lOMoARcPSD|12936282
Question Bank in AC Motors and Generators
Bachelor of Science in Electrical engineering (Manuel S. Enverga University Foundation)
StuDocu is not sponsored or endorsed by any college or university
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
Question Bank in AC Motors
1.
REE Board Exam October 1997
A single phase induction motor is rated 5 hp,
75% power factor and 220 volts. What is its full
load current?
A. 22.5 amperes
B. 20.5 amperes
C. 16.5 amperes
D. 18.5 amperes
2.
EE Board Exam April 1990
A 5 hp, 3-phase motor draws current when
connected to 230 V. Determine the current
drawn by the motor if the power factor is 0.90
and efficiency of 83%.
C. 13.25 A
A. 12.53 A
B. 15.13 A
D. 14.05 A
3.
EE Board Exam April 1994
A 3-phase motor is rated 750 hp at 460 volts
line to line, 0.85 pf lagging and 0.95 efficiency.
Solve for the rated current.
A. 869.64 A
C. 405.43 A
B. 702.23 A
D. 917.32 A
4.
EE Board Exam April 1985
A 40 hp, 3-phase, 4-pole, 230 volt, 60 Hz,
induction motor operating at 0.90 efficiency,
0.85 power factor and 3 percent slip, drives a
water pump. Determine the current at which the
motor is operating.
A. 94.531 A
C. 97.915 A
B. 96.234 A
D. 93.351 A
9.
REE Board Exam March 1998
A 50 HP three-phase motor, rated 220 V, 75%
power factor has 6 poles. The slip at full load is
3%. What is the frequency of the rotor current
at full-load?
A. 1.8 Hz
C. 5.4 Hz
B. 60 Hz
D. 58.2 Hz
10. EE Board Exam April 1986
A 150 HP, 3-phase, 6-pole, 460 V, 60 Hz
induction motor draws 195 A line current at fullload speed of 1170 rpm and 0.85 p.f. Solve for
the percent slip at full-load.
C. 2.8%
A. 2.5%
B. 3.0%
D. 2.0%
11. EE Board Exam October 1986
5.
6.
7.
8.
EE Board Exam April 1992
Calculate the speed of a 60-cycle, 14-pole
motor if the slip is 5%.
A. 514.28 rpm
B. 488.57 rpm
C. 456.32 rpm
D. 429.63 rpm
EE Board Exam April 1992
The rotor speed of a six-pole, 50-cycle
induction motor is 960 rpm. Calculate the
percent slip.
A. 5%
C. 4%
B. 2%
D. 3%
REE Board Exam October 1997
What is the speed of an induction motor of six
poles if the percent slip is 2.5%?
A. 1462 rpm
C. 877 rpm
D. 1755 rpm
B. 1170 rpm
EE Board Exam October 1984
A squirrel cage induction motor with nameplate
data of 150 HP, 3-phase, 460 V, 60 Hz, 6-pole,
0.85 p.f. was subjected to certain performance
tests. The test result readings were as follows:
Full-load current = 202 A
Full-load torque = 676.8 lb-ft
Solve for the percentage slip.
A. 3.28%
C. 3.05%
B. 4.15%
D. 2.25%
The deep well pump motor is 50 HP, 3-phase, 4
poles, 230 volts, 60 Hz induction motor,
operating at 0.90 efficiency, 0.85 power factor
and 3% slip. Determine the current at which the
motor is operating.
A. 112.7 A
C. 120.5 A
D. 124.7 A
B. 122.4 A
12. EE Board Exam April 1993
The rotor of a 220 V, 60 Hz, 4-pole induction
motor has a power input of 80 kW is observed
that the rotor emf makes 90 cycles per minute.
Calculate the rotor copper loss.
A. 2 kW
C. 3 kW
B. 5 kW
D. 4 kW
13. EE Board Exam October 1990
A 10-HP, 4 pole, 25 Hz, 3-phase induction
motor is taking 9100 watts from the line. Core
loss is 290 watts; stator copper loss is 568
watts; rotor copper loss is 445 watts and the
friction and windage loss is 121 watts.
Determine the output torque in Newton-meters.
