Abstract: Systems, methods, and computer-readable media are used for monitoring and diagnosing power system assets. An example of a power system asset may include an individual circuit breaker, a switchgear that may include multiple circuit breakers, or any other asset that may be included in a power system. A system for monitoring and diagnosing these power system assets may include one or more intelligent protection relay and switchgear monitor device(s) that may be communicatively coupled in a master-slave or peer-peer configuration in a time-synchronized manner of operation.

Abstract: A system and method for detecting a phase-to-ground fault in an AC electrical machine operates to receive measurements of three-phase voltages and currents provided to the AC electrical machine, compute at least one of a zero sequence component and a negative sequence component of voltage and current from the three-phase voltages and currents, and calculate a fault severity index (FSI) based on the zero or negative sequence component of voltage and current, so as to identify a phase-to-ground fault in the AC electrical machine. Calculating the FSI further includes determining a total value of the zero or negative sequence current, determining a noise-contributed value of the zero or negative sequence current included in the total value, determining a compensated value of the zero or negative sequence current based on the total value and the noise-contributed value, and calculating the FSI based on the compensated value.

Abstract: Systems and methods may be used to determine whether waveforms of at least two transmission lines are synchronous. More particularly, this disclosure relates to sensing operations that use signals received by a local relay and a remote relay to determine whether two waveforms on opposing ends (e.g., supply side and load side, local side and remote side) of a transmission line are synchronous with one another. A system may determine whether a first waveform is synchronous with a second waveform based at least in part on a comparison of delay between a representation of the first waveform and a representation of the second waveform. The system may actuate a device (e.g., close a circuit breaker) in response to determining the first waveform is synchronous with the second waveform.

Abstract: Control is performed such that, for generating an AC voltage from a DC voltage, a period during which a DC/DC converter boosts the DC voltage and an inverter performs one of polarity non-inversion passing and polarity inversion passing, and a period during which the DC/DC converter is stopped and the inverter performs step-down operation and one of polarity non-inversion passing and polarity inversion passing, arise alternately in one AC cycle. Gate blocking is temporarily performed for only the DC/DC converter, upon occurrence of a phenomenon in which, by start of power feeding to a load connected to an AC electric path, an absolute value of a current flowing through an AC reactor reaches a predetermined converter gate block threshold value lower than an instantaneous overcurrent protection threshold value.

Abstract: A method of queuing access to a power supply shared by a set of electrical access points. The access points turn on independently from one another and thus have independent power draws. Each access point has a specific power draw when on. The on state and associated power draw of each of access point is identified, and a load duration curve for each access point is normalized (i.e., combined with load duration curve(s)) from the other access points) into a probability distribution function. The probability distribution function is a normalized load duration curve that thus accounts for a varying set of “operating states” that may occur with respect to the set of access points (when viewed collectively). Each operating state has an associated probability of occurrence. As the operating state of the set (of access points) changes, access to the power supply is selectively queued, or de-queued (if previously queued).

Abstract: A distribution panel aboard an aircraft includes sites intended for the installation of functional electrical circuit breakers of which at least one of the sites is not occupied by a functional circuit breaker. The functional circuit breakers are wired up to a monitoring system via monitoring cabling so as to monitor a state of the circuit breakers. The at least one site not occupied by a functional circuit breaker is occupied by a nonfunctional circuit breaker, termed a false circuit breaker. The false circuit breaker is able to deliver a state signal and is wired up to the monitoring system by the monitoring cabling in a manner identical to that of a functional circuit breaker.

Abstract: A method of queuing access to a power supply shared by a set of electrical access points. The access points turn on independently from one another and thus have independent power draws. Each access point has a specific power draw when on. The on state and associated power draw of each of access point is identified, and a load duration curve for each access point is normalized (i.e., combined with load duration curve(s)) from the other access points) into a probability distribution function. The probability distribution function is a normalized load duration curve that thus accounts for a varying set of “operating states” that may occur with respect to the set of access points (when viewed collectively). Each operating state has an associated probability of occurrence. As the operating state of the set (of access points) changes, access to the power supply is selectively queued, or de-queued (if previously queued).

