Apparatus and method for filtering current sensor output signals
First Claim
1. An electronic filter for filtering the output signal of a current sensor of a circuit breaker, the current sensor having an output signal characteristic similar to that of a Rogowski coil output signal characteristic that includes a third harmonic noise component in response to a switching primary current of the circuit breaker, the circuit breaker having an electronic trip unit with an instantaneous pick-up setting responsive to the output signal of the current sensor, the electronic filter comprising:
- a first stage having a first transfer function that defines first characteristic poles, the first stage permitting passage of the third harmonic noise component; and
a second stage having a second transfer function that defines second characteristic poles, the second stage filtering the third harmonic noise component.
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Abstract
An electronic filter for filtering the output signal of a current sensor of a circuit breaker is disclosed. The current sensor has an output signal characteristic similar to that of a Rogowski coil output signal characteristic that includes a third harmonic noise component in response to a switching primary current of the circuit breaker, and the circuit breaker has an electronic trip unit with an instantaneous pick-up setting responsive to the output signal of the current sensor. The electronic filter includes a first stage and a second stage. The first stage has a first transfer function that defines first characteristic poles and permits passage of the third harmonic noise component. The second stage has a second transfer function that defines second characteristic poles and filters the third harmonic noise component.
43 Citations
19 Claims
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1. An electronic filter for filtering the output signal of a current sensor of a circuit breaker, the current sensor having an output signal characteristic similar to that of a Rogowski coil output signal characteristic that includes a third harmonic noise component in response to a switching primary current of the circuit breaker, the circuit breaker having an electronic trip unit with an instantaneous pick-up setting responsive to the output signal of the current sensor, the electronic filter comprising:
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a first stage having a first transfer function that defines first characteristic poles, the first stage permitting passage of the third harmonic noise component; and a second stage having a second transfer function that defines second characteristic poles, the second stage filtering the third harmonic noise component. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. An electronic trip unit for a circuit breaker having a current sensor with an output signal characteristic similar to that of a Rogowski coil output signal characteristic that includes a third harmonic noise component in response to a switching primary current of the circuit breaker, the electronic trip unit comprising:
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a two-stage filter in signal communication with the output of the current sensor, a first stage of the two-stage permitting passage of the third harmonic noise component, and a second stage of the two-stage filter filtering the third harmonic noise component; a comparator in signal communication with the output of the two-stage filter; and an actuating circuit in signal communication with the output signal of the comparator; wherein the electronic trip unit has an instantaneous pick-up setting, and in response to the filtered signal from the two-stage filter, the electronic trip unit has instantaneous pick-up accuracy equal to +/−
10% of the instantaneous pick-up setting. - View Dependent Claims (13, 14, 15, 16)
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17. A method of conditioning an output signal of a current sensor of an electronic circuit breaker, the current sensor having an output signal characteristic similar to that of a Rogowski coil output signal characteristic that includes a third harmonic noise component in response to a switching primary current of the circuit breaker, the circuit breaker having an electronic trip unit with an instantaneous pick-up setting responsive to the output signal of the current sensor, the method comprising:
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filtering the output signal of the current sensor to produce a first filtered signal, the first filtered signal including the third harmonic noise component; and filtering the first filtered signal to produce a second filtered signal, the second filtered signal being representative of the instantaneous primary current of the circuit breaker with an accuracy of equal to or greater than 90%, the second filtered signal excluding the third harmonic noise component. - View Dependent Claims (18, 19)
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Specification