Showing papers on "Relay published in 1994"

A caching relay for the World Wide Web

Abstract: We describe the design and performance of a caching relay for the World Wide Web. We model the distribution of requests for pages from the web and see how this distribution affects the performance of a cache. We use the data gathered from the relay to make some general characterizations about the web.

Adaptive relay setting for stand-alone digital distance protection

Abstract: Reach accuracy of a distance relay on transmission lines is adversely affected by fault resistance combined with remote-end infeed which is not measurable at the relaying point. Different network conditions correspond to different remote-end infeed behaviour and in conventional setting a safety margin is necessary so as to avoid maloperation. In this paper an adaptive setting concept which can overcome this disadvantage is proposed. A microprocessor based distance relay with this new technique can respond to network conditions that change from time to time and computer simulation has confirmed the validity of this new concept. >

Intelligent power switcher

Abstract: An intelligent power switching system for controlling the electrical connection of a power source to each of a plurality of outputs, such as personal computer components or electronic entertainment equipment. Switch circuitry is coupled to relay circuitry for generating signals responsive to user commands to select an "on" or "off" state with respect to each output. A processor receives switching signals and generates control signals to effect actuation of the relays. Responsive to user programming commands, the processor stores the switching signals, their sequence and the time delay between their generation. Responsive to a subsequent abbreviated user "power-on" command, the processor generates control signals by reading the stored switching signals, their sequence and time delay, and automatically actuates the relays with respect to each output in the same order and with the same time delay as defined by the user programming commands. A "power off" command causes the relays to be actuated in the reverse order.

Electromagnetic microrelays: Concepts and fundamental characteristics

Abstract: An electromagnetic microrelay is proposed as a practical application of microelectrochemical system (MEMS) technology and the basic performance of its key components is evaluated. The contact resistance and breakdown voltage of contact electrodes are measured for very small loads and gaps. The static and dynamic deflection of the contact springs is measured for very small movements. Based on these experimental results, design guidelines for key components are proposed. Two prototypes that partly use MEMS technology are produced and their switching performance is demonstrated. One prototype uses a flat microspring with a length and width of 0.3 mm; its switching speed is more than ten times that of a conventional relay. The other is a 2×2 matrix relay, with four self-latching switches; each switch has two stable positions, open and closed, and is driven by a current pulse. This component study and prototype development verify the suitability of MEMS technology for mechanical relays.

A fuzzy-set approach to fault-type identification in digital relaying

Abstract: Sometime the operations that a relay is required to perform cannot be easily described in a deterministic way. A significant example of this situation is given by the operations a line relay must perform in order to detect the type of fault (line-to-ground, line-to-line, line-to-line involving ground). Recently, the mathematical theory of fuzzy sets featured many practical applications, mainly in industrial controls, and fuzzy-set processors are available to allow real time applications. This paper shows that a fuzzy-set approach can be useful even in digital relaying, whenever "fuzzy" decisions have to be under-taken. A possible application to the detection of the type of fault when symmetrical component relaying techniques are adopted is proposed and the results of simulation tests are given. >

Data transfer and communication network

Abstract: A data transfer and communication system is disclosed including a central station and a plurality of remote, relay terminals. Each relay terminal includes a data entry device such as a keypad or bar code wand. A headset is associated with each relay terminal. Circuitry is provided to permit two-way wireless communication between the headset, relay terminal and central station. The relay terminal functions to transmit substantially unprocessed voice and data signals to the central station. The central station analyzes the signals and can retransmit a response which can be displayed on the relay terminal. The relay terminals are intended to be high volume, low cost items with the more expensive computational power being located at the central station.

