Showing papers on "Relay published in 1992"

A real time digital simulator for testing relays

Abstract: The structure and performance of a real-time digital simulator (RTDS) for testing relays are described. The RTDS uses parallel processing architecture based on a state-of-the-art digital signal processor (DSP) to run power system simulations in real time with a time step of 50-100 mu s. Physical devices such as relays, energy monitors for MOVs, or power system stabilizers can be fed with the appropriate signals from the RTDS and the output from the physical device can be fed back into the simulation. Examples are given of tests on a commercial distance relay. >

Dynamic capacity allocation CDMA spread spectrum communications

Abstract: A dynamic capacity allocation spread spectrum CDMA communications system for overlaying, at least in part, geographically and in frequency a radio-relay system A first receiver, located near the relay receiver of the radio-relay system, measures a first power level within the relay bandwidth of the radio-relay system A second receiver, located near the relay receiver, measures a second power level outside the relay bandwidth of the radio-relay system The first power level is compared to a predetermined threshold A ratio signal is generated from the first power level and the second power level When the first power level exceeds the predetermined threshold, the ratio signal is used to regulate the power level and dynamically allocate the capacity transmitted from each spread-spectrum-base station

Improved simulation models for current and voltage transformers in relay studies

Abstract: Improved models for current transformers (CT), potential transformers, and capacitive voltage transformers (CVT) for a relay software library are presented. The magnetizing characteristic in each of these transformers is based on the nonlinear power curve formulation of J.R. Lucas (1988). The flux-current loops of the transformer core are self-generated rather than predetermined or based on look-up tables. The results presented show that the models developed for the transformers behave as expected, and agree with reported field investigations. Models for the CT and CVT give acceptable results, including those under remanent conditions and ferroresonant conditions. These models are thus necessary components for relay studies carried out with electromagnetic transient programs whether offline or in real time. >

Multifunction protective relay system

Abstract: A protective relay system for generation apparatus connectable to a three-phase alternating current electrical utility system. The relay system includes a dual processing architecture wherein a digital signal processor executes all the signal-processing algorithms, and a separate microprocessor is used for input/output data processing. A dual-ported RAM is used to effect a fast communication link between the digital signal processor and the microprocessor to accomplish high-speed protective relaying functions to selectively trip and close a circuit breaker at a generator or cogenerator site, or that which connects it to an electric utility system.

An application of functional dependencies to the topological analysis of protection schemes

Abstract: The concept of functional dependency is applied to the problem of relay coordination in protection systems. An algorithm is developed for the identification of a minimal break point set (BPS) of relays of a protection topology. This algorithm is an improvement over existing algorithms in that it identifies a minimal BPS within a time period that is a polynomial function of the number of relays, while the earlier algorithms had exponential time behavior. In the case of large protection schemes, the saving in computation costs is considerable. An algorithm is developed for the selection of a relative sequence matrix; this algorithm also has polynomial time complexity. The functional dependency approach is seen to be more flexible and more powerful than the graph theoretic schemes, and holds out much promise for the development of efficient computer-aided design tools for the protection engineer. >

Design, implementation and testing of a microprocessor-based high-speed relay for detecting transformer winding faults

Abstract: The authors present the design, implementation and testing of a microprocessor-based high-speed relay that correctly detects transformer winding faults. Instead of relying on the presence of harmonics to identify magnetizing inrush, it uses a nonlinear model of the transformer to determine the state of its health. One version of the relay is suitable for protecting single-phase transformers, whereas another version is for protecting three-phase transformers. A three-phase delta-wye 15 kVA transformer was used to test the relay for a variety of operating conditions. The results show that the relay performs well. >

Control unit for occupancy sensor switching of high efficiency lighting

Abstract: A control unit for switching AC powered high efficiency lighting in response to a signal from an occupancy sensor. The lighting is switched by a hybrid mechanical relay/semiconductor switch. The semiconductor switch is connected in parallel with the relay switch contacts to protect them and is controlled by a noise-insensitive zero voltage crossing detector circuit which switches the semiconductor switch only at the zero crossings of the AC power. The semiconductor switch is preferably turned on by a pulse forming circuit only for a brief period of time spanning the time when the relay is switching.

