Abstract: The voltage and current conditions on a power transmission line are monitored to determine the coincidence of a low voltage condition and a lack of a high current condition. The coincidence of those two conditions is indicative of a CCVT transient, and the tripping action from zone 1 distance elements is delayed for a period of 1.375 cycles. The tripping delay is supervised by a fault impedance determination, which, if a threshold is exceeded, the remaining portion of the time delay is eliminated, so that a trip is allowed if the time delay period has not expired.

Abstract: The directional element produces a quantity related to the zero sequence source impedance of the power system relative to the location of the directional element, from values of zero sequence current and an adjusted value of zero sequence voltage. The impedance quantity is then compared against first and second threshold quantities to identify the direction of a fault. Further, the zero sequence voltage-polarized directional element can be combined with other individual directional elements, including a zero sequence current-polarized directional element and a negative sequence voltage-polarized directional element to form a universal directional element for unbalanced faults, in which the individual directional elements operate in a particular sequence, with the other directional elements being blocked from operating if a prior directional element in the sequence provides a direction indication.

Abstract: A one-terminal process for locating a fault associated with a transmission system is disclosed. The process is based on the principle fault sequence can be determined by a distribution factor in positive faults may be any defect among phases or ground. The process begins by one end of a transmission line. If the data is oscillographic data, measured data is in phasor form, or after phasors have been calculated determined. Thereafter, a decision is made whether the pre-fault data data is sound, an equation is selected to calculate the fault location decision is made whether the phase is a three-phase fault. Then, a employed to compensate for the fault through a resistance by measuring part of the apparent line impedance. If the fault is not a three-phase formula is not employed and the appropriate equation is selected for the fault location parameter. Accurate fault location techniques for also disclose.

Abstract: In order to achieve improved release characteristics in the case of a protective device for power supply lines, a protection release method is proposed in which at least one signal (i, u) is supplied to a filter device (3, 16), and a release decision is made as a function of its output signal (SA, Z). If the conditions are insufficient for release, a change is made to the filter characteristics. The filter device (3, 16) in this case preferably comprises adaptive filters or combinations of filters. In a further refinement, a fuzzy region, which is used as the release criterion, is formed as a function of a change in the output signal.

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: Method and apparatus for preventing reclosing of circuit breakers to reconnect a transmission line when a break fault occurs in the transmission line. A voltage at a fault point is estimated from opposite ends of the transmission line, and when those voltages are not equal, the break fault of the transmission line is determined, the break fault is displayed and the reclosing by a protective relay is prevented. By specifying a fault of the transmission line as a break fault, a recovery time of the transmission time is significantly reduced and an equipment is protected because the closing of the circuit breaker is blocked during the fault.

Abstract: A method and apparatus are provided for detecting an arcing fault on a power line carrying a load current. The apparatus monitors and analyzes energy values of the load current flowing through the line. The analyzed energy values are compared to several threshold values. The number of energy values being greater than the threshold values are compiled to determine whether an arcing fault exists on the power line.

Abstract: A sub-cycle digital distance relay which uses only the first N/2 samples after a fault to calculate the distance to the fault using a Full Cycle Fourier Algorithm which operates on N samples, where N is the number of samples taken in a cycle of the power signal. The DC offset in the first N/2 samples taken after detection of the fault is cancelled using the N/2+1 sample taken after detection of the fault. The resulting DC adjusted N/2 samples are then multiplied by -1 in order to take advantage of the symmetry of the sine wave of the power signal in estimating the remaining N/2 samples of the first cycle of the power signal after detection of the fault. By so calculating N/2 artificial samples from the first N/2 actual samples taken after the fault, the digital distance relay of the invention can estimate the distance to the fault and thus provide a reliable trip signal in less than one cycle of the power signal.

Abstract: A method and a device for determining the distance from a measuring station to a fault on a transmission line based on a fault model of a transmission network while taking into consideration the zero-sequence impedance and, where assuming a fault current, while taking into consideration the feeding of fault current to the fault point from both ends of the transmission line (FIG. 3 ).

