Abstract: An adaptive method and apparatus for detecting fault conditions in a power distribution system that services both single phase loads and three phase loads. The present invention accomplishes this by providing an adaptive ground fault detection method and an adaptive phase fault detection method. Both methods provide the capability to distinguish gradual changes in phase current, due to ordinary current fluctuations, from more substantial changes in phase current due to various fault conditions. By making this distinction, the present invention minimizes unnecessary service interruptions.

Abstract: An electric motor monitoring circuit apparatus for an electric motor has a three phase electric motor having an electric motor starter circuit. An insulation monitoring circuit is coupled to the electric motor and monitors insulation leakage of the electric motor and inhibits activation of the electric motor starter circuit when an insulation leakage exceeds a preselected threshold. A three phase monitor circuit is coupled to the electric motor for monitoring phase sequence in voltage amplitude for the electric motor.

Abstract: A method for measuring the current in an AC power transmission network, where a measurement quantity is obtained by means of a current transformer and digital samples are converted. To prevent faulty detection of the current due to a decaying DC component of the current transformer, two initial auxiliary measurement quantities that are normal to one another are formed from the digital samples by means of at least two FIR filters, and together with two additional auxiliary measurement quantities that are normal to each other, are used to produce a measured value corresponding to the amplitude of the current. The additional auxiliary measurement quantities are produced from samples formed from an older measurement quantity obtained earlier by a quarter period of the current to be measured. The differential angle is formed from the two measurement quantities. An output signal is generated from the two measured values in an evaluation device when the measured values exceed preset threshold values.

Abstract: A method and apparatus are provided for detecting an arcing fault on a power line carrying a load current. Parameters indicative of power flow and possible fault events on the line, such as voltage and load current, are monitored and analyzed for an arc burst pattern exhibited by arcing faults in a power system. These arcing faults are detected by identifying bursts of each half-cycle of the fundamental current. Bursts occurring at or near a voltage peak indicate arcing on that phase. Once a faulted phase line is identified, a comparison of the current and voltage reveals whether the fault is located in a downstream direction of power flow toward customers, or upstream toward a generation station. If the fault is located downstream, the line is de-energized, and if located upstream, the line may remain energized to prevent unnecessary power outages.

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 phase monitor and protection circuit is shown in which an impedance network (21, 23, 25) in a respective branch (20, 22, 24) connected to a neutral (26) is coupled to each phase of a three phase power supply (L1, L2, L3) to create a known voltage profile across the respective networks. A relay network (36) is coupled to one branch (20) and a control network (30) is coupled to a second branch (24) to monitor the voltage levels and deenergize the relay (R1) upon the occurrence of the reversal of any two phases or the loss of a phase. The control circuit can also be used to detect low voltage conditions and in a second embodiment provides a time delay network (44) to avoid nuisance tripping due to transient low voltage or brown out condition.

Abstract: A phase sequence protection circuit is shown in which first and second resistors (R1, R2) and a first capacitor (C1) all having equivalent impedance are connected in a Y configuration and coupled to power source leads (A, C, B) of a three phase power supply, resistor R1 being coupled to phase A, capacitor C1 to phase B and resistor R2 to phase C. A comparator network (12) is connected in line with the first resistor (R1) and, in one embodiment will cause a solid state switch (Q1) to conduct when the phases are out of sequence. In a second embodiment a buffer portion (COMP2) is provided to add switching hysteresis which also reverses the switching logic causing the solid state switch (Q1) to conduct when the phases are in sequence. In another embodiment the comparator network (12") is provided with the buffer portion (COMP2) for switching hysteresis and arranged to cause the solid state switch (Q1) to conduct when the phases are out of sequence.

Abstract: A missing phase detector circuit which monitors the ac three-phase output voltages of power equipment or sources and produces an output signal in the event a missing ac phase is detected. The circuit reduces the monitored phase voltages to low values and produces an ac ripple voltage waveform where each ripple represents a phase. An analyzer circuit examines the ac ripple voltage waveform for its zero crossings and produces a pulsed dc waveform where the width of the pulses is normally small. If any of the pulses is found to be wide, indicating a missing phase, a positive high signal is output by an AND gate. This output signal may be used to initiate illumination of a "Missing Phase" indicator or it may be used for equipment control purposes. Provision is made to prevent a false output signal when there is no input power. The circuit is not sensitive to frequency, power factor or unbalanced loads.