A digital multifunction protective relay

Abstract: The author describes the development of a digital multifunction relay for the protection of the intertie between a customer-owned generator and a utility system. The relay uses state-of-the-art digital signal processing techniques to measure the relay parameters, thereby eliminating analog hardware. The hardware design uses a dual microprocessor architecture to achieve flexibility and high speed operation. The relay uses the DFT (discrete Fourier transform) to obtain the fundamental frequency phasor measurements, and hence the frequency and power related functions are immune to harmonic distortion in the voltage and current signals. In addition to costing less than the existing package of single function relays, the relay also provides improved performance, user friendly human interface, remote communication, self-checking, and self-calibration functions. >

A digital protection technique for parallel transmission lines using a single relay at each end

Abstract: A novel digital relaying technique for parallel transmission lines is presented. Only one relay at each end of the two lines is used. The idea of the protection algorithm is based on the comparison of the average current of corresponding phases. The technique is simple and avoids many problems of parallel lines. Simulation studies show that the trip signal is generated about 5 ms after the inception of the fault. The stability of the relay under different operating conditions is also examined. >

Switcher for redundant signal transmission system

Abstract: A switcher applicable to a redundant signal transmission system is capable of maintaining impedance matching when an input line associated with a faulty active transmitter is connected to a standby transmitter. Switching means has first type of switch means (110) assigned to the standby transmitter (50), a plurality of second type of switch means (121,122) associated one-to-one with a plurality of active transmitters (51,52), and a pair of connection lines (161,171,162,172) cascading the first and second types of switch means. When a faulty active transmitter is replaced with the standby transmitter, relay switches (11,12,21,22,23) constituting the first and second types of switch means disconnect a portion (162,172) of the connection lines which is remoter than the second type of switch means (121) associated with the faulty active transmitter (51), as viewed from the first type of switch means (110).

High voltage, high current switching apparatus

Abstract: A high voltage, high current DC switch is shown having a single pole, double throw relay and a solid state power switch such as an IGBT or MOSFET transistor. Voltage is switched by means of the solid state switch while steady state current is conducted through the relay load contact. Several different protector devices are used in the event of circuit malfunction including a combination of thermal and current fuses and resettable thermostats.

Ground fault interruptor circuit with electronic latch

Abstract: A ground fault interruptor circuit interrupts the flow of current to a pair of lines extending between a source of power and a load. The ground fault interruptor circuit includes a circuit brewer comprising a normally open switch located in one ar both of the lines, a relay circuit for selectively closing the normally open switch, an electronic latch circuit operable in first and second bi-stable states and a fault sensing circuit for sensing the presence of a fault condition in at least one of the lines. The electronic latch circuit causes the relay circuit to close the normally open switch and maintain the normally open switch in its closed position when the electronic latch circuit is in the first bi-stable state. The electronic latch circuit also causes the relay circuit to permit the normally open switch to return to its normally open condition when the latch circuit is in its second bi-stable state. A fault sensing circuit senses the presence of a fault condition in at least one of the lines and causes the electronic latch circuit to latch in its second state upon detection of the fault condition.

