Electricity: electrical systems and devices – Safety and protection of systems and devices – Motor protective condition responsive circuits
Patent
1979-05-08
1981-02-17
Moose, Jr., Harry E.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Motor protective condition responsive circuits
361 80, H02H 326
Patent
active
042518466
ABSTRACT:
Apparatus is provided for sensing and responding to short circuit faults, in particular in three phase alternating current supply lines for direct-on-line starting three phase squirrel cage induction motors. Line current in each line is sensed by a respective current transformer and signals representing both the amplitude and phase of each line current are produced. Line-to-line or line-to-neutral voltage for each phase is also sensed, by photo-electric isolator circuitry, and signals produced representative of the respective phases of these voltages. Logic circuitry is used to produce from the signals representative of current and voltage phases three phase difference signals in the form of currents each varying substantially directly with the difference between the respective current and voltage phases of the respective line. The relationships between these difference signals and the respective current amplitude signals are compared with the relationship which corresponds to conditions from starting to normal running of the motor, and an output signal is produced representing whether there is correspondence or not between the compared relationships. If lack of correspondence is indicated, a circuit breaker is operated to break the supply lines upstream of the sensing equipment.
REFERENCES:
patent: 3543092 (1970-11-01), Hoel
patent: 4179651 (1979-12-01), Vitins
"Phase Sensitive Short Circuit Protection"-Gray Mining Technology Apr. 1978, pp. 133-136.
Lord Harold
Pearson Frank K.
Moose Jr. Harry E.
National Research Development Corporation
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