Abstract: A fault location system comprises current and voltage transducers 10, filters 12, and a multiplexor 14, the latter outputting an interleaved stream of analog phase current and voltage signal samples, as well as neutral current samples. The analog multiplex output by the multiplexor 14 is digitized by an analog-to-digital converter 16. The output of the analog-to-digital converter 16 is fed to a digital signal processing block 18. The multiplexor necessarily introduces a time-skew between the successive samples for each channel and also introduces a time-skew between the respective channels. The system corrects the sample-to-sample time-skew for each channel, and then derives current and voltage phasors from the time-skew corrected data. Thereafter, the phasors are adjusted to correct for channel-to-channel phase-skew. In this manner, the digital signal processing block produces phasor data for each of the sampled channels. The phasor data is stored in a memory 20.

Abstract: Voltage and current on a power transmission line are first obtained, filtered and converted to digital representations. The positive sequence components of the voltage and current are determined and the impedance at the relay is then calculated from those positive sequence voltages and currents. The positive sequence impedance is converted into a magnitude and phase angle representation and then compared against a load pattern which is also represented by magnitude and phase angle representations. If the calculated impedance at the relay is within the load impedance pattern, the distance relay is prevented, i.e. blocked, from sending an output signal to trip a circuit breaker protecting the transmission line.

Abstract: A directional element measures the negative sequence voltage and the negative sequence current and from those quantities produces a scalar quantity related to the negative sequence impedance of a power transmission line relative to the location of the directional element. The magnitude of the negative sequence impedance is calculated from the magnitude of the negative sequence voltage and magnitude of the negative sequence current. The scalar quantity is then compared against two threshold quantity settings, one to determine a forward fault and the other to determine a reverse fault. The threshold quantity settings include, respectively, a selected fraction of preselected basic threshold values and a selected fraction of the magnitude of the negative sequence impedance. The scalar quantity must be less than the forward threshold quantity for a forward fault and greater than the reverse threshold quantity for a reverse fault.

Abstract: A directional element measures the negative sequence voltage and the negative sequence current and from those quantities produces a scalar quantity related to the negative sequence impedance of a power transmission line relative to the location of the directional element. The scalar quantity is then compared against two threshold quantity settings, one to determine a forward fault, the other to determine a reverse fault. The scalar quantity must be less than the forward threshold quantity for a forward fault and greater than the reverse threshold quantity for a reverse fault.

Abstract: The relay includes means for obtaining current and voltage samples on the power transmission line for a particular possible fault type. The current sample is multiplied by the replica impedance of the power transmission line, while the voltage sample is multiplied by a polarizing voltage to provide a first complex expression having a real portion and an imaginary portion. The product of the current sample and the replica impedance is multiplied by the polarizing voltage to produce a second complex expression having a real portion and an imaginary portion. The real portion of the first complex expression is then divided by the real portion of the second complex expression to produce a scale value m which is compared against known reference scale values for each zone, so as to determine underimpedance conditions in any one of the zones.

Abstract: A protective relay system for generation apparatus connectable to a three-phase alternating current electrical utility system. The relay system includes a dual processing architecture wherein a digital signal processor executes all the signal-processing algorithms, and a separate microprocessor is used for input/output data processing. A dual-ported RAM is used to effect a fast communication link between the digital signal processor and the microprocessor to accomplish high-speed protective relaying functions to selectively trip and close a circuit breaker at a generator or cogenerator site, or that which connects it to an electric utility system.

Abstract: A distance relay for protection of power transmission lines, having a plurality of mho elements, each with a predetermined mho impedance characteristic. The relay has the capability of calculating a polarized reference voltage which remains constant through fluctuations in measured transmission line voltage. The difference voltage between the measured line voltage and the product of the measured line current and the mho element characteristic impedance is then compared against the polarized reference voltage in a product-type phase comparator to determine under-impedance conditions. If an under-impedance condition is present, the mho element produces a set output and a calculated "torque" value. The set outputs, if any, are then compared against a look-up table for fault type determination. If more than one set output is present, the magnitudes of the respective torque values are compared for fault type determination.