A. 108.4
C. 101.2
B. 112.5
D. 103.3
14. EE Board Exam April 1993
The rotor of a 220 V, 60 Hz, 4 pole induction
motor has a power input of 80 kW is observed
that the rotor emf makes 90 cycles per minute.
Calculate the mechanical power developed.
A. 72 kW
C. 75 kW
D. 77 kW
B. 78 kW
15. EE Board Exam April 1993
Determine the speed in rpm of the motor at full
load with the following circuit elements per
phase:
Rotor leakage reactance = 0.65
Stator leakage reactance = 1.12
Rotor resistance = 0.10
Stator resistance = 0.25
Connection = Y – Y
This motor is 500 HP, 3-phase, 2200 volt, 60cycle, 6- pole induction motor with additional
core loss of 2,000 watts and the friction and
windage losses total is 10,000 watts.
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
A. 1200 rpm
B. 1196 rpm
C.
D.
1190 rpm
1188 rpm
A. 1.9 kW
B. 1.8 kW
C.
D.
2.0 kW
2.1 kW
22. EE Board Exam October 1997
16. EE Board Exam April 1981, April 1989
A 30 HP, 4 poles, 3-phase, 230 volts, 60 Hz
squirrel cage induction motor operating at 90%
efficiency, 85% power factor and 2.5% slip
drives a water pump for a reservoir. Find the
current and speed at which the motor is
operating.
A. 73.4 A, 1755 rpm
B. 62.4 A, 1755 rpm
C. 73.4 A, 1800 rpm
D. 62.4 A, 1800 rpm
A wound rotor motor, 7.5 HP, 230 volts, 3phase takes a line current of 18.4 amperes,
when operating at rated output at an efficiency
of 88%. Calculate the indications on wattmeters
when these are inserted to measure power by
the two wattmeter method.
A. 4.035 kW, 2.325 kW
B. 4.232 kW, 2.126 kW
C. 3.902 kW, 2.456 kW
D. 3.855 kW, 2.503 kW
23. EE Board Exam June 1990
17. EE Board Exam October 1980
A 50 HP, 3-phase, 4-pole, 60 Hz, 230 volt
squirrel cage induction motor has an efficiency
of 90%, a power factor of 85% and a slip of 2%
at full-load. Find the torque in lb-ft at full-load.
A. 152.45
C. 121.34
D. 150.56
B. 148.87
Two wattmeter method is used to test a 25 HP,
230 volt, 1800 rpm, 60 cycle, 3-phase induction
motor. When the line voltages are 230 volts,
one wattmeter reads +13,400 watts and the
other +7,400 watts. Determine motor line
current.
A. 55.6 A
C. 52.3 A
D. 50.8 A
B. 58.4 A
18. EE Board Exam October 1992
The losses in a 220-V, three-phase, 25 Hz, 4pole induction motor at full-load are as follows:
Core = 3.0%
Friction and windage = 2.0%
Stator Cu loss = 4.0%
Rotor Cu loss = 2.0%
At 70% of full-load of the machine, determine
its efficiency.
A. 90.52%
C. 87.24%
B. 88.15%
D. 89.81%
19. EE Board Exam October 1980
A 100 HP, 440 volt, three-phase, 60 Hz
induction motor operates with 92 percent
efficiency, 0.85 power factor, at rated load.
What is the current of the motor?
C. 98 A
A. 125 A
B. 115 A
D. 55 A
20. EE Board Exam October 1991
A three-phase wound rotor induction motor, 440
V, 60 cycles, 4 pole is connected to a pump that
delivers 1000 cfm of water against an effective
head of 8 ft. Under this load, the motor draws
15 kW at a power factor of 0.90. When
operated without load, the motor draws 800
watts. The stator resistance per phase is 0.21
ohm and the rotor resistance per phase is
0.022 ohm. The turns ratio between stator and
rotor is 4:1. Determine the efficiency of the
pump.
A. 83.62%
C. 83.16%
B. 84.65%
D. 84.24%
24. EE Board Exam April 1992
An induction motor of 30-hp, 220-volts, 3-phase
draws 450 percent of the rated current with the
rated voltage and delivers during the starting
period 130 percent of the rated torque. The fullload efficiency and full-load power factor of this
motor is 80% and 70% respectively. If an
autotransformer is used as a starting unit and
starting torque of the load is only 50 percent of
the rated torque of the motor, find the starting
voltage.
