Unit 34 Single-Phase Motors

Unit 34 Single-Phase Motors

Objectives: Unit 34 Single-Phase Motors List the different types of split-phase motors. Discuss the operation of split-phase motors. Reverse the direction of rotation of a splitphase motor. Discuss the operation of a shaded-pole motor.

Objectives: Unit 34 Single-Phase Motors 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.

Resistance-Start Induction-Run Motor The start winding has much smaller wire that the run winding.

Resistance-Start Induction-Run Motor The start winding is more resistive than the run winding, creating a rotating magnetic field.

Resistance-Start Induction-Run Motor 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.

Capacitor-Start Induction-Run Motor 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.

Capacitor-Start Induction-Run Motor With the capacitor, the run and start-winding currents are 90 out 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 Split-Phase Motors 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.

Dual-Voltage Split-Phase Motors Low-voltage connection for a split-phase motor with two run and two start windings.

Dual-Voltage Split-Phase Motors Dual-voltage motor with one start winding labeled T 5 and T 8.

Dual-Voltage Split-Phase Motors High-voltage connection with one start winding.

Dual-Voltage Split-Phase Motors 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.

Capacitor-Start Induction-Run Motor The start winding and run winding have the same size wire.

Capacitor-Start Capacitor-Run Motor A capacitor-start capacitor-run motor.

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.

Shaded-Pole Induction Motor A shaded pole motor has a shading coil which creates the rotating magnetic field.

Shaded-Pole Induction Motor The shading coil opposes a change of flux as current increases.

Shaded-Pole Induction Motor There is no opposition to magnetic flux when the current is not changing.

Shaded-Pole Induction Motor The shading coil opposes a change of flux when the current decreases.

Shaded-Pole Induction Motor 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.

Repulsion Motor Brushes placed at a 90 angle 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-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

Repulsion-Start Induction-Run Motor Short-circuiting ring for brush-riding-type repulsionstart induction-run motor.

Repulsion-Start Induction-Run Motor A radial commutator is used with the brush-liftingtype motor.

Repulsion-Start Induction-Run Motor Brush-lifting-type repulsion-start induction-run motor.

Repulsion Induction Motor Repulsion-induction motors contain both armature and squirrel-cage winding.

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)

Single-Phase Synchronous Motor 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.

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

Stepper Motor The magnet aligns with the average magnetic pole.

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.

Universal Motor Armature and brushes of a universal motor.

Universal Motor Conductively compensated universal motor.

Universal Motor Inductively compensated 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: Unit 34 Single-Phase Motors 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 shadedpole motor is created by placing shading coils on one side of the pole pieces.

Review: Unit 34 Single-Phase Motors 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: Unit 34 Single-Phase Motors 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.