Abstract: A protection device for high resistance ground faults in a power network according to the invention has a fault detection principle which is based on an indirect study of non-harmonic frequency components of the phase currents. When such a fault has occurred, a considerable change of the energy contents of these frequencies arises. This change can be detected by a device according to the invention. If by comparison (4e) between digitized input signals (I') and a harmonic Fourier model (4d) of the same signals, i.e. generation of the residuals of the system, it is found that a difference exists, and if the corresponding loss function V.sub.N (4f) for a certain time exceeeds a lower limit value - all on condition that a zero sequence current (I.sub.O) exists - then there is a high resistance ground fault on any of the phases of the network.

Abstract: a protective relay for detecting faults in electrical power distribution system generates a signal .DELTA.i(t) which is substantially equal to the magnitude of the power distribution system current i measured at a first time subtracted from the magnitude of the power distribution system current i measured at a second time, the second time occurring later than the first time. The signal .DELTA.i(t) is utilized to generate measurement of the distance of a fault to the relay and is also utilized to generate operate signals if the fault occurs within the zone protected by the relay.

Abstract: A digital fault locator of this invention comprises a memory for storing input electric amount from a system and a plurality of digital filters having different filter functions to which electric amounts are supplied from the memory. A fault location is determined by selectively providing a specific one of outputs from the digital filters according to a fault time.

Abstract: Protective relay apparatus for providing a compensated fault impedance measurement for the determination of a better estimate of fault location along a transmission line is disclosed. In a power system network including local and remote generating sources disposed at respective ends of a transmission line segment of the transmission line, the protective relay apparatus is disposed at the local end of the line segment to measure the fault impedance for use in determining fault location. However, load flow conditions rendered by the generating sources interact with a fault which contributes resistance substantially to the fault impedance of the transmission line to cause an erroneous component in the fault impedance measurement rendering the determination of an erroneous fault location.

Abstract: A protective relay for detecting faults within a predetermined protected zone of a three phase alternating current electrical power distribution system generates a polarizing signal V.sub.POL which includes a signal V.sub.1 related to a positive sequence component of a phase voltage of the three phase power distribution system. A signal I.sub.1 Z.sub.R, which is a signal related to a positive sequence component of a phase current of the three phase power distribution system multiplied by a replica impedance of the protected zone of the three phase power distribution system, is also generated. The coincidence of the V.sub.POL and I.sub.1 Z.sub.R signals are compared and an operate signal is generated as a result of positive coincidence. A first restraint signal is generated as a result of negative coincidence. A second restraint signal related to V.sub.1 is also generated.

Abstract: An Adaptive Kalman Filtering scheme for statistically predicting the occurence and type of a fault on a three phase power transmission line. Additionally, estimations of the steady-state postfault phasor quantities, distance protection and fault location information is provided. Current and voltage data for each phase is processed in two separate Adaptive Kalman Filtering models simultaneously. One model assumes that the phase is unfaulted, while the other model assumes the features of a faulted phase. The condition of the phase, faulted or unfaulted, is then decided from the computed a posteriori probabilities. Upon the secure identification of the condition of the phase, faulted or unfaulted, the corresponding Adaptive Kalman Filtering model continues to obtain the best estimates of the current or voltage state variables. Thus, the Adaptive Kalman Filtering model having the correct initial assumptions adapts itself to the actual condition of the phase faulted or unfaulted.

Abstract: A method to detect voltage and current of an electric power system and, based on the detected values, calculate resistance and inductance of the power transmission line and thereby to measure the distance from the relay apparatus to the point of the fault of the power transmission line. The voltage (v) and current (i) of the electric power system are detected at constant sampling intervals and the thus detected values at the sampling time points from t.sub.n to t.sub.n+2 are used in the approximate integration formula: ##EQU1## where K.sub.1 and K.sub.2 are constants, and through this approximation the resistance (R) and inductance (L) of the power transmission line as the object of the measurement are obtained, and thus, even when a current including components of different frequencies is flowing through the power transmission line, the distance sought can be measured precisely.