A. 136.44 volts
B. 130.65 volts
C. 132.36 volts
D. 134.20 volts
25. EE Board Exam October 1989
A 10-HP, 550 volts, 60 Hz, 3-φ induction motor
has a starting torque of 160% of full-load torque
and starting current of 425% of full-load current.
If the motor is used on a 440 volt, 60 Hz
system, what will be the starting torque
expressed in percent of full-load value?
C. 104.2%
A. 102.4%
B. 101.8%
D. 103.5%
26. EE Board Exam October 1989
A 10-HP, 550 volts, 60 Hz, 3-φ induction motor
has a starting torque of 160% of full-load torque
and starting current of 425% of full-load current.
What will be the voltage in order that the
starting current be limited to the full-load value?
A. 132.47 V
C. 125.52 V
D. 136.75 V
B. 129.41 V
21. REE Board Exam April 1997
A resistor assembly for a wound rotor consists
of 20 elements of cast iron grid elements. The
rating of each is 0.10 ohm. When joined in
series and tested across 220 volts, the
measured current was 100 A. How much power
was lost in the joints?
27. REE Board Exam October 1998
A 25 hp, 230 V, three-phase motor with 85%
power factor has a starting current of 5.5 times
rated current. To reduce the starting current, a
wye-delta is installed. What shall be the new
starting current?
A. 195 amps
C. 135 amps
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
B. 302 amps
D.
175 amps
A. 3,500 rpm
B. 1,780 rpm
C.
D.
875 rpm
3,450 rpm
28. REE Board Exam October 1997
A squirrel cage motor is started at 50% its rated
voltage. What is the starting torque relative to
its rated voltage starting torque?
A. 50%
C. 25%
B. 100%
D. 75%
29. EE Board Exam April 1989
A delta-connected load induction motor draws
100 A from each line of a three-phase source
and develops 40 lb-ft torque at standstill. Find
the torque when connected to the same source
if the motor is reconnected in wye.
A. 13.3 lb-ft
B. 120 lb-ft
C. 40 lb-ft
D. none of these
35. EE Board Exam April 1993
In a certain industrial plant, they have two
motors that are connected in concatenation to
drive a load. Machine A has 4 poles is
connected to a 50-Hz source, while machine B
which has 8 poles is connected to the rotor of
machine A. Find the speed of the combination if
the slip is 8%.
A. 460 rpm
C. 690 rpm
B. 750 rpm
D. 1500 rpm
36. REE Board Exam October 1997
A three phase motor is rated 50 hp, 440 volts
and 85% power factor. What is its rated
current?
C. 55 amps
A. 57.8 amps
B. 57.5 amps
D. 59 amps
30. EE Board Exam April 1992
An induction motor of 30-hp, 220-volts, 3-phase
draws 450 percent of the rated current with the
rated voltage and delivers during the starting
period 130 percent of the rated torque. The fullload efficiency and full-load power factor of this
motor is 80% and 70% respectively. If an
autotransformer is used as a starting unit and
starting torque of the load is only 50 percent of
the rated torque of the motor, find the starting
voltage and starting current of the line.
A. 245.78 volts and 301.4 amps
B. 136.44 volts and 292.7 amps
C. 178.90 volts and 288.6 amps
D. 220 volts and 227.3 amps
37. EE Board Exam October 1992
The losses in a 220 V, three-phase, 25 Hz, 4pole induction motor at full-load are as follows:
Core = 3.0%
Friction and windage = 2.0%
Stator Cu loss = 4.0%
Rotor Cu loss = 2.0%
At 70% of full-load of the machine, determine
its speed and efficiency
A. 1,170 rpm and 88.78%
B. 740 rpm and 89.81%
C. 1,200 rpm and 89.81%
D. 1,800 rpm and 78.93%
38. EE Board Exam April 1992
31. EE Board Exam October 1986
The deep well pump motor is 50 HP, 3-phase, 4
poles, 230 volts, 60 Hz induction motor,
operating at 0.90 efficiency, 0.85 power factor
and 3% slip. Determine the discharge of the
pump in cubic meters per minute, assuming
that the total head against which the pump is
working is 50 meters and that the density of
water is 1000 kg per cubic meter.
