Abstract: An arrangement for protecting equipment of an AC electrical power system comprises first means configured to measure the frequency of the current and voltage at at least one location in the electrical power system along an interconnection between two theoretical electric machines of an equivalent two machine system. Fourth means are configured to use the values of the frequency of the current and voltage measured to determine whether a power swing has occurred and if an occurrence of a power swing has been determined determine whether the measuring location is located on a motor side or a generator side of a potential pole slip electrical centre along said interconnection, the electrical centre being defined as the location where the voltage becomes zero during a pole slip, and send this information further to third means for use in a control for protecting equipment of the electrical power system.

Abstract: A circuit breaker for protecting a power line. The circuit breaker includes a control unit and a circuit breaking element disconnecting the power line from a power source. The control unit detects a fault on the power line, opens the circuit breaking element, which opening starts a disconnection time interval, injects a test signal into the power line, measures a response, determines an impedance of the power line from the response, analyses the impedance during the time interval based on comparing the impedance with a reference threshold, determines a permanent or a temporary fault based on the analysed impedance, re-closes the circuit breaking element after the time interval if the fault is temporary and keeps the circuit breaking element open after the time interval if the fault is permanent.

Abstract: A method for detecting a ground fault in an electrical supply system includes using a combination of components and their connections within the supply system to form virtual components, allowing presetting of fault indicators for incoming and outgoing supply lines to individual components. A fault index can be determined for each virtual component in conjunction with a respective association of a correlation coefficient with fault indicators and a subsequent normalization over all fault indicators using a correlation coefficient. Comparison of the indices of all virtual components of the supply system permits a determination of that virtual component in which the highest fault index occurs, and therefore in which there is the highest probability of a fault. The fault search in a supply system can therefore be determined quickly and easily independently of power supply system geometry and configuration. An apparatus performing the method and computer program product, are also provided.

Abstract: A current differential relay device is described. The device has two transmission parts provided in parallel and communicating with an other end of a power transmission line through two transmission paths and transmitting and receiving a quantity data of electricity of each of the terminals to and from an other end in the form of the digital data obtained through analog/digital conversion. Two current differential operation parts are connected to each of the two transmission parts and perform a current differential operation independently for each of the transmission paths by using the digital data of the quantity data of electricity of the one end of the power transmission line and of the other end of the power transmission line. A signal generation part generates a trip signal from the current differential operation result of the two current differential operation parts.

Abstract: A safety discharge apparatus for an electrical storage element includes a load device for discharging the electrical storage element connected to the safety discharge apparatus via input connections. The apparatus includes a clocked switching device connected to a control device that serves to produce and interrupt a discharge current via the load device and the storage element, and a voltage detection device that detects a storage voltage of the electrical storage element to be discharged. The voltage detection device is connected to a discharge condition monitor that checks a dischargeability of the electrical storage element. An operating method for a safety discharge apparatus is also disclosed.

Abstract: A semiconductor device includes: a first output unit configured to output a first phase; a second output unit configured to output a second phase different from the first phase, the second output unit being disposed to be stacked on the first output unit; and a controller configured to control the output units.

Abstract: During single operation of a distributed power supply system that has been disconnected from a commercial electric power system, a frequency increase monitoring circuit is operated and an instruction to output a larger amount of a constant reactive current is given to a reactive current controlling unit. After the output frequency of the distributed power supply exceeds a frequency increase level, the level of an active current is limited in accordance with the level of the outputted reactive current.

Abstract: Disclosed herein is a Fourier transform-based phasor estimation method and apparatus capable of eliminating the influence of exponentially decaying DC offsets. According to a Fourier transform-based phasor estimation method according to an embodiment of the present invention, an input signal is sampled, and samples of one-cycle data of the input signal are separated into at least two sample groups. A Discrete Fourier Transform (DFT) is performed on each of the sample groups. A DC offset included in the input signal is calculated on a basis of results of the DFT on each of the sample groups, and an error caused by the DC offset is calculated using the calculated DC offset. A phasor of a fundamental frequency component included in the input signal is estimated by eliminating the calculated error, caused by the DC offset, from the results of the DFT on the input signal.

Abstract: Systems and methods for discriminating a negative-going load fault from a positive-going input voltage (VIN) surge are disclosed. The system includes a circuit that senses the VIN voltage to generate a disable signal, if the positive-going VIN surge is identified. Specifically, the circuit can include a high pass filter to facilitate identification of the positive-going VIN surge. Moreover, the disable signal is employed to control an overcurrent comparator that provides an overcurrent shut-off. Typically, when the positive-going VIN surge is identified, the disable signal is generated, which masks the overcurrent response, such that, normal operation can be continued without erroneously shutting-off the load.

