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Protective relay circuit providing a combined distance and overcurrent function

  • US 4,092,690 A
  • Filed: 01/31/1977
  • Issued: 05/30/1978
  • Est. Priority Date: 01/31/1977
  • Status: Expired due to Term
First Claim
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1. A protective relay circuit for providing a combination distance and overcurrent relay function for controlling the trip coil of a circuit breaker protecting an alternating current power transmission line, comprising:

  • difference circuit means for producing a difference signal proportional to the difference between a signal proportional to an a-c power line current multiplied by a preselected constant reference impedance and a signal proportional to line voltage;

    an alternating current level detector responsive to the difference signal from said difference circuit means for producing an output signal when said difference signal exceeds a predetermined threshold value representative of a preselected parameter of said power line;

    means for generating a voltage polarity signal from a line voltage signal of said alternating current power transmission line;

    coincidence detector means for producing a coincidence signal output in response to detecting coincidence between the output of said alternating current level detector and the voltage polarity signal;

    coincidence-responsive means for receiving said coincidence signal output and being operative, when enabled, to effect operation of said trip coil in response to a coincidence signal output of a predetermined minimum duration; and

    said protective relay circuit permitting production of an effective coincidence signal output only if said difference signal exceeds said predetermined threshold value.

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