Abstract: In an apparatus for producing data concerning a fault in an AC electric power system, an AC electric quantity is sampled at a frequency which is a multiple of the rated frequency of the AC electric quantity, and is stored, for later use as predicted values, and an arithmetic operation is performed on the sample values to produce a data concerning a fault in the power system. The predicted values are determined by the following equation: ##EQU1## where l and m represent natural numbers;n represents a natural number;Y.sub.m represents the predicted value for a specific time point;S.sub.o represents a sample value in advance of the specific time point by m/2 times the rated period;S.sub.l represents a value equal to (-1).sup.l times the sample value at a time point in advance of the specific time point by l/2 times the rated period; andK.sub.o and K.sub.l represent constants satisfying the following relationship: ##EQU2## where .epsilon.

Abstract: In a transformer protection system, data of voltages and currents detected at individual terminals of a transformer connected to an electric power system are supplied to a computer. The computer computes driving point admittances or shunt admittances of the transformer on the basis of the voltage and current data and predetermined transfer admittances of the transformer and decides that an internal fault has occurred in the transformer when the values of the driving point admittances or shunt admittances deviate from pre-set reference values, thereby disconnecting the transformer from the electric power system.

Abstract: In a short-circuit distance relay for protecting a single-channel power transmission system with power supplies installed at two ends thereof, when there exists any resistance at a fault point on the power transmission line, an error is induced in measurement of the distance up to the fault point by a voltage drop component flowing through the fault-point resistance from the remote-end power supply. In order to eliminate such error in measuring the distance, the relay of this invention computes the impedance up to the fault point from the information including a positive-phase voltage and a positive-phase current in a normal state of the power transmission system, and also a positive-phase voltage, a positive-phase current and a negative-phase current in a faulty state of the system, whereby the fault-point resistance is rendered unconcerned with the distance to consequently avert the measurement error.

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

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

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

Abstract: In a digital protective relay system for protecting an electric power system, a first digital operation device receives digital data on the electrical quantities of the power system and performs an operation on the digital data to produce an intermediate result, which is then stored in a memory unit. A second digital operation device reads the intermediate result from the memory unit and performs an operation on the intermediate result to produce a final result. The memory unit is so connected as to permit writing by the first operation device only, and to permit reading by the second operation device only.

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

Abstract: In a digital distance relay, the distance measuring operation is performed only regarding the phase on duty in the third step if there is no fault, and it is performed regarding either the third and first steps or the third and second steps if a fault is detected within the third step. Thereby the processing time for the distance measuring operation may be reduced is that corresponding to two steps per sampling.

Abstract: A phase comparison type ground distance relay for a predetermined phase of three-phase AC transmission line includes a phase coincidence detector responsive to phase coincidence between an operating signal and a plurality of polarizing signals. Zero suppression networks are utilized for deriving second and third polarizing signals in order to improve discrimination between internal and external faults; thereby increasing the reliability of the relay operation and the security of the protection system. The second polarizing signal comprises that portion of a signal which exceeds a predetermined threshold value and which is related to the product of a signal proportional to the net current flowing in all three phases of the power system and the positive sequence replica impedence of the transmission line.

Abstract: A network impedance protection device operates in dependence on the quotient of voltage and current at a measuring point and is set to initiate a protective action when the measured impedance is lower than an impedance level set in the device. Known designs comprise analog components and functions both as regards quotient formation, comparison and compensation etc. An impedance relay constructed according to the invention utilizes the same principles as the analog design, but all units and functions are digitized. Incoming voltage and current signals are converted in an A/D converter, filtered in tuned filters, rectified in rectifiers, and so on, and deliver an output signal, via summators, when the measured impedance is lower than a set impedance value.

Abstract: A fault in a section of an electrical power supply line is detected by measurement of voltage and current, filtering out high frequency components, and calculating approximations of Fourier transforms of a time window of the voltage and current at a predetermined frequency modified by a continuous phase change at that frequency and then calculating the impedance of the section from the modified Fourier transforms of voltage and current (FIG. 2).

Abstract: In a machine implemented method and a system for protecting an electric power system, a differential equationv=L(di/dt)+Riis solved by using an approximation ##EQU1## to determine the inductance L and to measure or discriminate the distance from the determined inductance, wherev represents the voltage,i represents the current,R represents the resistance,t represents the time,t.sub.k and t.sub.k-1 represent time points,i.sub.k+p and i.sub.k-p-1 represent values of the current i for time points represented by t.sub.k+p and t.sub.k-p-1,p represents integers (0, 1, . . . N),N represents a natural number,K.sub.p (p=0, 1, . . . N) represents constants, with at least K.sub.0 and K.sub.1 being values other than zero and being so determined that the errors in the approximation for the inductance is zero for specified frequencies.