Abstract: A circuit for indicating operating status of a plurality of hardware devices of a computer includes a detecting module, a decoding module, and an indicating module. The indicating module includes a dual color indicator and two electronic switches connected to a first input and a second input of the dual color indicator respectively. The detecting module detects an operating status of the plurality of hardware devices, and outputs state signals of each hardware device during power on self test of the computer. The decoding module decodes the state signals, and outputs level control signals to turn on or off the two electronic switches. The dual color indicator indicates operating status of the plurality of hardware devices by shifted to be at different indicating states by the two electronic switches correspondingly.

Abstract: A device and method for dynamically determining an impedance of a network is disclosed. The device includes at least a processing system for measuring a network voltage and network current when said network is determined to be in a first state, measuring a network voltage when said network is determined to be in a second state, estimating said impedance value dependent upon said measured voltages and current, adapting said estimated impedance based on at least one prior impedance value and storing at least said adapted impedance.

Abstract: An arrangement for controllably disconnecting a utility power service from a load includes a utility meter housing, a service switch, an energy storage device and a control circuit. The utility meter housing includes metrology circuitry configured to generate metering information regarding electrical power provided to the load. The service switch is configured to controllably interrupt a connection between the utility power service and the load, and has a controller. The control circuit is configured to cause the energy storage device to be connected to the controller responsive to a service disconnect command. The control circuit is further configured to cause a portion of the metrology circuit to be connected to the energy storage device and the meter power supply to be disconnected from the portion of the metrology circuit responsive to a power interruption detection signal.

Abstract: A control apparatus for a multiphase AC electric motor having an inverter includes a current control including an abnormal-state current controller; an abnormal-state detector that detects an abnormal state of any of a wire of an electric motor, a wire of an inverter, and a wire connecting the electric motor to the inverter as an abnormal phase; and an abnormal phase disconnect. The abnormal phase disconnect disconnects one or more of phases detected to be in an abnormal-state and the abnormal-state current controller generates an abnormal state voltage command in accordance with detection of an abnormal state, and uses phases other than the disconnected phases of the inverter to control individual currents of the phases, with the abnormal-state voltage command used as a multiphase voltage command.

Abstract: Device protection using temperature compensation. A logic module associated with groups of capacitors adjusts complex impedance planes associated with the capacitor groups to account for ambient temperature variations. In particular, the logic module is configured to adjust a center of a circle of each complex impedance plane based on an average impedance. The average impedance for a selected capacitor group includes impedance measurements for groups other than the selected group, to prevent capacitor failures in that group from skewing the average. The logic module can adjust the circle center in response to changes in average impedance over periods of time. For example, the logic module can filter measured differences in average impedance using a low pass filter, to distinguish slow impedance changes caused by temperature variations and rapid impedance changes caused by capacitor failures. The logic module can adjust the circle center in accordance with the filtered difference value.

Abstract: A circuit breaker for protecting a power line. The circuit breaker includes a control unit and a circuit breaking element disconnecting the power line from a power source. The control unit detects a fault on the power line, opens the circuit breaking element, which opening starts a disconnection time interval, injects a test signal into the power line, measures a response, determines an impedance of the power line from the response, analyses the impedance during the time interval based on comparing the impedance with a reference threshold, determines a permanent or a temporary fault based on the analysed impedance, re-closes the circuit breaking element after the time interval if the fault is temporary and keeps the circuit breaking element open after the time interval if the fault is permanent.

Abstract: An adaptive relaying control system and method is disclosed for adapting coordination of protective measures provided to an electric-energy distribution system as a function of at least an ambient weather condition. A weather sensor senses the ambient weather condition within a region adjacent to at least a portion of the electric-energy distribution system. A control unit is operatively coupled to the weather sensor to receive a weather signal indicative of the ambient weather condition and determine whether a storm condition exists based at least in part on the weather signal. The control unit establishes a suitable control philosophy for adapting coordination of the protective measures provided to the electric-energy distribution system based at least in part on whether the storm condition exists.

