Abstract: There is provided an apparatus for producing a trip signal to activate a circuit breaker in an alternating current power line, said apparatus comprising: a sensing circuit operable to sense values representing: a phase difference between current and voltage in said power line; and current amplitude in said power line; a comparison circuit operable to compare said sensed values of phase difference and current amplitude with a trip characteristic defining fault conditions and non-fault conditions and to generate a fault indication signal when a fault condition arises; a fault discriminator operable in response to said fault indication signal to generate a fault-identifying signal discriminating between: a first class of fault in which a mean current value after said fault indication increases relative to a mean current value before said fault indication; and a second class of fault in which a mean current value after said fault indication does not increase relative to a mean current value before said fault indi

Abstract: A controller is disclosed for determining that the currents from the two AC power sources are correctly phased. Required circuitry can be disposed within a housing from which extend power cables having single phase 240V AC, 50 A male connector plugs connected at remote ends. Prongs in each of plugs can be arranged so that the plugs are connectable to a 240V, single phase AC source. A power cable, having a connector at a remote end, can also extend from the housing. The power cable connector can be connected to an AC power supply. The power cable connector supply a power transformer with single phase AC power at 240V and 100 A. The circuitry can assure that the phases and voltages of the two AC sources driving the connectors are properly connected to the connectors to enable the cable to supply the power cable connector with single phase AC.

Abstract: A power line phase coupler system for repeating data signals between power line phases that can be easily installed by a user. The power line phase coupler system includes a housing, a female connector positioned within the housing, a male connector electrically connected to the female connector by a length of cord, and a repeater coupler electrically connected to the male connector. The repeater coupler is electrically connected between Phase A and Phase B of the male connector for repeating and amplifying a data signal received from either phase to the opposite phase.

Abstract: U.S. Ser. No. 2002009312A cooking appliance having an electric resistance heater is connected to a multiple phase external power source and includes a system for compensating for whether the cooktop is connected to 240V split phase system wherein the two phases are 180° out of phase with each other or a 208V three phase system which has two phases that are only 120° out of phase. In particular, the cooktop includes a system for distinguishing whether the multiple phases of the external power source are 180° out of phase such that the electric resistance heater is compensated against whether it is connected to a three phase external power supply.

Abstract: The present invention is directed to a comparator circuit for use with in-phase and quadrature phase signals and a method of comparing a resultant vector of the in-phase and quadrature phase signals. In one embodiment, the comparator circuit includes a non-titled comparison circuit that compares a resultant vector of the in-phase and quadrature phase signals to vertical and horizontal comparison boundary member pairs. The comparator circuit also includes a tilted comparison circuit, coupled to the non-tilted comparison circuit, that compares the resultant vector to comparison boundary member diagonals coupled to the vertical and horizontal comparison boundary member pairs. The comparator circuit may still further include a combiner circuit that provides a comparison signal based on signals from the non-tilted and tilted comparison circuits.

Abstract: A solid state relay coupleable to first and second phase busses of an AC power source for switching power from the first and second phase busses to a load comprises: first and second power semiconductor switches connected in a series circuit configuration and coupleable to the first and second phase busses for switching power from the first and second phase busses to the load, each of the first and second power semiconductor switches controllably operative in conductive and non-conductive states; first and second power diodes coupled respectively across the first and second power semiconductor switches; and a control circuit for monitoring a polarity relationship of the first and second phase busses and controlling the first and second switches between conductive and non-conductive states based on the monitored polarity relationship. A method of operating the solid state relay is further disclosed.

Abstract: A directional ground relay (50) for receiving electric values relating to voltage and current from a power transmission line (1) to be protected. The directional ground relay may decide a direction of a fault in the power transmission line based upon the electric values. The directional ground relay comprises a zero-phase sequential current calculation unit (10-2) for calculating a zero-phase sequential current based upon the current detected from the power transmission line. The directional ground relay further comprises a phase-comparison unit (10-3) configured to compare a phase of the zero-phase sequential current to a phase of voltage corresponding to the voltage in the power transmission line, to decide whether the zero-phase sequential current is within a pre-determined range, and to output the phase of the voltage as a faulty phase of voltage, when the zero-phase sequential current is within the pre-determined range.

