I4 Learning Task 12 thru 16

Question 1

List the four principle components of a split-phase induction motor

Answer 1

stator (main and aux) windings
rotor
centrifugal (starting) switch
end bells and bearings

Question 2

Describe the Stator windings of a split-phase induction motor

Answer 2

main or run windings is made of larger wire and is placed deep in the slots of the stator core. (low resistance and high inductance)
auxiliary winding is made of smaller wire and is placed near the top of the slots in the stator core. (higher resistance and a lower inductance)

Question 3

When the two winding of a split-phase induction motor are connected in parallel across the same source the current

Answer 3

in the main winding will lag behind the current in the start winding.

Question 4

The two main windings in a split-phase induction motor are placed in the stator core so that they will be

Answer 4

90 electrical degrees apart from each other

Question 5

the split-phase induction motor is sometimes called the

Answer 5

the resistive-start, induction-run motor

Question 6

For a split-phase induction motor why is the centrifugal switch set to cut the start winding out at about 75% of rated rpm?

Answer 6

because at about 75% of rated speed the flux from the run windings alone creates as much torque as the combined flux from the start and run winding together therefore it is pointless to keep the start windings energized.

Question 7

Resistive-start, split-phase motors have relatively low starting torque because

Answer 7

of the low phase angle between the two winding currents

Question 8

A split-phase induction motor my be reversed by

Answer 8

interchanging the connections to either the run windings or the start windings.

Question 9

Adding a capacitor to a split-phase induction motors causes a

Answer 9

phase displacement in the two field fluxes that matches the physical displacement of the two windings
much higher starting torque as much as 450%
improved power factor during starting
reduced inrush current

Question 10

For the Dual capacitor (capacitor-start, capacitor-run), split-phase induction motor

Answer 10

both capacitors are connected parallel
at about 75% of rated speed the start capacitor is removed with the centrifugal switch
the run capacitor maintains optimum phase angle between the two stator field currents.

Question 11

What advantages does the dual capacitor (capacitor-start, capacitor-run), split-phase induction motor have over the standard capacitor- start motor?

Answer 11

better power factors
better efficiency when fully loaded
as much as 25% more overload capacity
well-suited for air compressors.

Question 12

AC series (universal) motor can be run on either

Answer 12

AC or DC

Question 13

State three constructional differences between AC series motors and DC series motors

Answer 13

pole cores and portion of stator are laminated
series winding has fewer turns to reduce the inductive reactance
High resistance brushes are used to reduce commutator sparking

Question 14

What is the relationship between load and speed for a AC series motor?

Answer 14

the speed decrease as the load is added.