Abstract: A circuit protection system for a power panel is disclosed. The circuit protection system includes a transistor connected in a channel of a power panel, the transistor connected between return connections of a load and a return path, and the power panel including a plurality of channels connected to the load. The circuit protection system also includes control circuitry electrically connected in parallel with the transistor, the control circuitry configured to selectively activate the transistor to allow current to pass through the transistor based on an observed voltage across the transistor.

Abstract: An apparatus and method compensate for the sensitivity of at least one line current differential element of a first current differential relay providing differential protection for a transmission line of a power system during a single-phase pole-open condition. The apparatus includes a first delta filter configured to remove a first pre-fault current from a first fault current of the transmission line to derive a compensated first current phasor. The apparatus also includes a second delta filter configured to remove a second pre-fault current from a second fault current of the transmission line to derive a compensated second current phasor. The compensated first and second current phasors are provided to the at least one line current differential element to compensate the sensitivity of the at least one line current differential element.

Abstract: An arc detection means for detecting arcs in a plasma process includes at least one comparator to which an evaluation signal such as an output signal or an internal signal of an AC generator relating to the output signal and a reference value are supplied. The comparator is connected to a logic component that generates a signal for an arc suppression device.

Abstract: A circuit breaker includes separable contacts, an operating mechanism structured to open and close the separable contacts, and a trip mechanism. The trip mechanism includes a sensor structured to sense current flowing through the separable contacts, a processor cooperating with the sensor to determine a plurality of different trip conditions responsive to the sensed current, a nonvolatile memory operatively associated with the processor, and a trip actuator cooperating with the processor and the operating mechanism to trip open the separable contacts responsive to one of the different trip conditions from the processor. The processor is structured to save in and retrieve from the nonvolatile memory cause-of-trip information for the different trip conditions including the one of the different trip conditions.

Abstract: A method of operating a relay device, in an electrical circuit comprising first and second main circuit breakers, and a bus tie circuit breaker connecting the first and second main circuit breakers, the method comprising computing a first positive sequence current phasor for the first main circuit breaker and a second positive sequence current phasor for the second main circuit breaker computing a first positive sequence voltage phasor for the first main circuit breaker and a second positive sequence voltage phasor for the second main circuit breaker; computing a correction of the first positive sequence voltage and second positive sequence voltage to a line-to-neutral phase angle reference if there is any rotation in a potential transformer connection; determining a fault has occurred when a magnitude of a current through at least one of the first main circuit breaker or the second main circuit breaker exceeds a predetermined threshold; determining a phase angle difference by comparing the phase angle of the

Abstract: A protection device for circuit-breakers that comprises a wireless communication system for transmitting locally, to a dedicated computerized device, information corresponding to measurements of electrical quantities, to the setting of the parameters typical of the protection functions, or to diagnostics information corresponding to the electrical system, to the circuit-breaker or to the protection device itself.

Abstract: Two current differential relay devices 1 are installed at each terminal 3 of a two-terminal power transmission line 2, and connected to each other via two transmission paths 5 and 6, and perform current differential operations by transmitting and receiving the quantity data of electricity to each other. In the current differential relay device 1, two transmission means 14 normally each perform communications with the current differential relay device 1 of the other end of the power transmission line in parallel through the two transmission paths 5 and 6. Two current differential operation means 14 are connected to the two transmission means 14 respectively and perform independently two-series of current differential operations independently for each series associated with each of the transmission paths 5 and 6.

Abstract: A method of operating a relay device, the method comprising the steps of: providing main circuit-breakers and a bus-tie-breaker connecting the main-circuit-breakers; defining a partial-differential-zone comprising a main circuit breaker and the bus-tie breaker; assigning a first value to the direction of the fault current flowing into the partial differential zone;—assigning a second value to the direction of the fault currents flowing out of the partial-differential-zone, wherein the first value is not equal to the second value;—comparing the values assigned to the fault currents; determining if the fault currents are flowing into the partial differential zone; and determining if at least two of the fault-currents is flowing in a different direction with respect to the partial-differential-zone wherein one of the fault currents is flowing into the partial-differential-zone and one of the fault currents is flowing out of the partial differential zone.

Abstract: In a drive circuit in which a plurality of drive motors are connected to a power source through a protective device which trips when the flow of current is excessive, provision is made to detect which circuit or circuits were active at the time of the failure. A microprocessor is provided to both control the activation of each of the various circuits and to also sense which circuits were active at the time of the failure. Appropriate signals are sent from the microprocessor to a user interface so that proper diagnostic and repair action can be taken.