Adaptive distance protection of a double-circuit line

Abstract: Due to changes in the power system, such as generator and line outages and changes in load and generation, the performance of distance relays can vary. In the case of a distance relay protecting a phase of a double-circuit line, the state of the parallel circuit is of major importance. Simulations show that, depending on the power system state, a distance relay can cover from less than 50% up to far more than 100% of the total line length. This is demonstrated with a double-circuit line under the single-line-to-ground fault (SLG) fault condition, since this is the most common type of fault. In this paper the distance protection of a double-circuit line under the SLG fault condition is formulated. To achieve correct operation, the relay does not only use the measured quantities of the circuit-to-be-protected, but also the zero sequence current of the parallel circuit. Such a relay requires extra measuring equipment, and, moreover, the zero sequence current of the parallel circuit cannot always be measured. Therefore, another approach is chosen. A correction factor is introduced, set adaptively according to the actual power system state. In this way, the appropriate setting of the relay is provided, in relation with the actual power system state. A side-effect of the adaptive setting of the relay is that the safety margin in the relay settings is decreased, due to the uncertainty in the power system state. By adapting the relay to the actual power system state, maximum selectivity is achieved, and the protection system as such will be more reliable. >

Relay feedback auto-tuning of cascade controllers

Abstract: It is shown that the relay feedback auto-tuning technique can be extended to auto-tune cascade controllers. The use of the relay allows the tuning of the secondary loop to be done without necessarily placing the primary controller in manual mode. It also turns out that the relative speeds of the loops in cascade can be derived from the limit cycle oscillations obtained from relay feedback auto-tuning. >

Transients computation for relay testing in real-time

Abstract: This paper discusses characteristics of a new digital simulator for protection relay testing. The most demanding design requirement is computation of fault transients under the condition of real-time change of power system configuration due to relay operation. This problem is solved using EMTP computational techniques enhanced with novel numerical solutions for dynamic power system configuration change and nonlinear element modeling. An advanced computer architecture is utilized to achieve further optimization of the execution time for the transients computation code. The main advantage of this design is the use of conventional single processor computer architecture in combination with advanced digital signal processors (DSPs). This makes this simulator an off-the-shelf product with all the benefits of commercially available computers priced at a relatively low cost. >

Congestion processing mode and congestion processing circuit in frame relay exchange apparatus

Abstract: A frame relay exchange apparatus which accommodates a plurality of subscriber lines and relay lines and transmits the frames received from these lines to a destination line, constituted so as to measure the amount of communication data for every PVC line along with an elapsed time and so as to calculate the limiting coefficient α varying in accordance with the degree of the queue length of the transmission queue. When the measured amount of communication data exceeds the upper limit value of the terms of subscription of communication of the respective subscribing PVC lines, that upper limit value is changed to a reference value limited by the limiting coefficient α, and then a frame discard operation and advance notification are performed. By this, the PVC performing communication within the range of the terms of subscription of communication is protected from unjust limitation from another PVC performing communication exceeding this, while utilizing the resources inside the switching network to the maximum level.

Cellular mobile communication system having apparatus for changing boundaries of cells according to traffic condition

Abstract: Cellular mobile communication system includes a plurality of base stations connected to a relay station, each base station having adaptability for coping with change in traffic volume within a relevant cell covered thereby. Each base station includes a variable gain power amplifier for amplifying a pilot signal and a power control circuit for controlling the gain of the power amplifier. The power control circuit controls gain of a pilot signal sending power in accordance with a control signal supplied from a device installed in a relay station for monitoring traffic states of the individual base stations. The relay station issues a command for lowering the power gain for the base station which covers a traffic-concentrated cell while raising the power gain for the base stations covering the neighboring cells, to thereby contract the size of the traffic-concentrated cell. With a smaller number of base stations, communication demand can be controlled over a broad area.

Method for Radio transmitting information using aircrafts as open transmission relays

Abstract: In order to transmit information between an emitting station and a receiving station separated by a distance exceeding the range of direct communications of said stations, the method according to the invention consists in equipping aerodynes, travelling in the space included between these two stations, with open communications relay systems of limited range which can momentarily interconnect, when within range of one another, in order to pass information from relay system to relay system up to its destination. The invention applies notably to air-to-ground communications for data links in the field of air transport.

