Review Master Electrician (Part 2) Questions With Complete Solutions
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Course
Master Electrician
Institution
Master Electrician
The ordinary direct current series motor does not operate satisfactorily with alternating
current. One of the main reasons for this is
a. excessive heating due to eddy currents in the solid parts of the field structure
b. that the armature current and field current are out of phase with each o...
Review Master Electrician (Part 2) Questions
With Complete Solutions
The ordinary direct current series motor does not operate
satisfactorily with alternating
current. One of the main reasons for this is
a. excessive heating due to eddy currents in the solid parts of the
field structure
b. that the armature current and field current are out of phase
with each other
c. that the field flux lags 120 in time phase with respect to the
line voltage
d. excessive heating due to the low voltage drop in the series
field correct answer: a. excessive heating due to eddy currents
in the solid parts of the field structure
A DC elevator motor, on a gearless traction machine, has a
series field for compounding
during the acceleration period. This field is cut out when the
motor has reached full speed,
for the purpose of
a. preventing excessive heat
b. reducing the line current
c. providing constant speed over a wide range of load conditions
d. saving the cost of losses in the series field correct answer: c.
providing constant speed over a wide range of load conditions
,The protective device for a motor branch circuit
a. should have a rating equal to or greater than the starting
current of the motor
b. should have a rating equal to the full load current of the motor
c. should not be of the instantaneous type
d. should have a rating equal to the current capacity of the
circuit conductors correct answer: c. should not be of the
instantaneous type
When both fuses and thermal cutouts are used in a motor circuit,
the
a. ratings of the fuses should be the same as those of the thermal
cuts
b. fuses are used to protect against continuous, but not large
overloads
c. thermal cutouts are used to protect against continuous
overloading
d. thermal cutouts are used to protect against short-circuits in the
motor and branch
circuit correct answer: c. thermal cutouts are used to protect
against continuous overloading
To temporarily change the direction of rotation of a single-
phase, shaded-pole, induction
motor you would
a. do nothing since it cannot be done
b. reverse the connections to the starting winding
c. shift the brushes to the opposite neutral
, d. reverse the line leads correct answer: a. do nothing since it
cannot be done
For maximum safety the magnetic contactors used for reversing
the direction of rotation
of a motor should be
a. electrically interlocked
b. electrically and mechanically interlocked
c. mechanically interlocked
d. operated from independent sources correct answer: b.
electrically and mechanically interlocked
Silver electrical contactors are tarnished most readily by
a. oxygen
b. hydrogen
c. nitrogen
d. sulphur correct answer: c. nitrogen
The lubricant used for sleeve bearings on motors is usually
a. vaseline
b. oil
c. graphite
d. grease correct answer: b. oil
The correct method of measuring the power taken by an AC
electric motor is to use a
a. wattmeter
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