Abstract: A signal analyzer for calculating the power consumption and power factor of a three-phase power system driving a motor includes logic that determines whether the analyzer's own input terminals are wired in a proper or inverted manner. To do this, the signal analyzer observes a pattern of zero crossing slope values of the three line-to-line voltages of the three-phase power system and observes a pattern of zero crossing slope values of the current in the three power lines. The analyzer also compares the slope of a voltage signal as the signal passes through zero volts and the sign of a corresponding current signal that exists as the voltage signal crosses zero volts. Based on the observed voltage and current patterns and the voltage-to-current relationships, the analyzer can positively identify which of a plurality of inputs or signal wires are inverted.

Abstract: A system and method for determining power use in a system are disclosed. Briefly described, one embodiment of a method comprises metering power flow into a metered front end rectifier system using a metering circuit residing in the metered front end rectifier system and coupled to an alternating current (AC) power source, determining information corresponding to the metered power flow and communicating the determined metered power flow information to a user interface.

Abstract: A method and apparatus for protecting a discharge lamp lighting device from damage due to mis-wiring of a source of electrical power to the discharge lamp lighting device. The protection apparatus includes a detector, a comparer and an inhibitor. The detector samples at least one monitor point associated with the discharge lamp lighting device to obtain at least one detection voltage. The comparer compares the at least one detection voltage with a reference voltage. The inhibitor inhibits an operation of the discharge lamp lighting device when the comparer determines that a mis-wiring of the source of electrical power to the discharge lamp lighting device exists.

Abstract: A safety switching apparatus for failsafe disconnection of an electrical load has a first and a second connecting terminal for connecting a first signaling switch and a third and a fourth connecting terminal for connecting a second signaling switch. It also has a first and a second output switching element, which are designed to produce a redundant output switching signal. The first connecting terminal is connected to a first potential and the third connecting terminal is connected to a second potential. The potentials differ from one another. In addition, the second connecting terminal is coupled to the first switching element in such a way that the first switching element receives the first potential via the first signaling switch. Likewise, the fourth connecting terminal is coupled to the second switching element in such a way that the second switching element receives the second potential via the second signaling switch.

Abstract: The present invention relates to methods for providing impedance protection differentiating between in-zone and out-of-zone faults based on instantaneous, digitally derived operating and polarizing, distance comparator signals. The method uses a pair of fast orthogonal filters to derive D and Q components of the input voltages and currents. Two sets of operating and polarizing signals are derived for better speed of response under varying fault moment with respect to the peaks and zero crossings of power signals. Three stages of comparison between the operating and polarizing impedance terms are used. These comparator stages use half a cycle averaging windows, and three-quarters-of-a-cycle windows. The first stage of comparison is based on energy comparator responding to both magnitude and phase information in the signals. Stages 2 and 3 are of phase comparison type, responding mostly at the phase information and neglecting the magnitude information for better immunity to noise and signal distortions.

Abstract: A circuit is provided that provides for the same power characteristics to an assembly of electrical resistive elements wired in parallel as to the assembly as wired in series. An input power source provides electrical resistive power to a plurality of load elements, wherein the plurality of load elements are connected in parallel to each other. A plurality of power splitters divide the power source into separate and equal power subsources such that there is one power splitter and one power subsource for each load element, wherein the power provided to each of the plurality of load elements is equal to the power of the electrical power source. Redundancy and fault tolerance is provided to the circuitry by permitting remaining load elements to continue to operate should one or more load elements fail.

Abstract: A distribution automation system is disclosed. The system includes a switch for detecting a voltage/current status of electric power equipment to output the resulting detect signal, and supplying or cutting off power to the power equipment, and a control box including a control unit for converting the detect signal from the switch into a control signal, a distribution automation terminal unit for determining the presence or absence of a failure in the power equipment based on the control signal and controlling the switch according to a result of the determination, and a communication unit for transmitting the control signal to a central control station, wherein the control unit, the distribution automation terminal unit and the communication unit are formed on one board.

Abstract: A method and apparatus for protecting a discharge lamp lighting device from damage due to mis-wiring of a source of electrical power to the discharge lamp lighting device. The protection apparatus includes a detector, a comparer and an inhibitor. The detector samples at least one monitor point associated with the discharge lamp lighting device to obtain at least one detection voltage. The comparer compares the at least one detection voltage with a reference voltage. The inhibitor inhibits an operation of the discharge lamp lighting device when the comparer determines that a mis-wiring of the source of electrical power to the discharge lamp lighting device exists.