Modeling the protective system for power system dynamic analysis

Abstract: Mathematical models for power system dynamic analysis including the dynamics of the protective system are presented. The formulation of the equations is based on establishing explicit relations between the protection system and the rest of system dynamic elements through the node admittance matrix Y/sub BUS/. This relationship is achieved by representing the circuit breakers of interest as part of the transmission network elements. The protective relays, reclosing relays and circuit breakers are modeled as dynamic devices for tracking the dependence of these devices on the voltage and current inputs using the phasor state variables. A simple example illustrates the concepts. As a direct consequence of the analytical model, the concept of a protection success region is introduced and the implications for stability analysis, relay coordination, adaptive relaying and cascade tripping are discussed. >

An expert system for power systems fault analysis

Abstract: This paper describes an expert system for fault analysis which has been put into field tests in the dispatch centre of the North East China Electric Network. Previous expert systems for fault analysis on transmission power systems are mainly based on information about the operation of protective relays, whereas this new expert system mainly uses information on tripped circuit breakers, which is more readily available. For some complicated faults, a small number of relay signals are needed. Data concerning the distribution and characteristics of protective relays are concealed in the fault models in the knowledge base of the expert system. And consequently the large database normally required for these data is unnecessary. This also enables the expert system to be more easily transplanted to other networks. Furthermore, because it can distinguish the operational performances of different relays, it analyses faults more accurately. >

Zero crossing circuit for a relay

Abstract: A relay control circuit that includes a zero cross detector, a latch, and a delay circuit. The zero cross detector circuit detects when the voltage waveform or current waveform on an AC power line is at the zero crossing. The output of the zero cross detector clocks the latch (flip-flop), which receives a control signal at its data input. The flip-flop latches the control signal on the zero crossing point and outputs the latched signal to the delay circuit. The delay circuit delays the control signal for a predetermined time period depending on the make and break times of the relay so that the relay is switched ON and OFF substantially near the next zero crossing point of the AC voltage waveform.

Programmable time interval power strip

Abstract: A programmable time interval power strip comprising a power input mechanism for receiving external alternating electrical power; a power supply including a power switch having an enabled orientation for allowing delivery of constant electrical power and a disabled orientation for preventing such delivery; a plurality of adjustable timers coupled to the power supply with each timer having an output for generating a relay activation signal; a plurality of receptacles coupled to the power input means and coupleable with a plug-connected appliance; and a plurality of relays coupled to the power input means with a first relay further coupled to the power switch and with the remaining relays each further coupled to the output of a timer and receptacle, the first relay delivering alternating electrical power to its receptacle when the power switch is placed in the enabled orientation and with the remaining relays delivering alternating electrical power to their receptacles upon receipt of the associated relay activation signal.

Time transfer position location method and apparatus

Abstract: A time transfer position location method and arrangement. A mission control station initiates a number of relays placed throughout a simulated battlefield. Each of the relays then obtains position and time information from a Global Positioning System (GPS) satellite. Each relay repeatedly transmits position information (timing pulse) in a particular time slot over the playing field. In addition, fire mission information which includes type of munition deployed and its range and affects is also transmitted.

Adjustable electronic potential relay

Abstract: A starting circuit for a single-phase induction motor having a start capacitor, an auxiliary or start winding, and a run winding includes user adjustable pick-up voltage means to allow a user to select a pick-up voltage in the field to correspond to the pick-up voltage of a particular induction motor such that a relay disconnects the start winding from the power supply when the start winding voltage exceeds the selected pick-up voltage. Protective circuitry is provided including a timing circuit to protect from missetting of the pick-up voltage or when the motor will not start for any reason and a relay current circuit to control the current flowing in the relay to protect from high voltage overloading.

