Ground fault circuit interrupter and electronic module therefor
AssigneeGeneral Electric Company
InventorsEdward Keith Howell, Donald Leland Watrous, Robert George Hodgins
Life of this patent
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Abstract
An electronic module for ground fault circuit interrupters (GFCI) in both circuit breaker and receptacle configurations includes a signal processor having a plurality of fault signal threshold stages for differentially charging an integrating capacitor in accordance with the magnitude of the fault signal as amplified by a high gain differential amplifier. The accumulated charge on the integrating capacitor controls the generation of a trip signal. The processor also includes a highly stable grounded neutral excitation oscillator and a noise rejection network to combat nuisance tripping.
Claims24
A ground fault circuit interrupting device for interrupting an AC power distribution circuit including line and neutral conductors in response to a ground fault on either conductor;
- said device comprising, in combination:
- A. contacts for interrupting at least one side of the distribution circuit;
- B. a solenoid energizable from the distribution circuit to initiate circuit interruption by said contacts;
- C. a normally non-conductive switch connected in the solenoid energization circuit, said switch having a control input;
- D. a differential current transformer responsive to a current imbalance in the line and neutral conductors signifying a ground fault for developing a fault signal of a magnitude proportional to the fault current;
- and
- E. a signal processor for processing said fault signal, said processor including:
- 1. an amplifier for amplifying said fault signal,
- 2. a trip signal bus,
- 3. an integrating capacitor connected to said trip signal bus,
- 4. a plurality of threshold circuits connected in parallel to said trip signal bus and individually responsive to the amplified fault signal developed by said amplifier for establishing respectively increasing charging rates for said integrating capacitor depending on the amplified fault signal amplitude, and
- 5. means connected to said trip signal bus and responsive to the voltage thereon developed by the charge accumulating on said integrating capacitor for generating a trigger signal input to render said switch conductive when said trip signal bus voltage reaches a predetermined level,
- a. whereby to actuate said solenoid and initiate circuit interruption by said contacts.
A signal processor for use in a ground fault circuit interrupting device adapted to interrupt an AC power distribution circuit including line and neutral conductors in response to a ground fault on either conductor;
- said processor comprising, in combination:
- A. an amplifier for amplifying a fault signal developed in response to a detected imbalance in the currents flowing in the line and neutral conductors as the result of a ground fault, said fault signal having a magnitude proportional to the fault current;
- B. a trip signal bus;
- C. an integrating capacitor connected to said trip signal bus;
- D. a plurality of threshold circuits connected in parallel to said trip signal bus and individually responsive to the amplified fault signal developed by said amplifier for establishing respectively more rapid charging rates for said integrating capacitor depending on the amplified fault signal magnitude;
- E. means connected to said trip signal bus and responsive to the voltage thereon developed by the charge accumulating on said integrating capacitor for generating a trip signal to precipitate circuit interruption of the ground fault circuit interrupting device when said trip signal bus voltage reaches a predetermined level;
- and
- F. an additional threshold circuit having a first input connected to receive the fault signal and a second input coupled to said trip signal bus, said additional threshold circuit connected to control charging of said integrating capacitor at a more rapid rate than accommodated by said plural threshold circuit in response to a high magnitude fault signal appearing at said first input and in response to a voltage on said trip signal bus within a predetermined limited range of said predetermined level.
An electronic module for use in a ground fault circuit interrupting device having contacts separable in response to energization of a trip solenoid to interrupt an AC power distribution circuit including line and neutral conductors in the event of a ground fault on either conductor, said module comprising, in combination;
- A. a normally non-conductive switch for connection in the energizing circuit for the trip solenoid, said switch having a control input;
- B. a differential current transformer for developing a fault signal in response to a current imbalance in the line and neutral conductors signifying a ground fault, said fault signal having a magnitude proportional to the fault current;
- C. a power supply section for connection to the distribution circuit to develop a rectified DC voltage at a regulated level on a supply bus;
- D. an amplifier for amplifying said fault signal;
- E. a trip signal bus;
- F. an integrating capacitor connected between said supply bus and said trip signal bus;
- G. first means responsive to the output of said amplifier for controlling the charging of said capacitor at a rate indicative of the magnitude of said fault signal, thereby to develop a trip signal voltage on said trip signal bus;
- H. means connected to said trip signal bus and operable when said trip signal voltage reaches a predetermined level to issue a triggering signal to said control input, thereby rendering said switch conductive to enable energization of the trip solenoid;
- and
- I. nuisance trip prevention means including switching means connected in shunt with said switch control input and controlled by said trip signal voltage on said trip signal bus to shunt triggering signals from said control input so long as said trip signal voltage remains below said pre-determined level.
Dependencies are inferred from the claim text.