Abstract: Monitoring and control of analog electromechanical protective relays and digital mcroprocessor based relays is integrated through a system including slave stations which record and time tag contact activity at each of the analog relays. The slave stations continuously retain digital samples of a predetermined number of the most recent cycles of the currents and voltages at the analog relays and when a trip occurs store the retained samples as pre-fault values together with a preset number of post-fault samples. A master station communicates with the slave stations monitoring the analog relays and with the digital relays through a two way communications network. The master station repetitively polls the slave stations and digital relays for contact activity. Detailed data such as the time tags and pre-fault and post-fault currents and voltages are then requested from those stations reporting contact activity.

Abstract: A rotating disc electromagnetic relay has an operating element which applies a torque to the disc tending to close the main contacts and a restraint element generating a torque which together with a spring tends to open the relay contacts. The operating and restraint elements each have an E-shaped core defining two magnetic circuits with a common center leg. Two voltages to be compared are applied to two input coils on the center leg of each element in the same sense to generate a flux representative of the sum of the voltages in the operating element and in the opposite sense to produce a flux representative of the difference between the two voltages in the restraint element. The flux in the common leg of each element divides between the two magnetic circuits. The flux in one magnetic circuit of each element is shifted in phase by a first lag coil on an outer leg of the core to generate the opening and closing torque, respectively.

Abstract: The square wave phase comparison signals generated for each phase of a power distribution system by phase comparison relays at each end of a protected three phase transmission line segment are combined to generate a single, multi-level signal with discrete values for each instantaneous combination of square wave signals. The single, multi-level signal is used to modulate a carrier signal which is transmitted over a single channel of a two-way communications link to the other terminal where the carrier signal is demodulated to reproduce the multi-level signal. The reproduced multi-level signal is then decoded to generate remote square wave signals which are compared with the phase of locally generated square wave signals to generate trip signals for circuit breakers at the respective terminals. Square waves representative of priority functions, such as direct transfer trips, can be integrated into the single, multi-level signal transmitted to the other terminal.

Abstract: The multiplexer in a multichannel, secure digital communication system repetitively embeds a sequence of byte length uniquely coded synchronizing signals in each of n successive frames of one channel of a multichannel, time multiplexed digital bit stream. Redundant protective relay data and associated parity check data are embedded in four of the n frames in a second, preferably adjacent channel, with the remaining of the n frames in the second channel containing additional of the uniquely coded synchronizing signals. The time multiplexed serial bit stream is transmitted to a remote station, preferably by fiber optic communications media. The most recent bits of the received serial bit stream equal in number to the number of bits spanned by the two channels in n frames are retained in n-1 serially connected serial in, serial out shift registers. Sixteen bit portions, a frame apart, of the retained most recent bits of the serial bit stream are applied to n serial in, parallel out shift registers.

Abstract: An electronic protective relay which offers a very sensitive detection of a reverse power condition of a three-phase alternating current generator for the protection against generator motoring is disclosed. A current signal is generated from a current transformer coupled to one phase of the ac generator; and a voltage signal is generated from a potential transformer coupled across the one phase and another phase of the generator. A current input circuit is operative to maintain the phase angle between the voltage and current signals over a wide variation of input current, e.g. from one milliamp to 75 amperes. In addition, a phase-rectification type multiplier affords a relatively simple, but effective method for detecting the power flow direction of the generator. Once the power flow is determined to be in the reverse direction and above a preselected magnitude, a signal indicative of a potential generator motoring condition is geneated.

Abstract: Active pilot wire apparatus for replacing a passive continuous metallic wire pair coupling between the electromechanical units of a conventional electromechanical pilot wire protective relay is disclosed. For the protection of a power line section, an electromechanical unit is coupled to each end thereof. Each electromechanical unit includes an operating relay coil which when energized operates breaker contacts to interrupt current through the protected power line section. A signal representative of the potential across the operating coil of each electromechanical unit is transmitted through an active communication channel to the other electromechanical unit where it is buffered by a high impedance amplifier. In each case, the output signal of the buffer amplifier is representative substantially of the corresponding operating relay coil potential. An impedance element is coupled between each buffer amplifier and the other operating relay coil.

Abstract: Direct transfer trip apparatus for sharing a common active communication channel utilized for signal transfer between at least two electromechanical units which form a current differential protective relay for protecting at least one power line in a power system network is disclosed. Each electromechanical unit includes an operating relay coil for effecting an interruption of current through the protected power line when an internal fault of the power line is detected. The direct transfer trip function induces signals to be transmitted through the common active communication channel either upstream or downstream from a faulted power line section where a breaker has failed to open. These direct transfer trip signals are supplied directly to an upstream or downstream breaker unit to operate the breaker to interrupt current through the faulted section independent of the energization of its corresponding operating relay coil.

