Electricity: electrical systems and devices – Safety and protection of systems and devices – Motor protective condition responsive circuits
Patent
1978-08-21
1980-02-05
Moose, Jr., Harry E.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Motor protective condition responsive circuits
361 42, 361 65, 361 79, H02H 708
Patent
active
041875230
ABSTRACT:
A dynamo-electric machine is provided with a protective circuit arrangement whereby the machine is caused to be switched off if a short circuit current flowing in the machine exceeds a predetermined level.
False operation of the protective circuit is avoided by incorporating a discriminating circuit which is able to distinguish the phase angle between the current and the voltage. This causes the protective circuit to trip for an over load current where the phase angle difference is small and the power factor near unity, which occurs with resistive fault situations; and not to trip where the phase angle difference is high, and thus there is a low power factor indicating a reactive condition, which occurs on start-up of the machine. A machine is able to run more safely as a result.
REFERENCES:
patent: 2462799 (1949-02-01), Young et al.
patent: 3590322 (1971-06-01), Carr
patent: 4106069 (1978-08-01), Trautner et al.
Coal Industry (Patents) Limited
Moose Jr. Harry E.
Wray James C.
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