A. 4.103
C. 4.563
B. 4.224
D. 4.205
32. REE Board Exam September 2000
Find the rotor frequency of an induction motor if
the rotor speed is 1,145 rpm.
C. 1.25 Hz
A. 2.75 Hz
B. 5.50 Hz
D. 60 Hz
A 460-volt, 3-φ motor draws 208 amperes with
a power factor of 0.91 lagging. Calculate the
cost of energy input to the motor during a 40hr/wk with 5.5 cents/kW-hr.
A. Php545.56/week
B. Php331.78/week
C. Php145.78/week
D. Php267.89/week
39. EE Board Exam October 1990
A 10-hp, 4-pole, 25-Hz, 3-φ induction motor is
taking 9,100 watts from the line. The core loss
is 290 watts; stator copper loss is 568 watts;
rotor copper loss is 445 watts; and the friction
and windage loss is 121 watts. Determine the
output torque in Newton-meter.
A. 150.56
C. 103.32
B. 190.32
D. 178.76
33. REE Board Exam October 1997
A three-phase induction motor is rated 50 hp,
220 volts and 1745 rpm and 78% power factor.
What is the percent slip?
A. 2.5%
C. 3.5%
D. 4.0%
B. 3.1%
40. EE Board Exam April 1988
A Ball Mill rotor is rated 750-hp, 460 volts line to
line, 60 Hz, 0.85 power factor lagging and 0.95
efficiency. Solve for the rated current.
A. 900 amps
C. 780 amps
D. 990 amps
B. 870 amps
34. REE Board Exam October 1996
An AC squirrel cage induction motor has a
speed rating of 1,750 rpm. If the leads are such
that they could be reconnected for consequent
winding, what would be the resulting speed?
41. REE Board Exam September 2001
A 70-hp, 230-volts, 3-φ induction motor
operating at 0.77 power factor has a starting
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
current of 5 times its full-load current. Calculate
the starting current.
A. 851 amps
B. 170 amps
C. 295 amps
D. 1,475 amps
42. REE Board Exam September 2001
Which of the following is not a reason why a
single phase induction motor will not run?
A. one of the current is made out of phase
between the lines
B. hysteresis
C. shaded poles
D. two windings displaced from each other
43. REE Board Exam October 1996
The following are types of AC motor starters
except one
A. reactance starter
l
B. wye-delta starter
C. across the line starter
D. capacitance starter
44. REE Board Exam April 1995
Motor starting device that will reduce the
voltage impressed at motor’s terminals during
starting periods.
A. autotransformer
B. primary resistor-type
C. wye-delta starter
D. all of these
45. EE Board Exam April 1994, April 1992
Basically all electric motors operate on the
principle of repulsion or ____.
A. induction
B. magnetism
C. resistance
D. capacitance
46. EE Board Exam April 1994
The principle of operation of induction motor is
based on
A. Fleming’s right hand rule
B. rotating magnetic field
C. Faraday’s law
D. Ohm’s law
47. EE Board Exam October 1993
A compensator is a device that is used with
alternating current motors to ____.
A. boost the supply voltage during starting
periods
B. compensate for low power factor when
motor is not fully loaded
C. reduce the supply voltage during starting
periods
D. compensate for voltage drop in the circuit
48. EE Board Exam April 1992
A single-phase motor provided with a squirrel
cage winding on its rotor in addition to its
regular winding is called
A. split-phase induction motor
B. repulsion induction motor
C. universal motor
D. repulsion-start induction motor
49. EE Board Exam April 1992
A test used to determine the equivalent
resistance of an induction motor is
A. no-load test
B. short circuit test
C. blocked rotor test
D. polarity test
50. EE Board Exam April 1991
Rapid stopping of a motor by momentarily
connecting the motor in reverse direction is
called
A. jogging
B. inching
C. plugging
D. sequence operation
51. EE Board Exam October 1990
Repeated starting and stopping of a motor is
referred to as
A. stepping
B. jogging
C. phasing
D. none of these
52. EE Board Exam June 1990
An induction motor driven above synchronous
speed is called
A. induction regulator
B. frequency changer
C. induction generator
D. phase converter
Unsolved problems
53. REE Board Exam September 2004
In an induction motor, what is the percent slip if
the speed is 3,510?