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 error compensating system and method is used in electric power monitoring systems, e.g. protective relays, and includes a test unit for applying a test signal to the front end of a data acquisition section of the power monitoring system and a phase reference module which converts the test signal to a square wave having falling and rising edges corresponding to transitions between the positive and negative portions of the test signal. A programmable logic device determines the zero crossings of the sampled digital signal from the data acquisition system and then determines the time difference between a falling edge of the module output signal and the zero crossing of the sampled digital signal. The time difference is representative of the phase shift produced by the data acquisition components. A compensation circuit adjusts the digitally sampled signals with the amount of the determined phase shift.

Abstract: A programmable controller has an overcurrent detection portion, an overcurrent indication portion and a transistor for interrupting a load current at the time of occurrence of an overcurrent are provided in an output circuit portion of the programmable controlled. An overcurrent detection resistor is provided in the output transistor circuit, and a detected voltage across the resistor is compared with a reference voltage in an overcurrent detection circuit to judge an overcurrent. If an overcurrent is recognized, the overcurrent indication portion is operated, and the base current of the output transistor circuit is controlled to perform protection of the output circuit from the overcurrent. Accordingly, when an overcurrent is flowing and an input signal is in ON state, the output transistor is turned OFF automatically and, the overcurrent state is showed to a user.

Abstract: The invention relates to a method for generating an error signal which characterizes a fault current in an electrical conductor (130) provided with two conductor ends (120, 123, 126, 129) and comprising charge measuring devices (100, 103, 106, 109) which are connected to each other by data lines (112). At least one device is attached to each end of the conductor. In the inventive method, charge measuring values are determined using charge measuring devices. The measured charge values take into account the direction of the charge flow a total measured charge value is formed by addition. Said error signal is generated when the total measured charge value exceeds a certain threshold value. According to the invention, the measured charge values are determined synchronously and determined repeatedly at regular intervals in such a way that the time interval between each sequential determination is smaller than the predefined measuring period.

Abstract: A phase control switch apparatus incorporating a phase-based break/make controller (80A, 80B, 80C) for protecting a reactive load such as a transformer (10) from transient surge phenomena taking place upon power-supply breaking/making operation.

Abstract: A method and relay for magnetizing inrush restraint in protective relays for power transformers. The method utilizes the phase angle relation between the fundamental component and the second harmonic in addition to the magnitude ratio. This is accomplished by calculating and utilizing the complex second harmonic ratio. The specially shaped operating characteristic for the complex second harmonic ratio is made dynamic providing for better security without jeopardizing dependability of the transformer protective relay.

Abstract: The present invention offers a low cost, reliable, on chip implementation that takes advantage of the nature of the average current mode topology to detect phase failures within a multi-phase system. The invention further includes sensing average current to the load, generating error voltages and changing duty cycles when the sensed load current is not at the desired level.

Abstract: A power switch connecting a load to an ac source is turned off when the RMS value of the supply voltage is outside selected limits and is turned back on when the RMS voltage returns to within the limits. Adaptive hysteresis is applied to the switch controller to eliminate chattering of the power switch when the voltage fluctuates around the selected limits. To this end, the selected limits are repetitively, incrementally narrowed each time the power switch is turned off and back on a selected number of times, such as twice, within a selected time interval. The RMS voltage is rapidly determined from samples gathered over ¼ cycle so that the voltages in a three phase system can be successively repetitively calculated. Phase loss is rapidly determined by checking for the leading edge of a square wave generated from the supply voltage wave form.

