Abstract: A synchronism check relay includes both a high set and a low set slip cut-off circuit. The low slip cut-off setting is based upon the maximum slip frequency that can be tolerated and still allow reclosing. The high slip cut-off setting is a function of the maximum phase angle difference permissible between the voltages on the bus and line sides of the circuit breaker, and the time that the line is de-energized.

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: An overload-sensing circuit for an electric motor driven by an alternating signal comprises a supply line connecting the motor to a power source, a resistance in the supply line, and a first comparator for measuring the phase relationship between the power source voltage signal and the motor current signal. A variable resistor is employed to select a phase relationship which represents a load limit for the motor. A second comparator compares the measured phase relationship to the selected phase relationship and produces a signal representing an overload condition of the motor when the measured phase relationship generally equals the selected phase relationship.

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: 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: A characteristic timer for a protective relay utilized as part of a system that provides protection for a portion of a high voltage transmission line is disclosed. The characteristic timer provides a time-base for measuring the duration of a signal developed by the protective relay indicative of a normal or an abnormal condition related to the protective portion of the high voltage transmission line. The characteristic timer is comprised of digital devices, such as; programmable counters for preselecting the frequency related limits to which the developed signal is compared, counters that monitor the duration and presence of the developed signal, and a shift register that controls the resetting of the characteristic timer. If the developed signal is disrupted for a predetermined time the shift register resets the digital devices and awaits for the reoccurrence of the developed signal for a revised determination of its time duration.

Abstract: A water pump protector which includes electrical circuitry through which an electric motor is energized. The electric motor operates a water pump. The circuitry senses the phase angle between the voltage and the current applied to the electric motor. When the phase angle indicates that the motor is operating without a load, the circuitry deenergizes the electric motor. Thus, the water pump is protected against damage which may occur when the water pump is operated without pumping water.

Abstract: A protective relay system for providing pilot protection for two and three terminal alternating current transmission lines, which system does not require a continuous metallic circuit between the relaying points. The evaluation circuit develops operating and restraining quantities, modified by a predetermined constant which determines the operating characteristic of the relay system.

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: Phase line currents of a polyphase power supply are rectified and applied to a common input terminal of a sine wave detector circuit to sense the presence of a signal current that is injected from a low voltage DC source into any time gaps that are formed between phase currents only when one or more phase line failures occur. Failure of the DC source disables the detector circuit.

Abstract: A solid-state load protection system whereby a poly-phase alternating current system is monitored enabling a loss of phase feature to be used. A current sensing function is utilized so as to produce an output signal which is related to the current in an electrical circuit. Attached to the current sensing function are two capacitors each having their own signal path so as to have different charging and discharging rates. During a loss of phase condition, one capacitor discharges more quickly than the remaining capacitor with the result that the voltage across the quickly discharging capacitor, which during normal conditions is greater than the remaining capacitor, now becomes less than the remaining capacitor. A loss of phase sensing function detects this difference in potential levels thereby initiating a trip signal to the output function.

Abstract: A system for identifying which of the phases of an N-phase electric-power transmission network has experienced an electrical disturbance. For each phase there is produced a first signal representative of the transient variations of an electrical parameter of the respective phase, or of a linear combination of at least two of these parameters. A set of N second signals is generated from the product of two linear combinations of at least N-1 signals selected among the first signals. The sum of all coefficients for each linear combination is set to zero, with each of the second signals being related to a given phase. Each of the second signals is then integrated to produce a set of N third signals associated with the respective phases. A fourth signal is generated by combining all of the N first signals in a symmetrical manner with respect to all of the first signals, such that the fourth signal is independent of the associated phases.

Abstract: In polyphase AC load circuits, the current of each phase, which varies over a wide range, is led out to detect the unbalances of currents in the respective phases at arbitrarily adjustable predetermined unbalance factor by stationary-type device. The DC voltages (E.sub.U to E.sub.W) corresponding to the currents in the respective phases are divided into forward constant-voltage elements (D.sub.1 to D.sub.3) and passive voltage varying elements (VR.sub.1 to VR.sub.3). The voltages at the elements (VR.sub.1 to VR.sub.3) are defined as current comparison voltages (e.sub.1 to e.sub.3), and the voltages (E.sub.U to E.sub.W) in the respective phases are reduced by level adjusting circuits (LA.sub.1 to LA.sub.3) to reference level voltages (e.sub.U to e.sub.W). Both voltages (e.sub.U to e.sub.W) and (e.sub.1 to e.sub.3) are applied to the positive and negative terminals of the same elements (D.sub.4 to D.sub.6) to thus form an unbalance detecting circuit.