Abstract: A harmonic analyzer using a short sampling window eliminates truncation artifacts in the sampling of an AC power waveform by equating the length of the sample period to a period of the sampled waveform. The period of the AC power waveform is estimated from the waveform and used to produce a set of "resampled" points evenly spaced within that period as estimated from the sampled. By performing a spectrum analysis on the resampled points, artifacts at the harmonic intervals are reduced to zero.

Abstract: Disclosed is a negative-sequence time-overcurrent relay for use in a polyphase synchronous rotary electric machine having a main-circuit breaker and an exciting circuit.

Abstract: A phase sequence indicator with two measuring contacts for contacting with connections of the object to be measured has a grouring contact touchable by the user, an evaluation circuit connected to the measuring contacts and the grounding contact, and an indicating device controlled by the evaluation circuit for indicating the direction of the rotary field. The evaluation circuit has a voltage-testing circuit for detecting the value of the voltage occurring between the measuring contacts, and the indicating device comprises additional indicating elements for indicating the value of the voltage.

Abstract: The invention provides a zero phase sequence current zig-zag filter with adjustable zero phase sequence impedance and a method for adjusting the impedance of the filter. Impedance is adjusted in discrete increments by detuning the filter one phase at a time. Detuning is accomplished using taps or auxiliary windings, whereby the ratio of the effective number of turns of the first winding relative to the second winding on the same core leg is changed independently for each phase of a three phase power supply.

Abstract: A method and a device for phase selection for single-pole tripping of high-impedance ground faults in direct grounded power networks. Starting from the ratio of the negative-sequence voltage to the zero-sequence current (U2/I0) and the ratio of the negative-sequence voltage to the positive-sequence voltage (U2/U1), two criteria with different conditions are formed, each of which indicating a faulted phase, and if both criteria indicate the same phase as faulted, single-pole tripping can take place.

Abstract: An electrical apparatus for visually indicating phase sequence, phase asymmetry and presence of three phases of an AC network comprising two transistors connected by their emitters to a first voltage terminal of the three phase network, the bases of the transistors being connected through diodes to a first voltage terminal and through crosscoupled phase shifting means to two other terminals of the three phase network. The collectors of the transistors are connected through resistors, light emitting diodes and diodes to two other voltage terminals and the emitters of the two transistors are connected through two other light emitting diodes to the first voltage terminal.

Abstract: A zero phase voltage measuring device for measuring a zero phase voltage of the three phase power system having an earth-fault includes an optic voltage sensor provided at any one of three power lines for detecting a current ground-to-line voltage thereat, a line-to-line voltage sensor provided between any two of the three power lines for detecting a current line-to-line voltage therebetween. A phase shifter and a multiplier are provided for calculating an ideal ground-to-line voltage at the power lines when no earth-fault is observed by changing the phase and multiplying the magnitude of the current line-to-line voltage. A subtracter is further provided to obtain a zero phase voltage signal by subtracting the ideal ground-to-line voltage from the current ground-to-line voltage.

Abstract: A polyphase reversal detection and correction system which operates over a wide range of line frequencies and produces an automatic phase correction for maintaining proper phase sequence to a rotating device. The system includes a circuit arrangement for developing peak integrated signals by comparing the relation of various input phases, and developing an integrated reference phase signal. The input phase signals and the reference phase signals are compared to determine and correct the input phase sequence.

Abstract: The sectionalizer control provides a restraint signal responsive to a harmonic current which exceeds a threshold current for less than a preset time.

Abstract: A voltage rotation indicator for testing the phase sequence of live multi-phase electrical power is mounted within a housing. The housing is provided with structure for removably mounting the indicator on a meter box or can during voltage rotation testing. Contact plungers extend from the housing and contact meter jaw test points in the meter box during testing. Field personnel are thus not required to insert their hands into the meter box to attach test clips to the live circuit.

Abstract: A method of locating a phase-to-ground fault in a radial distribution system with a tapped load. The method includes determining the positive-sequence impedance from the residual current, the residual current compensation factor and the phase-to-ground voltage of the faulted line. The positive-sequence impedance is then used to determine the distance to the fault.

Abstract: A safety device for an elevator which has a converter for converting a 3-phase A.C. power source into a D.C. power source, a control circuit for the elevator employing as a power source the D.C. power source outputted from the converter, a level converter for converting the voltage of the D.C. power source outputted from the converter into a logic level, and defective phase detecting means for detecting the defective phase of the 3-phase A.C. power source by dividing the output signal of the level converter in a time division manner.

Abstract: The present invention discloses electrical testing apparatus to test an AC multiphase supply outlet. The apparatus is located within a flame proof enclosure and provides a visual indication of phase energization, direction of phase rotation, and supply voltage.