Abstract: An intelligent electronic device (IED) provides harmonic blocking and harmonic restraint differential protection operating in parallel. The IED includes a harmonically-blocked differential element supervised by one or more even harmonics of a raw operating current (a current comprising the fundamental operating current and the harmonics thereof). The IED also includes a parallel, harmonically-restrained differential element, which is restrained by harmonics of the raw operating current. Tripping signals output by the parallel harmonically-blocked differential element and the harmonically-restrained differential element may be selectively combined into a single tripping signal output. An additional harmonic blocking element may supervise both differential elements and/or the combined tripping signal. The additional harmonic blocking element may provide odd-harmonic blocking, such as harmonic blocking based on a fifth harmonic of the raw operating current.

Abstract: A system and method for operating an autoloop system on an electrical distribution system is provided. The system includes a first branch circuit having a first recloser and a midpoint recloser and a second branch circuit having a second feeder recloser and a midpoint recloser. A tie recloser is electrically coupled between the first branch circuit and the second branch circuit wherein the tie recloser closes only after a fault is detected. A master controller associated with the first and second branch circuits communicates with the reclosers of the first and second branch circuits. The master controller includes a processor for blocking a fast tripping function of a feeder recloser in response to the detection of a fault on the other branch circuit. The portion of a circuit where a fault is detected may be isolated to minimize the portion of the first and second branch circuits without power.

Abstract: The present invention provides a remote operable over-current protection apparatus. The apparatus includes control circuitry integrally arranged on a current path and a micro electromechanical system (MEMS) switch disposed on the current path, the MEMS switch responsive to the control circuitry to facilitate the interruption of an electrical current passing through the current path. The apparatus further includes a communication connection in signal connection with the control circuitry such that the control circuitry is responsive to a control signal on the communication connection to control a state of the MEMS switch.

Abstract: A cable fault detection component (168) receives input data indicative of a fault in an electrical power system. The component (168) analyzes the input data to determine if the fault is indicative of a self-clearing cable fault and generates corresponding output data (276). In one implementation, the cable fault detection component (168) is implemented as a software module which operates on a computer (105) of a substation intelligence system (104).

Abstract: A method and means for controlling the operation of a machine by an operator having a transmitter mounted to a machine, a sensor attached to an operator or an operator's clothing, and a tracking device that receives signals from the sensor and determines the position of the sensor. Based on the determined position of the sensor, the tracking device sends signals to the operator and an actuator on the machine based on a comparison with a danger zone, warning zone, or operator zone.

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 circuit breaker communication system is provided including a circuit breaker, an electronic module to record and store data associated with the operation of the circuit breaker, and a portable communication unit for downloading the stored data. The portable communication unit includes a power source, a display unit, a processor unit, a communication interface, and a keypad. Also, a cable is provided for interconnecting the portable communication unit to the electronic module. The cable is configured to carry a data signal between the portable communication unit and the electronic module, and to conduct power to the electronic module from the power source. The system may include an optical communication link to transmit to or receive signals from the circuit breaker, a transmitter to transmit data to the optical communication link; and a receiver to receive signals from the optical communication link.

Abstract: A “digital data stream,” “binary sequence” or word can be generated by a logic circuit such as a processor and the sequence can be converted to a series of pulses such that the content of the sequence can be utilized to accurately control/drive a plurality of power transistors. Accordingly, a regulated voltage can be provided through such a data type output of a processor. Thus, a standard processor that executes data processing operations can provide a low level logic signal as a serial digital transmission, possibly a four bit word, and control a power supply without significant modification. To achieve such a conversion the processor can be capacitively coupled to a voltage level shifter and a delay module to provide a plurality of power transistor drive signals. The converter can be wholly integrated onto a processor or motherboard to eliminate devices and stand alone assemblies that are commonly required in data processing systems.

