Ground fault circuit interrupter with grounded neutral protection
First Claim
1. A ground fault protective apparatus for use on an AC electrical circuit having a line conductor and a neutral conductor grounded at a power source, comprising:
- means for sensing current imbalance on said line and neutral conductors, said sensing means providing an output signal proportional to said imbalance;
means for integrating said output signal and for providing a trip indication whenever said signal integration value exceeds a predetermined reference level;
means for inducing a test voltage on said neutral conductor, whereby a current imbalance is produced between said line and neutral conductors which is proportional to the neutral-to-ground conductance;
means for providing a reference current proportional to said test voltage;
means connected to the input of said integrating means for comparing said reference current to the output signal of said sensing means, said comparing means supplying a signal current to the input of said integrator whenever the output signal of said sensing means rises above said reference current, said signal current being of sufficient amplitude to cause said integrator means to produce a trip indication.
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Abstract
A ground fault circuit interrupter includes a differential current transformer sensing winding supplying input to an integrator which is reset to zero at the end of each half-cycle of AC line current. A line-to-ground fault current will cause the integrator output to exceed a predetermined limit value and produce a trip indication. A saturable neutral transformer supplies a voltage to the neutral line and a reference current proportional to the neutral voltage to a comparator. The peak value of the reference current is compared to the peak value of the sensing winding output. A low-resistance neutral-to-ground path causes the sensing winding output to exceed the reference current and a signal to be added to the integrator input, thereby producing a trip indication which energizes an SCR to activate a solenoid. Means are provided to produce a positive feedback signal to insure a "hard" turn-on of the SCR upon receipt of a trip indication, the feedback means also including capability to "remember" a trip indication at the end of a half-cycle near current zero, and to produce the positive feedback signal at the beginning of the next succeeding half cycle.
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Citations
16 Claims
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1. A ground fault protective apparatus for use on an AC electrical circuit having a line conductor and a neutral conductor grounded at a power source, comprising:
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means for sensing current imbalance on said line and neutral conductors, said sensing means providing an output signal proportional to said imbalance; means for integrating said output signal and for providing a trip indication whenever said signal integration value exceeds a predetermined reference level; means for inducing a test voltage on said neutral conductor, whereby a current imbalance is produced between said line and neutral conductors which is proportional to the neutral-to-ground conductance; means for providing a reference current proportional to said test voltage; means connected to the input of said integrating means for comparing said reference current to the output signal of said sensing means, said comparing means supplying a signal current to the input of said integrator whenever the output signal of said sensing means rises above said reference current, said signal current being of sufficient amplitude to cause said integrator means to produce a trip indication. - View Dependent Claims (2, 3, 4, 5)
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6. Ground fault protective apparatus for use on an AC electrical circuit having a line conductor and a neutral conductor, comprising:
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means for sensing current imbalance on said line and neutral conductors, said sensing means providing an output signal proportional to said imbalance; means for integrating said output signal; means connected to said integrating means for providing a trip indication whenever the output of said intergating means exceeds a predetermined reference; means for resetting said integrating means after each half cycle of said AC electrical circuit; and means for generating a feedback signal to the input of said integrating means when the output of said integrating means exceeds a predetermined level.
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7. Ground fault protective apparatus for use on an AC electrical circuit having a line conductor and a neutral conductor, comprising:
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means for sensing current imbalance on said line and neutral conductors, said sensing means providing an output signal proportional to said imbalance; means for integrating said output signal; means connected to said integrating means for providing a trip indication whenever the output of said integrating means exceeds a predetermined reference; and means for resetting said integrating means after each half cycle of said AC electrical circuit; said trip indicating means comprising a switching device having an input terminal connected to said integrating means and an output circuit operable between open and closed positions in response to said input terminal, said apparatus comprising memory means connected to said input terminal for maintaining electrical parameters produced at said input terminal when said integrating means output exceeds said predetermined reference, whereby said switching device output terminals are maintained in the closed position for a period exceeding one half cycle on said line and neutral conductors. - View Dependent Claims (8, 9, 10)
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11. Ground fault protective apparatus for use on an AC electrical circuit having a line conductor and a neutral conductor, comprising:
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means for sensing current imbalance on said line and neutral conductors, said sensing means providing an output signal proportional to said imbalance; means for integrating said output signal; means connected to said integrating means for providing a trip indication whenever the output of said integrating means exceeds a predetermined reference; and means for generating a feedback signal to the input of said integrating means when the output of said integrating means exceeds a predetermined level.
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12. Ground fault protective apparatus for use on an AC electrical circuit having a line conductor and a neutral conductor, comprising:
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means for sensing current imbalance on said line and neutral conductors, said sensing means providing an output signal proportional to said imbalance; means for integrating said output signal; first trip means connected to said integrating means for providing a trip indication whenever the output of said integrating means exceeds a predetermined reference; means for inducing a test voltage upon said neutral conductor, whereby a current imbalance is produced between said line and neutral conductors which is proportional to the neutral-to-ground conductance; and second trip means connected to said sensing means and responsive to the instantaneous value of said sensing means output signal for producing a trip indication when the instantaneous value of said output signal exceeds a second predetermined reference level. - View Dependent Claims (13, 14, 15, 16)
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Specification