Abstract: This invention relates to a voltage sensor for sensing a voltage on an electrically charged object such as a distribution line or the like, the sensor being disposed with an insulation space to the object. The voltage sensor includes an amplifier circuit for outputting a signal having a waveform similar to that of a displacement current inflowing from the electrically charged object via the insulation space, and a filter circuit for extracting a signal having predetermined frequencies from the output of the amplifier circuit and outputting an alternating current waveform similar to the potential of the electrically charged object.

Abstract: A line current to time interpolator circuit senses the magnitude of current in a power distribution line and develops and AC voltage indicative of the current magnitude. The AC voltage is phase shifted multiple times to produce a number of phase shifted replica AC voltages, and the replica voltages are applied to a multiple input absolute value amplifier to develop a DC voltage indicative of the current magnitude. The DC voltage is applied to a ladder voltage comparator which controls the overall resistance of a discharge path coupled to a charged capacitor. The ladder comparator varies the discharge path resistance in inverse relationship to the DC voltage level to vary the discharge time constant of the capacitor. By controlling operation of a circuit interrupter in accordance with the charge level of the capacitor, the interpolator circuit provides a desired inverse time-current response characteristic.

Abstract: An apparatus for visually indicating abnormal phase relationships between incoming or outgoing phases for a plural phase device, comprised of a plurality of light emitting means interconnected between phases by a logic circuit arrangement whereby the various combinations of on/off indicators present a coded, visual presentation representing the specific mismatch condition of the network. The invention encompasses the concept of incorporating the indicating circuitry within the multiple phase device enclosure and providing an aperture in the enclosure so that the indicators may be viewed without the necessity of gaining access to the interior of the device and exposing individuals to the danger of high voltage/current circuits.

Abstract: A protective relay for detecting faults within a predetermined protected zone of a three phase alternating current electrical power distribution system, of the type which utilizes at least one restraint signal in conjunction with at least one operate signal to generate a net operate signal, generates an operate quantity which is related to a zero sequence component of current flowing in the power distribution system and a second operate quantity which is related to a negative sequence component of the current flowing in the power distribution system. The operate quantities are summed to form an operate signal. An adaptive restraint, which is proportional to a negative sequence component and a zero sequence component of a phase voltage of the power distribution system, is generated and utilized to provide increased sensitivity to higher resistance ground faults.

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: A phase selector for identifying a faulted phase in a three-phase alternating current electrical current distribution system generates, for each of the three phases, an output signal which includes the phasor sum of a signal related to a fault component of current flowing in the phase, a signal related to a negative sequence component of current flowing in the phase and a signal related to a zero sequence component of current flowing in the phase. The phase selector also generates at least one restraint signal which includes the phasor sum of a signal related to a fault component of current flowing in one of the two other phases of the three phase power distribution system, a signal related to a fault component of current flowing in the other of the two other phases of the three phase electrical power distribution system and a signal related to the negative sequence component of current flowing in the phase.

Abstract: Faults in a three-phase power transmission line are identified by vectorially subtracting from the postfault current for each phase, the zero sequence current and the prefault current. The resultant currents which are the vectorial sums of the postfault positive and negative sequence currents are then compared. If the magnitude of the resultant current in one phase exceeds that in each of the other two phases by a preselected factor, than one phase is identified as the phase to ground faulted phase. If the magnitudes of the resultant currents of two phases exceed that of the third, those two phases are involved in either a phase to phase or a phase to phase to ground fault with the distinction being made by the presence of zero sequence current in the later case.

Abstract: A power active filter circuit for an electric power system includes a reference generator for producing a plurality of balanced, constant amplitude, positive sequence, AC reference voltages, each being phase-locked to a corresponding phase voltage of the power system. Error signals are produced by subtracting the reference voltages from their corresponding phase voltages and a plurality of correction signals, which are proportional to the error signals, are combined with the phase voltages to produce a plurality of output voltages having substantially only a fundamental component.

Abstract: A microcomputer based fault detector for identifying a phase reversal, a phase loss, and a power loss in three-phase circuits. A microcomputer samples a pattern of timing signals generated in response to three current transformers associated with each of the three phases. The changing pattern of timing signals represent the phase relationship of each of the three phases. The sampling rate of the microcomputer is synchronized to the alternating current in each of the three phases by an interrupt signal indirectly generated by one of the phases. In the absence of current in this interrupt generating phase, a backup interrupt, internal to the microcomputer, is enabled which directs the microcomputer to determine if the absence of the first interrupt is due to a phase loss or a power loss. Either interrupt prompts the microcomputer to sample the pattern of signals and compare it to a predetermined pattern.