Abstract: A percent unbalance or ratio ground relay which detects open phase conductors on electrical distribution circuits, as well as single-phase-to-ground faults regardless of fault impedance, by providing an operating quantity responsive to zero sequence current, and a restraining quantity responsive to a pre-fault balanced phase current minus the zero sequence current. This restraint torque arrangement causes the relay to operate on true ratio unbalance, regardless of load.

Abstract: Ratio ground induction disc relays for detecting open phases and phase-to-ground faults. An operating torque is applied to the induction disc which varies as a function of the zero sequence current. The phase currents are utilized in different arrangements to provide a restraining torque which varies as a function of predetermined different parameters, such as the sum of certain phase currents, the positive sequence current, or the positive sequence current minus the negative sequence current.

Abstract: A ratio ground induction disc relay which detects open phase conductors on electrical distribution circuits, as well as single-phase-to-ground faults regardless of fault impedance, by providing an operating quantity responsive to zero sequence current, and a restraining quantity responsive to the positive sequence current I.sub.1 minus the negative sequence current I.sub.2. The restraint quantity is provided by an electromagnetic having first and second outer legs and an inner leg. Electrical windings are disposed on only the first and second outer legs, arranged and energized by the three phase currents to provide equal length flux paths, and thus equal torques, regardless of the faulted phase.

Abstract: A solid state overload relay protective apparatus for electric motors which includes not only the overload feature, but the additional features of underload and single phase protection. Small current transformers for sensing the current flow in each phase of the motor are utilized, like those found in the ground fault sensing art because a current-to-voltage converter circuit reflects a short circuit back to the secondary of the transformers. The signal from the current transformers which is proportional to the sensed current in the motor is fed through the converter, a scaling and summing amplifier adjustable for a wide range of motor full load currents, an ideal diode peak detector, a time integrator amplifier, to one input of a comparator circuit having a trip reference voltage signal at another input. The comparator provides an output signal to a transistorized trip level circuit that deenergizes a coil of an overload relay opening its contacts and interrupting power to the motor.

Abstract: The invention relates to a memory circuit in a relay protection device with a phase-locked loop, a monitoring circuit and an updating circuit. When a fault detector, a phase-change detector and/or an amplitude-change detector monitoring an a.c. network to which the protection device is connected supply an output signal indicative of a fault in the network, no updating of a storing member in the loop takes place.

Abstract: A distance protective relay employing phase angle comparator measurement is provided with an improved polarizing signal. In one embodiment, a phase distance relay is provided with a two-component polarizing signal which includes one component representative of a faulted transmission line voltage and a second component representative of the product of a predetermined constant and the positive sequence component of the faulted transmission line voltage. One preferred polarizing signal for a phase AB phase distance relay is V.sub.POL =V.sub.AB +KV.sub.AB1, where K is approximately 0.3. Such a polarizing signal results in improved relay operation under certain fault conditions, especially under steady state conditions. In another embodiment, a ground distance relay is provided with a two-component polarizing signal. For, example, one preferred polarizing signal for a phase A ground distance relay is V.sub.POL =V.sub.A +KV.sub.AJ, where K is approximately 0.3. Other embodiments are disclosed.

Abstract: Electrical apparatus to monitor electrical three-phase power includes circuitry to protect three-phase equipment from excessive variations in line voltage, phase to phase unbalance, and reverse phase sequencing; to protect personnel against automatic restart of equipment at return of line power; and protect power sources against overload at return of line power, after power interruptions.

Abstract: There is disclosed apparatus for detecting phase unbalance in a 3-phase electric power system and initiating protective shutdown for motors or other loads in the system which includes a 3-phase rectifier, a peak voltage measuring circuit, a comparison circuit for comparing each phase maximum with a predetermined proportion of the peak voltage and generating a pulse whenever a phase maximum exceeds the predetermined proportion of the peak voltage, a missing-pulse detection circuit receiving the pulses, a fault circuit producing a fault signal in response to a signal from the missing-pulse circuit, a delay circuit responsive to the fault circuit and a visual indicator and relay for indicating a persistent phase unbalance fault and initiating protective action.

