Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific quantity comparison means
Patent
1995-03-14
1997-06-24
Gaffin, Jeffrey A.
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific quantity comparison means
361 93, 361115, 361 66, H02H 318
Patent
active
056422504
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
So-called protective devices which monitor lines for faults are used to protect the operation of power supply lines. One such protective device is, for example, a distance protection device. Distance protection measures the impedance of the line and monitors this line for undershooting an impedance value which can be predetermined. Undershooting occurs, for example, in the case of short circuits.
A problem with modern distance protective devices of digital design is that filters are used which have a fixed window width and a fixed release criterion. In this case, there is a contradiction between the two criteria "high accuracy of impedance determination" and "short command time for the off command". Specifically, if a protection algorithm is to operate quickly at a fixed technically sensible sampling frequency, then digital filters having few coefficients must be used. When disturbance variables occur, such filters have large errors in the impedance determination, which leads to a disturbance in the selectivity. In contrast, if a protection algorithm is to operate as selectively as possible, then filters having large numbers of coefficients must be used to damp interference variables. The protection algorithm then, however, has relatively long command times. This problem is known, for example, from "Proceedings of the 25th Universities Power Engineering Conference", Aberdeen, UK, Sep. 12-14, 1990, pages 155 to 158.
A test method is known from EP 0 284 546, in which filters having a fixed window width are used.
SUMMARY OF THE INVENTION
The present invention is based on the object of specifying a signal monitoring method in which the above-mentioned disadvantages of the contradicting criteria are addressed.
Proceeding from the prior art, the inventor found a new way by dispensing with measured-value filters having fixed filter characteristics. Specifically, he confirmed that very inaccurate filters are completely sufficient for certain faults, while high-precision filters are required only in some fault cases.
The object was achieved by a method including the steps of supplying at least one signal to a filter device which has a time-variant filter behavior deriving a fuzzy region from an output signal of said filter device, prompting a release when the fuzzy region is within a release range having limits which can be predetermined, and improving filter characteristics if the conditions are not sufficient for release.
A monitoring device includes a filter device for a signal, said device having a time-variant filter behavior, and downstream-connected release logic in which a fuzzy region is derived from an output signal of the filter device wherein a release signal is produced when the fuzzy region is within a release range having limits which can be predetermined, and wherein a comparison is carried out with improved filter characteristics if the conditions are not sufficient for release. In this way, a signal monitoring method is available which is matched to the present fault situation of the signal. In consequence, simple faults which require only a coarse filter function can be identified in a very short time and lead to a release, while faults which require a higher precision filter function are subject to more intensive filter processing. The method achieves release times which are improved over the prior art in the vast majority of cases.
A fuzzy region, which is used for the release decision, is preferably derived from the output signal, the change with time of the output signal being used in particular. In consequence, a further reduction in the release times can be achieved. In this case, the fuzzy region is to be understood to mean the probability of how precisely the determined impedance (measured-value impedance) corresponds with the actual line impedance (measured impedance). The fuzzy region can be dependent on the filter characteristic and/or the magnitude of a disturbance variable and is in this case used in the sense of a known measurement inaccuracy. If, for
REFERENCES:
patent: 5272428 (1993-12-01), Spiegel
patent: 5289095 (1994-02-01), Ushiyama
patent: 5327355 (1994-07-01), Chiba
patent: 5371695 (1994-12-01), Baraszu
patent: 5416702 (1995-05-01), Kitagawa
Gaffin Jeffrey A.
Jackson Stephen
Siemens Aktiengesellschaft
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