| 摘要 |
Apparatus for detecting the phase relationship and potential difference between the phases of a polyphase electrical circuit and for interrupting the circuit if a shift in phase or a decrease in potential difference occurs beyond acceptable limits. The current-passing terminals of a controlled switching device such as a silicon controlled rectifier are coupled in series with a control device across two phases of the polyphase circuit, while the control electrode such as the gate of the silicon controlled rectifier is coupled to a third phase. So long as the proper phase relationship and potential difference are maintained, current through the circuit is sufficient to maintain the control device in a first state. Should a phase shift or a decrease in potential difference, or a combination thereof, in excess of the allowable limits occur, current through the circuit is insufficient to maintain the control device in that first state, and the power applied from the polyphase source to its load is interrupted.
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