General Electric Company

James S Bishop

Fred H Sawada

Frank M Klementowski

Llewellyn A Blaize

High noise immunity instrumentation for monitoring brush arcing in a dynamoelectric machine is disclosed. In a preferred form the instrumentation includes a stabilized variable threshold discriminator operative in conjunction with a feedback network and a non-linear high frequency amplifier to provide a discriminator threshold which increases with increasing levels of background noise so that only the arc indicative portions of the signal are passed. A substantial increase in the signal to noise ratio is obtained. The feedback network includes a relatively long time constant integrator and buffer amplifier. Further, to provide an alarm upon the occurrence of brush arcing, an alarm network is provided which includes a comparator for continuously comparing the arc indicative signal with a reference signal which is automatically adjusted to compensate for changes in the average level of the signal from the non-linear high frequency amplifier. This compensation provides for automatically resetting the alarm comparator. This is achieved by providing a second integrator having a time constant somewhat longer than the first integrator. By appropriately selecting the relative time constants of the first and second integrators, resolution of the alarm network is narrowed to a unit time basis, thus quantifying the measurement to provide an indication of the condition of the brushes.

High sensitivity brush arcing monitor for a dynamoelectric machine

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.

Apparatus for monitoring arcing of brushes in a dynamoelectric machine

A system is provided for monitoring a composite signal at the brushes of a generator. The composite signal includes an information signal representative of brush arcing and a recurring noise signal. The system includes a gating network which eliminates the noise signal and passes the information signal therethrough. Timing of the gating network is controlled by a pulse forming network. On the occurrence of a noise signal the pulse forming network produces a disabling signal of predetermined time period exceeding the duration of the noise signal. The gating network blocks all signal passage therethrough for the duration of the disabling signal and thereafter passes signals until the occurrence of the next noise signal. Means is also provided for indicating when the information signal exceeds a predetermined magnitude.

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Schenectady, NY, United States of America

James S Bishop