Chapter10-DCMotors&Generators

Question 1

DC motors perform better than AC motors in most traction equipment applications

Answer 1

T

Question 2

The purpose of the compensating windings is to help interpoles maintain neutral position on the commutator.

Answer 2

T

Question 3

Since each DC source has one positive and one negative terminal, there must be at least two brushes and two brush holders

Answer 3

T

Question 4

Three styles of brushes are radial-edge, trailing, and leader brushes.

Answer 4

F

Question 5

A DC motor can be reversed by changing the polarity of both the armature winding and the field winding.

Answer 5

F

Question 6

A DC motor can be made into a DC generator if an external prime mover is coupled to the motor shaft.

Answer 6

T

Question 7

DC series motors can develop only about 125% of full load torque upon starting

Answer 7

F

Question 8

DC series motors are used where constant or adjustable speed is required and starting conditions are moderate.

Answer 8

F

Question 9

A DC shunt motor has lower starting torque than a DC series motor

Answer 9

T

Question 10

A DC shunt motor can be run above its full-voltage base speed by reducing the current in the shunt fields.

Answer 10

T

Question 11

The commutators are magnets or stationary windings used to produce the magnetic field in an alternator or motor.

Answer 11

F

Question 12

Because they cannot overheat, all DC permanent-magnet motors are designed to run continuously

Answer 12

F

Question 13

DC generators consist of field windings, an armature, a commutator, and brushes

Answer 13

T

Question 14

A DC generator always has a rotating field and a stationary armature

Answer 14

F

Question 15

A benefit of DC generators is their ability to increase the voltage under changing load conditions.

Answer 15

T

Question 16

A(n) _____________ is a machine that uses DC connected to the field windings and armature to produce shaft rotation.
a. alternator b. generator
c. direct-current motor d. shunt motor

Answer 16

c. Direct-current motor

Question 17

A ____________ is the stationary part in a DC motor or generator.
a. DC permanent magnet b. field frame c. neutral plane
d. brush

Answer 17

b. Field frame

Question 18

________________ are auxiliary poles placed between the main field poles of the motor.
a. windings b. interpoles c. spacers d. field poles

Answer 18

b. Interpoles

Question 19

_____________ brushes are at an angle to the commutator and have less restricted up-and-down movement.
a. Radial b. Trailing-edge c. Leading-edge d. All of the above

Answer 19

c. Leading-edge

Question 20

A(n) ______________ is a voltage induced in the windings that is opposite in polarity to that of the power supply.
a. counter voltage b. indirect voltage c. armature reaction
d. back voltage

Answer 20

a. Counter-voltage

Question 21

_____________ is the process where the armature current is periodically reversed in order to keep the motor torque in the same direction during the entire armature rotation.
a. communication b. Alternating DC c. DC inversion d. Commutation

Answer 21

d. Commutation

Question 22

The basic types of DC motors are DC series motors and __________________ motors
a. DC Shunt b. DC compound c. permanent-magnet
d. All of the above

Answer 22

d. All of the above

Question 23

A(n)_______________ motor is a DC motor that has the field wiring connected in parallel with the armature.
a. series b. shunt c. design DC d. induction

Answer 23

b. Shunt

Question 24

A. _____________________ motor is a motor where the current flows in the opposite direction in the series and shunt coils and the resulting net flux is the difference between the two fluxes.
a. DC differential-compounded b. DC cumulative-compounded
c. DC permanent-magnet d. DC brushless

Answer 24

a. DC differential-compounded

Question 25

A ________________ motor is a motor that uses magnets, not a coil of wire, for the field windings. a. rare-earth magnet b. cobalt c. DC permanent-magnet d. nickel-chromium

Answer 25

c. DC permanent-magnet

Question 26

_______________ is the ability of a source to vary the output voltage in order to maintain system voltage as the load varies. a. Voltage regulation b. Voltage maintenance c. Constant voltage d. Constant current

Answer 26

a. Voltage regulation

Question 27

A ____________ - wound generator is a type of DC generator. a. Series b. Shunt c. Compound d. All of the above

Answer 27

d. All of the above

Question 28

A(n) ________________ is the rotating part of a DC motor, consisting of the laminated core with slots for the coils, the main shaft, and the commutator brushes a. stator b. rotor c. armature d. permanent magnet

Answer 28

c. Armature

Question 29

The ________________ is a line through the armature cross section that is perpendicular to the maximum amount of magnetic flux. a. armature field b. neutral plane c. armature plane d. magnetic field

Answer 29

b. Neutral plane

Question 30

In a _________________, the series field windings and shunt field windings are combined in a manner to take advantage of the characteristics of each. a. direct-current generator b. single-voltage motor c. self-excited shunt field d. compound-wound generator

Answer 30

d. Compound-wound generator

Question 31

_______________ are magnets or stationary windings used to produce the magnetic field in an alternator or motor.

Answer 31

Field windings

Question 32

_____________ is the distortion of the magnetic fields that happens when a current-carrying wire is placed with a fixed magnetic field.

Answer 32

Armature reaction

Question 33

A(n) ________________ motor is a DC motor that has the field winding connected in series with the armature.

Answer 33

Series

Question 34

____________________ is the position of the brushes where commutation can occur with minimal induced voltage in the armature coils.

Answer 34

Brush neutral

Question 35

A(n)________________ shunt field is shunt field connected to a different power supply than the armature.

Answer 35

Separately excited

Question 36

A(n) _________________ motor is a DC motor with the field connected in both series and shunt with the armature.

Answer 36

Compound

Question 37

A(n) _________________ generator is a generator that has its field windings connected in series with the armature and the external circuit (load).

Answer 37

Series-wound

Question 38

A(n)_________________ generator is a generator that has its field windings connected as a shunt in parallel with the armature and external circuit.

Answer 38

Shunt-wound

Question 39

_______________ motors provide excellent speed control for acceleration and deceleration, with effective and simple torque control.

Answer 39

DC

Question 40

_________________ are used to reduce sparking at the brushes of larger DC motors.

Answer 40

Interpoles

Question 41

Armature current in a(n)_________________ is forced to flow in the opposite direction to that of the countervoltage.

Answer 41

Motor

Question 42

A(n)______________ field winding is a small series field winding placed over the top of a shunt field winding that improves stability of the fields while running with the reduced current in the field circuit.

Answer 42

Stabilizing

Question 43

An external prime mover applies ________________ torque to the armature and series field circuit, which induces voltage and current in the generator.

Answer 43

Mechanical

Question 44

A(n)______________ generator includes series and shunt field windings.

Answer 44

Compound-wound

Question 45

A(n) _________________ is a ring made of insulated segments that keep the armature windings in the correct polarity

Answer 45

Commutator