Inverter controlled air conditioner capable of effectively reducing a rush current at starting

Abstract: This invention provides an inverter controlled air conditioner capable of employing a rush current preventing relay having a small capacitance, thereby decreasing the cost. An inverter circuit includes a rectifying circuit connected to an AC power supply, a smoothing capacitor connected to the output terminals of the rectifying circuit, and a switching circuit, connected to the two terminals of the capacitor, for outputting a voltage having a predetermined frequency upon performing switching. An auxiliary power supply circuit has a rectifying circuit connected to the AC power supply. A control section drives the switching circuit with an output from the rectifying circuit as the operation voltage. Relay drive circuits for receiving the output from the rectifying circuit as the operation voltage are connected to an electromagnetic contactor and a relay. When the air conditioner is started, the control section energizes the relay for a predetermined period of time t s through the relay drive circuits and thereafter energizes the electromagnetic contactor. Normally-open contacts of the electromagnetic contactor are connected between the AC power supply and the inverter circuit. The capacitor of the inverter circuit is connected to the output terminals of the rectifying circuit of the auxiliary power supply circuit through a resistor and normally-open contacts of the relay.

Controller for fixed-time pull-in of a relay

Abstract: A controller for a relay controls the pull-in time of the armature of the relay by controlling the power applied to the relay coil. To determine the actual pull-in time, the time of closure of the contacts is sensed and the time at which power is applied to the coil is subtracted from it. The actual pull-in time is then compared with a stored value of ideal pull-in time to produce an error signal. The error signal corrects the level of power applied to the relay coil upon the next actuation of the relay, to make the actual pull-in time approximately equal to the ideal pull-in time. In some embodiments to control the level of power on the coil, a Gray-code counter samples a duty-cycle register in a micro-computer and produces a train of pulses that is filtered to provide a DC control signal. The DC control signal controls the duty cycle of a pulse-width-modulated oscillator that rapidly switches (modulates) the power to the relay coil.

Security and communication system with location detection

Abstract: An improved security and communication system accurately and quickly locates the position of a signaling portable radio frequency transmitter. When a portable transmitter is activated, a first signal, including identification information, is emitted. The first signal is received by any of a number of radio frequency relays, the signal is manipulated and transmitted to a central processing station as a second signal. The central processing station can, by using the second signals received, either from one or a number of relay stations, determine which relay station is closest to the portable transmitter.

Battery charge monitor

Abstract: A battery charge monitor for automotive vehicles that includes electronic circuitry for connection to the vehicle battery and responsive to battery voltage to provide a first electrical signal when battery voltage decreases to a selected threshold level. A latching relay includes relay contacts for connection between the vehicle battery and vehicle battery loads, including the starter. A first relay coil is operatively coupled to the relay contacts and responsive to the first signal from the electronic circuitry to open the relay contacts and disconnect the battery from the battery loads including the starter. A second relay coil is operatively coupled to the relay contacts and responsive to a second electrical signal from an operator reset switch for reclosing the relay contacts and connecting the battery to the loads. Thus, when battery charge reaches a level below which starting may be difficult, the electronic circuitry cooperates with the latching relay to disconnect the battery from the loads. When the vehicle is to be started, the battery is reconnected to the loads, including the starter, by operation of the reset switch before energizing the starter.

Disconnection device for surge arresters

Abstract: A disconnection device for surge arresters has a current-interrupting device which is suitable for interrupting the fault current once the voltage-dependent resistor in the arrester becomes conductive as a result of aging or overloads. This fault current flows through the common earth line of the associated arrester, which line forms the primary winding of a straight-through transformer which is built into the disconnection device. The secondary winding is connected to an electronic energy storage circuit which is independent of the mains voltage. A converter relay is operated by this energy storage circuit in a pulsed manner when a fault current of predetermined intensity flows to earth through the earth line. The converter relay can be either a monostable or bistable electromechanical relay, or an electronic relay (e.g. a thyristor circuit). When the relay contact is closed, an electromagnetic trip device (latching trip device) is operated by the energising current taken from the mains, which trip device trips the latching mechanism of the current interrupting device. Thereafter, the monostable converter relay reverts back to its original position again, or the bistable converter relay is mechanically or electrically reset to its original position, as a result of which the relay contact opens and the disconnection device is ready to switch on again via an operating device.

