Deck 21: Energy-Efficient Motors

Question 1

Armature reaction in AC series motors may be compensated with an inductively coupled winding, which acts as a short-circuited secondary winding of a(n) ____________________.

Answer 1

transformer

Question 2

The direction of rotation of a(n) ____________________ motor is reversed if the brushes are shifted 15 electrical degrees from the stator field pole centers in a clockwise direction.

Answer 2

repulsion

Question 3

Identify two of the main construction features of universal motors?

Answer 3

Universal motors have the following construction features:
• The frames of universal motors are made of aluminum, cast iron, or rolled steel.
• The field poles are generally bolted to the frame.
• Field cores consist of laminations pressed together and held by bolts.
• The armature core is laminated and has a typical commutator and brushes.
• End plates resemble those of other motors except that in many universal motors, one end plate is cast as part of the frame.
• Both ball and sleeve bearings are used in universal motors.

Question 4

Although conductively compensated motors have a low starting torque, the speed regulation is very good.

Question 5

At start-up of a(n) ____________________ motor, the repulsion winding predominates; however, as the motor speed increases, the squirrel-cage winding is used most.

Question 6

Article 430 of the National Electrical Code® provides requirements for the motor branch-circuit overcurrent protection, motor overcurrent protection, and wire sizes for motor circuits.

Question 7

In a universal motor, severe arcing at the brushes from changing the direction of rotation is prevented by shifting the brushes to the neutral (sparkless) plane or by adding a compensating winding.

Question 8

The two types of ____________________ motors are the single-field compensated motor and the two-field compensated motor.

Question 9

When the brushes of a repulsion motor are in the ____________________ neutral position, there is no torque even though a heavy current exists in the armature windings.

Question 10

Universal motors are speed-regulated by inserting resistance in parallel with the motor.

Question 11

Briefly describe the two types of brush arrangements in a repulsion motor.

Question 12

Briefly describe how speed is regulated in universal motors.

Question 13

In a brush-riding type of motor, briefly describe how the centrifugal mechanism is involved in causing the motor to operate as an induction motor.

Question 14

A concentrated-field universal motor is usually a salient-pole motor with two poles and a winding of relatively few turns.

Question 15

Repulsion motors are divided into three distinct classifications. Name two of these classifications.