Abstract: In a method for testing the ground contact of parts of a networked system in which data are sent and received via at least one line, at least one line at each part is connected via a resistance arrangement to a common potential of the parts and is connectable via a controllable switch to a further potential. The voltage across the resistance arrangement is compared with a predetermined potential when the line is at one potential in a steady state, and the state of the ground contact of the part is deduced from a comparison of the voltage across the resistance arrangement with the predetermined potential.

Abstract: A method for determining switchgear-specific data at contacts in switchgear and/or operation-specific data in a network connected to the switchgear includes detecting a so-called contact follow-through travel at a switching path as an equivalent criterion for an erosion of contacts, particularly for contactor contacts. A resilience change during a shutdown cycle is measured, can be used to determine the erosion and can be converted into a remaining contact life for the contacts. Accurate measurement of the armature movement from a start of the armature movement to a start of contact opening is required for that purpose. Switching states of a switching device and of the electrical network are additionally detected from signals for resilience detection. An apparatus for carrying out the method is also provided.

Abstract: An improved reactance characteristic for an overall ground distance quadrilateral characteristic embodies a particular phase selector, possibly among a plurality of phase selectors and variables, that eliminates undesirable generation of a tripping signal other than only for a selected phase to ground fault. This phase selector is I1FZ1, where Z1 is the positive sequence replica impedance and I1F is the fault component of the positive sequence current component, referenced to the proper phase. Preferably, the pre-fault load current is removed from this quantity. Additionally, an improved restricted phase directional function is implemented, further improving the overall performance of the quadrilateral characteristic relay.

Abstract: A distribution series capacitor control system is provided with a sub-harmonic detection module connected to an input signal and operable to detect the presence of at least two distinct types of sub-harmonic content in the input signal. A logical signal processor is electrically connected to the sub-harmonic detection module, and operates to independently determine the existence of self-excitation during induction motor starting and ferroresonant phenomena based upon the at least two distinct types of sub-harmonic content, respectively. A system controller is electrically connected to the logical signal processor and operates to eliminate effects of self-excitation during induction motor starting and ferroresonant phenomena on the system.

Abstract: A system and method for measuring phase-angle in electrical power systems includes inputting a reference signal into a receiving terminal of a communication system at a reference station and then sending the reference signal through the communication system. The reference signal is received at a substation and shaped as a quasi-reference signal. A phase difference .beta. between the quasi-reference signal and a tested signal at the substation is then measured. Phase delay of the reference signal caused by the communication system, including phase delay produced from sending means, receiving means, relaying units, and communication channels, is calculated. A phase difference .alpha. is then calculated between the reference signal and the tested signal according to the phase difference .beta. between the quasi-reference signal and the tested signal and the phase delay of the reference signal caused by the communication system.

Abstract: A system and method which detects and responds to abnormalities in a distribution system by reconfiguring nodes of the system to minimize the effects of the abnormality without the requirement of communicating with a central controller. The nodes in the system coordinate a response to a system abnormality through a process of self-organization in which each node acts based on its own programming, sensors, and stored data. Each node keeps other nodes apprised of its actions so that they may in turn decide what actions are appropriate for them to take.

Abstract: The system first identifies the existence of a fault involving ground using the phase angle difference between negative sequence and zero sequence current on the power line. Phase angle differences within three specific ranges provide an indication of the presence of particular faults. Once a particular fault has been identified, such as a BC-to-ground fault, the fault condition is monitored to determine if the fault evolves, such as to a C-to-ground fault from the BC-to-ground fault. If an evolution is recognized, the protective relay is reset so as to coordinate its operation with downstream protective elements for the evolved fault.

