Chapter 4

Armature

The DC current of a motor is connected to the field and ___ to produce rotation.

Interpoles

____ are auxiliary poles placed between the main field poles of the motor.

rectifer

An ___ is a device that converts AC to DC by allowing the current to move in one direction.

pigtail

An ___ is an extended, flexible connection

high

The DC permanent-magnet motor produces relatively __- torque at low speeds.

compensated

An __ universal motor is a universal motor with extra winding added to the field poles.

eddy

___ current is unwanted current induced in the metal field structure of a motor, due to the rate of change in the induced magnetic flux.

thyristor

An __ is a solid-state switching device that switches current on by a quick pulse of control current.

armature

An _____ is the rotating part of a DC motor

rotor

An ___ is the rotating part of an AC motor

brushes

An ____ is the stationary part of the DC motor

stator

An ____ is the stationary part of the AC motor

Hysteresis

_____ is the power loss that occurs when a universal motor is connected to AC.

magnetic field

The field windings of a DC motor are used to develop an ____

tapped

An ____ field may be used to vary the speed of a universal motor.

graphite

brushes are made of carbon or ____.

permanent magnet

The DC _____ motor uses magnets for the field winding.

1/4

Compensated universal motors are usually ____ HP and larger

conduction

An SCR can be triggered into ___ in only one direction

laminations

The armature core is made up of notched ___ which form slots when stacked.

high

DC motors are used in applications that require very ___ torque

Brushes

___wear faster than any other component of the DC motor

1/8

The brush holder of DC motor should be 1/16" to ____ from the commutator.

brown

Any discolorations on a commutator other than a polished, ____ color indicate a problem.

True

A universal motor can be operated on either DC or 1 phase, AC.

True

Universal motors may be nonreversible or reversible

false

a revolving field is produced in a universal motor

false

The no-load speed of a universal motor is very low

true

a fixed resistor has a fixed value for one set speed

false

a triac is triggered by a large current to its gate

true

the field pole strength of a universal motor may be changed by moving the brushes

false

AC motors perform better than DC motors in most traction equipment

true

DC power is delivered into the armature through the brushes

true

The brushes of DC motors should be replaced when they have worn down to half their original size

false

The brushes of a DC motor should be lubricated on a scheduled basis

True

a commutator should be smooth and concentric

false

An armature winding is grounded whenever one or more windings make contact with the iron core.

parallel

The field of a DC shunt motor is connected in ____ with the armature

decreases

When a load is placed on a universal motor, the motor speed ____

intensity of the magnetic field

The amount of force exerted on the shaft of a DC motor is based on the ___-

to reduce sparking at the brushes

Interpoles are used ____

produces the heist torque of all DC motors

The DC series motor ____

a series field and a shunt field

The DC compound motor has ___.

has extra windings added to the field poles

A compensated universal motor ____.

anode, gate, and cathode

The three terminals of a SCR are the ___

reversing the direction of current in the field

A reversible universal motor may be reversed by ___.

rotating

The armature is the ___ part of a DC motor.

1/16" to 1/8

When troubleshooting DC motor brushes, the brush holder should be ___from the commutator

5

The brush pressure of a DC motor should be approximately 1.5 to ____ psi of surface area.

1/32" to 1/16

Mica insulation should be approximately ___ below the commutator segments.