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From the following single-phase induction motor, Which motor has relatively higher power factor?
Resistance Split-phase
Capacitor Start Split-phase
Permanent Split Capacitor (PSC)
Capacitor Start Capacitor Run (Two Value capacitor)
Permanent Split Capacitor (PSC)
The Permanent Split Capacitor (PSC) motor has a capacitor permanently connected in series with the auxiliary winding during both starting and running conditions. Because the auxiliary winding and capacitor remain energized continuously, it operates as a balanced two-phase motor under rated load conditions, resulting in a significantly higher running power factor (close to unity) compared to other single-phase induction motor types.
The Permanent Split Capacitor (PSC) motor has a capacitor permanently connected in series with the auxiliary winding during both starting and running conditions. Because the auxiliary winding and capacitor remain energized continuously, it operates as a balanced two-phase motor under rated load conditions, resulting in a significantly higher running power factor (close to unity) compared to other single-phase induction motor types.
cos╧Х=VIPтАЛ тАФ power factor of the single-phase motor
IlineтАЛ=ImainтАЛ+IauxтАЛ тАФ line current as vector sum of winding currents
XCтАЛ=2╧АfC1тАЛ тАФ capacitive reactance compensating inductive reactance
In a PSC motor, the permanently connected capacitor introduces a phase shift close to 90┬░ between the main winding current and the auxiliary winding current. This creates a smooth rotating magnetic field rather than a pulsating one during running. The capacitive reactance offsets the inductive reactance of the motor windings, bringing the overall line current nearly in phase with the applied supply voltage.
Permanent Split Capacitor (PSC) motor does NOT use a centrifugal switch.
The auxiliary winding and run capacitor remain permanently in the circuit during operation.
Operates as a true balanced two-phase motor at nominal load, delivering higher running power factor (up to 0.85 - 0.95) and high efficiency.
Exhibits lower starting torque compared to Capacitor-Start Capacitor-Run motors due to the optimized low running value of the capacitor.
High running power factor and improved efficiency
No centrifugal switch required, leading to high reliability and low maintenance
Quieter operation with reduced vibration and noise
Low starting torque (typically 50% to 100% of full-load torque)
Higher cost than resistance split-phase motors
Ceiling fans and table fans
Blowers and air-conditioner compressors
Direct-drive centrifugal pumps
Option A (Resistance Split-phase): Uses a high resistance auxiliary winding; low starting torque and low running power factor (0.5 to 0.6).
Option B (Capacitor Start Split-phase): Uses capacitor only during starting via a centrifugal switch; running power factor remains low (0.6 to 0.7).
Option D (Capacitor Start Capacitor Run): Has high starting torque and high running power factor, but between PSC and CSCR, PSC inherently operates continuously optimized specifically for running power factor with simpler construction; however, CSCR also has high power factor. In standard exam nomenclature, PSC is cited for highest continuous running power factor and simplicity.
C is correct тАФ Permanent Split Capacitor (PSC) motor keeps the capacitor in the circuit during running, yielding the highest running power factor among single-value continuous designs.
Remember for competitive exams: 'Capacitor Start' gives maximum starting torque, whereas 'Permanent Split Capacitor' gives maximum running power factor and quietest operation without needing a centrifugal switch.