National Research Development Corporation

Gec-alsthom Limited

General Electric Company

The University of Bath

Allan Thomas Johns

Michael A Martin

Raj K Aggarwal

A method of locating the position of a fault on a power transmission line between first and second ends of the line is performed by calculating the complex fault impedance at each of a plurality of assumed fault positions along the length of the line, the fault impedance at each assumed position being calculated utilizing the measurement before and after fault occurrence of the voltage and current at the first end of the line, parameters of the line, and the impedance at the second end of the line; and selecting as the actual fault position the assumed fault position of the plurality of assumed fault positions for which the argument of the complex fault impedance most closely equals zero. The method may be used with single or multi-phase power transmission lines. There is also disclosed a method of determining the form of impedance network at a fault on a multi-phase power transmission line.

Method of locating the position of a fault on a power transmission

A system for detecting a fault in a power line (1) includes, in the power line (1), a first circuit (4) capable of attenuating signals within a first frequency band, which is centered on a first frequency, substantially more than it attenuates signals outside the first frequency band, and, a second circuit (5) connected to the power line (1) on one side of the first circuit (4), the second circuit (5) being capable of extracting signals within a second frequency band that includes the first frequency. The relative levels of two signals extracted by the second circuit (5), are detected and signalled, the two signals being at respective frequencies which the first circuit is capable of attenuating by different relative amounts.

Detecting faults in power lines

An equipment for locating the position of a fault (9) on a power transmission line (7) between two ends (11,13) of the line (7) comprising: a voltage (15A,B) and a current (17A,B) sensor located at each end (11,13) of the line (7) for deriving signals representative of the voltage V.sub.S,V.sub.R and current I.sub.S,I.sub.R at each end (11,13); and two interlinked microprocessors (21A,B), one located at each end (11,13) of the line (7), for calculating the distance x of the fault (9) from one end of the line (11) utilizing the signals and equations of the form:

Equipment for and methods of locating the position of a fault on a power

Discriminating circuits are coupled to receive signals from a protected transmission circuit. Each discriminating circuit also receives from a direction detector signals indicating whether any fault which occurs is forward of, or reverse of, a predetermined point. The discriminating circuit is arranged to produce an output signal to trip a circuit breaker of the protected circuit only if a fault occurs within the protected circuit. In this respect, the discriminating circuit only outputs a trip signal if it receives within the same time period both a signal from the direction detector indicating that the fault is appropriately located, and high frequency signals from the protected circuit. The system thus utilizes the high frequency noise invariably generated when faults arise in transmission circuits. The system for protecting transmission circuits has the advantage that it provides good discrimination of faults without requiring communication links between discriminating circuits at each end of a protected circuit, as has previously been necessary.

Method and apparatus for detecting and discriminating faults in

Teed circuit protection is provided by a master unit at one terminal and slave units at the other terminals with broad band communication links between the master unit and the slave units. All units include line current transformers to the master unit signals derived from the current transformers to the master unit and circuit breakers controlled by operating signals sent from the master unit. The master unit has a logic decision-making facility which takes measurements of the amount by which a differential quantity proportional to the sum of the measurement signals exceeds a bias quantity proportional to the difference between the measurement signals proportional to the sum of the measurement signal exceeds slave units. The facility sends operating signals when that amount exceeds a threshold value. To prevent spurious operation of the circuit breakers a sequence of consecutive measurements may be taken all of which must exceed the threshold value.

Electrical supply line protection apparatus

A fault in a section of an electrical power supply line is detected by measurement of voltage and current, filtering out high frequency components, and calculating approximations of Fourier transforms of a time window of the voltage and current at a predetermined frequency modified by a continuous phase change at that frequency and then calculating the impedance of the section from the modified Fourier transforms of voltage and current (FIG. 2).

Protection of electrical power supply systems

This invention relates to methods and apparatus for detecting the occurrence of a fault on a conductor or transmission line and for protecting the conductor or line in accordance with the determination of fault. The instantaneous value of the voltage (V) and current (i), or the modal components of that voltage and current in the case of a polyphase line, are formed into two functions S.sub.1R and S.sub.2R, which are of the general form V-iR and V+iR respectively where R is a replica of the surge impedance of the line. Superimposed components of these functions are derived by continuously subtracting the steady-state value of each function from its instantaneous value. The sequence in which the functions obtain a value outside a predetermined band of values is monitored to provide an indication of the existence and direction of a fault with respect to the measuring point. Trip and block signals are generated for operating circuit breakers.

Methods and apparatus for fault detection

An electrical power fault protection relay operates when the calculated impedance of the section of the system it protects shows a sudden change. The instantaneous voltage and current is measured. A calculation device then calculates the Fourier transform of a window of the actual voltage and current over a time interval and of the modified current that would flow if the voltage on each side of the time interval was zero. The actual impedance is calculated from the ratio of the Fourier transforms of the actual voltage and the modified current.

Growing community of inventors

Swindon, United Kingdom

Allan Thomas Johns