Abstract: A protective thermal relay comprises a main heater for heating a snap-action element of a bimetallic switch to open the switch. The main heater is connected in series with the motor or other device to be protected by the relay. There is also an auxiliary heater for the bimetal element that is energized through an abnormal condition detection relay, e.g., a negative phase sequence detector, when the abnormal condition occurs. The auxiliary heater is a positive temperature coefficient type and will heat and hold the switch in the motor off mode as long as the negative phase sequence or other abnormal situation remains.

Abstract: Negative sequence filters employing one to three operational amplifiers and a single reactive element generate the negative sequence voltage of a three phase AC power system by generating two line-to-line voltages, phase shifting one of them to bring them into phase and summing the resultant signals. The phase shifting circuit includes a potentiometer, one end of which serves as the input to the circuit and the other end of which is connected to the inverting input of an operational amplifier. A capacitor is connected between the tap point of the potentiometer and ground and the values of the components are selected so that the tap point of the potentiometer can be positioned to compensate for variations in the capacitive reactance of the capacitor without affecting the magnitude of the phase shifted signal.

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: Sequence network circuits are provided for use in three-phase protective relaying applications. In one embodiment, the circuit includes input circuit means for receiving input signals, one of which comprises a reference input signal, and signal processing means for processing such input signals. The signal processing means includes an operational amplifier and a single capacitor. A plurality of resistors couple the input signals to the operational amplifier. The value of the resistors and the capacitor are selected such that the output signal of the operational amplifier is representative of the quadrature voltage, relative to the reference input signal, and shifted 90.degree. lagging with respect to its normal phase position. 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: A network protector relay produces a close signal entirely from sequence components based on the magnitude and phase relationships between the positive sequence component of the phase-to-ground voltages on the network side of the protector and the positive sequence component of the phasing voltages. The close signal may be inhibited by either the presence of the negative sequence component of the phase-to-ground voltages on the network side of the protector or if a trip contact is closed. The trip contact will be closed under certain specified conditions which make it advantageous to prevent manual closing of the contacts.

Abstract: Pilot protective relay apparatus for high-voltage, three-phase alternating current transmission lines which provides the functions of an electromechanical pilot-wire protective relay, without the necessity of having a continuous, metallic conductor connected between the points to be compared. The protective relay apparatus is completely solid state, making trip decisions based upon three separate comparisons of the near and far line current conditions represented by line current derived single-phase voltage signals. The three comparisons indicate the magnitude of the phasor difference, the magnitude of the phase angle, and the relative average absolute magnitudes.

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: Protective relay apparatus which includes monitoring and detecting functions related to subsynchronous currents in a three-phase electrical power system. The monitoring function provides signals related to the positive sequence component of any subsynchronous current flowing at a monitored subsynchronous frequency. The detecting function is responsive to the signals provided by the monitoring function, distinguishing between subsynchronous currents due to self-excited oscillations, and those due to transient oscillations, to provide a timely trip signal for a circuit breaker in either instance.

Abstract: A phase unbalance detecting system that includes also low-voltage detection and wrong-phase-sequence detection. The system can be packaged in a small volume because it is a solid state type that uses a minimum of electronics and does not require transformers for obtaining signals from the several phases of the plural-phase power line but only one transformer for the D.C. power supply circuit for the detection system. The system incorporates means for allowing it to be used at 50 or 60 Hz without separate adjustment, for making it insensitive to noise and harmonics of the power line, and for providing a good estimate of the negative sequence voltage caused by a phase unbalance. It provides external terminals whereby it can be adapted for use at different power line voltages.

Abstract: A circuit for detecting whether, or not, a three-phase load is correctly connected to a three-phase supply employs an inductance, capacitor and resistor connected in the three branches of the load circuit so as to generate a single phase output signal when connected to the supply, to voltage of the signal depending upon the connection to the supply. The circuit requires only three wires and not connected to a ground, or neutral. The output signal controls a reversing switch to ensure that the load is always automatically connected correctly; in a preferred form only one of the voltages is sufficient to light a source of radiant energy to activate a sensor to energize the reversing switch.

Abstract: A method and apparatus are disclosed for accurately determining negative sequence current in a three-phase turbine-driven generator, the currents indicative of power oscillations and of torques harmful to turbine buckets. A signal conditioner and phase-shifter network are described which provide precise amplitude and phase angle adjustments and null balancing features which permit accurate determination of the magnitude of negative sequence current even though this current is a very small quantity determined as the difference between two large signals.

Abstract: The circuitry for generating filter excitation signals from a multi-phase alternating current input is provided with the following circuitry for each phase of the multi-phase alternating current input. A current transformer connected to a respective phase of the multiphase alternating current input is connected to a bridge rectifier having one node connected to a neutral conductor and including a resistor of equal resistance value connected in each parallel branch of the bridge rectifier between the neutral conductor and the input of the current transformer. An operational amplifier having inputs respectively responsive to the voltage across each of the respective resistors in the bridge rectifier generates an output for one phase of the excitation signal to the filter. The filter excitation circuitry has application to two-phase and three-phase systems wherein the excitation circuitry is identical for each phase.

Abstract: A symmetrical component sequence filter which provides a signal responsive to a predetermined sequence quantity of an electrical power system, while using only one phase shift other than 180 degrees. A single reactive element provides the phase shift. A single adjustable resistor calibrates the filter when the reactive element is non-precision. Selecting a precision reactive element eliminates even the single adjustment. The symmetrical component sequence filter enables both a positive and a negative sequence component to be simultaneously derived from common processing circuitry, requiring only one additional reactive element.

