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Which motor have relatively high power factor?
Capacitor start
Capacitor run
Split phase
Shaded pole
Capacitor run
A capacitor-run (or permanent-split capacitor) motor keeps a run-capacitor continuously connected in series with the auxiliary winding during both starting and running operations ┬╖ This continuous presence of the capacitor improves the power factor during normal running conditions to near unity (typically 0.8 to 0.95), compared to other single-phase induction motors where starting components are cut out after starting.
A capacitor-run (or permanent-split capacitor) motor keeps a run-capacitor continuously connected in series with the auxiliary winding during both starting and running operations ┬╖ This continuous presence of the capacitor improves the power factor during normal running conditions to near unity (typically 0.8 to 0.95), compared to other single-phase induction motors where starting components are cut out after starting.
PF=cos╬╕=ZRтАЛ тАФ Power factor of the motor circuit
ICтАЛ=VтЛЕ2╧АfC тАФ Current drawn by the run capacitor leading the voltage by 90┬░
In a capacitor-run motor, the main winding and auxiliary winding (with a series-connected capacitor) create a continuous two-phase balanced rotating magnetic field ┬╖ The capacitive reactance offsets the inductive reactance of the motor windings throughout its operation ┬╖ As a result, the stator input current vector is pulled closer in phase with the applied supply voltage, yielding a significantly higher running power factor and smoother operation.
The capacitor remains connected in the auxiliary circuit during both starting and running conditions.
Eliminates the need for a centrifugal switch, increasing reliability and lowering maintenance.
Provides continuous two-phase balanced operation at rated load, resulting in high efficiency, higher power factor, and quiet (non-humming) performance.
Relatively high running power factor (0.80 to 0.95)
Higher running efficiency and smoother, quieter operation
No centrifugal switch required, leading to reduced mechanical wear
Lower starting torque compared to capacitor-start motors
Higher cost than simple split-phase or shaded-pole motors
Ceiling fans and table fans
Air conditioners and refrigerator compressors
Blower drives and office machinery
| Feature | Capacitor Start Motor | Capacitor Run Motor |
|---|---|---|
Power Factor | Low to Moderate (~0.5 - 0.6) | High (~0.8 - 0.95) |
Starting Torque | High (up to 300% of full load) | Low to Moderate (50-100% of full load) |
Centrifugal Switch | Present (disconnects capacitor after starting) | Absent (capacitor stays permanently connected) |
Option A (Capacitor start): The capacitor is disconnected by a centrifugal switch at ~75% speed, leaving only the main winding operating at a low power factor during normal run time.
Option C (Split phase): High resistance auxiliary winding creates phase difference, resulting in very low power factor during operation.
Option D (Shaded pole): Has extremely low starting torque, low efficiency, and the lowest operating power factor (~0.4 - 0.5) among single-phase induction motors.
B is correct тАФ In a capacitor-run motor, the capacitor stays continuously in the circuit, providing reactive power compensation during operation and significantly raising the running power factor.
Always distinguish between starting performance and running performance: Capacitor-Start gives maximum starting torque, while Capacitor-Run gives optimal running power factor and efficiency.