Sudden-stop brake-light warning system

Abstract: A sudden-stop brake-light warning system (10) that causes the brake lights (56) of a vehicle to intermittently pulsate. The pulsation of the lights (56) is achieved by a flashing brake-light circuit (12) that is only activated when the brake pedal is depressed during a panic stop. The circuit (12) consists of a mercury switch (51), located in an inertia operative switching circuit (16), that closes only when the brake switch (54) is depressed during a panic stop. When the switch (54) closes, the power from the vehicle battery (52) is applied to the gate of a silicon controlled rectifier (CR1) located in a silicon controlled rectifier circuit (18). The energizing of CR1 enables a multivibrator circuit (14) connected via a relay driven transistor (Q3) to the coil (20A) of a relay (K1) located in a relay drive/relay circuit (20). The relay is pulsed in accordance with the time constant of the multivibrator and as the coil (20A) pulses, so are the brake lights (56).

Relay contact monitoring system

Abstract: A switching system for switching on and off heating and air conditioning units in an environmental control system. The switching system includes a thermostat and a relay conductively coupled to the thermostat. The relay has a contact, which is responsive to a change signal for changing its position. The system further includes a programmable monitor having predetermined positions stored in a memory. The monitor is conductively coupled to the contact and to the thermostat for continually determining the position of the contact, and for sending a change signal to the relay for switching the position of the contact, as needed, to be in conformance with a predetermined position stored in the memory.

A computer-aided design tool for developing digital controllers and relays

Abstract: The design, development, and implementation of a computer-aided design (CAD) tool for developing digital controllers and relays are presented. The development includes modeling A/D converters, software, and the necessary logic. Procedures for modeling A/D converters and simulating the software are described. Application of the CAD tool is demonstrated by evaluating and comparing three different designs of a digital overcurrent relay. The designs are evaluated to determine both the speed and accuracy of the relays. The effects of the size of the A/D converters, the word-size used in computations, and the truncation/rounding are included in the simulation. Also described is the algorithm used in the relay design. >

Solid-state relay

Abstract: A circuit technique for reducing the sensitivity of solid-state relays, having a normally-on (closed) contact, to transients on the output thereof when the contact is open (relay is actuated). The relay has series of photodiodes, a switch, and a pair of depletion type output transistors coupled to the output of the relay. The output transistors are driven by the photodiodes with the switch in parallel with the input of the transistors. The switch allows for the rapid deactuation of the relay. A resistor, disposed in series with the switch, reduces the susceptibility of the relay to the transients by slowing the turn-on of the switch.

Uniquely decodable codes for deterministic relay channels

Abstract: The deterministic relay channel is analyzed and explicit code constructions for all binary and all ternary/binary channels are given. An explicit set of equivalence conditions is used to make a classification of all such relay channels, for which also the capacity is evaluated. The coding problem is then reduced to finding all possible output sequences of a certain finite-state channel determined by the relay coding strategy. The channel states correspond to the possible relay memory contents. For some relay channels capacity is reached by using simple uniquely decodable codes, thus establishing the zero-error capacity of those channels with finite-memory relay strategies. For other relay channels the relay memory must be arbitrarily large to achieve zero-error rates arbitrarily close to capacity. One such code construction is given. It is not known whether there exist relay channels for which the zero-error capacity is strictly smaller than the average-error capacity. The code construction problem for the semideterministic relay channel and for the nonsynchronized relay channel is briefly considered. >

Ground fault circuit interrupter

Abstract: A fault current circuit breaker has a summary current transformer whose secondary coil is connected to a voltage-independent energy storage circuit. A monostable or bistable transformer relay is actuated by an impulse by way of this energy storage circuit when a fault current flows to earth in the protected installation. When the relay contact is made, an electromagnetic lock trigger is actuated by the energizing current received from the mains supply, which triggers the switch lock of the FC switch. After this, the bistable transformer relay is returned to its initial position, either mechanically by way of an appropriate coupling with the switch lock, or electrically by way of a time delay or switch circuit, whereby the relay contact opens and the FC switch is again ready for switching on. With the monostable transformer relay, the relay returns to its initial position automatically, whereby the energy storage circuit is adjusted to the coil of the relay such that the duration of the impulse delivered by the energy storage circuit is sufficiently long for the lock trigger to be actuated by the energizing current from the mains supply.

