Features of Other Types of Single Phase Motors

Question 1

State the three constructional differences between an AC series motor and a DC series motor.

Answer 1

• The pole cores and that portion of the stator that completes the magnetic circuit are laminated to reduce eddy-current losses
• The series winding has fewer turns to reduce the inductive reactance
• The cross-sectional area of the core is increased and the air gap is decreased to decrease the reluctance of the magnetic circuit
• High-resistance brushes are used to reduce commutator sparking

Question 2

State the relationship between load and speed for a series motor

Answer 2

The speed decreases as load is added

Question 3

How does the rotor part of the series motor receive its energy?

Answer 3

Through brushes and commutator

Question 4

How is the direction of rotation reversed in a series motor?

Answer 4

By interchanging the two armature leads, or the two series field leads

Question 5

What may happen if a large series motor is operated with no load connected?

Answer 5

The motor may run away

Question 6

What two variables affect the counter emf generated in the armature?

Answer 6

The speed of the armature and the strength of the series field

Question 7

What two variables affect the torque developed by the rotor of the series motor?

Answer 7

The current through the armature and the strength of the series field

Question 8

Will an AC series motor operate on DC?

Answer 8

The AC series motor will operate satisfactorily from DC and up to 60Hz AC

Question 9

Why does the direction of rotation not change each time the alternating current changes direction?

Answer 9

Both the field polarity and the current through the armature change at the same time, resulting in no torque reversal

Question 10

Why are the stator and rotor cores of the universal motor laminated?

Answer 10

To reduce eddy-current losses

Question 11

What are the two types of windings in the stator of a shaded-pole motor?

Answer 11

Exciter winding, shading coil

Question 12

How do the two stator windings receive their energy from the source?

Answer 12

The exciter winding receives its energy by conduction. The shading coil receives its energy by electromagnetic induction

Question 13

In what direction does the field move across the pole face in a shaded-pole motor?

Answer 13

From the unshaded portion to the shaded portion

Question 14

How is the direction of rotation of a shaded-pole motor reversed?

Answer 14

By removing the stator and turning it end-for-end before replacing it over the rotor

Question 15

Is the starting torque of a shaded-pole motor high or low compared to a split-phase motor?

Answer 15

Low

Question 16

At what speed does the rotor of a hysteresis motor rotate?

Answer 16

synchronous speed

Question 17

From what type of steel is the rotor of a hysteresis motor rotor made? Why is this the case?

Answer 17

hard steel; because of its large hysteresis loss (retains permanent magnetism)