Deck 31: Wound Rotor Motors

Question 1

What are the three factors that determine the amount of torque developed by a three phase induction motor?

Answer 1

Three factors that determine the amount of torque developed by a three phase induction motor are:
1) Strength of the magnetic field of the stator
2) Strength of the magnetic field of the rotor
3) Phase angle difference between rotor and stator flux

Question 2

How is the starting current and speed of a wound rotor induction motor controlled?

Answer 2

The starting current and speed of a wound rotor induction motor is controlled by adding or subtracting the amount of resistance connected in the rotor circuit.

Question 3

What is one advantage and one disadvantage of frequency control?

Answer 3

Frequency control has an advantage over other types of control in that it is very responsive to changes in motor load. The main disadvantage of frequency control is that some amount of resistance must remain in the circuit at all times.

Question 4

Capacitive reactance is proportional to the rotor frequency.

Question 5

Small wound rotor motors are often controlled manually by a three-pole make-before-break rotary switch.

Question 6

The difference between rotor speed and synchronous speed is called ____________________.

Question 7

The wound rotor induction motor is often called the ____________________ motor.

Question 8

What is the principle on which frequency control operates?

Question 9

How is the construction of the rotor different between the wound rotor induction motor and the squirrel cage motor?

Question 10

The operating characteristics of a wound rotor motor with the rotor leads shorted together are very similar to those of a(n) ____________________ motor.

Question 11

Starting circuits generally employ resistors of a lower wattage value than circuits that are intended for speed control.

Question 12

In an alternating current circuit, the current limiting effect of a capacitor is called ____________________.

Question 13

The wound rotor motor has a lower starting torque per amp of starting current than any other type of three phase motor.

Question 14

The wound rotor motor can be started in multiple steps to provide smooth acceleration from 0 RPM to maximum RPM.

Question 15

Maximum torque is developed when the ____________________ of the stator and rotor are in-phase with each other.