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: Apparatus for performing selective-pole trip determination is included in each protective relay of a current only monitoring protective relay system for protecting an electrical transmission segment of a power system network against faults. Current signals from the phases of the transmission segment are provided to a sequence network of the apparatus for conversion into positive and negative sequence component signals for each phase. A zero sequence component signal is also derived. A logic circuit is provided for each of the phases of the transmission segment and is governed by the corresponding sequence component signals and phase shifted variations thereof to detect a single-pole fault exclusively in the corresponding phase and generate a signal in response to the detection. An internal trip detection enables each phase logic circuit to generate its corresponding trip signal.

Abstract: A reduced voltage starter for gradually starting a polyphase motor having an acceleration control circuit for gradually applying power to the motor and detector circuits for detecting various fault conditions for terminating power to the motor. A shorted solid state switch detector senses when one of the semiconductor switches applying power to the motor is shorted to terminate the application of power from the remaining phases. A phase angle control circuit insures a uniform application of power to the motor. A phase rotation detection circuit detects when the three phases are in other than their correct sequence and terminates power in the event of such detection. An underload detection circuit senses when the current drops beneath a preselected reference after the motor has reached its full speed and terminates power in response to such detection. A line-to-line to line-to-neutral converter produces signals representative of the line-to-neutral voltages which are necessary for other circuit functions.

Abstract: A negative sequence occurring in a polyphase power system control including a continuous wave frequency transducer causes a second harmonic to be generated which for a 60 Hz system comprises a 120 Hz signal. In a preferred embodiment of the invention, the continuous wave frequency transducer includes an active 120 Hz notch filter having one stage which provides a component of the 120 Hz second harmonic. This signal is coupled to a second harmonic detector implemented by a semiconductor diode connected to the output of an operational amplifier. The detector diode is coupled to one input of a comparator circuit whose other input is coupled to a selectable DC reference signal. The comparator operates to generate a fault indicating signal indicative of a negative sequence when the output from the second harmonic detector exceeds the reference.

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 current sensor for use in a three phase ac system for producing a signal indicative of the average value of the sum of the squares of the ac current and of the phase imbalance between the three phases using two current transducers and an associated method.

Abstract: A protective relay for detecting high-impedance ground faults on a three-wire distribution system. The protective relay operates independently of the current in the ground path by using the positive and negative sequence currents to detect a fallen conductor. The ratio of the negative sequence to positive sequence current is calculated and when this ratio exceeds a predetermined value, a trip signal is produced.

Abstract: A method of and apparatus for protecting three phase electrical equipment where a signal is derived for each phase representing current in each phase, and the three signals combined to form an analog composite signal. The analog composite signal is converted to digital form. One of the analog signals is used to relate the values of the digital signals to respective phases. The largest value is used to determine heating in the equipent and from the heating the temperature of the equipment is derived. The temperature is compared to critical temperature levels and when a critical level is exceeded, the supply of power to the equipment is interrupted. The digital signals representing the current peaks in each phase are used to determine phase loss and phase unbalance, and the power supply is interrupted when there is a phase loss or when the unbalance exceeds a predetermined critical level.

Abstract: A multiphase imbalance monitor utilizes a resistive summing network for sampling the ac voltage in each phase of the system under consideration. The summing network provides a zero voltage output under normal conditions. When a phase imbalance or missing phase condition occurs, the summing network provides a finite output voltage which can be used to actuate indicating and/or interrupting means.

Abstract: A power distribution apparatus, and related method, for coupling single-phase power from a three-wire input line to a power outlet only when the ac power signals carried on the input line have the correct polarity. Particular wires of the three-wire input line are designated to carry a positive power signal, a neutral power signal, and a negative power signal, with the positive and negative power signals having opposite polarities. The apparatus detects the voltage difference between the power signals carried on the two wires designated to carry the positive and negative power signals and couples power to the power outlet only when the detected voltage difference exceeds a prescribed threshold. Since the detected voltage difference exceeds the threshold only when the polarities of the power signals on the input line are correct, the system prevents the coupling of incorrect voltage levels to the power outlet and thus eliminates electrical shock hazards of this kind.