Abstract: A solid state relay prevents the damage to photothyristor couplers when their performance characteristics vary slightly and enables phase angle control of an AC power supply using a less costly configuration than relays with photothyristor couplers having zero-crossing functions. The solid state relay includes a pair of input terminals configured to receive a control signal, a pair of output terminals configured to be connected to an AC power supply, a thyristor in parallel to the pair of output terminals configured to switch the AC power supply in response to the control signal. The solid state relay further includes two photothyristor couplers, each having a photothyristor, that are connected in series at a midpoint connection. The two photothyristor couplers are connected in parallel to the thyristor and are configured to control the thyristor. The solid state relay further includes two surge arresters connected in series at a midpoint connection that is connected to the photothyristor midpoint connection.

Abstract: A multi-function protection system (8) for protecting electrical equipment such as a screw compressor motor is shown having a housing (10, 20) mounting current sensing toroids (CT1, CT2, CT3) and associated circuitry as well as associated circuitry for temperature sensing PTC resistors (S1, S2, S3) adapted to be placed in heat conductive relation with respective windings of the motor. The circuitry is connected to an analog-to-digital converter or ADC (U6) which provides a binary coded input to a micro-controller (U5). The micro-controller performs protection sub-routines to control an output switch (Q4) which in turn controls the state of energization of a relay (K1) coupled to the screw compressor motor.

Abstract: The present invention relates to protection circuit and method for the EMI/RFI suppression system (2) of such a five-conductor electrical system in which the neutral conductor (N) is provided with a bandstop-type filter circuit (2) for the suppression of a harmonic interference current component. According to the invention, on the neutral conductor (N) is placed a current transformer (CT) having over its secondary a resistive branch (R.sub.1), and in parallel therewith, a filter branch (5) comprising a bandpass filter (LC) tuned to the fundamental frequency of said neutral-conductor filter circuit (2) and said filter branch (5) having in series with said bandpass filter branch (LC) a switch element (4) suitable for short-circuiting said neutral-conductor filter circuit (2) when current in said filter branch (5) exceeds a preset upper limit level.

Abstract: A protection apparatus for a spot network substation has a plurality of receiving lines connected between a network bus and a plurality of power sources. Each receiving line is connected to a primary switching device, a network transformer and a protector CB. A detector for detecting a phase of each receiving line voltage and a judging unit for judging the detected phase are provided on the primary side of each network transformer. A previously stored basic phase is compared with the detected phase of the receiving line voltage. If there is a lag in the detected phase of the receiving line voltage, it is judged to be a power-stop of the corresponding power source and the protector CB is tripped.

Abstract: The positive sequence voltage on the power line is measured at a given time, i.e. the present time, and also for one cycle earlier, and the ratio thereof is then compared against a threshold value of 0.9. There are four other supervisory tests which also must be true for a loss of potential condition to be indicated. These include determination of change in positive sequence current and angle and zero sequence current and angle. If the change in those values is smaller than selected thresholds, then a loss of potential condition is indicated.

Abstract: A digitally controlled circuit breaker includes a conventional thermal circuit breaker (10) which is controlled by a solenoid (16) to override the thermal aspect thereof. The solenoid (16) is controlled by a digital processing section (20). The digital processing section (20) has a digital control module (22) with multiple profile tables associated therewith. The profile tables allow the digital control module (22) to compare a sensed current from a sensor (24) with a predetermined current value as a function of time and to generate the control signal for the solenoid (16) if the sensed current exceeds that in the profile. The profiles can optionally be downloaded to the module (22) through a serial communication port (36). The digital control module (22) is also operable to sense the voltage of the circuit breaker to determine zero crossing points and phase angle, which phase angle can be utilized to determine the type of load and, therefore, can alter the profile to be utilized.

Abstract: A power source miswiring detection apparatus for detecting a miswiring of wires of a power source, including a pulse generator for generating a first pulse having a pulse width corresponding to a first phase difference between a first pair of two phases of a three-phase alternating power source, and a second pulse having a pulse width corresponding to a second phase difference between a second pair of two phases of the three-phase alternating power source which is different from the first pair of two phases, and a microcomputer for detecting a third phase difference between the first pulse and the second pulse to judge whether the third phase difference is in a predetermined range, and detecting the miswiring if the third phase difference is judged to be out of the predetermined range.