Abstract: A signal quality monitor, and a protective relay system using the monitor, which utilizes both AC and DC signals from the receiver agc stage to monitor a plurality of different signal parameters. A signal responsive to the noise in the communication channel which transmits at least one of the protective relay signals used in a protective relay comparison function, is also used in the trip circuits of the associated circuit interrupter to continuously adapt or modify the trip level in response to channel noise.

Abstract: A new protective relay for determining the occurrence of a single-phase-to-ground fault and tripping the appropriate circuit breaker. At local and remote terminals of a protected line segment, three signals representative of an electrical parameter on each phase conductor are input to a local and remote protective relay. In both the local and remote protective relays, the three electrical parameter signals are manipulated to produce two evaluation signals. The two local evaluation signals produced in the local protective relay are transmitted to the remote protective relay, and the two remote evaluation signals produced in the remote protective relay are transmitted to the local protective relay. In the local protective relay the two local evaluation signals are manipulated to produce a third local evaluation signal, and the two remote evaluation signals are manipulated to produce a third remote evaluation signal.

Abstract: A signal quality monitor, and a protective relay system using the monitor, which utilizes both AC and DC signals from the receiver agc stage to monitor a plurality of different signal parameters. A signal responsive to the noise in the communication channel which transmits at least one of the protective relay signals used in a protective relay comparison function, is also used in the trip circuits of the associated circuit interrupter to continuously adapt or modify the trip level in response to channel noise.

Abstract: A demodulator for demodulating alternating signals modulated by pulse modulation, or by frequency modulation. The demodulator requires only a single constant current source, a single ramp voltage producing capacitor, and a sample-and-hold function. The intelligence contained in the modulated carrier is transformed into a first pulse train, and a second pulse train is produced in response to the first pulse train. The first pulse train samples and holds the ramp voltage, and the second pulse train immediately resets the ramp voltage circuit following each sample. The held voltage is a replica of the modulating signal, produced without the use of filters for removing the carrier.

Abstract: In a motor-generator set, the frequency of the AC generator outputted voltage is automatically adjusted by field winding regulation of the DC motor, through a closed loop in which a dual-slope converter is charged during a clock-defined time interval in accordance with a potentiometer setpoint, and the charging plus discharging period of the dual slope converter encompasses the period of the outputted voltage.

Abstract: A protective relay for protecting a power system from sub-synchronous current oscillations. The protective relay determines both the amplitude and frequency of sub-synchronous current oscillations occurring in the power system. A series of logic relationships, based in part on the parameters of the power system, are implemented by the protective relay such that when the frequency and amplitude of the sub-synchronous oscillation signal satisfy these relationships a trip signal is produced.

Abstract: Protective relaying apparatus of the pilot type, incorporating a direct transfer trip function (DTT) which reliably and securely utilizes the same communication channel utilized by the pilot relaying function. The DTT function operates within the constraints of a PPM modem, utilizing a signal extracted from the carrier signal, to provide a perfectly synchronized tone for the DTT signal.

Abstract: A self-starting, non-latching, pulse modulator which will function as an analog divider of first and second input quantities, or as a linear pulse period modulator responsive to one of the quantities, or as a linear pulse frequency modulator responsive to the other of the quantities, depending upon how the first and second input quantities are controlled. The first input quantity is connected to charge a capacitor. The second input quantity is compared in a first comparator with the voltage across the capacitor. A second comparator compares the voltage across the capacitor with a reference voltage. The outputs of the first and second comparators are connected, respectively, to the first and second inputs of a flip-flop which has its first output connected to a monostable multivibrator. The second output of the flip-flop and the output of the monostable multivibrator are both connected so that either one can momentarily activate a discharge circuit for discharging the capacitor.

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: An electrical device for protecting an alternating current network in which a static inverse time-overcurrent relay obtains network current information and relay circuit operating power from a current transformer having two secondary windings. Low transformer burden and accurate network information signals that are linearly responsive to a wide range of network current magnitudes are achieved through the use of a switching circuit that prevents the simultaneous operation of both secondary windings. The relay circuit employs an RC network with a short, precision time constant for curve shaping and employs digital counting techniques to provide time delay multiplication, precision time scale selection and a variable delay time variable in accordance with the magnitude of system current.

Abstract: Protective relay apparatus for developing signals responsive to subsynchronous current oscillations in a three-phase electrical power system, and for analyzing the signals to determine when corrective action is necessary. The positive sequence component of a subsynchronous current oscillation is developed via a summing arrangement, which eliminates the need for sequence filters. The positive sequence component of a subsynchronous current oscillation is processed to determine if it is an electrical transient which would shock the mechanical system of a turbine generator, or machine, to be protected, into mechanical resonance. It is also processed to determine if it is due to a growing mechanical oscillation of a turbine generator, such as might be initiated by a change in a parameter related to the turbine generator.

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.