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: A method and an adaptive distance protection relay for compensating for a remote line end infeed effect during determination of a distance to a resistive fault on a three-phase power transmission line. It is assumed that a fault current flows through the fault resistance. A fault loop impedance is first calculated by a known algorithm from phase voltages and phase currents. A shift of the fault loop impedance is determined from the fault loop impedance, the impedance of the transmission line for the positive current sequence and the phase angle of a complex fault current distribution factor, where the fault current distribution factor is the ratio of the fault loop current to the fault current. The distance to fault is calculated by subtracting the impedance shift from the fault loop impedance and dividing the result by the impedance of the transmission line for the positive current sequence.

Abstract: Provided is a system relay-to-relay direct communication system and method in a power system. The relay-to-relay direct communication system includes a first protective relay having a first transmit module where the first transmit module includes a first microcontroller adapted to provide a plurality of data channels. Each of the plurality of data channels is associated with channel data having a variety of bit-lengths. The relay-to-relay direct communication system also includes a second protective relay directly coupled to the first protective relay via a communication link. The second protective relay includes a first receive module where the first receive module including a second microcontroller adapted to provide the plurality of data channels. A speed of receipt of the channel data by the first receive module is adjustable based on an assignment of the channel data to the plurality of data channels of the first transmit module.

Abstract: A system and method for accomplishing power swing blocking and unstable power swing tripping schemes during disturbances of electrical networks is disclosed. The disclosed system and method eliminates the requirement of stability studies. The no-setting scheme utilizes the swing center voltage of the electrical network to carry out its functions.

Abstract: A device and system for the wireless communication with a circuit breaker is provided which allows for obtaining data associated with a circuit breaker to quickly and easily access information associated with the trip event. The circuit breaker contains an electronic module which is configured to record and transmit data associated with the circuit using wireless technology.

Abstract: An extendable enclosure for circuit cards provides the capability for a customer to purchase a low cost system up-front, but still allow for growth.

Abstract: A protection system for an electrical power line system of the type comprising radially connected power line sections, wherein a first electrically upstream one of the line sections is connectable to a power source. The protection system comprises at least one relay installed at or near at least the upstream end of each line section to protect that line section, each relay having an associated circuit breaker. The relays are provided with a first set of accelerated overcurrent functions and a second set of under-current/under-voltage functions, the relays being directional and the first and second sets of functions being time graded in reverse to each other.

Abstract: The system provides communication of information between at least two protective relays serving a power system line. The communication comprises a series of successive data messages of four characters, each of which includes eight data bits, on eight data channels. The data bits include output function status bits from the transmitting relay on user selected channels, serialized analog data bits on other user selected channels, and virtual terminal data bits on still other user selected channels. A synchronization channel produces information to synchronize the transmission/receiving of the analog data and the virtual terminal data, on the basis of frames of data, each frame containing 18 messages.

Abstract: A directional comparison distance relay system for protecting a power transmission line. The relay system comprises a fault detection unit which includes a directional distance relay element for deciding whether a fault is in forward or reverse directions; a short-circuit distance relay element for deciding whether a fault is within a protection zone by distance calculation; and an evolving fault detecting unit for deciding an evolving fault when a forward earth fault directional relay in a single phase and a reverse directional relay in a phase are in operation. The relay system further comprises a block unit for blocking trip of a circuit breaker at a near end due to the short-circuit distance relay, and for blocking permissive trip signal to a circuit breaker at the far end, based on an operation of the evolving fault detecting unit.

Abstract: When a disturbance (for example, lightning strike) occurs on a high-voltage overhead transmission line, the line must be checked for any possible damage. If the distance-to-fault is known, line crews can be quickly dispatched for any necessary repair. The present invention is a fault location method and system that uses filtered, time-synchronized positive- or negative-sequence voltage and current measurements from both ends of the overhead transmission line to determine the exact distance to the fault with respect to either end.

Abstract: The apparatus detects an out-of-step condition following the clearing of an external multi-phase fault in a protective relay. The apparatus includes a circuit which detects the presence of an external multi-phase fault on the power line and a timing circuit for readying an out-of-step logic detection circuit in the protective relay if the external fault remains for a pre-selected period of time. An out-of-step condition is declared and a signal blocking operation of selected distance elements in the protective relay is produced if the positive sequence impedance on the line remains inside an outer protection zone boundary in the impedance plane for a selected period of time, wherein the out-of-step blocking signal continues as long as the positive sequence impedance remains inside the second boundary.