Abstract: A method and apparatus is disclosed for complete three-phase sensing using two current transformers. Two phases of a three-phase system are used as the primary windings in each current transformer such that each current transformer produces a phasor representation of a sum of the two phases. A three phase sensor is provided to add the phasor representations produced by each of the current transformers and to produce a third phasor representation from the summation. The three phasor representations can then be applied to any conventional overload relay control to monitor each phase and produces a trip signal to open the three-phase system when a phasor representation exceeds some predetermined value, or the magnitudes of the phasors differ by more than a predefined value.

Abstract: A digital decaying current offset correction method and apparatus, in one aspect, separates the requirements of detecting fault existence from the requirements of detecting fault location. Once the decaying offset removal routine is initiated, current and voltage are sampled and, for each current and voltage sample, current and voltage phasors are generated. The current phasor values, which are not offset corrected, may be used to determine whether to trip a breaker. Once the breaker is tripped, the decaying offsets are removed from the current phasors. The offset corrected current phasors are then used to locate the fault.

Abstract: Apparatus for protecting and starting a three-phase motor uses the three-phase field rotation torque produced by three voltage coils, connected to a three-phase power supply, spaced 120 degrees apart from each other, acting on an aluminum disk having a limited range of rotation. When a start button is pushed connecting the voltage coils in wye configuration, the tendency of the disk to turn is converted to an electrical signal for starting the motor. The apparatus prevents the motor from starting if phase energization is abnormal or phase rotation is not in a predetermined direction. The present apparatus also provides continuous monitoring of the motor with three-phase rotation torque produced by three current coils, which are connected in series with the motor and, in one embodiment, may be wound around the same cores as the voltage coils.

Abstract: A method of and apparatus for actuating an automatic transfer switch for disconnecting a motor load from a normal source of voltage and reconnecting the load to an alternate source of voltage at a time when phase differences between the output voltage of the disconnected motor load and of the alternate source voltage are minimized to prevent excessive in-rush currents to the motor upon reconnection. Actuation of the transfer switch is commenced when the difference in phase between the normal source and alternate source is equal to a predetermined number of degrees depending upon whether the alternate source frequency is greater or less than the normal source frequency.

Abstract: A monitor for an ac electrical system generates on-line a display presenting the values, either in magnitude or as a percent of the fundamental, of 50 harmonics of any of the currents and voltages in the system. The display also incudes the phase angle of each harmonic relative to a reference waveform, which is preferably phase A-B voltage or phase A to neutral voltage.

Abstract: A circuit analyzing system includes a current transformer for extracting current from a phase or neutral conductor of a three phase line, a filter connected to the output of the current transformer and functioning to substantially trap current at the fundamental frequency while substantially passing currents at various harmonic frequencies thereof, and signal processing circuitry connected to the output of the filter to perform various functions with the harmonic frequency current input thereto. Among these functions, as shown in various preferred embodiments, are measurement of the harmonic signal in RMS and conveyance of the output to a display instrument for a user or utility's convenience in monitoring harmonic frequency circuits, which have become more corrosion with the advent of electronic equipment having internal power supplies such as personal computers, work stations, printers, and the like.

Abstract: A circuit interrupter including an improved arc detection system which trips the interrupter in response to currents having frequencies and/or characteristics associated with arcing within the associated alternating current electrical system. The arc monitoring circuit determines if the signal produced by a current transducer is the result of arcing. The arc detection system includes two swept filters and associated amplifiers which produce a signal which has an amplitude representative of the frequencies present in the alternating current of the electric system. The portion of the filtered signal which has amplitudes above a predetermined level is integrated to produce a trip signal for the circuit interrupter when the value of the integration exceeds a predetermined limit.

