Trip Signal Research Articles

Development of the On-Line Operator Aid System OASYS Using A Rule-Based Expert System and Fuzzy Logic for Nuclear Power Plants

The On-line Operator Aid SYStem (OASYS) has been developed to support the operator`s decision making process and to ensure the safety of a nuclear power plant by providing operators with proper guidelines in a timely manner, according to the plant operation mode. The OASYS consists of four systems such as a signal validation and management system (SVMS), a plant monitoring system (PMS), an alarm filtering and diagnostic system (AFDS), and a dynamic emergency procedure tracking system (DEPTS). The SVMS and the PMS help operators to maintain a plant in a condition to withstand the adverse events during a normal operation condition. The AFDS covers the abnormal events until it exceeds the limit range of reactor trip signals, while after a reactor trip, the DEPTS aids operators with proper guidelines so as to shut down safely. The OASYS uses a rule-based expert system and fuzzy logic. The rule-based expert system is used to classify the predefined events and track the emergency operating procedures (EOPs) through data processing, and the fuzzy logic is used to generate the conceptual high-level alarms for the prognostic diagnosis and to evaluate the qualitative fuzzy criteria used in the EOPs. Evaluation results show that the OASYS ismore » capable of diagnosing plant abnormal conditions and providing operators appropriate guidelines with fast response time and consistency. The proposed system is implemented on a SUN-4/75 workstation using C language and Quintus prolog language. Currently, the OASYS is installed in the real-time full scope simulator for validation.« less

PC based comprehensive relaying scheme for generator-transformer unit

This paper reports the development of a comprehensive protective relaying scheme for generator-transformer unit using digital filters. An efficient algorithm based on the recursive constraint transfer function model of the IIR band pass filter has been developed which extracts the various frequency components such as 50, 100, and 150 Hz for realizing the protective functions such as variable bias differential logic, and earth fault protection logic for the combined unit, differential protection logic, rotor over heating relaying logic, reverse power flow relaying logic, rotor earth fault protection logic and field failure relaying logic for the generator, differential protection logic for unit transformer and over fluxing protection logic for the main transformer. In addition to the above relaying functions, the proposed scheme also incorporates a voltage controlled over current relay with IDMT characteristics to give back up for the short-circuit protection for the combined unit. The proposed scheme was tested for different simulated conditions representing normal and abnormal conditions of the system using a PC-80386 computer system. The set limit for discriminating between internal fault and normal condition is considered in terms of the average value rather than RMS value of the three frequency components resulting in reduction of the arithmetical complexity and computational efforts. The proposed scheme as a whole operated satisfactorily by issuing trip signals during internal fault conditions and restraining from tripping during the external fault and normal conditions.

A microprocessor-based quadrilateral distance relay for [formula omitted] transmission line protection

This paper presents an Intel 8086 microprocessor-based quadrilateral distance relay suitable for the protection of EHV UHV transmission lines. The digital filtering algorithm used for extracting the fundamental frequency components from the complex post-fault relaying signals is based on rationalized Haar transform (RHT). The real and reactive components (R and X) of the apparent impedance of the line as seen by the relay are computed by using the real and imaginary components of the fundamental frequency voltage and current phasors. Using the computed values of R and X, the microprocessor examines whether the fault point lies within the quadrilateral relay's protective zone or not. If the fault point lies in the protective zone of the relay, the microprocessor issues a trip signal to the circuit breaker. The proposed distance relay is reliable, flexible, accurate and fast.

Open conductor detector system

An open phase conductor detector system consisting of one or more transmitters and a receiver which communicate through the distribution line neutral conductor is described. The design holds a promise to provide reliable protection for most down and open 5 to 35 kV distribution phase conductors in contact with high impedance surfaces. The transmitter(s) detects the open phase conductor by monitoring the phase conductor voltage using redundant inputs. When an open phase conductor is detected, the transmitter injects a signal to the distribution line neutral conductor by means of a coupling current transformer. The signal is frequency and duration coded. The receiver decodes the signal and generates a trip signal which may activate a breaker, a ground switch, or a recloser, causing isolation of the distribution line with the open (downed) phase conductor. The system is presently implemented for single distribution lines. A prototype open conductor detector system has been constructed and field tested on a Georgia Power Company distribution system. >

A method for tracking power line frequency with millihertz resolution and high/low cut-off

A method for the accurate measurement, tracking and displaying of power line frequency with millihertz resolution is presented which has the facility of generating trip signals in the case of violations of presettable high or low frequency limits. A phase locked loop is used in the multiplier configuration to increase the measurement accuracy. Design equations are established and transient response of the system is simulated.