Abstract: A technique for detecting high impedance faults on solidly grounded, wye connected distribution circuits is disclosed herein. This technique bases its detection on the status of the third harmonic current component in each three-phase line current of the distribution circuit and specifically by the change in the phase of any one of the components during a period when the phases of the other third harmonic components remain unchanged. AT the same time, the technique disclosed herein discriminates between high impedance faults and many of the normal system disturbances such as capacitor switching, line switching, fuse blowing and others.

Abstract: An electronic sensing circuit monitoring the voltage on each of two alternating current power lines indicates when a load may be transferred from one of the power lines to the other without generating undesirable transient voltages or currents in the load.

Abstract: A distance-selective short-circuit monitoring device with a low response time (FIG. 3, FIG. 5) results from sequence detection of first and second monitoring signals (US.sub.1, US.sub.2) which are selectively allotted to the zero cross-overs of detection signals (Ud.sub.1 -Ud.sub.4) which determine a polygonal triggering zone, the selective allocation being in accordance with the sign of the signal change rate, and by counting the alternations between first and second monitoring signals (US.sub.1, US.sub.2) within a predetermined monitoring interval (Tu), the duration of which corresponds at least approximately to a half-period of the mains frequency.

Abstract: A method of, and apparatus for, the distance-selective monitoring of faults at electrical lines by means of a quadrilateral trigger or trip region. There are formed at least two reference signals of at least approximately the same phase and from each of these reference signals and the line voltage there is formed a respective difference signal. Each difference signal experiences a separate comparison with a related threshold phase angle in order to determine whether the monitored fault lies within or without the trip region.

Abstract: A method of monitoring open phase, phase reversal and voltage unbalance conditions in a polyphase source includes shifting the phase of signals which are proportional to the line voltages in a three-phase A.C. power source by 180.degree., +60.degree., and -60.degree., respectively, and summing the phase-shifted signals to generate a signal which is proportional to the negative-sequence component of the three-phase line voltage. This signal is rectified and compared with a reference signal. If a net negative-sequence signal is generated over a sufficient time period a positive output signal decreases until it crosses a switching threshold to disconnect a load from the source. The output signal will not rise again to the switching threshold, thereby allowing reconnection of the load, until the negative-sequence signal subsides and is less than the reference signal. A circuit is disclosed with three operational amplifiers and two passive filters to carry out the invented method.

Abstract: Open conductors in an electric power distribution system are detected by sensing the abrupt change in balance of transformer magnetizing current among phases, particularly the third harmonic of the power system frequency. The current is sensed in each phase and the absolute magnitude of the third harmonic current is compared among the phases. When imbalance exceeds a predetermined value, a signal is produced.

Abstract: A method of, and apparatus for, monitoring the run-up to speed of asynchronous motors which are turned-off within a permissible blocking or cutoff time of the motor when the speed run-up is improper, wherein after turning-on the motor there is determined a first value of an electrical magnitude which is dependent upon the phase angle between the motor current and the motor voltage after expiration of a first time-delay following turning-on of the motor, and there is then determined a second value of said electrical magnitude after expiration of a second time-delay following the turning-on of the motor. Both the first and second values are compared with one another, and the motor is turned-off when, following such comparison, there is present a magnitude indicative of improper run-up to speed of the motor.

Abstract: The timer circuit includes ramping circuit means for producing a substantially linear ramping voltage output signal. Control circuit means is provided for receiving a timer input signal and controlling the ramping circuit means wherein the presence of the timer input signal causes the ramping voltage output signal to ramp with a positive slope. Level detector circuit means is coupled to the ramping voltage circuit means to receive the ramping voltage output signal and to produce a level detector output signal when the positively ramping voltage output signal is of a predetermined threshold. The level detector output signal continues as long as the timer input signal continues and is coupled back to the control circuit means. The presence of the level detector signal develops a truncating signal which causes the positively ramping voltage output signal to truncate. When the timer input signal terminates, the ramping voltage output signal ramps negatively and the level detector signal terminates.

