Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Patent
1975-04-17
1977-10-11
Miller, J. D.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
361 63, 361113, H02H 328
Patent
active
040538150
ABSTRACT:
In a distribution circuit for connecting a load to an a-c source, it is known that a ground-to-neutral short tends to reduce the sensitivity of ground fault detectors that use a differential current transformer to sense line-to-ground leakage. A resonated coil on a core links the neutral conductor forming part of a protective device for interrupting the load circuit in the event of reduced Q of the resonated coil caused by a neutral-to-ground fault. The core must also link the line conductor, for otherwise a loop including the line, the load and the neutral would wrongly have a like effect.
The same core and coil are used with a common amplifier for the neutral-to-ground fault detector and for the line-to-ground leakage detector, so that the apparatus can be economical and compact. Furthermore, so long as there is no neutral-to-ground fault, the amplifier delivers a signal of normal strength that monitors the integrity of both detectors. The detector also responds to "run-away" of the monitoring signal generator.
REFERENCES:
patent: 3638072 (1972-01-01), Kobayashi
patent: 3713003 (1973-01-01), Benham
patent: 3754194 (1973-08-01), Camp, Jr.
patent: 3786356 (1974-01-01), MacPhee
patent: 3800189 (1974-03-01), Montz
patent: 3801871 (1974-04-01), Loh
patent: 3879639 (1975-04-01), Sircom
Federal Pacific Electric Company
Hoffman Lawrence A.
Martin Paul S.
Miller J. D.
Salce Patrick R.
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