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

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. >

Walsh transform realization for microprocessor implementation of distance protection

Abstract In recent years there has been a growing trend towards application of digital methods to power line relaying. This has resulted in the design and implementation of very fast distance relays, operating in conjunction with modern circuit-breakers, to meet the growing system requirements of ultra-high-speed fault clearance. This paper describes simple computational procedures, based on the fast Walsh-Hadamard transform (FWHT), for real-time calculation of the fault impedance of transmission lines. These algorithms are implemented on an Intel 8086 microprocessor using 16 samples per cycle of current and voltage signals. Special attention has been paid to the reduction of errors produced by DC offset and by high frequency components in the currents and voltages. A quadrilateral characteristic has been used in the relay for trip decision. Other characteristics such as restricted admittance can also be realized easily, thus providing flexibility to the relay. The hardware and software architecture of the relay is described. The paper also presents the results of tests carried out on the relay using simulated fault data. A tripping signal is sent in less than three-quarters of a cycle of a 50 Hz system for different types of faults. The relay is also evaluated for its dynamic performance characteristics which include directional discrimination, variation of speed and accuracy with fault level, distance to fault, transient components, etc.

Amplitude Comparator Based Algorithm for Directional Comparison Protection of Transmission Lines

When there is a source present at both terminals of the transmission line, the relays protecting the line are subjected to fault current flowing in both directions. Directional relays operate only when the fault current flows in the specified tripping direction. Using the quasi steady state components of the locally measured deviations of the voltage and phase shifted current from their prefault values, the direction to a fault is determined. This directional information is exchanged with the relay at the opposite end of the protected zone. If the combination of the locally detected direction and the information from the remote end indicates a fault inside the zone of protection, a trip signal is issued. The deviation signals of the voltage and phase shifted current are determined by subtracting the previous values from the corresponding values in the present cycle. The voltage and current deviation signals contain exponentially decaying dc and high frequency transient components in addition to the steady state component [1]. The exponentially decaying dc component in the current signal is eliminated by phase shifting the current signal by a replica impedance. The current signal is lowpass filtered in the analog part of the processor before phase shifting it. A 1st order digital lowpass filter is used to filter the voltage deviation signal. An amplitude comparator method is used to determine the direction to a fault. An amplitude directional discriminant value, ADIS, as given by the equation below is evaluated from the filtered deviation signals.

Microprocessor-based overfluxing relay for a generator transformer

This paper describes a microprocessor-based overfluxing relay meant to protect a generator transformer under over-excitation conditions. The relay continuously monitors the system voltage and frequency and takes alarm and trip decisions on the basis of transformer iron losses computed by the microprocessor. An alarm signal is given when the total iron loss exceeds a predetermined threshold value continually for half a second and a trip signal is issued if the condition continues for 5–99 s (adjustable). The operating value of iron loss is adjustable over the range of 1·1 to 1·5 times the iron loss at rated voltage and rated frequency. A relay prototype based on an 8-bit microprocessor 8085A has been tested successfully in the laboratory.

The Availability of Neutron Channels and Power Range Monitoring Systems with In Situ Detection of Channel Degradation

The availability of power range monitoring systems (PRMSs) is important to reliable and safe operation of nuclear plants, since the primary functions of PRMSs are to provide control signals and generate a trip signal if the neutron flux level exceeds preset values during operation. The PRMS can be inspected for degraded modes of neutron channel failure with conventional methods during the time the plant is shut down. Recently, techniques have been developed for in situ inspection of neutron flux channels. The effect of in situ surveillance of PRMS channels on the channel and system availability is investigated as a function of the probability of detecting the degraded channels and the frequency of inspection. The PRMS and its subsystems are modeled as M-out-of-N systems with identical and statistically independent three-state units. It is shown that the single channel unavailability can be appreciably decreased (4 to 10 day/yr) using in situ surveillance techniques. The improvement in PRMS availability in pressurized water reactors, however, is predicted to be small (<1.5 h/yr) because of channel redundancy. The effect of these techniques on PRMS availability in boiling water reactors is virtually unobservable.

