Question

The speed of the rotating magnetic field created in a three-phase induction machine corresponds to the machine

1. no-load speed.
2. synchronous speed.
3. slip speed.
4. nominal speed.

The synchronous speed of a three-phase induction machine depends on the

1. number of magnetic poles in the machine and the frequency of the three- phase ac power source.
2. actual speed of the machine and the amount of active power supplied to it.
3. intensity of the machine’s rotating magnetic field and the voltage of the three-phase ac power source.
4. the number of phases of the three-phase ac power source.

The difference between the actual speed and the synchronous speed of a three-phase induction machine is

1. known as the nominal machine speed.
2. zero.
3. known as the machine slip.
4. always constant.

Which of the following statements correctly describes what happens to the speed of a three-phase induction motor as the torque produced by the motor increases? Consider only the linear portion of the motor’s torque versus speed curve.

1. The motor speed decreases until the breakdown torque region is reached.
2. The motor speed increases until the breakdown torque region is reached.
3. The motor speed remains constant.
4. The motor speed increases until the motor synchronous speed is reached.

The reactive power that a three-phase induction machine draws from a three- phase ac power source is used to

1. reduce the vibrations produced in the machine.
2. increase the power factor of the machine.
3. create the machine’s rotating magnetic field.
4. maintain the machine slip constant.

Answer 1

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