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: This protective relay circuit responds to interphase faults on a three-phase power line by causing a circuit breaker connected in the power line to be tripped three-pole in response to interphase faults, but does not respond to a single line to ground fault, allowing a single pole to be tripped for this latter type of fault.

Abstract: In a phase monitoring arrangement for a three phase network which supplies a controlled d.c. motor through a controlled converter, a power line dependent discriminator along with R-C circuits forms a smoothed, rectified monitoring voltage which depends on the phase sequence and is sensitive thereto and to phase failure along with a supplementary monitoring voltage dependent only on phase failure, the rectified monitoring voltage and supplementary monitoring voltage being supplied to an evaluating circuit comprising differential comparing amplifiers at which the monitoring voltages are compared with constant reference voltages independent of faults and the output thereof used to control switching means and a current regulator so that in the event of incorrect phase sequence or of a phase failure, the switching means feed a blocking signal which suppresses firing pulses to the controlled converter and the current regulator feeds a control signal to control the converter to its operating limit.

Abstract: A filter, energized by a polyphase power source, is adapted to detect positive or negative sequence components present in the source. Means are provided for summing a first phase quantity with a second phase quantity which has been shifted by 180 electrical degrees. Additional means are utilized to phase shift the summed resultant itself by 120 electrical degrees and to sum the phase shifted resultant with the phase shifted second quantity and a third quantity. The second summation yields an output quantity proportional to only one of the sequence components, if any, present in the polyphase source.BACKGROUND OF THE INVENTIONThis invention relates to active symmetrical component sequence filter networks and, more particularly, to an economical filter network of such type. In the electrial art, especially that concerned with protective relaying, it is desirable in many instances to detect the presence and magnitude of the positive, negative and zero sequence components of a polyphase power source.

Abstract: A digital firing control for a three-phase full wave silicon controlled rectifier converter. An error signal, in digital form, representing a desired change in firing angle which is a function of the difference between the current being supplied by the converter and a desired current, is utilized to advance or retard the firing angle of the SCR's as required to eliminate the error. Each subsequent firing command is referenced on a time basis from the firing command of the previously fired SCR in the firing sequence rather than being referenced from the zero voltage point of the alternating current supply voltage. The error signal is averaged over the time interval between firing commands so that the control responds to the average difference between the current being supplied and the desired current.

Abstract: A protection circuit for use with circuit breakers for electrical apparatus operated by multiple phase, alternating current power systems characterized by a plurality of electrical distribution lines for transmitting electrical energy, with the electrical energy in the lines having a spaced phase relationship. The protection circuit includes a first sensor coupled to the lines for detecting an undesirable phase imbalance between two or more of the lines, and for detecting a low voltage on one or more of the lines, and initiating a first signal responsive to either or both of these conditions. The protection circuit also includes a second sensor coupled to the lines for detecting a phase reversal between two or more of the lines and initiating a second signal responsive thereto. A circuit breaker operating circuit is coupled to the second sensor for operating the circuit breaker responsive to the second signal.

Abstract: A detector for a dynamic phenomenon with a cyclically varying condition, as motion of a rotating part. At least three digital sensors are separated in phase with respect to the cyclic condition. The instantaneous outputs of the sensors have a plurality of repeating sequential states so long as the dynamic phenomenon exists. The instantaneous outputs of the sensors have at least one state which does not occur during existence of the dynamic phenomenon but which does occur in the absence thereof. Logic circuits respond to the digital sensor outputs and detect information about the dynamic phenomenon. Detection of the repetition rate of an instantaneous output state of the sensors provides a measure of speed. An absence of rotation is indicated by the occurrence of another output state. In another disclosed embodiment, the detector monitors a three phase power system and detects a phase outage by the occurrence of an abnormal sensor output state.

Abstract: A method and means of interrupting multiphase supply current to selected electronic equipment at selectable phase angles, and restoring said supply again at preselected phase angles, in order to test and study equipment performance under controlled interrupt-restore conditions.

Abstract: Motor protector apparatus for independently sensing the respective positive, negative, and zero sequence currents flowing in the supply lines to a three phase motor for interrupting power to the motor whenever such positive, negative, or zero sequence components reach levels indicative of abnormal operating conditions. The protector network includes bridge means for segregating the negative and positive sequence components, indicators for visually displaying the source of the abnormality, and means for restoring power to the motor after a defined time period.

Abstract: Sequence analyzers or wave filters having resistance and capacitance elements only, for providing output signals having a magnitude proportional to the magnitude of the positive or negative sequence symmetrical component of a three-phase power source. By eliminating the need for inductors or transformers substantial reductions in size, weight and cost are realized. Four, five and eight element embodiments are disclosed, the latter providing an output referenced to the power system neutral.

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.

Abstract: Motor protector apparatus for independently sensing the respective positive, negative, and zero sequence currents flowing in the supply lines to a three phase motor for interrupting power to the motor whenever such positive, negative, or zero sequence components reach levels indicative of abnormal operating conditions. The protector network includes bridge means for segregating the negative and positive sequence components, indicators for visually displaying the source of the abnormality, and means for restoring power to the motor after a defined time period.