Power Engineering 4A8
Electrotechnology C4-6 Test With Full
Set Correct Solutions
The armature core of a DC machine is built up of laminations of:
a. Silicon steel plates
b. Mica sheets
c. Reinforced carbon plates
d. Electromagnets
e. Copper bars - Ans--a. Silicon steel plates
Synchronous motors have construction that is identical to:
a. centrifugal fans
b. alternators
c. air driven motors
d. gas turbines
e. reciprocating equipment - Ans--b. alternators
In order to produce the strength of magnetic flux required in larger DC
machines:
a. copper switches are used
b. electromagnets are used
c. permanent magnets are used
d. booster transformers are used
e. the field windings are double wound - Ans--b. electromagnets are used
Alternators must run at constant speed in order to maintain:
a. power
b. resistance
c. current
d. voltage
e. frequency - Ans--e. frequency
The rotating field of an alternator is obtained by exciting the windings on the
rotor with:
,a. DC power
b. stator current
c. magnetic particles
d. carbon poles
e. AC power - Ans--a. DC power
A power factor higher than what is generally not required as the savings do
not equate to the cost of the extra capacitors.
a. 0.85
b. 0.75
c. 0.90
d. 0.80
e. 0.95 - Ans--e. 0.95
The electromagnets for a DC machine are termed the:
a. field poles
b. yokes
c. commutators
d. brush gears
e. armatures - Ans--a. field poles
Brush gear for DC machines have brushes made from carbon because they:
a. are softer, wear to a smooth finish, have a low coefficient of friction
b. are softer, are low cost, can produce large quantities of heat
c. wear to smooth finish, can produce large quantities of heat, have a low
coefficient of friction
d. are softer, are low cost, have a low coefficient of friction
e. are low cost, can produce large quantities of heat, have a low coefficient of
friction - Ans--a. are softer, wear to a smooth finish, have a low coefficient of
friction
Determine the speed (rpm) of a synchronous motor operating with a line
frequency of 60 Hz where the motor has 8 poles.
a. 1200
b. 1800
c. 600
d. 2400
e. 900 - Ans--e. 900
, A shunt type DC generator has what type of output voltage?
a. smooth
b. very low
c. erratic
d. very high
e. nearly constant - Ans--e. nearly constant
Which category on a nameplate identifies whether the motor is weather
proof:
a. Bearings
b. NEMA
c. ENC
d. Rating
e. HP - Ans--c. ENC
Three types of DC motors are shunt, series and
a. compound
b. cross compound
c. reverse wound
d. stator
e. armature - Ans--a. compound
Permanent magnets are used for:
a. the largest DC motors and generators
b. constant speed alternators
c. variable speed alternators
d. the smallest DC motors and generators
e. ensuring less maintenance - Ans--d. the smallest DC motors and
generators
An advantage of having an alternator with a rotating field is, that the size of
the rotating mass is:
a. reduced
b. constant
c. removed
d. easily heated
e. enlarged - Ans--a. reduced
Electrotechnology C4-6 Test With Full
Set Correct Solutions
The armature core of a DC machine is built up of laminations of:
a. Silicon steel plates
b. Mica sheets
c. Reinforced carbon plates
d. Electromagnets
e. Copper bars - Ans--a. Silicon steel plates
Synchronous motors have construction that is identical to:
a. centrifugal fans
b. alternators
c. air driven motors
d. gas turbines
e. reciprocating equipment - Ans--b. alternators
In order to produce the strength of magnetic flux required in larger DC
machines:
a. copper switches are used
b. electromagnets are used
c. permanent magnets are used
d. booster transformers are used
e. the field windings are double wound - Ans--b. electromagnets are used
Alternators must run at constant speed in order to maintain:
a. power
b. resistance
c. current
d. voltage
e. frequency - Ans--e. frequency
The rotating field of an alternator is obtained by exciting the windings on the
rotor with:
,a. DC power
b. stator current
c. magnetic particles
d. carbon poles
e. AC power - Ans--a. DC power
A power factor higher than what is generally not required as the savings do
not equate to the cost of the extra capacitors.
a. 0.85
b. 0.75
c. 0.90
d. 0.80
e. 0.95 - Ans--e. 0.95
The electromagnets for a DC machine are termed the:
a. field poles
b. yokes
c. commutators
d. brush gears
e. armatures - Ans--a. field poles
Brush gear for DC machines have brushes made from carbon because they:
a. are softer, wear to a smooth finish, have a low coefficient of friction
b. are softer, are low cost, can produce large quantities of heat
c. wear to smooth finish, can produce large quantities of heat, have a low
coefficient of friction
d. are softer, are low cost, have a low coefficient of friction
e. are low cost, can produce large quantities of heat, have a low coefficient of
friction - Ans--a. are softer, wear to a smooth finish, have a low coefficient of
friction
Determine the speed (rpm) of a synchronous motor operating with a line
frequency of 60 Hz where the motor has 8 poles.
a. 1200
b. 1800
c. 600
d. 2400
e. 900 - Ans--e. 900
, A shunt type DC generator has what type of output voltage?
a. smooth
b. very low
c. erratic
d. very high
e. nearly constant - Ans--e. nearly constant
Which category on a nameplate identifies whether the motor is weather
proof:
a. Bearings
b. NEMA
c. ENC
d. Rating
e. HP - Ans--c. ENC
Three types of DC motors are shunt, series and
a. compound
b. cross compound
c. reverse wound
d. stator
e. armature - Ans--a. compound
Permanent magnets are used for:
a. the largest DC motors and generators
b. constant speed alternators
c. variable speed alternators
d. the smallest DC motors and generators
e. ensuring less maintenance - Ans--d. the smallest DC motors and
generators
An advantage of having an alternator with a rotating field is, that the size of
the rotating mass is:
a. reduced
b. constant
c. removed
d. easily heated
e. enlarged - Ans--a. reduced