High-resistance faults on a multi-terminal line: analysis, simulated studies and an adaptive distance relaying scheme

Abstract: The presence of a T-connection to a third terminal can drastically affect the performance of a distance relay at the other terminals. Fault resistance, especially high fault resistance, makes this problem more severe and complicated. Detailed analysis of the apparent impedance for these cases as seen from the relaying point is derived and, based on extensive simulations of the infeed/outfeed and fault-resistance effects on the relay characteristics, an adaptive distance relaying scheme is proposed. A microprocessor based distance relay using this new technique can quickly respond to very-high-resistance faults with maximum coverage of the protected line. The validity of this new scheme has been confirmed by real-time testing on a prototype hardware scheme. >

Pulse circuit using a transmission line

Abstract: A pulse discharge circuit for pulse testing an integrated-circuit device under test (DUT) is provided which uses three separate switching relays S1, S2, and S3, which are operated in a predetermined sequence. For charging the capacitance of a pulse-forming transmission line, the relay contact of S1 is closed while the relay contacts of relays S2, S3 are both open. For discharging the charge on the transmission line to form a test pulse, the relay contact of S1 is first opened, and the relay contact of S2 is then closed while the relay contact of S3 is open. After each test pulse is generated and applied to a DUT, the condition of the DUT is determined by a leakage current measurement. The relay contact S2 is opened to isolate the pulse generator circuit and then the relay contact S3 is closed.

Necessary conditions for limit cycles in multiloop relay systems

Abstract: The paper examines the behaviour of multivariable systems under multiloop relay feedback control. The analysis is a generalisation of the Tsypkin method (1984) for the prediction of forced oscillations in single variable systems. It is exact in the sense that a complete harmonic balance is considered in all the loops. The results are valid for systems with characteristic loci with phase lags more than 180 degrees . It is shown that such multivariable systems under multiloop relay feedback may exhibit limit cycle oscillations in three possible modes. The first mode consists of identical relay outputs which are square waves with precisely one fundamental frequency. The second mode is characterised by relay outputs which are square waves of different fundamental frequencies in each loop. In this mode, each loop behaves like a single variable system oscillating at a unique limit cycle frequency. The third mode is one of periodic complex oscillations consisting of multiple relay switches within one fundamental period. The necessary conditions derived show that the modes are related to the strength of the interactions in the respective loops. The authors derive a graphical technique to determine when unique oscillations (with distinct frequencies) at the output of each relay may occur and when single frequency or complex oscillations may exist instead. Simulation results are given to illustrate the possible scenarios.

Transformed current sensing relay for use in switched network modems and circuit incorporating same

Abstract: A transformed current sensing relay (k2) with reduced AC impedance of the operating coil is accomplished by adding a shorted secondary winding (14) to an otherwise conventional current sensing reed relay The shorted secondary winding (14) is preferably implemented with a copper tube over the existing coil and inside the magnetic circuit This transformed current sensing relay (k2) is particularly advantageous for the line current sensing function in switched network communications equipment such as high speed modems, where the transformed relay (k2) exhibits substantially lower impedance at high frequencies than the conventional current sensing relay This transformed current sensing relay (k2) allows for the elimination of bypass capacitors and results in significant cost and space savings Moreover, the transformer nature of the transformed current sensing relay (k2) allows for the elimination of suppression resistors from the interface resulting in additional cost and space savings

Extensive evaluation of high performance protection relays for the Hydro-Quebec series compensated network

Abstract: This paper reports on an extensive study to compare the performance of 8 preselected high performance power line protection systems on the Hydro-Quebec series compensated network. The paper first presents an evaluation of the commissioning aspects and manufacturing quality of the tested relays. It then describes the simulated network, the relay testing procedure, and the laboratory test results obtained on a modern real time power system simulator. Published results of relay performance on series compensated lines are scarce and this paper provides valuable information for utility protection engineers. A total of 115,000 network disturbances were simulated and recorded on 20 different 735 kV lines; fractional test results for 84,030 cases are presented in the paper. The approach using real time power system simulation proved to be an efficient technique for evaluating protection relay performance. The laboratory test results demonstrated that the two best protection principles to be applied on the Hydro-Quebec series compensated network are those based on current differential and segregated phase comparison. The analysis does not take into account telecommunication requirements or other external constraints. >

