Apparatus for monitoring arcing of brushes in a dynamoelectric machine

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.