Chapter 5

The Three-Phase Induction Motor

Industry uses more three-phase induction motors than other types of motors because they require less maintenance. The squirrel cage rotor is the motor’s only moving part (excluding ball bearings). This motor is smaller physically (per horsepower) than single-phase or DC motors (Fig. 5.1). Sizes range from fractional to thousands of horsepower (Fig. 5.2).

Three-phase power is divided among three lines. This reduces the supply line’s wire size.

The three-phase induction motor has no switching or commutation of circuits. This makes it possible to use very high voltage. High voltage allows the motors to be designed in large sizes (as volts go up, amperes go down-watts and horsepower stay the same).

The ...

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