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Output equation of single-phase induction motor = ___________ * Output equation of three-phase induction motos
3
1/3
2/3
3/2
2/3
The output equation of a single-phase induction motor is effectively 2/3 of a three-phase induction motor of equivalent frame size, assuming identical physical dimensions and magnetic loading ┬╖ This reduction is primarily due to the single-phase motor's pulsating magnetic field compared to the constant rotating magnetic field in a three-phase motor.
The output equation of a single-phase induction motor is effectively 2/3 of a three-phase induction motor of equivalent frame size, assuming identical physical dimensions and magnetic loading ┬╖ This reduction is primarily due to the single-phase motor's pulsating magnetic field compared to the constant rotating magnetic field in a three-phase motor.
P1╧ХтАЛ=32тАЛP3╧ХтАЛ тАФ Ratio of output power for identical frame sizes
In a three-phase motor, the stator windings produce a constant magnitude rotating magnetic field using all three phases ┬╖ In a single-phase motor, only one phase is present, creating a pulsating field which can be decomposed into two counter-rotating fields of equal magnitude, reducing the effective torque-producing capacity per unit volume of the machine.
The output equation is derived from the machine constant C=D2LnPтАЛ
Single-phase motors have lower utilization of active material compared to three-phase machines
The 2/3 factor assumes similar current density, flux density, and cooling conditions
Operates from widely available single-phase supply
Simpler wiring and control for small domestic applications
Inherent pulsating torque requires centrifugal switches or capacitors
Lower power density compared to three-phase induction motors
Domestic fans
Small centrifugal pumps
Washing machines
| Feature | Single-Phase | Three-Phase |
|---|---|---|
Magnetic Field | Pulsating (Decomposed) | Constant Rotating |
Relative Output | 2/3 of 3-Phase | Base (1) |
The design of induction motors relies heavily on the 'Output Coefficient' C0тАЛ, which relates the machine dimensions to its power capacity.
Option B (1/3) is incorrect as it underestimates the contribution of auxiliary windings and improved design practices in modern motors.
C is correct тАФ The output capability of a single-phase induction motor is effectively 2/3 of a comparable three-phase induction motor.
Always remember that 3-phase machines provide superior torque stability and power-to-weight ratios compared to single-phase equivalents due to the phase displacement of currents.