Electricity: motive power systems – Induction motor systems – Primary circuit control
Patent
1988-02-16
1989-04-18
Smith, Jr., David
Electricity: motive power systems
Induction motor systems
Primary circuit control
318775, 318777, 318779, H02P 540
Patent
active
048230677
ABSTRACT:
Power consumed by an ordinary a.c. induction motor is reduced by having two parallel sets of separately excited RUN windings. When the motor is lightly loaded, a.c. power feeds only one of the two RUN windings, thereby reducing the flux density in the motor stator and as a result reducing eddy current losses and copper losses. Whe the load increases, a.c. power is immediately fed to the other RUN winding thereby increasing the magnetic flux density and the motor power. The a.c. power fed to the second winding is variably controlled by a thyristor, and the amount of thyristor coupled power may be determined from sensing changes in the speed slip of the induction motor wrought by load changes. Through having the one RUN winding permanently connected with the power source, while the other RUN winding power is modulated by the phawe controlled gating action of the thyristor, less a.c. power line waveform distortion occurs due to the swamping action of the always-connected winding with the result that the effective a.c. power factor is improved. A smaller thyristor may also be used to control the motor in this manner, permitting economical energy conservation in major applliances such as washing machines, dishwashers, and refrigerators.
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