Dynamic admission control for telecommunications relay service with text-to-speech synthesis

Abstract: In a system for providing telecommunications relay service, the delay in assigning an attendant to an established relay session after the text-to-speech conversion process may be controlled by establishing new relay sessions, in response to requests therefor, only if a) less than a predetermined maximum number K of relay sessions have already been established, b) none of the established relay sessions are queued and waiting for an attendant and c) an attendant is available. An established relay session is one that is 1) being served by an attendant, 2) is waiting to be reconnected to an attendant or 3) is in the midst of the text-to-speech conversion process. The value of K is greater than or equal to the number of attendants. It is determined dynamically, as a function of 1) a given set of performance objectives, 2) the current set of traffic characteristics, 3) the current performance characteristics and 4) the resources available at the telecommunications relay service center.

Frequency trend and discrete underfrequency relaying practices in India for utility and captive power applications

Abstract: A typical application procedure for a coordinated load shedding scheme using both frequency trend relays and normal discrete underfrequency relays is described. By using such a combination of relays it is possible to develop comprehensive protection against frequency disturbances, both sudden and gradual. It is emphasized that in a system where the causes of frequency disturbances are quite varied and complex, a fully automatic scheme may not be the ideal solution and manual load shedding as a backup may be necessary. A typical procedure for a captive power plant system operating in parallel with the grid is described as applicable to a continuous process plant industry. The strategy for islanding such industrial power systems from the grid during grid disturbances is described. >

Digital telephone, cable tv system and local exchange bypass network.

Abstract: Cordless telephones (38) generate call relay packets. Packets from each cordless telephone are polled by an upstream polling unit avoiding multi-unit interference. Cell packets are transmitted via a cable TV system (36). Radiated frequencies of the cordless telephones are shifted in frequency as they enter or leave the TV feeder cable to allow frequency reuse. The upstream polling unit appends header information on the cell packets and converts them into standard SONET ATM protocol packets. The cell relay packets are switched by a cell relay type switch to create a cost-effective, alternative telephone system.

Short circuit detector and isolator

Abstract: An isolation circuit (30), which draws essentially zero current in a normal or stand-by state, uses a normally closed relay (34) in combination with a storage element (32). A capacitor (46) can be used as the storage element (32) to energize the relay (34), using previously stored energy, in the event that a communication line (L1; L2) to which the isolator is coupled exhibits a short circuit or low voltage condition. In this instance, the prestored energy on the capacitor activates the relay for a predetermined period of time, thereby open circuiting the communication line. When voltage is reapplied to one side of the isolator circuit, the relay is continuously energized and maintained in its open circuit condition until the low voltage or short circuit has been remedied.

Field experience with a digital relay for synchronous generators

Abstract: The authors provide the specifications and characteristics of a digital relay for synchronous generators that performs seven protection functions. They also present preliminary performance results, following installation on one of the units at the Carillon generating station in the Hydro-Quebec power system. During a period of four months, although no fault was recorded in the unit, the relay watchdog system and self-monitoring routines functioned flawlessly. The prototype provides the basis for a new standard protection system for Hydro-Quebec's future and existing generating stations. >

Locating Postal Relay Boxes Using a set Covering Algorithm

Abstract: SYNOPTIC ABSTRACTIn a mail delivery network, relay boxes along postmen's routes are made necessary by the fact that postmen can carry only a limited amount of mail at any time and must replenish their mail bags at specific points on their route. The problem studied in this paper is that of minimizing the number of relay box locations. It is formulated as a set covering problem and solved heuristically. Computational results confirm the efficiency of the proposed solution and indicate that important savings can be achieved.