Overcurrent and ground fault responsive trip unit for circuit br

Details Overcurrent and ground fault responsive trip unit for circuit br Overcurrent and ground fault responsive trip unit for circuit br

1977-05-06

1978-09-19

Moose, Jr., Harry E.

Electricity: electrical systems and devices

Safety and protection of systems and devices

Ground fault protection

361 44, 361 96, H02H 316

Patent

active

041158296

ABSTRACT:
A circuit breaker electronic trip unit is equipped with a plurality of current transformers for sensing overcurrent and ground fault conditions in a distribution circuit. A ground fault signal voltage is applied to a differential amplifier together with an adjusted voltage establishing a desired ground fault signal pick-up level. The differential amplifier controls a variable duty cycle switch to establish charging versus discharging rates for a timing capacitor in accordance with the ground fault signal amplitude. When the voltage across the capacitor exceeds a predetermined threshold, a thyristor is triggered to draw a safe level of energizing current through a trip coil. Secondary open circuited protection is provided for any of the current transformers disposed externally of the circuit breaker.

REFERENCES:
patent: 3328638 (1967-06-01), Reis
patent: 3329870 (1967-07-01), De Viney et al.
patent: 3713005 (1973-01-01), Engel
patent: 3959695 (1976-05-01), Shimp

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