Importance

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Abstract

There is disclosed a monitoring apparatus for a multiphase electrical system of very simple and reliable circuit design capable of monitoring such a system and producing fault signals to operate protective relays and for visual indication. A main component of the apparatus is a multiphase, full-wave bridge rectifier circuit having matched voltage dropping input resistors so that the output of the bridge is a low voltage fluctuating DC signal such that neither the semiconductor diode rectifiers of the full-wave bridge or other internal components of the monitoring apparatus are exposed to high power line voltages. Phase unbalance in the apparatus is detected by evaluating the ratio of the peak to trough voltage of the fluctuating DC signal produced by the full-wave bridge. If the trough voltage drops below approximately 85% of the peak voltage, this is a very reliable indication of phase unbalance; the apparatus is adjustable to determine the magnitude of unbalance required to produce a fault signal and/or visual indication. The apparatus also incorporates high and low-voltage monitoring features utilizing some of the same signals produced by the full-wave bridge for phase monitoring purposes; any one of the monitoring features can cause a general fault signal, and operation of a protective device or individual visual indications may be provided to distinguish out of range voltage conditions and phase unbalance conditions.

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First Claim