H - Electricity – 02 – H
Patent
H - Electricity
02
H
324/35
H02H 3/32 (2006.01) G01R 29/16 (2006.01) G01R 29/18 (2006.01) H02H 3/34 (2006.01) H02H 7/09 (2006.01)
Patent
CA 1123055
METHOD AND APPARATUS FOR MONITORING LINE VOLTAGE IN A POLYPHASE SOURCE Abstract of the Disclosure A method of monitoring open phase, phase reversal and voltage unbalance conditions in a polyphase source includes shifting the phase of signals which are propor- tional to the line voltages in a three-phase A.C. power source by 180°, +60°, and -60°, respectively, and summing the phase-shifted signals to generate a signal which is proportional to the negative-sequence component of the three-phase line voltage. This signal is rectified and compared with a reference signal. If a net negative- sequence signal is generated over a sufficient time period a positive output signal decreases until it crosses a switching threshold to disconnect a load from the source. The output signal will not rise again to the switching threshold, thereby allowing reconnection of the load, until the negative-sequence signal subsides and is less than the reference signal. A circuit is disclosed with three operational amplifiers and two passive filters to carry out the invented method.
327096
Allen-Bradley Company Inc.
Fetherstonhaugh & Co.
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