuit controls the load circuit.

Abstract: An electrical control system for sensing instantaneous total electrical power consumption being delivered into a facility and for interrupting selected electrical current consuming loads within the facility when the total incoming current consumption exceeds one or more preselected maximum level for a continuous first preselected time period. The system utilizes existing power transmission lines within the facility to sequentially transmit at least two pulsed digital shut down signals on each of at least two phases or legs of transmission lines within the facility to one or more remote shut down units at the end of the continuous time period. Each remote unit then interrupts electrical power to at least one electrical load within the building for a second preselected time period, after which power is restored to the electrical load until the total current consumption again exceeds one of the preselected maximum load levels continuously for the first time period.

Abstract: A non-ferrous current sensor is used to continuously measure the charging current magnitude in step-graded foil and paper insulation systems and capacitive insulation systems used on high voltage measurement and control apparatus such as instrument transformers and on the condenser bushings of power transformers and circuit breakers. The low voltage measured signal is conditioned by an electronic circuit such that it modulates a DC signal in a system current control loop to provide continuous remote monitoring and alarm functions. Remote power is supplied to the sensor and conversion circuits through the current loop. The sensor detects changes in the charging current through the insulation ground conductor, indicating the degradation of the dielectric properties between the foil layers. The sensor and associated electronic circuitry are enclosed in a housing adaptable to be used with a capacitance tap common to high voltage measurement and control apparatus.

Abstract: The method is to detect a fault on a busbar and to specify the faulted point to a specific section of the busbar in order to provide a proper protection. If the fault has occurred, for instance, on a point P of a section between current transformer BCT- and a connecting point thereof to the busbar, or on a point Q of a busbar section between adjacent line outlets, the resulting fault current is expressed as a calculation sum of an output current of the current transformer BCT-. The foregoing current is zero in a normal condition, but in case of a fault, it reaches a definite value other than zero. Noticing this point, the fault current is computed for each section on the basis of the observable output current of the current transformer BCT-, and it is judged that if the foregoing current of a specific section exceeds a predetermined threshold, the fault has occurred on the above section.

Abstract: A solid-state circuit breaker with fault current conduction is described. The circuit includes a power sensor connected to a power line having an up-stream side and a down-stream side. The output of the power sensor is conveyed to a switch selection circuit that identifies a line disturbance on the power line. In response to a line disturbance, the switch selection circuit generates a set of output signals. The output signals force the opening of a fault current interruption circuit including a set of turn-off thyristors. The turn-off thyristors respond to the line disturbance within a fraction of a power signal cycle to provide isolation between the up-stream side and downstream side of the power line. An alternate power source may then be applied to the down-stream side of the power line. If the line disturbance exists on the down-stream side of the power line, the output signals force the closing of a fault current conduction circuit including a set of thyristors connected in series with a reactor.

Abstract: A fault sensor device which can detect and distinguish abnormal current and voltage events on an alternating current overhead and underground power transmission or distribution line. The abnormal current events are momentary outage, sustained outage, normal overload, and inrush on transmission or distribution lines. The sensor can further distinguish whether the momentary or sustained fault is a line to ground fault, line to line fault or a three phase fault. It can also identify the faulted phase(s). In the overload scenario, the sensor can identify if the overload has occurred on all three phases or only on one or two phases of the power line in an unbalanced situation. The voltage events are open line(s) on one, or two of the phases with a possibility of a fallen live wire and voltage sag. The sensor can identify which of the three phases or if all three phases of the power line are open or on the ground.

Abstract: The present invention relates to an apparatus and method for distributing electrical power from power substation circuits. The apparatus of the present invention is responsive to overcurrent conditions and selectively actuates a switching network so as to restore power to at least a portion of the users connected to the faulty circuit of the power distribution system.

Abstract: A system of protection for an electric power distribution system which has at least two parallel power feeders for each electrical phase coupling a source of electrical energy through a contactor device to a load distribution bus comprises a controller, and a parallel feeder current sensor for each parallel power feeder which sense electrical current conducted therein. The parallel feeder current sensors produce output parallel current sense signals proportional to the magnitude of the parallel feeder current sensed, and are coupled to the controller by conductors which communicate the output parallel current sense signals thereto. The controller comprises circuitry which compares the magnitudes of the output parallel current sense signals for each electrical phase.

Abstract: The system includes a blocking counter which is set to 255 quarter cycles and the output contacts of the protective relay are blocked for five quarter cycles if the first order difference between two successive quarter-cycle samples of current is above a selected threshold, referred to as the last previous and the first samples. The first order difference between the first and the next successive (second) samples is compared against a second threshold and the instantaneous value of the current sample is compared against the second threshold. If both comparisons are above the second threshold, then the output contacts are unblocked. If not, such that a constant DC A/D converter output or an A/D spike is indicated, then the outputs remain blocked for the full five quarter cycles, which is sufficient time to permit the A/D spike to disappear and to recognize a constant DC output from the A/D converter.