Inductively activated control and protection circuit for refrigeration systems

Abstract: The present invention involves an inductively activated silicon switch for a control and protection circuit for motors and compressors. The circuit includes a logic gate for combining both motor control and protection functions. The logic gate has inputs from a thermostat, a compressor shell temperature circuit, a fan overheat detection circuit, a motor start relay circuit, and motor load sensing circuits. The logic gate output is connected to an oscillator for inductively activating the power output stage, as well as a start relay, a compressor shell temperature hysteresis circuit, and a fan timer circuit connected to the fan control circuit. The control circuitry further includes an over-ride circuit for manually allowing a limited number of immediate restart attempts.

On site relay transient testing for a series compensation upgrade

Abstract: This paper describes tests on the relays on a long 500 kV AC line carried out on site using the RTDS (Real Time Digital Simulator) of the Manitoba HVDC Research Centre. The purpose of the tests was to examine the relay behaviour when series compensation is inserted in the line in 1993. New settings for the relays have been found which will give adequate cover for all faults although some faults will be entirely dependent on the communication link for short clearance times. >

Method and apparatus for rms current approximation

Abstract: A method and apparatus provides for a measurement technique which approximates the true rms value of a current waveform. The technique involves converting the current waveform to a voltage by rectification and determining the peak value and the average value of the resultant voltage. A summing circuit (42) combines the two values at a predetermined ratio to create a DC voltage that is approximately equal to the rms value of the input currents. The DC voltage output is suitable for a wide range of applications. A combination of the approximation circuit (32) with a time integrating circuit (44) and a level detecting circuit (46) produces a low cost solid state overload relay in a preferred embodiment of the invention. Other uses include metering and use as a current feedback control signal for controlling PWM inverters and the like.

Branching unit for submarine systems

Abstract: A branching unit for use in submarine telecommunications optical cable systems which employs electrical power feeding for repeater/regenerators of the cable system, in particular a system employing multiple branching units The unit terminates three line cables (at 1, 2, 3) and a sea earth (at 4) and includes first, second the third high voltage relays (A, A1, B, B1, C, C1), only one of which is energized at a time When electrical power is supplied between any two line terminations, eg 1 and 3, an associated relay coil, eg C is energized so that its contacts C1 isolate the third line termination, eg 2, and connect it to the sea earth termination (4) via fourth, or fifth, relay contacts (D1, E1 ) The branching unit also includes a plurality of optical regenerators, for optical path switching purposes, which require electrical power feeding and whose power feed circuits 20 are connected in parallel with each of the relay coils When any relay is energized, ie the cable system is powered up, the regenerators are also powered The zener diodes (21) provide voltage supply to the regenerator power feed circuits as well as providing surge protection for them and the relay coils simultaneously The fourth-and fifth relays (D, D1, E, E1) serve to prevent arc transfer in the first, second and third relays (FIG 4)

Electronic defrost controller with fan delay and drip time modes

Abstract: An apparatus controls an appliance, the appliance including a compressor, a fan, and a heater. The apparatus includes a first switch for selectively coupling a first terminal with one of a second terminal and a third terminal in response to a first control signal. The first terminal is coupled with an energy source and the third terminal is coupled with the compressor. The apparatus further includes a second switch for selectively coupling the second terminal with the heater and the third terminal with the fan in response to a second control signal. The apparatus still further includes a control circuit coupled with the first switch and the second switch for generating the first control signal and the second control signal. A relay drive circuit couples relay coils in series to control the first switch, the second switch, and the third switch. A bypass switch allows a single current to selectively energize one or both relay coils.