Abstract: A circuit interrupter arrangement for interrupting current in a circuit path includes a hysteresis control circuit arranged to control a power supply charge-accumulation switch and an undervoltage trip-lockout circuit in parallel. More specifically, the arrangement includes a current inducer circuit for inducing a current signal having a magnitude corresponding to the current in the circuit path; an energy accumulator for accumulating a magnitude of energy to cause an interruption of the circuit path; an energy accumulator control circuit controlling the magnitude of energy accumulating; a trip lock-out circuit, responsive to an insufficient magnitude of accumulated energy, for preventing an interruption of the circuit path; and a range control circuit, responsive to the current inducer circuit, for operating a power-related signal between a first level and a second level to control the energy accumulator control circuit and the trip lock-out circuit.

Abstract: Electronic device for thermal protection of a load (M) by cutting off the polyphase power supply to said load, including current transformers (Ti.sub.1, Ti.sub.2, Ti.sub.3) installed on the wires (L.sub.1, L.sub.2, L.sub.3) of the polyphase line supplying power to said load and connected to an electronic processor circuit (3) adapted to generate a command, characterized in that the outputs of the current transformers (Ti.sub.1, Ti.sub.2, Ti.sub.3) are connected to detector means (51, 52, 53) which supply to the processor circuit (3) logic signals the levels of which depend on the direction or the magnitude of the output current of each current transformer.

Abstract: A method and apparatus for detecting high impedance faults and other arcing phenomena in an electrical distribution system. Electrical signals on the distribution system are monitored and a number of frequency components isolated, such as zero-sequence current and voltage, second harmonic voltage, third harmonic current, eighth harmonic voltage and current, and a measure of magnitude of the components are taken over successive data acquisition periods. The measures of the component magnitudes are formed into a pattern for each data acquisition period, and the difference between patterns for successive periods are compared against a pattern threshold which is set to suit the characteristics of the distribution system. A pattern difference greater than the pattern threshold indicates the possibility of an arcing fault, which can then be confirmed by determining whether the frequency components are modulated at twice the fundamental frequency of the distribution system.

Abstract: Voltage comparisons are made for each of the phase-phase voltages on a low side of a distribution transformer in a power system against a threshold, approximately 0.7 nominal secondary voltage, which is less than the value of at least one phase-phase voltage when only one high side fuse has operated. High outputs result when the phase-phase voltages exceed the threshold. At the same time voltage comparisons are made of each of the phase-phase low side voltages and a second threshold, approximately 0.2 nominal secondary voltage, which is substantially less than the first threshold. High outputs result when the voltages are below the threshold. A circuit output is provided which can be used to trip a low side circuit breaker when at least one output of the first comparisons is high and at least one output of the second comparisons is high.

Abstract: The invention relates to a device for controlling a mechanism driven by at least one electric motor (11, 12), said device comprising a circuit (20, 38) for detecting the power consumption of the mechanism and for comparing the detected value with at least one current threshold, with confirmation during a defined time and a circuit (54) for controlling the stopping of the mechanism for a given time, as a function of the result of said comparison.Application more particularly to the field of high-capacity or wide-body aircraft, for the generation of pressure in their hydraulic circuits.

Abstract: A sensor arrangement for producing a signal representative of currents having frequencies and/or characteristics associated with arcing within an alternating current electrical system. The arrangement is coupled to an appropriate arc monitoring circuit which determines if the signal produced by the sensor is the result of arcing within the electrical system. One embodiment of the sensor arrangement includes an inductor, and a capacitor connected in series with the primary winding of a transformer. The inductor is typically connected in series with a phase conductor of the electrical system, and the capacitor and the primary winding are connected to the phase conductor in parallel to the inductor. Another embodiment of the sensor arrangement includes a capacitor and the primary winding of a transformer connected in series between the phase conductor of the electrical system and either a ground or neutral conductor of the system.

