Apparatus for monitoring arcing of brushes in a dynamoelectric machine
First Claim
1. Apparatus for monitoring arcing of brushes in a generator wherein said arcing may be masked by high-amplitude noise spikes produced by solid-state switching devices in the excitation system of said generator, said apparatus comprising:
- signal receiving means for receiving from a generator brush a composite signal including a brush arcing signal of amplitude S, a noise spike of amplitude N, and a low-frequency signal, said brush arcing signal and said noise spike occurring in the same high-frequency band and having a signal-to-noise ratio, S/N, which may be so low that said noise spike substantially masks said brush arcing signal from accurate detection;
a filter for removing said low-frequency signal from said composite signal;
a clipping network for removing from said composite signal all components above a preselected amplitude to provide a clipped signal with S'"'"'/N'"'"' ratio at least equal to a preselected value, where S'"'"' and N'"'"' are respectively the amplitude of said brush arcing signal and said noise spike after their passage through said clipping network;
an amplifier responsive to said filtered and clipped composite signal to produce an amplified signal;
an integrator connected to said amplifier and operable to produce an integrated signal in response to said amplified signal; and
an alarm system operable to compare said integrated signal with a reference signal and to produce an alarm signal when said integrated signal exceeds said reference signal.
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Abstract
Apparatus is described for monitoring arcing of brushes used in the transfer of current signals to and from the field of a generator. Electrical signals from the brushes, which are applied to the disclosed monitor for analysis, may include brush arcing signals to be monitored and in addition high-amplitude noise spikes in the same frequency band as the brush arcing signals, the noise spikes thus masking accurate detection of low level brush arcing by conventional devices. A two-stage clipping network is provided in the monitor to raise the brush arcing/noise ratio and thus mitigate the masking effect of the noise spikes without loss of a portion of sampling interval during which arcing may occur. Other features described as part of the brush monitor are discriminator diodes biased for constant threshold sensitivity to maintain arc detection accuracy over a wide range of ambient temperatures; an alarm system which functions to indicate and record the occurrence of brush arcing so that corrective action may be initiated to prevent serious damage to rotor slip rings and brush components; and a reference signal generator which automatically adjusts the level of reference signal used in the alarm system for changes in generator noise level.
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Citations
11 Claims
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1. Apparatus for monitoring arcing of brushes in a generator wherein said arcing may be masked by high-amplitude noise spikes produced by solid-state switching devices in the excitation system of said generator, said apparatus comprising:
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signal receiving means for receiving from a generator brush a composite signal including a brush arcing signal of amplitude S, a noise spike of amplitude N, and a low-frequency signal, said brush arcing signal and said noise spike occurring in the same high-frequency band and having a signal-to-noise ratio, S/N, which may be so low that said noise spike substantially masks said brush arcing signal from accurate detection; a filter for removing said low-frequency signal from said composite signal; a clipping network for removing from said composite signal all components above a preselected amplitude to provide a clipped signal with S'"'"'/N'"'"' ratio at least equal to a preselected value, where S'"'"' and N'"'"' are respectively the amplitude of said brush arcing signal and said noise spike after their passage through said clipping network; an amplifier responsive to said filtered and clipped composite signal to produce an amplified signal; an integrator connected to said amplifier and operable to produce an integrated signal in response to said amplified signal; and an alarm system operable to compare said integrated signal with a reference signal and to produce an alarm signal when said integrated signal exceeds said reference signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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Specification