Abstract: Apparatus and method for protecting a squirrel cage induction motor against excessive temperatures which can occur in the rotor, provides a thermal model of the rotor. The thermal model has three regions A, B and C representing the starting portion of the rotor conductor, and the rotor core. The rotor is frequency sensitive and currents of higher frequency induced in the conductors tend to be in region A, and currents of lower frequency tend to be in region B. Equipment connected to the stator winding determines values for the positive and negative sequence components of the supply for the fundamental frequency and preferably also for the second and third harmonics present, and provides signals representing these values. Heat calculation circuitry receives the values for all the positive and negative sequence components and a signal representing speed, determines the currents that would be induced in regions A, B and C, and derives equivalent currents which would produce the same heat.

Abstract: A waveform crossing detector circuit for a pair of waveforms of a three-phase AC supply applied to respective input terminals (7,8,9). The circuit includes a pair of opto-couplers (1,3; 2,4) for isolating an output terminal (21) from the supply. In order to obtain an accurate indication of the instants of crossing the light-emitting diodes (1,2) of the couplers are driven by respective transistors (5,6) which act as the actual crossing detectors. The collector circuits of these transistors are driven from the third phase, the potential of which is at a maximum when the relevant instants occur. Two further such arrangements may be connected to the taps (22,23,24) of an input potential divider in a cyclical manner and the output signals of the three resulting arrangements combined by means of logic gates to produce pulses which occur once every 60.degree. of the input waveform.

Abstract: When the positive-phase voltage of one terminal of a transmission line involved in a fault detected by a positive-phase relay exceeds a predetermined value, an output is supplied to the reclosing instructing device from an AND circuit to first reclose this terminal. When it is less than the predetermined value, this terminal is reclosed only if reclosing of the other terminals have been successfully completed.

Abstract: Procedure for monitoring the phase sequence in a three-phase network, for instance in lift operation. Between the normal voltage vectors (R,S,T) indicating the phases are added extra vectors (R',S') which are mutually opposed and equal vectors, and that the extra vectors (R',S') and the voltage vectors (R,S,T) are added up and on the basis of the sum thus obtained, necessary steps are taken.

Abstract: A three-phase symmetrical component active band-pass filter includes three 120.degree. phase shift circuits which are connected in a closed loop fashion such that each phase shift circuit receives an input signal from one phase of an associated power system and a second signal from the output of one of the other phase shift circuits. A voltage tunable filter is formed by using multipliers to couple some fraction of the output of each phase shift circuit to a summing point at the input of another phase shift circuit. Phase comparators and an integrator can be added to achieve a self-tracking tuning arrangement.

Abstract: A microprocessor controlled motor starter is utilized in which the sign values of two phases of voltage are sampled and stored prior to actual motor startup to determine if a phase reversal, a phase imbalance, or a phase loss exists. If any of the preceding conditions exist, the motor start operation is aborted. This generally requires sampling the signs of the appropriate voltages three times during each voltage cycle at approximately equal intervals of 120.degree., give or take 10.degree. or so, and then forming a matrix of voltage signs versus sampling intervals. By comparing diagonal measurements of the sign values in the matrix for three diagonals in a direction of advancing time, phase loss or imbalance can be determined. The determining factor is that each diagonal must contain two values which should be equal, that is, both should be digital ones or both should be digital zeros. If such is the case for the three diagonal measurements, then no phase imbalance or loss exists.

Abstract: A static protective relay at least includes a plurality of current transformers inserted in poly-phase AC power lines, a half-wave rectifying circuit for rectifying the output voltages from said current transformers, wave-shaping circuits for wave-shaping two of the pulsate output voltages from the half-wave rectifying circuit into rectangular wave output voltages, and a negative phase failure detecting circuit including a data flip-flop for detecting the level of the rectangular wave output to be phase-retarded at the instant of rising up of the rectangular wave output to be phase-advanced.

Abstract: Disclosed is a phase sequence network. The network is compensated for frequency variations in the signal applied to the sequence network so as to develop a desired sequence component output that is accurate over a limited but adequate range of frequencies.

Abstract: A current limiting protector for use in electric power transmission lines includes a conductive strip of material and a chemical charge for physically interrupting the conductive strip in response to a fault current. A current sensor triggers the chemical charge when the line current is symmetrical and the RMS value of the line current exceeds a first value, and the current sensor triggers the chemical charge when the line current is asymmetrical and the RMS value of line current exceeds a second value.

Abstract: A voltage rotation indicator for testing the phase sequence of live multi-phase electrical power is mounted within a housing. The housing is provided with structure for removably mounting the indicator on a meter box or can during voltage rotation testing. Contact plungers extend from the housing and contact meter jaw test points in the meter box during testing. Field personnel are thus not required to insert their hands into the meter box to attach test clips to the live circuit.