Unit 34 Single-Phase Motors

Unit 34

Single-Phase Motors

Unit 34 Single-Phase Motors

Objectives:

• List the different types of split-phase motors.

• Discuss the operation of split-phase motors.

• Reverse the direction of rotation of a split-

phase motor.

• Discuss the operation of a shaded-pole

motor.


Objectives:

• Discuss the operation of a repulsion-type

motor

• Discuss the operation of a single-phase

synchronous motor.

• Discuss the operation of a stepping motor.

• Discuss the operation of universal motors.


Split-Phase Motors

• Split-phase motor classifications:– the resistance-start induction-run motor

– the capacitor-start induction-run motor

– the capacitor-start capacitor-run motor

• Split-phase motors use two separate

windings to create the necessary rotating

magnetic field. These windings are named

the start winding and the run winding.


Resistance-Start Induction-Run Motor

• The start winding is more resistive than the

run winding which creates a phase shift

between the start and run windings.

• The start winding is removed when the

motor reaches 75% of its rated speed.

• The direction of rotation can be changed by

reversing the connection of either the start

winding or the run winding.


The start winding has much smaller wire that the

run winding.



The start winding is more resistive than the run

winding, creating a rotating magnetic field.



Running and starting currents are 35 to 40 out of

phase with each other.



Capacitor-Start Induction-Run Motor• A capacitor in series with the start winding creates a

90°phase shift between the start and run windings.

• The start winding and capacitor are removed when

the motor reaches 75% of its rated speed.

• The capacitor-start induction-run motor has more

starting torque that the resistance-start induction-run

motor, but the running characteristics are the same.

• The direction of rotation may be changed by

reversing the connection of either the start or the run

winding.


The start winding has much smaller wire that the

run winding.

Capacitor-Start Induction-Run Motor


An electrolytic capacitor is connected in series with

the start winding.



With the capacitor, the run and start-winding

currents are 90out of phase with each other.



Disconnecting the Start Winding

• When the motor reaches approximately

75% of its rated speed the start winding

will be disconnected from the circuit.

• The following methods may be used to

remove the start winding:• Centrifugal switch

• Hot wire relay

• Current relay

• Solid-state starting relay


A centrifugal switch may be used to disconnect the

start winding from the circuit.


A hot wire relay may be used to disconnect the

start winding from the circuit.


A current relay may be used to disconnect the start

winding from the circuit.


A solid-state starting relay may be used to

disconnect the start winding from the circuit.


Dual-voltage windings for a split-phase motor.

Dual-Voltage Split-Phase Motors


High-voltage connection for a split-phase motor

with two run and two start windings.



Low-voltage connection for a split-phase motor

with two run and two start windings.



Dual-voltage motor

with one start

winding labeled T5

and T8.



High-voltage connection with one start winding.



Low voltage connection with one start winding.



Capacitor-Start Capacitor-Run Motor

• The start winding and run capacitor remain in the

circuit after the motor has started.

• A second capacitor may be used to improve

starting torque that will be removed from the circuit

when the motor is near its rated speed.

• The run capacitor is typically an oil filled capacitor.

• Since the capacitor remains in the circuit the

power factor is close to unity.


The start winding and run winding have the same

size wire.



A capacitor-start capacitor-run motor.



A capacitor-start capacitor-run motor with an

additional starting capacitor.



Shaded-Pole Induction Motor

• Shaded pole motors are fractional horsepower

motors used for low torque applications and generally

have a long life.

• A shaded-pole motor works on the principal of a

rotating magnetic field.

• The rotating magnetic filed is created by a shading

coil wound on one side of each pole piece.

• The direction of rotation is toward the shading coil.


A shaded pole motor has a shading coil which

creates the rotating magnetic field.



The shading coil opposes a change of flux as

current increases.



There is no opposition to magnetic flux when the

current is not changing.



The shading coil opposes a change of flux when

the current decreases.



Four-pole shaded-pole motor..



Repulsion-Type Motor

• There are three basic repulsion-type motors:

• Repulsion Motor

• Repulsion-Start Induction-Run Motor

• Repulsion-Induction Motor

• Operates on the principal that like magnetic

poles repel each other.

• Highest starting torque of any single-phase

motor.


Brushes placed at a

90angle to the

poles does not

create any starting

torque.

Repulsion Motor


Brushes placed

at a 0 angle to

the poles does

not create any

starting torque.

Repulsion Motor


Shifting the

brushes to a 15°angle creates

maximum starting

torque.

Repulsion Motor


Shifting the brushes

to the other side of

the pole piece will

change the

direction of rotation.

Repulsion Motor


Repulsion-Start Induction-Run Motor

• A short circuiting ring short circuits the armature

windings at approximately 75% of the rated speed

causing the motor to run as an induction motor.

• There are two type of repulsion-start induction-run

motors:

• Brush lifting

• Brush riding


Short-circuiting ring for brush-riding-type repulsion-

start induction-run motor.



A radial commutator is used with the brush-lifting-

type motor.



Brush-lifting-type repulsion-start induction-run

motor.



Repulsion-induction motors contain both armature

and squirrel-cage winding.

Repulsion Induction Motor


Single-Phase Synchronous Motors

• Will operate at the synchronous speed.

• Use a shaded pole stator to create a rotating

magnetic field.

• Small and develop only fractional horsepower.

• Use the path of least reluctance to maintain the

synchronous speed.

• Two types of single phase synchronous motors are:

• Warren (General Electric motor)

• Holtz (Hysteresis)


A Warren motor with a two pole stator will run at

3600 RPM.

Single-Phase Synchronous Motor


A Holtz motor with a two pole stator will run at

1200 RPM.

Single-Phase Synchronous Motor


Stepping Motor

• Rotor is a permanent magnet

• Convert DC electric impulses into mechanical

movement

• Output shaft moves through a specific angular

rotation each time the motor receives a pulse.

• The rotor can be held in its position by applying DC

power.

• Will operate as a two phase synchronous motor when

connected to two phase AC power


The magnet aligns with the average magnetic

pole.

Stepper Motor


Universal Motor

• Referred to as an AC series motor.

• May be operated on AC or DC.

• Creates high horsepower for it size and

weight because of its high operating speed.

• Constructed similarly to a DC series motor

by having a wound armature and brushes.


Universal Motor

• A compensating winding is used to counteract the

inductive reactance of the armature winding.

• Direction of rotation can be reversed by changing

the armature leads with respect to the field leads.

• Used in many power tools and household

appliances.


Armature and brushes of a universal motor.

Universal Motor


Conductively compensated universal motor.

Universal Motor


Inductively compensated universal motor.

Universal Motor


Review:

1. There are three types of split phase

motors:

– Resistance-start induction-run

– Capacitor-start induction-run

– Capacitor-start capacitor-run

2. Split phase motors use a start and run

winding which are out of phase with each

other to create a rotating magnetic field.


Review:

3. The direction of rotation of a split phase

motor is changed by reversing the

connection of either the start or the run

winding.

4. The rotating magnetic field in a shaded-

pole motor is created by placing shading

coils on one side of the pole pieces.


Review:

5. There are three types of repulsion motors:

– Repulsion

– Repulsion-start induction-run

– Repulsion-induction

6. There are two types of single-phase

synchronous motors

– Warren

– Holtz


Review:

7. Stepping motors generally operate on DC

and are used to produce angular

movement in steps.

8. Universal motors contain a wound

armature and brushes.

9. The direction of rotation of a universal

motor can be reversed by changing the

armature leads with respect to the field.

Unit 34 Single-Phase Motors

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Transcript of Unit 34 Single-Phase Motors