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 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 circuit interrupter with a digital trip unit automatically sets the sampling interval appropriate for the 50 Hz or 60 Hz distribution system to which the interrupter is connected. In order to avoid falsely shifting the interval in response to distorted currents, the trip unit only changes the interval if the number of zero crossings of the current within a fixed number of samples is within two zero crossings of the number of zero crossings for an undistorted current of the other frequency for two consecutive time periods in which the fixed number of samples are taken. Furthermore, changes in the interval are only written into an EEPROM for use on power-up a fixed number of times to preclude disabling the EEPROM. In one embodiment, a 2 pole filter is utilized in the zero crossing counting circuit to eliminate false counts from noise originating in a chopper used in the trip unit power supply.

Abstract: A digital signal processor implemented monitoring circuit for detecting phase and magnitude disruptions in multi-phase alternating current input signals. A phase lock loop receives multi-phase alternating current input signals and provides one set of alternating current output signals in phase with a time average of the multi-phase alternating current input signals and provides a second set of alternating current output signals phase shifted in relation to the first set of output signals. In a three phase system the phase lock loop provides six alternating current signals. A demodulation circuit multiplies the first set of output signals from the phase lock loop circuit with the multi-phase input signals to produce demodulated sets of signals. An output circuit coupled to the demodulation circuit sums the first set of demodulated signals to provide a first source quality signal. The second set of demodulated signals is also summed to provide a second source quality signal.

Abstract: A solid state overload relay utilizes an apparatus that converts the current of a polyphase electrical load to a voltage signal approximately proportional to the RMS current of the load. In addition to providing the overload function, the voltage signal is used to provide an improved phase current unbalance protection. Conventional current transformers sense the current flow in each phase of the load. The current waveform for each phase is converted to a voltage by rectification and the peak value and the average value of the resultant voltage is determined. A summing circuit combines the two values at a predetermined ratio to create a DC voltage that is approximately equal to the rms value of the input phase current. A combination of the approximation circuit with a time integrating circuit and a level detecting circuit produces a low cost solid state overload relay in one embodiment of the invention.

Abstract: A circuit for detecting phase imbalance in a three phase electrical system. The circuit includes a three phase current transformer or three separate current transformers for monitoring the current flowing in each phase of a three phase electrical system. The current transformers provide an induced current proportional to the monitored current. The induced current passes through a full-wave bridge rectifier which produces a voltage output proportional to the induced current. This voltage signal is passed to a two pole Sallen-Key filter which allows a desired signal having a particular frequency range to pass through and blocks the passage of an undesired signal having a particular frequency range. A scaling circuit then receives a portion of the desired signal and produces a scaled average signal which is of a preselected magnitude lower than the desired signal.

Abstract: A circuit analyzing system includes a current transformer for extracting current from a phase or neutral conductor of a three phase line, a filter connected to the output of the current transformer and functioning to substantially trap current at the fundamental frequency while substantially passing currents at various harmonic frequencies thereof, and signal processing circuitry connected to the output of the filter to perform various functions with the harmonic frequency current input thereto. Among these functions, as shown in various preferred embodiments, are measurement of the harmonic signal in RMS and conveyance of the output to a display instrument for a user or utility's convenience in monitoring harmonic frequency circuits, which have become more common with the advent of electronic equipment having internal power supplies such as personal computers, work stations, printers, and the like.

Abstract: An apparatus and method for protecting an induction motor from momentary power loss in a three-phase, alternating current, power supply. The apparatus includes a circuit for detecting when the motor switches from a mode of operation as a motor to a mode of operation as a generator, and a microprocessor connected to the detector to receive the detection of a switch in mode of operation, and for generating a fault disconnect signal in response thereto to initiate disconnecting the motor from the power source. The method includes the steps of detecting when the motor switches from a mode of operation as a motor to a mode of operation as a generator and generating a fault disconnect signal in response thereto to initiate disconnecting the motor from the power source. The apparatus and method provide for robustness of the fault detection data, and for avoiding false detections of momentary power loss.