Detection of subsidence current in the determination of circuit breaker status in a power system
First Claim
1. An apparatus for detection of subsidence current in a current transformer which is part of a power system which includes a protective relay and an associated circuit breaker, wherein the dropping-out of a current-responsive element in the protective relay indicates that the circuit breaker is open and wherein subsidence current applied to the current-responsive element prevents the current-responsive element from dropping out for an amount of time following opening of the breaker, the apparatus comprising:
- means for detecting a zero crossing during a predetermined period of time for at least one of (a) unfiltered secondary current from the power system and (b) filtered secondary current from the power system, wherein the predetermined time is greater than half the period of the frequency of the power system signal and the lack of zero crossings indicates the presence of subsidence current; and
means for processing the output of the detector and the output status of the current-responsive element to generate a resulting signal which indicates that the breaker has in fact opened, in the event that no zero crossings are detected during said predetermined time.
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Accused Products
Abstract
The apparatus detects subsidence current from unfiltered as well as filtered secondary current values in the current transformer. A lack of zero crossings during a predetermined period is a reliable indication of the presence of subsidence current. If subsidence current is detected, then a signal is generated which indicates that the circuit breaker for the power system has opened, providing an accelerated indication thereof relative to an indication produced by an overcurrent element dropping out.
20 Citations
36 Claims
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1. An apparatus for detection of subsidence current in a current transformer which is part of a power system which includes a protective relay and an associated circuit breaker, wherein the dropping-out of a current-responsive element in the protective relay indicates that the circuit breaker is open and wherein subsidence current applied to the current-responsive element prevents the current-responsive element from dropping out for an amount of time following opening of the breaker, the apparatus comprising:
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means for detecting a zero crossing during a predetermined period of time for at least one of (a) unfiltered secondary current from the power system and (b) filtered secondary current from the power system, wherein the predetermined time is greater than half the period of the frequency of the power system signal and the lack of zero crossings indicates the presence of subsidence current; and means for processing the output of the detector and the output status of the current-responsive element to generate a resulting signal which indicates that the breaker has in fact opened, in the event that no zero crossings are detected during said predetermined time. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A process for detection of subsidence current in a current transformer which is part of a power system which includes a protective relay and an associated circuit breaker, wherein the dropping out of a current-responsive element in the protective relay indicates that the circuit breaker is open and wherein existence of subsidence current applied to the current-responsive element prevents the current-responsive element from dropping out for a time following opening of the breaker, the process comprising the steps of:
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detecting a zero crossing during a predetermined period of time for at least one of (a) unfiltered secondary current from the power system and (b) filtered secondary current from the power system, wherein the predetermined time is greater than half the period of the frequency of the power system signal and the lack of zero crossings indicates the presence of subsidence current; and processing the output of the detector and the output status of the current-responsive element to generate a resulting signal which indicates that the breaker has in fact opened, in the event that no zero crossings are detected during said predetermined time. - View Dependent Claims (14, 15, 16, 17, 18)
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19. An apparatus for detection of subsidence current in a current transformer which is part of a power system which includes a protective relay and an associated circuit breaker, wherein the dropping-out of a current-responsive element in the protective relay indicates that the circuit breaker is open and wherein subsidence current applied to the current-responsive element prevents the current-responsive element from dropping out for an amount of time following actual opening of the breaker, the apparatus comprising:
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means for detecting whether a zero crossing has occurred in the time interval between a present sample and a prior sample of unfiltered secondary current from the power system; means for detecting whether a sign change has occurred for a first derivative of said present sample and said prior sample during said time interval; means for determining whether a zero crossing or a sign change has been detected during a preestablished time; and means responsive to said determining means for generating an output signal which is indicative of the presence of subsidence current, if no zero crossings or sign changes have occurred during said preestablished time, wherein the output signal is useful in indicating that the circuit breaker has opened. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26, 27)
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28. A process for detection of subsidence current in a current transformer which is part of a power system which includes a protective relay and an associated circuit breaker, wherein the dropping-out of a current-responsive element in the protective relay indicates that the circuit breaker is open and wherein subsidence current applied to the current-responsive element prevents the current-responsive element from dropping out for an amount of time following actual opening of the breaker, the apparatus comprising the steps of:
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detecting whether a zero crossing has occurred in the time interval between a present sample and a prior sample of unfiltered secondary current from the power system; detecting whether a sign change has occurred for a first derivative of said present sample and said prior sample during said time interval; determining whether a zero crossing or a sign change has been detected during a preestablished time; and generating an output signal which is indicative of the presence of subsidence current if no zero crossings or sign changes have occurred during said preestablished time, wherein the output signal is useful in indicating that the circuit breaker has opened. - View Dependent Claims (29, 30, 31, 32, 33, 34, 35, 36)
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Specification