Abstract: An electric cutoff circuit for preventing overheating of a load. The current shutoff circuit includes an FET connected to a motor circuit. A relay fault detection circuit is connected to the motor circuit to detect potential at the motor circuit. A CPU sends a control signal to a relay. The CPU determines whether a fault has occurred in the relay based on the control signal sent to the relay and the detection of the relay fault detection circuit. When determining that a fault has occurred in the relay, the CPU opens the FET to configure an open circuit with the motor circuit.

Abstract: A status indicator indicates an operating state, including an electrical malfunction, of an electrical load that is located and controlled from locations remote from a monitoring location.

Abstract: A method and system for providing protection for a superconducting electrical cable located in a utility power network includes detecting a fault current on the superconducting electric cable, determining the cumulative total energy dissipated in the superconducting electrical cable from the fault current and at least one prior fault current over a predetermined time period, and determining whether to disconnect the superconducting electrical cable from the utility power network on the basis of the cumulative total energy dissipated.

Abstract: A reliable uninterruptible DC power supply device. The DC backup power supply device includes an AC/DC converter, a DC/DC converter, voltage step-up/down choppers and a battery connected to a DC path of a main circuit connected with a load via a switch, and a microcomputer. In the device, under control of the microcomputer, the voltage step-up/down choppers are first operated under a condition that the MOS FET was turned OFF for self diagnosis of the backup power supply device. Next, the switch is turned ON to execute the remaining self diagnosis. The DC backup power supply device can execute its self diagnosis with a reduced likelihood of danger of exerting an adverse effect on the main circuit and also can exhibit a reliable uninterruptible power supply function.

Abstract: A circuit breaker (100), in particular a medium voltage circuit breaker, having a current (20) and/or a voltage measuring device (30) integrated thereon. The integration can be functional and/or physical. The functionally integrated current and/or voltage measuring device provides primary current and voltage representative signals to an on-board electronic device (50) in order to realize the measure, process, and protection functions as a whole.

Abstract: An electric power monitoring and response system using electromagnetic field sensors located remotely beside the phase conductors. The system determines unknown system variables for one or more three-phase power lines based on measured values obtained form the field sensors and, in some cases, known power system values. For a given physical configuration, the field sensors may include a magnetic or electric field sensors, and the known system values as well as the unknown system variables may include phase currents, phase voltages and distances defining the physical configuration of the system. The response equipment may be a display, a circuit interrupting device, a voltage regulator, a voltage sag supporter, a capacitor bank, communication equipment, and reporting system.

Abstract: A connector system includes a circuit board having a plurality of holes extending therethrough. First and second connector bodies, each having a front wall, are positioned on first and second sides of the circuit board, respectively. The front walls of the connector bodies have a plurality of signal pin openings aligned with the circuit board holes. A plurality of signal pins extend through the signal pin openings of the first and second connector bodies and through the circuit board holes. At least one of the plurality of circuit board holes has a diameter larger than a diameter of the signal pin extending therethrough, such that walls of the at least one circuit board hole are spaced apart from the signal pin extending therethrough.

Abstract: In one embodiment, an integrated differential isolation loss detector is disclosed that generates a first temperature that is a function of a high side current and a second temperature that is a function of a low side current. A temperature sensor senses the difference between the first and second temperatures and provides an output signal that is indicative of the magnitude and the polarity of the sensed difference. A controller receives the output signal and if the difference is greater than a predetermined magnitude the high side current, the low side current, or both can be disconnected from the load. In another embodiment, an integrated differential isolation loss detector is disclosed that includes a first temperature difference generator that generates first and second temperatures where the difference between the first and second temperatures is a function of the magnitude of the high side current.

Abstract: For the control of an electric power transmission network, where local protection functions are implemented by a plurality of local protection devices (3,3a,3b,3b?,3c) located at a plurality of locations throughout the network, the following steps are executed measuring phasor data for voltages and currents at a plurality of locations (A,B) of the network, transmitting said phasor data to a central processing device (2), emulating, in the central processing device (2), protection functions that are implemented in the local protection devices (3,3a,3b,3b?,3c), and executing, in accordance with a given redundancy strategy, control commands that are issued redundantly by the local protection devices (3,3a,3b,3b?,3c) and by the central processing device (2). In a preferred variant of the invention, values of predetermined parameters that are used in the protection function, in particular protection threshold values, are adapted to measured values.