Abstract: An apparatus and method for removing a transient exponential noise signal from a sinusoidal signal. The effects of the transient are removed by sampling the sinusoidal signal, averaging the transient over a time interval corresponding to an integral number of cycles of the sinusoidal signal, and subtracting this average from the sample at the midpoint of the time interval. The result is a compensated sinusoidal signal wherein the effects of the transient have been removed. The time interval is progressively moved ahead to produce a complete compensated signal by subtracting the average of the exponential from the value thereof at the midpoint of each successive time interval.

Abstract: A fault finder for locating faults along a high voltage electrical transmission line. Real time monitoring of background noise and improved filtering of input signals is used to identify the occurrence of a fault. A fault is detected at both a master and remote unit spaced along the line. A master clock synchronizes operation of a similar clock at the remote unit. Both units include modulator and demodulator circuits for transmission of clock signals and data. All data is received at the master unit for processing to determine an accurate fault distance calculation.

Abstract: A protective relaying system which detects a fault in an electric power system having a circuit breaker by using a current and a voltage of the electric power system. The protective relaying system includes input conversion unit adapted for connecting the electric power system to receive a first and a second input signals corresponding to the current and the voltage and for converting the magnitude and/or the phase of the first and second input signals to produce a first, a second and a third electrical quantities. The protective relaying system also includes comparing unit connected to receive the first, second and third electrical quantities, for comparing the first and second electrical quantities to produce a first logical state signal, and comparing the third and a fourth electrical quantities to produce a second logical state signal cyclically, and for producing a logical state signal including the first and second logical state signals cyclically.

Abstract: A protective relaying system is disclosed which detects a fault in an electric power system having a circuit breaker by using a current and a voltage of the electric power system. The protective relaying system includes an input conversion/unit adapted to receive a first and a second input signals corresponding to said current and voltage, for converting the magnitude and/or the phase of the first and second input signals to produce least two electrical quantities a first electrical quantity and a third electrical quantity, and for outputting the second input signal without conversion as a second electrical quantity.The protective relaying system also includes a comparing unit connected to receive first, second and third electrical quantities from the input conversion unit for comparing the first and second electrical quantities to produce a first logical state and comparing the third and fourth electrical quantities to produce a second logical state signal cyclically.

Abstract: A protective relay system for opening local and remote circuit breakers of a protected line segment when a fault occurs thereon. The protective relay system includes local and remote fault detectors for producing local and remote blocking carrier signals, respectively, for transmission to the other terminal when a fault is in the forward direction from the terminal. Reception of a blocking signal blocks tripping of the circuit breaker at the receiving terminal. When the fault is internal, the blocking signals are transmitted for only a short duration, sufficient to allow the protective relays at both terminals to detect the internal fault. When transmission of the blocking signals stops, the trip coils at both terminals are energized because the relays at both terminals see the fault in the forward direction and do not receive the blocking signal. For an external fault the relays at the terminal from which the fault is seen in the forward direction transmit a blocking signal to the other terminal.

Abstract: The invention relates to a low impedance excitation system for use in distance relays. In such a system the low impedance check is carried out by comparing the phases of signals (U.sub.D,U.sub.S) which are obtained by forming the sum and the difference from an image voltage signal (U.sub.A) and a line voltage signal (U.sub.K). The triggering characteristic is formed in the complex impedance plane by means of the combination of at least two different triggering characteristics, mainly a circular (K) and a lenticular (L) characteristic, in order to avoid overlapping between the triggering area and the active load area (W) and in order to achieve an adequate arc reserve on the whole length of line to be monitored. The switching over between the different triggering characteristics (K,L) takes place as an operational function of the phase difference (.beta.) between the image voltage signal (U.sub.A) and the line voltage signal (U.sub.K).