Abstract: A method of precisely determining velocity of propagation and the location of a fault on an electric transmission line, using a system of high frequency transmitter and receiver combinations to monitor and detect high frequency bursts produced by the transmitters and by faults, including memory and analysis capability to store and analyze high frequency data before and after a detected fault.

Abstract: An apparatus for determining a failure of an electromagnetic clutch, which is capable of properly determining whether or not a failure, a typically a layer short-circuit, has occurred due to a change in a resistance value of a solenoid coil of the electromagnetic clutch. The electromagnetic clutch is configured such that the engagement force thereof is varied according to an amount of current flowing through the coil. An output control value for control of the amount of current is calculated by feedback control such that an actual amount of current actually flowing through the coil becomes equal to a desired amount of current. A predetermined reference control value is stored which defines a standard for the output control value and has a standard relationship with respect to the amount of current. The actual amount of current is detected. The calculated output control value is compared with the predetermined reference control value corresponding to the detected actual amount of current.

Abstract: A distance relay for protection of a transmission line, which is capable of estimating apparent impedances with respect to faults on the transmission line involving fault resistances, more particularly faults at local and remote ends of a protection zone of the transmission line, and compensating for the magnitudes and phases of the estimated apparent impedances, so as, to minimize a reactance effect resulting in a mal-operation or non-operation or the distance relay. If a fault occurs on the transmission line, the distance relay determines whether the amount of zero-sequence current resulting from overcurrent exceeds a predetermined threshold value, so as to determine whether the occurred fault is an earth fault or a short fault.

Abstract: The invention is directed to a method for producing a fault signal indicating a short-circuit between a first phase conductor and a second phase conductor of two different, parallel-running, three-phase power transmission lines. The method produces a fault signal indicating a short-circuit which has occurred between a first phase conductor and a second phase conductor of a power transmission arrangement.

Abstract: A protective relay, system, and relay operation method which allows logic functions to be distributed amongst multiple protective relays associated with a power distribution system. The protective relays include communications ports for exchanging messages over a peer-to-peer communications network, and include programmable logic. Each protective relay receives logic operands contained in the messages from remote protective relays, executes logic equations using the received operands, provides protective control if needed, and outputs operands to other protective relays.

Abstract: A short-circuit distance relay has a short-circuit distance relay element that calculates a fault impedance from voltage and current which are introduced from a power system and that compares the fault impedance with a set impedance and uses the fault impedance comparison result within its protection zone. It calculates the amplitudes of the phase-to-phase differences of these voltage amplitudes and a sensitivity constant Vk.

Abstract: A fault protection apparatus is disclosed for use in a time graded fault protection scheme. The apparatus comprises a circuit breaker having a normally closed trip contact provided in a line, current measurement apparatus adapted to produce an output signal indicative to the current in the line at the circuit breaker, and fault signal processing apparatus adapted to process the output signal from the current measurement apparatus to detect an initial fault on the line at a first instance. The fault signal processing apparatus is further adapted to process the output of the current measurement apparatus after the initial fault has been detected and to produce an accelerated opening signal in the event that the output signal meets a predetermined criteria, and a control device which is adapted to open said circuit breaker trip contact in response to said accelerated opening signal.

Abstract: A differential relay for protecting a power apparatus portion of a power system, such as a bus line, includes incoming and outgoing power lines on which incoming and outgoing currents are present. The incoming and outgoing currents of each phase are applied through current transformers and then through filtering and normalizing circuits prior to application to the differential relay. The differential relay includes a circuit for determining the presence of an external fault, and maintains security by avoiding a tripping action of the relay for said external faults.

Abstract: A circuit configuration for actuating active- and/or passive-operated warning signal generators or warning lamps (WL1, WL2) comprises an integrated circuit (IC1) having individual actuating steps (1,2) and connections for the individual warning signal generators. Moreover, an adapter connection (WLCON) is provided which upon connection to chassis configures the circuit (IC1) for the actuation of two passive warning lamps (Wlp) or other warning signal generators, permitting upon connection to an ohmic resistance (R) leading to chassis, actuation of an active (Wla) and a passive (Wlp) warning signal generator and configuring—if left open—the circuit (IC1) for actuating two active warning signal generators (Wla).