A. 1
C. 2
B. 1.5
D. 2.5
54. REE Board Exam September 2002
The speed of an induction motor is 1170 rpm.
What is the frequency of the rotor current?
A. 2.5 Hz
C. 1.5 Hz
B. 37.5 Hz
D. 3.3 Hz
55. REE Board Exam September 2002
A 3-phase, 220 volt induction motor having a
power factor of 0.8 has 3% losses. Determine
the current drawn by the motor.
A. 25.23 A
C. 20.18 A
B. 43.69 A
D. 14.56 A
56. REE Board Exam April 2002
A three-phase squirrel cage motor is started by
wye-delta starter. What shall be its starting
torque relative to its rated voltage starting
torque?
A. 33.3%
C. 57.7%
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
B. 42.3%
D.
100%
66. Regarding skewing of motor bars in a squirrel57. ECE Board Exam November 1999
How do you call the speed of an alternating
current (AC) induction motor?
A. Varying supply frequency
B. Varying series resistance of the field
C. Varying supply voltage
D. Varying both the supply voltage and
frequency at the same time
58. ECE Board Exam November 1995
The best way to control the speed of an AC
induction motor is by varying the _____.
A. supply frequency
B. both supply voltage and frequency
simultaneously
C. supply voltage
D. series resistance of the field
59. ECE Board Exam November 1997
A two pole, three phase motor has _____ field
poles.
A. 6
C. 2
B. 8
D. 4
60. ECE Board Exam November 2001
_____ refers to an AC generator.
A. Commutator
C.
B. Motor (AC)
D.
Rotor
Alternator
61. ECE Board Exam November 2000
Series motors operated on either AC or DC are
sometimes called _____.
A. Universal motors
B. General motors
C. Bavarian motors
D. Anglo motors
62. ECE Board Exam April 2001
What does the term single-phase indicate?
A. One input
B. One current (one input)
C. One time
D. One voltage (one input)
63. ECE Board Exam November 1996
Kind of AC-motor, light load high load low
speed.
A. Synchronous motor
B. Squirrel cage motor
C. Split phase motor
D. Universal motor
64. ECE Board Exam November 1996
A two pole, one phase motor has ___field
poles.
A. 8
C. 6
B. 2
D. 4
65. What is the percent slip of a 4-pole induction
motor if the output speed is 1,755 rpm?
A. 3
C. 2.5
B. 5
D. 4
cage induction motor, (SCIM) which statement
is false.
A. it prevents cogging
B. it increases starting torque
C. it produces more uniform torque
D. it reduces motor ‘hum’ during its operation
67. The principle of operation of a 3-phase
induction motor is most similar to that of a
A. synchronous motor
B. repulsion-start induction motor
C. transformer with a shorted secondary
D. capacitor-start, induction-run motor
68. The magnetizing current drawn by transformers
and induction motors is the cause of their ____
power factor.
C. lagging
A. zero
B. unity
D. leading
69. The effect of increasing the length of air-gap in
an induction motor will be to increase the
A. power factor
B. speed
C. magnetizing current
D. air-gap flux
70. In a 3-phase induction motor, the relative speed
of stator flux with respect to ____ is zero.
C. rotor flux
A. stator winding
B. rotor
D. space
71. An eight pole wound rotor induction motor
operating on 60 Hz supply is driven at 1800
r.p.m. by a prime mover in the opposite
direction of revolving magnetic field. The
frequency of rotor current is
A. 60 Hz
B. 120 Hz
C. 180 Hz
D. none of the above
72. A 3-phase 4 pole, 50 Hz induction motor runs
at a speed of 1440 r.p.m. The rotating field
produced by the rotor rotates at a speed of
____ r.p.m. with respect to the rotor.
A. 1500
C. 60
B. 1440
D. 0
73. In a 3- induction motor, the rotor field rotates at
synchronous speed with respect to
A. stator
B. rotor
C. stator flux
D. none of the above
74. Irrespective of the supply frequency, the torque
developed by a SCIM is the same whenever
____ is the same.
A. supply voltage
B. external load
C. rotor resistance
D. slip speed
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
75. The number of stator poles produced in the
rotating magnetic field of a 3-Ф induction motor
having 3 slots per pole per phase is
A. 3
C. 2
B. 6
D. 12
76. The power factor of a squirrel-cage induction
motor is
A. low at light loads only
B. low at heavy loads only
C. low at light and heavy loads only
D. low at rated load only
77. Which of the following rotor quantity in a SCIM
does NOT depend on its slip?