Abstract: A power supply device for an electronic protection unit for AC/DC low- and/or medium-voltage power networks, comprising: first electronic means, which are suitable to transduce electric power from an AC/DC low- and/or medium-voltage power distribution line in nominal operating conditions; and second electronic means, which are suitable to transduce energy from an AC/DC low- and/or medium-voltage power distribution line in current transient conditions.

Abstract: A fault protection system whose trip logic considers power magnitude and direction at first and second points on a conductor is provided. Under normal operating conditions, power flows in the same direction through first and second points on the conductor. Under faulted conditions, a differential power condition exists; that is, the power flowing at a first point on the conductor is of different magnitude and/or direction than the power flowing at a second point on the conductor. The trip logic identifies the differential power condition as the result of a fault between the first and second points on the conductor and causes a protective device on each side of the fault to trip open, thus isolating the fault.

Abstract: A network protector relay controls a circuit breaker connected between polyphase feeder and network busses. A circuit samples polyphase circuit breaker current and network voltage to generate digital polyphase current and voltage samples. A microcontroller generates positive sequence current and voltage vectors from the current and voltage samples. A first trip algorithm trips the breaker in response to the positive sequence current vector being in a first trip region of a first trip characteristic with respect to the positive sequence voltage vector. The first trip characteristic is defined by a reverse trip setpoint and a first positive angle. A second trip algorithm trips the breaker in response to the positive sequence current vector being in a second trip region of a second trip characteristic with respect to the positive sequence voltage vector. The second trip characteristic is defined by the reverse trip setpoint and a second negative angle.

Abstract: A distributed bus differential relay system has a separate differential relay element at each feeder location to trip the associated circuit breaker in response to a fault in the protected bus. The only conductors between feeders form a set of leads connecting current transformers in each of the feeders in parallel. Preferably, the current transformer in each feeder also serves as the current transformer for the associated circuit breaker and the differential relay element is incorporated into the overcurrent relay or trip unit of the circuit breaker which is implemented by a microprocessor. Compliance voltage across the cts is limited by a varistor or saturating reactor which is protected from overheating by a time delayed shorting device.

Abstract: A distributed monitoring and protection system for a distributed power network. The system includes a plurality of high-speed measuring units (MUs), wherein each MU is coupled to a power line to measure values of electrical parameters of the power line. Electrical parameters, such as current, voltage, power and frequency are measured by the MUs. The MUs communicate with a control unit (CU) over a high-speed communications network. The CU includes a processor executing algorithms for evaluating the measured parameters to determine the status of the power network and the MUs. The processor also executes fault detection and isolation by comparing the measured values against predetermined threshold values. When a fault is detected by the CU, protective action, such as tripping of a circuit breaker, may be initiated by the CU directly or by transmitting the tripping command over the high speed data network to a local MU. The local MU may then trip the circuit breaker.

Abstract: A method and apparatus are provided for detecting a short circuited semiconductor switch. The apparatus comprises a semiconductor switching device and a short circuited switch detection device. The semiconductor switching device comprises an input, an output, and a control input for switching the semiconductor switching device. The short circuited switch detection device comprises an input and an output. The input of the short circuited switch detection device is coupled to the semiconductor switching device, wherein the short circuited switch detection device detects a short circuit in the semiconductor switch switching device.

Abstract: A distributed monitoring and protection system for a distributed power network. The system includes a plurality of high-speed measuring units (MUs), wherein each MU is coupled to a power line to measure values of electrical parameters of the power line. Electrical parameters, such as current, voltage, power and frequency are measured by the MUs. The MUs communicate with a control unit (CU) over a high-speed communications network. The CU includes a processor executing algorithms for evaluating the measured parameters to determine the status of the power network and the MUs. The processor also executes fault detection and isolation by comparing the measured values against predetermined threshold values. When a fault is detected by the CU, protective action, such as tripping of a circuit breaker, may be initiated by the CU directly or by transmitting the tripping command over the high speed data network to a local MU. The local MU may then trip the circuit breaker.

Abstract: In a protective relay system according to an aspect of the present invention, a direction of a fault is correctly determined during system oscillation using one of a negative-phase-sequence relay and a zero-phase-sequence relay. A circuit breaker is tripped only when an internal fault is determined at both terminals to be protected using a carrier signal. Thus, even though a fault occurs during system oscillation, the circuit breaker can be tripped against the internal fault.