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Portable ground fault detector

  • US 5,363,047 A
  • Filed: 10/30/1992
  • Issued: 11/08/1994
  • Est. Priority Date: 10/30/1992
  • Status: Expired due to Fees
First Claim
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1. Apparatus for detecting a ground fault condition in a normally ungrounded supply system including conductors from a supply for supplying power to a load connected in the system, the apparatus comprising:

  • (a) divider means for connecting a test impedance across the power supply, the test impedance having a tapping point;

    (b) grounding means for periodically connecting the tapping point to ground potential;

    (c) a current transducer for measurement of electrical current in one or more of the conductors at a location downstream of the divider means during operation of the system; and

    (d) a detector circuit for signalling the ground fault condition, comprising;

    (i) a gain circuit for producing a first voltage signal, the first voltage signal being proportional to the electrical current measured by the current transducer over a range of the current in excess of 10 A;

    (ii) an integrator for producing an integrator signal, the integrator having a summing input that is maintained proximate a first reference voltage;

    (iii) an oscillator for producing a variable frequency oscillator output, the frequency of the oscillator output being smoothly proportional to an average DC component of the integrator signal;

    (iv) a reference resistor connected between the gain circuit and the summing input for converting the first voltage signal to a current feeding the integrator;

    (v) a reference capacitor; and

    (vi) a switch controller responsive to the oscillator for sequencing the reference capacitor among a first connection wherein opposite sides of the capacitor are connected between the first reference voltage and a second reference voltage, a second connection between the summing input and the second reference voltage, a third connection between the summing input and the first reference voltage, and a fourth connection of both sides to the same potential, the frequency of the oscillator being a repeatable function of the net current sensed by the current transducer.

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