Recovery of Spectral Moments from Overlaid Echoes in a Doppler Weather Radar

This paper presents a technique that enables the estimation of spectral moments of overlaid first and second trip weather echo signals in a pulsed Doppler radar. The transmitted pulses are phase coded with a sequence that allows manipulation of the signal spectrum in such a way that either the first or the second trip signal autocorrelation can be made zero, thus removing the bias error in mean velocity estimates due to overlaid echo. With a sufficiently large number of samples, desired mean velocities can be recovered using autocovariance processing provided that the interfering overlying echo power is not more than 10 dB higher than the desired echo power. Also presented is a spectral processing technique that, in conjunction with autocovariance processing, can recover all three spectral moments of both the first and second trip echoes, when their spectrum widths are narrow compared to the Nyquist interval and their power ratio is in the range ±15 dB. An algorithm is developed that can be easily implemented in existing Doppler radars, with the addition only of a lowpower switchable phase shifter and associated drive circuit.

Design and Testing of a Microprocessor-Based Distance Relay

This paper describes the design and testing of a digital distance relay for high voltage systems. It shows how a prototype has been built using two single board computers in a multiprocessor configuration. This design allows simultaneous real-time filtering of the voltage and current signals and computation of the apparent impedances "in parallel". The paper presents the results of the tests carried out on a prototype of the relay using a transient signal generator test circuit. A trip signal is produced by the relay in less than one 60 Hz cycle after fault occurrence for all faults.

A Prototype of Multiprocessor Based Distance Relay

This paper concerns the design and realization of a digital relay for EHV systems. It describes the algorithm which has been used and the main principles of operation. Then it shows how a prototype has been built with four 16-bit microprocessors, to allow the simultaneous real-time computation of three apparent impedances. The hardware and software architecture are described. The paper also presents the results of the tests carried out on the relay: a tripping signal is sent within one period of 50 Hz for all faults (half a period for near-by short-circuits). Furthermore, single-phase tripping, directional discrimination and power-swing detection are provided.

A New Approach to Optimizing a System for Intertrip Signalling

We have developed a detector unit for intertrip signalling which discriminates between guard and trip signals. The theoretical considerations show that such a unit can be constructed in a simple manner with the aid of an up-down counter. The basic construction of the unit around. the up-down counter, and its mode of operation are explained. We further discuss equipment for normally quiescent selective protection. The graphs of the results achieved, which are in agreement with the demands laid down for the equipment are enclosed

Design Considerations for Meeting Separation Criteria for Class IE Systems within the Control Board

The logic diagram for an engineered safety features protection system is shown in Figure 1. The engineered safety feature system is similar for Babcock and Wilcox, Combustion Engineering, General Atomic, General Electric, and Westinghouse. As a result, the system will be used to illustrate the design considerations and techniques for meeting separation criteria for Class 1 systems. The engineered safety features system employs local coincidence logic. The system uses transmission logic, i.e., the transmission of electric power is required to initiate protective action. Transmission logic is used to prevent unwanted actuation of engineered safety features in the event of loss of electric power or safe channel failure. The system has three instrument channels for each variable. Bistable trip signals from the three instrument channels for each variable are fed to two two-of-three logic matrices; one for logic channel A and one for logic channel B. Two-of-three logic matrices are provided for each variable in both logic channels. The output of each two-of-three logic matrix is transmitted to a one-of-one logic matrix or actuator module which acts to transmit power to engineered safety feature equipment. Either output logic channel is capable of actuating the engineered safety features. In logic language, a one-of-three logic arrangement of three sets of three instrument trip signals and a one-of-one logic arrangement of two logic channels and electrical energizing signals initiate the engineered safety features actuation.1

Fourier-series techniques applied to distance protection

For distance-relay applications, the fundamental system impedance as seen from the relaying point is used as the basis for the decision to give the trip signal. This system impedance can be calculated from knowledge of the fundamental frequency components of the voltage and current waveforms, these, in turn, being determined by processing appropriate waveforms sampled at the relay point. Fourier-series analysis is one method suitable for processing the sampled waveforms and for determining their fundamental components. The analysis is designed for continuous, periodic waveforms and, in these circumstances, separates the various harmonic components of the waveform. Its behaviour under the nonperiodic conditions of fault incidence and transient interference will be demonstrated.