Abstract: A ground distance relay employing phase angle comparator measurement is provided with additional input signals. In one embodiment, a two input ground distance relay is provided with two additional input signals. In this embodiment, the first two input signals comprise an OPERATE SIGNAL of the form IZ-V and a POLARIZING SIGNAL of quadrature shifted form. The third input signal comprises a #2 POLARIZING SIGNAL which is related to the zero sequence voltage at the relay. The fourth input signal comprises a CURRENT SUPERVISION SIGNAL which is related to the zero sequence current at the relay. These four input signals are directed to coincidence and timer circuitry. The presence of these four inputs provides improved relay security against undesirable relay operation for several existing problems. For example, additional security is provided for situations in which a single line to ground fault occurs at or just beyond the relay balance point where fault resistance may cause undesirable relay operation.

Abstract: A three-phase rectifier utilizes three feedback controlled ferroresonant regulators to convert a three-phase signal into a regulated DC voltage. A monitoring circuit is included which responds to a signal loss at any input phase to actuate an alarm signal.

Abstract: A thyristor fault-detecting apparatus comprises a thyristor bridge with A.C. terminals connected to a three-phase A.C. power supply and having six thyristor arms, and an inductive load connected to D.C. terminals of the bridge. Each of the A.C. paths has a saturable reactor with an output winding so set as to be excited by the line current within the range from .pi./3 to 2.pi./3 (rad). Output voltages of the reactors are rectified and added, so that a fault in the thyristor is detected by the disappearance of the added output.

Abstract: An out-of-step relay for an alternating potential electric power transmission line is disclosed wherein the decision to trip is determined by the rate of change of the phase relationship of the voltages at the remote and local ends of the transmission line as well as by the magnitude of the phase difference of the remote and local voltages. More particularly, there is described a pair of AND networks which provide two timing signals proportional to the phase difference of the voltages and a pair of timing devices; one of said devices timing the difference in the time of the two timing signals to establish the rate of change of the phase relationship and the other of said devices timing the sum of the two timing signals to establish a signal which is representative of the magnitude of the phase relationship.

Abstract: Phase comparison relaying apparatus associated with the local and remote end terminals of a protected line section wherein the phase comparison is performed at one terminal by unsupervised circuitry to generate an echo trip signal which is employed to effect breaker tripping at the other terminal. Additional circuitry supervises the generation of a breaker trip signal for use at the terminal where the echo trip signal is generated without preventing generation and transmission of the echo trip signal.The use of such circuitry is described in the operating context of phase comparison relaying apparatus adapted to utilize offset keying. Also described is the effectiveness of such circuitry during open breaker or zero-feed conditions.

Abstract: A circuit interrupter responsive to ground-fault conditions is disclosed that is rendered relatively immune to many possible failures of components and connections. A differential current transformer has a pair of differential primary windings in series with the conductors of the protected load circuit (or a ground-fault-current primary winding in a modification), and a secondary winding in control of an AC-energized SCR that controls a "hold-in" coil of a circuit interrupter, and an AC - excited biasing winding. The arrangement is such that, in the absence of ground fault current, the hold-in coil is energized, whereas in case of a ground fault the AC biasing flux is opposed so as to be cancelled or reversed, releasing the circuit interrupter for opening.

Abstract: A protective relay circuit. An electrical system signal quantity is monitored and applied to a filter and to a bipolar threshold device in parallel with the filter. The bipolar threshold device has a zero output signal level as long as the magnitude of the monitored signal is less than some predetermined value. When the monitored signal exceeds the predetermined value, the output of the bipolar threshold device will be substantially equal to the monitored signal level minus the predetermined value. The output of the filter and the output of the bipolar threshold device are combined in a summing amplifier to provide a signal for controlling the trip coil of a circuit breaker. When the circuit is used in an overcurrent or overvoltage protective relay, the combined signal is rectified and applied to a level detector which provides the signal for controlling the trip coil of the circuit breaker.

Abstract: A phase imbalance logic module for a solid state motor protection system for a three-phase motor. Three-phase line currents are converted to corresponding voltages and rectified. The resultant output voltage is a poorly regulated DC voltage having a ripple of approximately 4% during normal operating conditions. In the event of a phase failure, even if not total, the corresponding ripple percentage increases. The phase imbalance logic network senses ripple and provides an output signal to trip a protective circuit breaker if the component of ripple becomes significantly large.