Abstract: A data switch for transferring data from either actual line readings or from stored memory to the input of a relay tester. The device uses a digital switch set between the A/D converter and the CPU of an electronic relay. The switch permits technicians and engineers to either pass data to the CPU from the system through the A/D converter or, by switching, feed the CPU data from the RAM, which has been loaded with the archived data. In this way, the relay system software can be examined and tested using actual event data under ordinary conditions as desired, with relay settings changed between tests to verify the efficacy of the changed settings to perform as desired for the recorded conditions. The digital switch can be either a hard-wired element, or can be a soft switch, operated through software instructions.

Abstract: A relay test apparatus for testing a protective relay operation of a protective relay system comprises GPS receivers, respectively connected to the protective relays, each GPS receiver analyzing time data included in a signal transmitted from a satellite and outputting a time signal, simulation signal generators, respectively connected to the protective relays, each simulation signal generator generating a simulation signal and inputting the simulation signal to a corresponding protective relay, and synchronous starting units, respectively provided in the protective relays, each synchronous starting unit starting a corresponding simulation signal generator to generate the simulation signal, when time signals output from the GPS receivers coincide with a preset time at a same time.

Abstract: A relay test apparatus for testing a protective relay operation of a protective relay system comprises GPS receivers, respectively connected to the protective relays, each GPS receiver analyzing time data included in a signal transmitted from a satellite and outputting a time signal, simulation signal generators, respectively connected to the protective relays, each simulation signal generator generating a simulation signal and inputting the simulation signal to a corresponding protective relay, and synchronous starting units, respectively provided in the protective relays, each synchronous starting unit starting a corresponding simulation signal generator to generate the simulation signal, when time signals output from the GPS receivers coincide with a preset time at a same time.

Abstract: A power switching apparatus includes a positive-sequence fundamental signal magnitude detector. The positive-sequence fundamental signal magnitude detector derives a positive-sequence fundamental signal from a three-phase voltage signal carried by a power line; it also generates a switch firing command when the positive-sequence fundamental signal exceeds a predetermined threshold value indicative of a fault condition on the power line. The power switching apparatus also includes a solid state switch connected to the power line and the positive-sequence fundamental signal magnitude detector. The solid state switch bloch power on the power line in response to the switch firing command.

Abstract: A relay test apparatus for testing a protective relay operation of a protective relay system comprises GPS receivers, respectively connected to the protective relays, each GPS receiver analyzing time data included in a signal transmitted from a satellite and outputting a time signal, simulation signal generators, respectively connected to the protective relays, each simulation signal generator generating a simulation signal and inputting the simulation signal to a corresponding protective relay, and synchronous starting units, respectively provided in the protective relays, each synchronous starting unit starting a corresponding simulation signal generator to generate the simulation signal, when time signals output from the GPS receivers coincide with a preset time at a same time.

Abstract: An electrotechnical power supply system includes several power sources and interconnectable feeders, and an overall isolation monitor and at least one locator on each power source.All the overall isolations monitors and locators are connected together by a local data bus transmission network.A plurality of connecting circuit breakers are arranged between the power sources. A management unit is electrically connected to the transmission network for transmitting control signals to the overall isolation monitors, so as to switch some of the monitors to an inaction excluded mode, with the exception of a single one of them which operates as pilot in an active mode.

Abstract: A remote control residential and commercial circuit breaker system (320) provides overload current protection and load management. The system includes a plurality of remote control circuit breakers (20, 322) each including a switch (188, 190, 150, 152) responsive to a control signal (330) for controllably completing and interrupting a respective load circuit (184), a plurality of pole controllers (336, 338) each responsive to a respective address signal (342, 344) and coupled to a respective circuit breaker and supplying the respective control signal to the respective switch. Each pole controller includes a status circuit responsive to actuation of the switch and supplying a status signal indicative thereof. A common controller (348) is coupled to the pole controllers and supplies addresses signals.