A. reactance
B. speed
C. induced emf
D. frequency
motor depends on the following three factors:
A. speed, frequency, number of poles
B. voltage, current and stator impedance
C. synchronous speed, rotor speed and
frequency
D. rotor emf, rotor current and rotor p.f.
87. If the stator voltage and frequency of an
induction motor are reduced proportionately, its
A. locked rotor current is reduced
B. torque developed is increased
C. magnetizing current is decreased
D. both A and B
88. The efficiency and p.f. of a SCIM increases in
78. A 6-pole, 50-Hz, 3- induction motor is running
at 950 rpm and has rotor Cu loss of 5 kW. Its
rotor input is ____ kW.
A. 100
C. 95
B. 10
D. 5.3
79. The efficiency of a 3-phase induction motor is
approximately proportional to
A. (1 – s)
C.
B. s
D.
86. The torque developed by a 3-phase induction
N
Ns
proportion to its
A. speed
B. mechanical load
C. voltage
D. rotor torque
89. A SCIM runs at constant speed only so long as
A.
B.
C.
D.
torque developed by it remains constant
its supply voltage remains constant
its torque exactly equals the mechanical
load
stator flux remains constant
90. The synchronous sped of a linear induction
80. A 6-pole, 50-Hz, 3- induction has a full-load
speed of 950 rpm. At half load, its speed would
be ____ rpm.
A. 475
C. 975
B. 500
D. 1000
81. If rotor input of a SCIM running with a slip of
10% is 100 kW, gross power developed by its
rotor is ____ kW.
A. 10
C. 99
B. 90
D. 80
motor does NOT depend on
A. width of pole pitch
B. number of poles
C. supply frequency
D. any of the above
91. Thrust developed by a linear induction motor
depends on
A. synchronous speed
B. rotor input
C. number of poles
D. both A and B
82. Pull-out torque of a SCIM occurs at that value
of slip where rotor power factor equals
A. unity
C. 0.866
B. 0.707
D. 0.5
83. When applied rated voltage per phase is
reduced by one-half, the starting torque of a
SCIM becomes ____ of the starting torque with
full voltage.
A. ½
C.
B. ¼
D.
84. If maximum torque of an induction motor is 200
kg-m at a slip of 12%, the torque at 6% slip
would be ____ kg-m.
A. 100
C. 50
D. 40
B. 160
85. The fractional slip of an induction motor is the
ratio
A. rotor Cu loss/rotor input
B. stator Cu loss/stator input
C. rotor Cu loss/rotor output
D. rotor Cu loss/stator Cu loss
92. The stator of a 3-phase induction motor
produces ____ magnetic field.
A. steady
B. rotating
C. alternating
D. none of these
93. An induction motor is preferred to a dc motor
because it
A. provides high starting torque
B. provides fine speed control
C. has simple and rugged construction
D. none of the above
94. A 3-phase induction motor is
A. essentially a constant speed motor
B. a variable speed motor
C. very costly
D. not easily maintainable
95. The air gap between stator and rotor of a 3phase induction motor ranges from
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
A.
B.
C.
D.
2 cm to 4 cm
0.4 mm to 4 mm
1 cm to 2 cm
4 cm to 6 cm
104. If the induction motor shown in Fig. 6.1 runs at
96. If the frequency of 3-phase supply to the stator
of a 3-phase induction motor is increased, the
synchronous speed
A. is decreased
B. is increased
C. remains unchanged
D. none of the above
97. If Ns is the speed of rotating flux and Nr the
speed of the rotor, then the rate at which the
flux cuts the rotor conductors is directly
proportional to
A. Ns
C. Ns – Nr
B. Nr
D. Nr – Ns
98. In a 3-phase induction motor, the rotor speed is
____ the synchronous speed.
A. greater than
B. smaller than
C. equal to
D. none of these
1450 rpm, then slip is
A. 50%
B. 3.3%
C. 5%
D. none of these
105. In Fig. 6.1, the rotor frequency ____ is when
the motor is at standstill.
