Electricity: motive power systems – Induction motor systems – Power-factor control
Patent
1988-05-23
1989-02-21
Smith, Jr., David
Electricity: motive power systems
Induction motor systems
Power-factor control
318775, H02P 540
Patent
active
048068381
ABSTRACT:
Electric power consumed by an a.c. induction motor is measured and sensed changes in power factor are used to modulate the combined magnetic flux produced in the motor field by two sets of RUN windings. A main RUN winding set, which normally couples fully with the a.c. power, is engineered to have sufficient ampere-turns to produce just enough magnetic flux to operate the motor with a light load and maintain a moderately high power factor. Motor driven load increases are determined by sensing a corresponding increase in the power factor of the main RUN winding set, whereupon power flow to a secondary RUN winding is proportionately increased. Considerable energy savings occurs when the motor drives a fluctuating load due to reduced magnetic field excitation under all but full load conditions, with the result that energy ordinarily wasted by eddy currents, copper losses, and poor power factor operation is considerably lessened. Other possible losses due to harmonic distortion of the a.c. power waveform brought about by the phase-delayed thyristor control of the second run winding power are mostly swamped out and masked by the parallel, always-on major power draw by the main run winding. A motor speed-sensitive switch or relay may divert current around the thyristor and fully excite the second run winding during motor start-up, thereby producing full available motor torque during start-up while negating any electrical stress on the control thyristor.
REFERENCES:
patent: 3819996 (1974-06-01), Hablsohn
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patent: 4263540 (1981-04-01), Brandt et al.
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patent: 4453118 (1984-06-01), Phillips et al.
patent: 4533857 (1985-08-01), Chang et al.
"Scientific American" magazine, `Energy-efficient Buildings` (Rosenfeld and Hafemeister), Apr. 1988, pp. 56-63.
"New England Business" magazine, `NEB Reports-Energy` (Dana Bottorff), May 2, 1988, pp. 39-40.
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