Abstract: A system for detecting a high impedance fault in a phase conductor having a potential device connected to the phase conductor, the system including a signal injection device having an input from the potential device which detects a reduction in voltage at the phase conductor and outputs a first signal in response to detecting a reduction in voltage at the phase conductor and a signal receiver which receives the first signal and provides a second signal to an interruption device in response to having received the first signal to cause the interruption device to open the circuit to the phase conductor.

Abstract: In a protective relay (10), which contains a microprocessor (30), for monitoring a power transmission line, an output enable decoder (72) and a one-shot timer (74) produce a very short (5 microsecond) signal in response to an address signal from the microprocessor. The output from the timer is applied as one input to AND gate (70). A conventional address decoder, responsive to an address signal identifying a particular output port from the microprocessor, provides another output to AND gate (70). AND gate (70) produces a latch control signal when the two signals are coincident in time. The latch control signal enables the particular output port to receive instructions from a data bus (60).

Abstract: An addressable relay module is provided for controlling a plurality of relay outputs associated with an electronic circuit breaker system using a trip unit for monitoring system functions or network parameters. The relay module is linked to a multi-drop serial communications network through which data pertaining to system functions is relayed to and from a communications microcontroller which controls the operational status of relay contacts linked thereto. The microcontroller addresses specific ones of associated relay outputs in accordance with address information contained within the network data. The addressable relay module effectively maps the plurality of relay contact outputs linked thereto to a corresponding plurality of network device parameters received through the multi-drop network.

Abstract: Monitoring and control of analog electromechanical protective relays and digital mcroprocessor based relays is integrated through a system including slave stations which record and time tag contact activity at each of the analog relays. The slave stations continuously retain digital samples of a predetermined number of the most recent cycles of the currents and voltages at the analog relays and when a trip occurs store the retained samples as pre-fault values together with a preset number of post-fault samples. A master station communicates with the slave stations monitoring the analog relays and with the digital relays through a two way communications network. The master station repetitively polls the slave stations and digital relays for contact activity. Detailed data such as the time tags and pre-fault and post-fault currents and voltages are then requested from those stations reporting contact activity.

Abstract: A device which protects a spot network type power receiving and transforming system when, while the system and an electric generator are operating in parallel, overall interruption of power supplied to the primary side of network transformers occurs suddenly. In the spot network type power receiving and transforming system, protector circuit breakers are provided on several branch buses connected to a common bus and a generator circuit breaker is connected to the electric generator; a link circuit breaker is connected to the common bus between the spot network type power receiving and transforming system and the electric generator; and network relays are connected in parallel with the protector circuit breakers respectively.

Abstract: The invention comprises a protective relay with selective phase selection in electric power distribution systems when there are double transmission lines (M1-P1,M2-P2) between two stations (TM, TP) and where the ends of the line are connected to a common busbar system located in each station. The protective device includes a protection unit, terminal, at both ends of each line. All the terminals (M1, M2, P1, P2) include an identical basic design for measurement of phase quantities (17), filtering (18) and A/D conversion (19); furthermore, the identical part includes a parameter estimator (20) for Fourier series expansion of measured phase signals and generation of the respective residuals. The parameter estimator cooperates with a frequency estimator (21) and a sampling regulator (22).

Abstract: The present invention comprises a longitudinal differential protective relay for protection and supervision of power line zones in a distribution system. The protective relays are located at each end of the zones that are desired to be monitored. One of the protective relays operates as a master for the other slave protective relays. A TRIP function indicating a line fault in any protected zone is performed by transmitting locally processed measured signals to the central protective relay which determines if and when any measure is to be taken. Each local protective relay comprises a measuring device, a filter and an A/D converter for phase currents and voltages. The digital signals are used to generate a truncated Fourier model of the measured signals in a parameter estimator which cooperates with a frequency estimator and a sampling regulator which, via a synchronization unit, ensures that sampling is performed simultaneously in all protective relays included in the protective system.

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.