DSTE Unit 34

What is the advantage of the capacitor-start induction-run motor over the resistance-start induction-run motor?

It develops higher torque

What is the principle of operation of a stepping motor?

Stepping motors operate on the theory that like magnetic poles repel and unlike magnetic poles attract.

What is the speed of operation of the Holtz motor?

The Holtz motor operates at a speed of 1200 RPM.

What is the speed of operation of the Warren motor?

The Warren motor operates at a speed of 3600 RPM

When the motor is connected to DC voltage, how must the compensating winding be connected?

The compensating winding is connected in series with the series field winding

What is the function of the compensating winding?

The compensating winding is wound around the stator and functions to counteract the inductive reactance in the armature winding.

Why do stepping motors have teeth machined in the stator poles and rotor?

The number of teeth machined in the stator and rotor determines the angular rotation achieved each time the motor is stepped.

Why does a split-phase motor continue to operate after the start windings have been disconnected from the circuit?

The run winding maintains a rotating magnetic field in the rotor.

What causes the magnetic field to rotate in a shaded-pole induction motor?

The shading coil located on one side of each pole piece.

What does the term bifilar mean?

The term bifilar means that two windings are wound together.

When a stepping motor is connected to AC power, how many phases must be applied to the motor?

Two phases.

Why is the AC series motor often referred to as a universal motor?

Universal motors contain a laminated core to help prevent lost power to eddy current induction.

What are the three basic types of split-phase motors?

1. The resistance-start induction-run motor 2. The capacitor-start induction-run motor 3. The capacitor-start capacitor-run motor

On the average, how many degrees out of phase with each other are the start and run-winding currents in a resistance-start induction-run motor?

35-40 degrees

What is the synchronous speed of an eight-pole stepping motor when connected to a two-phase, 60-Hz AC line?

72 RPM

In order to produce maximum starting torque in a split-phase motor, how many degrees out of phase should the start- and run-winding currents be with each other?

90 degrees

The voltages of a two-phase system are how many degrees out of phase with each other?

90 degrees

What device is used to disconnect the start windings for the circuit in most nonhermetically sealed capacitor-start induction-run motors?

A centrifugal switch

When a repulsion-start induction-run motor reaches about 75% of rated full-load speed, it stops operating as a repulsion motor and starts operating as a squirrel-cage motor. What must be done to cause the motor to begin operating as a squirrel-cage motor?

A short-circuiting device short circuits the commutator.

Explain how to set the neutral plane position using the compensating winding.

AC is connected to the armature and a voltmeter is connected to the compensating winding. AC is then applied to the armature. The brushes are then moved until the voltmeter indicates its highest or peak voltage.

Explain how to set the neutral plane position of the brushes using the series field.

AC is connected to the armature leads. A voltmeter is connected to the series winding. Voltage is then applied to the armature. The brush position is then moved until the voltmeter connected to the series field reaches a null position.

How can the direction of rotation of a shaded-pole induction motor be changed?

By removing the stator winding and turn it around.

How can the direction of rotation of a split-phase motor be reversed?

By reversing the connection of the start winding leads in relation to the run winding.

How is the speed of a consequent-pole motor changed?

By reversing the current flow through alternate poles and changing the number of stator poles.

What type of split-phase motor does not generally contain a centrifugal switch?

Capacitor-start capacitor-run motor.

How is the direction of rotation of the universal motor reversed?

Change the armature leads with respect to the field leads.

How can the holding torque of a stepping motor be increased?

DC voltage can be applied to one or both windings when the motor is turned off.

When determining the direction of rotation for a split-phase motor, should you face the motor from the front or from the rear?

From the rear.

How are the start and run windings of a split-phase motor connected in relation to each other?

In parallel

If a dual-voltage split-phase motor is to be operated on high voltage, how are the run windings connected in relation to each other?

In series.

What is the principle of operation of a capacitor-start capacitor-run motor?

It operates on the principle of a continuous rotating magnetic field produced in the stator winding.

What is the principle of operation of a repulsion motor?

Like magnetic fields repel each other.

Why can a multispeed fan motor be operated at lower speed than most induction motors without harm to the motor windings?

Multispeed fan motors have high-impedance stator windings to prevent them from overheating when their speed is reduced.

What type of commutator is used with a brush-lifting-type repulsion-start induction-run motor?

Radial

What type of single-phase motor develops the highest starting torque?

Repulsion type motors.

Explain the difference in operation between a stepping motor and a common DC motor.

Stepping motors differ from other types of DC or AC motors in that their output shaft moves through a specific angular rotation each time the motor receives a pulse.