Abstract: An apparatus for detecting differences between zero-sequence current caused by load unbalance and fault current caused by fallen distribution conductors. The apparatus makes it possible to readily check a high impedance fault. The apparatus includes analog-to-digital converters for converting analog A-, B-, C- and neutral phase current signals to digital data, respectively. The apparatus further includes a data processing system for computing even order power, rate of the even order to odd order power, and incremental variance of even order power. The apparatus analyzes the digital data and determines the fault when the computed information is compared with respective setting values and is greater than the setting values.

Abstract: In a power receiving system, a network transformer, a protector breaker and a current detector are connected between the load side of each of a plurality of network lines and a network bus, a breaker is connected to the primary side of the network transformer, the current detector being operative to detect an accident current on the secondary side of the network transformer, and relays or an operation controller is provided which is responsive to the detection signal to open the breaker and protector breaker to switch off accident currents on the primary and secondary sides of the network transformer, whereby the protective range is so expanded as to cover a line section between the network transformer and the protector breaker and the scale of the overall power receiving system is reduced.

Abstract: An arrangement to coordinate protective devices is provided by defining operation of the instantaneous characteristic portion of an upstream protective device to coordinate with a downstream current-limiting fuse based on the peak let-through current of the downstream current-limiting device, with instantaneous operation being set to occur only above the peak let-through current of the downstream current-limiting fuse. Accordingly, for fault currents which are seen by both the instantaneous device and the current-limiting device and that are within the ratings of the current-limiting device, the upstream device will not respond and the downstream current-limiting fuse will interrupt the fault, as intended.

Abstract: A method and a device for preventing overstabilization of longitudinal differential protections in case of internal faults on power lines, which may take place when a fault situation, which is indicated as an external faults, is in reality an internal fault. The invention comprises criteria which finally provide information as to whether the longitudinal differential protection is to enter into operation. The criteria comprise level and directional determination of the currents which are measured in the terminals of the power lines, checking whether these have the same direction, and so on.

Abstract: A method and a device for preventing understabilization of longitudinal differential protections in case of external faults and current transformer saturation. The invention comprises an extension of the state of the art with regard to stabilization of longitudinal differential protections in such a way that the values (A1, A2, . . . An), (.phi.1, .phi.2, . . . .phi.n), obtained via current measurement (C1, C2, . . . Cn) and Fourier filters (4, 5, 6), for determining the function characteristic of the protection under certain conditions as regards current amplitude and current transformer saturation are given corrected values (A1k, A2k, . . . Ank), (.phi.1k, .phi.2k, . . . .phi.nk) (FIG. 2).

Abstract: A system for protecting a remote power supply for supplying power to an optical subscriber network, via a pair of power supply lines, from a remote power supply apparatus, being provided with power supply branch apparatuses inserted into the power supply lines in correspondence with each power receiving circuit respectively mounted in subscriber transmission nodes. Each of the power supply branch apparatuses comprises relay contacts inserted into its own power supply branch lines connected between the power supply lines and its own power receiving circuit, and a relay energized by an overcurrent detector or first and second communication units to change over the relay contacts. The relay contacts are opened and closed subscriber by subscriber sequentially to detect a faulty portion, and thereafter, the power is fed again selectively to the subscribers which have not experienced the fault.

Abstract: An electrical power system protection device includes a circuit breaker and a switch connected in series to a power line. The protection device also has a current limiting element connected in parallel to the circuit breaker. When the level of electrical current flowing in the power line, detected by a current detector, has exceeded a predetermined first set level, a first over-current detector delivers immediately a trip command to the circuit breaker. As a consequence, fault current is commutated to the current limiting element so that any drop of voltage in the power line upstream of the circuit breaker is greatly suppressed. When a state in which a predetermined second set level is exceeded by the detected current level is continued beyond a predetermined period, a second over-current detector delivers an off command to the switch, thus protecting the upstream portion of the power line against the fault in this power line.

Abstract: The disclosed faulted current indicator ignores temporary overloads and transients by inhibiting any trip resulting from an overcurrent signal until a disabling circuit senses that a fuse or circuit breaker has reduced the line current to zero.

Abstract: A plurality of switches are arranged in a distributive manner on a distribution line connected to a power distribution substation, and the switches are connected respectively to fault detection relays. Each of the fault detection relays includes a memory circuit for holding a voltage resulting from a ground fault on the distribution line, and the time constants of the memory circuits are set to become greater in an ascending order from the power outlet of the distribution line. Owing to difference in the time constants, there are differences in the holding voltage of the memory circuits resulting from intermittent ground faults which precede a full ground fault. By utilizing the differences of holding voltage, the switch closest to the full ground fault as viewed from the power outlet of the distribution line is the first to open the circuit.

