From Electrical Equipment Handbook: Troubleshooting and Maintenance

AC MACHINE FUNDAMENTALS (CHAP. 5)

1.

What is the difference between a motor and a generator?

2.

Why is the conversion of energy in motors and generators occurring between mechanical energy and real power only?

3.

What is the main principle of operation of an ac induction motor?

4.

What is the main principle of operation of an ac synchronous generator?

Answers

1.

Motors are identical to generators. The only difference is the flow of energy. A motor converts electric energy to mechanical energy. A generator converts mechanical energy to electric energy.

2.

The conversion of energy in motors and generators occurs between mechanical energy and real power only because the reactive power is not consumed. It is only stored in the machine to magnetize it. The real energy is consumed in a motor. It is converted to mechanical energy (torque speed) and heat losses. Reactive energy is generated in a generator by increasing the field current (dc) in the rotor of the generator. It does not require mechanical energy to generate it.

3.

The main principle of operation of an ac induction motor is summarized as follows: A three-phase set of currents, each of equal magnitude and differing in phase by 120 , is supplied to the stator (armature) of the induction motor. The three currents produce a rotating magnetic field of constant magnitude B S that rotates inside the stator at ? speed ?), where to equals 3 600 r/min for a two pole motor;

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