Abstract: Digital distance relaying of a three-phase electric power transmission line depends on accurate estimation of the postfault voltage and current phasors during the first postfault electrical cycle, when the line voltages and currents are corrupted by noise and transients. The digital relay herein responds to each postfault sample as it arrives and recursively electronically estimates the postfault phasors before the next sample arrives. The method involves a powerful state variable approach which for the voltages provides at least two state variables per voltage, and for the currents provides at least three state variables per current. Parallel processing of the samples equalizes computer burden, and an additional processor classifies the fault, computes faulted line resistance and reactance, relays the fault by tripping a circuit breaker, and documents the fault including its distance.

Abstract: Protective relay apparatus for detecting the direction or distance to a fault from the measuring point on an ac electrical power transmission line using current and voltage deviation signals. The deviation signals represent the changes induced by the fault from the steady-state pre-fault magnitudes. Trajectories are plotted on an X-Y plane using the voltage deviation signal as the X-axis coordinate and the differentiated current deviation signal multiplied by the line reactance to the balance point as the Y-axis coordinate. Due to the use of the differentiated current deviation signal, the trajectories are straight lines. The threshold boundaries for determining the distance to or direction of the fault are time-varying lines of unit slope representing the pre-fault voltage at the fault point.

Abstract: Disclosed is an improved reactance type protective relay that increases security against false tripping while still providing desired protection for a high voltage transmission line. The improved reactance relay employs a circuit arrangement having characteristic timers that optimize the performance of the reactance relay and also allows for desired coordination between the reactance relays that may be located along the high voltage transmission line.

Abstract: Disclosed is a positive sequence undervoltage distance relay that forms a part of a relay system that provides protection for a high voltage three phase transmission line. The undervoltage distance relay provides a high speed blocking function for use with the high speed tripping functions in the protective relay system. In one embodiment the undervoltage distance relay utilizes the positive sequence components of the three phase transmission line. In another embodiment the undervoltage distance relay utilizes the line to ground (or line to line) voltages and currents of the three phase transmission line.

Abstract: A process and device useful in the protection of AC current circuits, particularly of parallel lines supplied at both ends, provided with protection relays at both ends of the line against susceptibility to false triggering as a result of transient signal components and signals disturbances, and particularly useful in providing stepped protection upon initial disconnection at one side of a line after occurrence of a short circuit against the change of energy direction with reversal of the fault direction detected in the protection relay of the sound line on crossing the triggering range of the appropriate characteristics curve, which also leads to false triggerings in multi-system protection relays because of transient switching inaccuracies.

Abstract: A phase relay utilizes improved polarizing and operating signals in order to provide discrimination between internal faults within a protected zone of an AC power transmission line and external faults than can appear as internal faults due to transients induced by capacitive voltage transformers or series capacitors. A zero sequence restraint signal is used to block operation of the phase relay on close-in single line to ground faults. A filter is used in a by-pass circuit to attenuate high frequency transients which might delay, and possibly prevent a trip output on an internal fault. A high set by-pass circuit, including zero suppression to preclude an output on an external fault, is employed to provide faster operating times on severe internal faults. Forward offset and/or zero suppression of the polarizing signal is used to reduce the characteristic timer setting and therefore increase the speed of the phase relay operation.

Abstract: Disclosed is a system that provides protection for a high voltage transmission line. The system employs improved polarizing and operating signals for both a phase selector relay and a distance measuring relay. The improved polarizing and operating signals provide an accurate out-of-phase relationship during the presence of normal conditions existing on a high voltage transmission line and an in-phase relationship during the presence of fault or abnormal conditions existing on the high voltage transmission line. The accurate phase relationships are utilized by phase comparator circuits of each of the phase selector and distance measuring relays to obtain desired operating characteristics for each relay. In another embodiment, the desired operating characteristics of the phase selector and distance measuring relays are obtained by an amplitude comparator circuit.

Abstract: A power distribution system includes a plurality of power sources and load transfer units including transistors and diodes connected in series and leading to a common power output, each of the transistors being controller switchable subject to voltage levels of the respective input and output sides of said transistors, and the voltage and current level of said common power output. The system is part of an interconnection scheme in which all but one of the power sources is connected to a single load transfer unit, enabling the survival of at least a single power source with the failure of one of the load transfer units.