Abstract: A digital protective relay apparatus comprising an analog input section, a correction value-calculating section, a storage section, a correction section, a protective calculation section. A correction value for correcting the error of the analog input section is predetermined and stored in the storage section. Digital data obtained through the analog input circuit is corrected by the correction section using the correction value. The protective calculation section performs predetermined calculation using the corrected digital data, thereby determining whether or not a trip instruction should be supplied to a breaker.

Abstract: A fault current protective device contains a fault current protective switch (2) for the protection of at least two circuits formed by branching subsequent to the fault current protective switch (2) and having the same number of phases. One of these circuits is looped through the fault current protective switch (2) again at least once over connections (L2, L3, and L2', L3'), respectively, of the fault current protective switch (2) which are free of use, so that a higher protection level (lower nominal fault current I.sub..DELTA.n) is obtained relative to the other circuit. Only one fault current protective switch (2) is required for this purpose, so that the fault circuit protective device is compact and economical.

Abstract: A neutral connector of a standard three-phase, three-wire panelboard is replaced by a specific multiple termination assembly having a limited number of terminations specifically adapted for connection to ground at the panelboard, for grounding the termination assembly to the panelboard enclosure, and for connecting the multiple termination assembly to the power conductor of the system grounded phase which is also connected to one pole of the main circuit breaker, main switch or main lug of the panelboard. Standard AIC rated three-pole circuit breakers or fusible switches are wired to three-phase loads in the branch circuits and connected to the three bus bars of the panelboard to connect the grounded phase to the load through the circuit breaker or switch, and to open all phases when operated.

Abstract: Error-free, reliable registration of a fault in a power distribution circuit is achieved by a faulted circuit indicator that measures the current in the circuit after a discrete time delay following the detection of an overcurrent condition. A fault is registered only if the measured current is less than a prescribed level, evidencing that the overcurrent has operated a protection device (such as a fuse), upstream from the faulted circuit indicator, to interrupt the circuit and clear the fault. Hence, only actual (true) faults, resulting in circuit interruption and isolation of the fault, will be indicated, thereby precluding false registrations that may otherwise occur from non-faults such as transient currents, momentary overloads, inrush currents, and the like.

Abstract: A breaker failure relay circuit is responsive to either a trip signal from a protective relay or a manual trip signal, as well as the current through a circuit breaker protecting a transmission line. The trip signal is applied to an edge triggered timer (28) having selected pickup and dropout times, and is also applied as one input to one OR gate (24). The circuit breaker current is applied to an overcurrent element (34), the output of which is applied to a reset input of the edge triggered timer (28) to reset and disable the timer and also as one input to another OR gate (30). The other input to OR gate (30) is the output of the edge triggered timer (28). The outputs of OR gates (24, 30) are applied to an AND gate (26), the output of which is applied to a second timer (32) and as another input to the one OR gate (24). The output of the timer (32), if and when it occurs, is used as a trip signal for a backup circuit breaker.

Abstract: The disclosed faulted current indicator ignores temporary overloads and transients by inhibiting any trip resulting from an overcurrent signal until a disabling circuit senses that a fuse or circuit breaker has reduced the line current to zero.

Abstract: A device for detecting and isolating a downed conductor in a three-phase four-wire multi-grounded distribution system. The device cooperates with a power supply protective device if the device has a breaking capacity less than the maximum prospective short-circuit current of the distribution line, and the device is installed at a tap point of the distribution line. The device comprises a current detector, a low-pass filter, a high-pass filter, an arcing ground fault current-detecting circuit, a first overcurrent-detecting circuit that delivers an output when the output current from the low-pass filter exceeds a given value, a second overcurrent-detecting circuit that detects an overcurrent exceeding the breaking capacity of a device which has a breaking capacity less than the maximum prospective short-circuit current of the distribution line, a no-voltage detecting circuit for sensing that the distribution line is not electrically charged, a main contact and a trip mechanism.

Abstract: Circuitry is described for isolating a section of a loop circuit (L) from a bi-directional supply unit (20) in the event of a short circuit in the section. One or more circuit elements (21), such as fire detectors, are connected in respective portions of the loop circuit and between respective pairs of bi-directional isolators (1,2,3,4). Each isolator includes switching means (TR1,TR3) providing low and high impedance paths for respectively supplying current to said circuit elements and isolating said circuit elements from the supply unit (20). Each isolator also includes sensing means (TR2, D1, DS7) for sensing a short circuit in any one of the circuit elements (21) whereby the sensing means causes a change in state of the switching means from the low to the high impedance path thereby isolating the circuit elements in the respective section of the loop from the supply unit.