Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Patent
1977-06-20
1979-06-26
Moose, Jr., Harry E.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
361 44, 361 45, 361 46, H02H 316
Patent
active
041594991
ABSTRACT:
A circuit for detecting line-to-ground and neutral-to-ground faults and in response thereto interrupting the line conductor. Included in the circuit is a magnetic core about which the neutral conductor and line conductor are wound to produce a zero net magnetomotive force in the core in the absence of a line fault and a non-zero net magnetomotive force in the presence of a line fault. A secondary winding wound on the core has at least one diode or thermistor connected thereacross. The diode or thermistor has a dynamic impedance, which is reflected back to the neutral winding, which decreases when current flows through the diode or temperature rises in the thermistor in response to an induced voltage in the secondary winding caused by non-zero net magnetomotive force in the core produced by a current imbalance in the line and neutral conductors due to a line fault. Also included is a constant current high frequency oscillator and a voltage sensor connected across the neutral winding to detect decreases in neutral winding resistance due to a line fault and/or decreases in high frequency current through the neutral winding due to neutral fault. An electro-mechanical actuator responsive to the voltage monitor trips a circuit breaker to interrupt the line conductor when a neutral or line fault is detected by the voltage monitor. Alternatively, the constant current oscillator and voltage sensor could be replaced by a constant voltage oscillator connected between the load side of the neutral winding and ground and a current sensor in series with the oscillator for detecting line and neutral faults.
REFERENCES:
patent: 3614533 (1971-10-01), Douglas et al.
patent: 4021729 (1977-05-01), Hudson, Jr.
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