Power Reactor Flux-Tilt Protection Instrument

An instrument has been developed as part of a flux-tilt protective system for the light-water-cooled, heavy-water-moderated power reactor (CANDU-BLW) at Gentilly, Quebec. This system is independent of the normal over-power protection instrumentation and is designed to prevent overheating of fuel that could result from spatial flux distortions (or tilts). Three identical instruments are used in the system, each comparing currents from ion chambers located at three positions around the reactor. If flux differences become greater than a preset level a trip signal is generated. The reactor is shut down by dumping heavy water if any two instruments generate simultaneous trip signals. Each instrument contains three linear-logarithmic amplifiers, comparators to sense high flux-tilt levels and logic circuits that combine the comparator signals to produce the final output in the form of relay contact closures. A mixed linear-logarithmic signal is developed from the measured ion chamber current to provide a fluxtilt signal that is non-linear with respect to reactor power.

Pressure monitoring device

A pressure monitoring device is disclosed which is adapted to couple a source of fluid with a tripping device. The tripping device includes a tripping switch movable between a first position in which a tripping signal is generated and a second position in which a tripping signal is not generated, and biasing means for biasing the tripping switch into the first position. The pressure monitoring device comprises pressure transmission means which is operable in a first mode and in a second mode, and coupling means having a first position and a second position. The pressure transmission means when operating in the first mode is responsive to the pressure of the fluid being monitored and when operating in the second mode is independent of the pressure of the fluid. The coupling means is operatively associated with the pressure transmission means and the tripping device for coupling the pressure transmission means to the tripping device. The coupling means transmits a pressure signal proportional to the pressure of the fluid to the tripping switch when the coupling means is in the first position and the pressure transmission means is operating in the first mode whereby the tripping device generates a tripping signal when the pressure of the fluid passes a predetermined limit. Further, the coupling means forces the tripping switch into the second position independent of the pressure of the fluid when the coupling means is in the second position.

New approach to distance relays with quadrilateral polar characteristic for e.h.v.-line protection

A new technique is presented using principles of multisignal relaying for the synthesis of a universal-type quadrilateral polar characteristic. The modus operandi consists in the determination of the phase sequence of a set of voltage phasors and the provision of a trip signal for one sequence while blocking for the other. Two versions, one using ferrite-core logic and another using transistor logic, are described in detail. The former version has the merit of simplicity and has the added advantage of not requiring any d.c. supply. The unit is flexible, as it permits independent control of the characteristic along the resistance and reactance axis through suitable adjustments of replica impedance angles. The maximum operating time is about 20ms for all switching angles, and with faults within 95% of the protected section. The maximum transient overreach is about 8%.

Application of Reliability Theory to a Reactor Safety Circuit

The reactor safety circuit considered in this paper is that of a r from m'> design. Such a circuit comprises m guard lines in parallel, continuously monitoring the reactor performance. When r or more lines signal the presence of a dangerous reactor condition the reactor is automatically shut down. Two types of circuit failures are examined, a safe failure which results in a spurious reactor shutdown, and an unsafe failure when no tripping signal can be produced even if the reactor is in a dangerous condition. The repair of a guard line which failed safe starts at once, after the occurrence of a fault, provided that an engineer is available. No circuit failure will occur if the fault is eliminated before r-1 other faults have occurred. The effects of using a single short circuiting facility in the servicing of circuit faults have also been investigated. In this paper formulae for the calculation of the frequency of safe and unsafe circuit failures are derived, treating time as a continuous variable. The results obtained differ from those based on time represented by a series of discrete intervals. Some illustrative examples are given.