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Unit 34Single-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

Unit 34 Single-Phase MotorsSingle-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

Unit 34 Single-Phase MotorsReview:

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.


5. There are three types of repulsion motors:– Repulsion

– Repulsion-start induction-run

– Repulsion-induction

5. There are two types of single-phase synchronous motors

– Warren

– Holtz


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.

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