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Which of the following is not common between the construction of single-phase & three-phase induction motor?
Stator winning type
Centrifugal switch
electrolytic capacitor
All of these
All of these
Single-phase induction motors require auxiliary components for starting because they are not self-starting, whereas three-phase induction motors are inherently self-starting due to the production of a rotating magnetic field ┬╖ Consequently, components like centrifugal switches and capacitors, which are essential for single-phase operation, are entirely absent in standard three-phase motor designs.
Single-phase induction motors require auxiliary components for starting because they are not self-starting, whereas three-phase induction motors are inherently self-starting due to the production of a rotating magnetic field ┬╖ Consequently, components like centrifugal switches and capacitors, which are essential for single-phase operation, are entirely absent in standard three-phase motor designs.
TstтАЛ=kтЛЕ╬жmтАЛтЛЕ╬жaтАЛтЛЕsin(╬▒) тАФ Starting torque production principle in 1-phase motors
NsтАЛ=P120fтАЛ тАФ Synchronous speed formula applicable to both motor types
In a three-phase motor, the stator windings are fed with a balanced 3-phase supply, creating a constant magnitude rotating magnetic field ┬╖ In contrast, a single-phase motor produces a pulsating field that requires phase-splitting methodsтАФtypically implemented via capacitors or auxiliary windings disconnected by a centrifugal switchтАФto generate the torque necessary for rotation.
Three-phase induction motors generate a rotating magnetic field directly from the supply current.
Single-phase motors have a pulsating field that results in zero net torque at standstill without auxiliary phase-splitting.
Centrifugal switches are mechanical devices used to disconnect the starting winding/capacitor once the motor reaches 70-80% of synchronous speed.
Electrolytic capacitors provide the phase shift required for high starting torque in capacitor-start motors.
Three-phase: High efficiency and self-starting capability.
Single-phase: Convenience for domestic low-power applications.
Single-phase: Complex construction due to auxiliary components.
Single-phase: Lower power factor and efficiency compared to 3-phase motors.
Three-phase: Industrial pumps, compressors, and heavy machinery.
Single-phase: Household fans, refrigerators, and small portable tools.
| Feature | 1-Phase | 3-Phase |
|---|---|---|
Starting Method | Auxiliary winding/Capacitor | Rotating Magnetic Field |
Self-Starting | No (requires starting circuit) | Yes |
The stator winding of a 3-phase motor is distributed symmetrically by 120┬░ electrical degrees.
The 'electrolytic capacitor' mentioned is specifically used in the start circuit of capacitor-start motors for high torque pulses.
D is correct тАФ All listed components (stator winding type, centrifugal switch, and electrolytic capacitor) are specific to the complex starting requirements of single-phase motors and are absent in standard three-phase induction motors.
Always remember that 3-phase motors are inherently self-starting because the phase displacement is provided by the supply, whereas 1-phase motors must 'create' an artificial phase shift.