Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
1998-09-28
2001-01-16
Assouad, Patrick (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C702S069000, C702S072000, C324S076770, C324S086000, C361S076000, C361S079000
Reexamination Certificate
active
06175810
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of generating a signal identifying a three-pole short-circuit occurring in a three-phase power transmission line in which the phase currents and phase voltages are sampled forming phase current and phase voltage sampling values and the signal is formed from the phase current and phase voltage sampling values.
BACKGROUND INFORMATION
The reference “Bedienungshandbuch zum Schutzger{umlaut over (a)}t” (Protection Device Operating Manual), 7SA513 V3.1, Siemens AG, p. 68, describes a method in which phase currents and phase voltages are sampled to forming phase current and phase voltage sampling values. An impedance vector is formed from these sampling values and tested for its rate of change in the complex R-X impedance plane. A signal identifying a three-pole short-circuit is generated if the rate of change of the impedance vector in the R-X impedance plane is excessively high.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method with which three-pole short-circuits are particularly reliably detected during oscillations.
This object is achieved according to the present invention by forming a positive phase-sequence system effective power parameter proportional to the instantaneous value of the positive phase-sequence system effective power in the power transmission line. The positive phase-sequence system effective power parameter is supplied to a digital filter in which a component of the positive phase-sequence system effective power parameter is determined, exponentially decaying over time and oscillating with grid frequency. The positive phase-sequence system effective power parameter is supplied to a second digital filter where an additional positive phase-sequence system effective power parameter component, exponentially decaying over time, oscillating with grid frequency and orthogonal to the first parameter component, is determined. The positive phase-sequence system effective power parameter is supplied to a third digital filter, where an oscillating positive phase-sequence system component parameter that oscillates over time with a swing frequency is determined, the first and the additional parameter components are squared and added, forming a grid frequency component parameter of the positive phase-sequence system effective power parameter, and the signal is generated with the swing component parameter and the grid frequency component parameter.
An advantage of the method according to the present invention is that three-pole short-circuits can be very reliably detected even during power oscillations, since the swing component and the short-circuit component in the positive phase-sequence system effective power parameter are separated by the use of the digital filter, which allows a particularly reliable detection of three-pole short-circuits in the power transmission line.
In the method according to the present invention, the first signal identifying the three-pole short-circuit is determined from the swing component parameter and the grid frequency component parameter. This can be achieved in a particularly simple and therefore advantageous manner by squaring the swing component parameter, forming a quotient of the grid frequency component parameter and the squared swing component parameter, and generating the signal when the quotient exceeds a predefined threshold value.
The positive phase-sequence system effective power parameter can be formed in a particularly quick and advantageous manner by subjecting the phase current and phase voltage sampled values to an &agr;&bgr; transform (Clarke transform), forming transformed sampled values and forming the positive phase-sequence system effective power parameter from the transformed sampling values.
Non-recursive filters, for example, are digital filters that can be implemented in a particularly simple manner, so that it is considered advantageous if the first, second and/or third filters are non-recursive (FIR) filters.
In order to determine the three-pole short-circuit, a parameter component, oscillating with grid frequency and decaying exponentially over time, and another parameter component, oscillating with grid frequency and decaying exponentially over time, is formed from the positive phase-sequence system effective power parameter according to the present invention, the first and the second parameter components being orthogonal to one another. These method steps can be executed in a particularly simple manner if one parameter component is sinusoidal and the second parameter component is cosinusoidal.
In order to prevent low-frequency interfering signals in the positive phase-sequence system effective power parameter from affecting the measurement accuracy as the two parameter components are determined, it is considered particularly advantageous if the positive phase-sequence system effective power parameter is subjected to high-pass filtering prior to being supplied to the first and the second filters.
A particularly high measurement accuracy can be achieved in the method according to the present invention if the first and second parameter components are determined by using an optimum filter designed to filter out the signal component A*exp(−t/&tgr;)*sin(&ohgr;t) as the first filter, where A is an amplitude, &tgr; is a constant and &ohgr; is the grid circuit frequency, and by using an optimum filter designed to filter out the signal component B*exp(−t/&tgr;)*cos(&ohgr;t) as the second filter, where B is another amplitude.
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patent: 4261038 (1981-04-01), Johns et al.
patent: 4333119 (1982-06-01), Schoenmeyer
patent: 4479160 (1984-10-01), Stacey
patent: 4641088 (1987-02-01), Jacobsson
patent: 4795983 (1989-01-01), Crockett et al.
patent: 5224011 (1993-06-01), Yalla et al.
patent: 5378979 (1995-01-01), Lombardi
patent: 5544089 (1996-08-01), Hemminger et al.
Assouad Patrick
Bui Bryan
Kenyon & Kenyon
Siemens AG
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