A. zero
B. 25 Hz
C. 50 Hz
D. none of these
106. If one of the lines in Fig. 6.1 is interchanged,
then
A. flux speed increases
B. flux speed decreases
C. flux speed remains the same but direction
is reversed
D. none of the above
107. If a 4-pole induction motor has a synchronous
99. The synchronous speed of a 3-phase induction
motor having 20 poles and connected to a 50
Hz source is
A. 600 rpm
C. 1200 rpm
B. 1000 rpm
D. 300 rpm
100. The relation among synchronous speed (Ns),
rotor speed (Nr) and slip (s) is
A. Nr = (s – 1)Ns
B. Nr = (1 – s)Ns
C. Nr = (1 + s)Ns
D. Nr = sNs
speed of 1500 rpm, then supply frequency is
A. 50 Hz
B. 25 Hz
C. 60 Hz
D. none of these
108. The full-load slip of a 3-phase induction motor
ranges from
A. 10% to 20%
B. 20% to 30%
C. 2% to 5%
D. none of these
109. The direction of rotation of field in a 3-phase
101. When a 3-phase induction motor is at no load,
the slip is
A. 1
B. 0.5
C. practically zero
D. 0.2
induction motor depends upon
A. number of poles
B. magnitude of supply voltage
C. supply frequency
D. phase sequence of supply voltage
110. The rotor winding of a 3-phase wound rotor
102. When the rotor of a 3-phase induction motor is
blocked, the slip is
A. zero
B. 0.5
C.
D.
0.1
1
induction motor is generally ____ connected.
A. star
B. delta
C. partly star partly delta
D. none of the above
111. 3-phase wound rotor motors are also called
103. The speed of the rotating flux in Fig. 6.1 will be
3-phase
supply
50 HZ
P=4
3-Phase Induction Motor
Fig. 6.1
A.
B.
C.
D.
1500 rpm
1000 rpm
750 rpm
none of these
____ motors.
A. synchronous
B. slip ring
C. series
D. commutator
112. The advantage of wound rotor motor is that
A.
B.
C.
D.
it is inexpensive
it requires less maintenance
external resistance can be inserted in the
rotor circuit
none of the above
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
113. A wound rotor motor is mainly used in
application where
A. a high starting torque is required
B. speed control is not required
C. less costly motor is required
D. high rotor resistance is required during
running
122. When an induction motor is running at full-load,
rotor reactance is ____ rotor resistance.
A. comparable to
B. very large compared to
C. large compared to
D. none of the above
123. If the slip of a 3-phase induction motor
114. The torque characteristic of a 3-phase
induction motor is similar to that of
A. dc series motor
B. dc shunt motor
C. dc differentially compounded motor
D. dc cumulatively compounded motor
increases, the p.f. of the rotor circuit
A. is increased
B. is decreased
C. remains unchanged
D. none of the above
124. The magnetizing current drawn by a 3-phase
115. In a wound rotor motor, the rotor winding is
wound for poles ____ that of the stator winding.
A. equal to
B. greater than
C. smaller than
D. none of these
116. Wound rotors are less extensively used than
squirrel cage motor because
A. slip rings are required on the rotor circuit
B. rotor windings are generally Y-connected
C. they are costly are required greater
maintenance
D. none of the above
117. A 4-pole, 50 Hz induction motor operates at 5%
slip. The frequency of emf induced in the rotor
will be
A. 25 Hz
B. 50 Hz
C. 2.5 Hz
D. none of these
118. The maximum voltage is induced in the rotor of
a 3-phase induction when it
A. runs at no-load
B. runs at full-load
C. is blocked
D. none of these
119. The reactance of the rotor circuit of a 3-phase
induction motor is maximum at
A. no-load
B. full-load
C. half full-load
D. starting
induction motor is about ____ of full-load stator
current.
A. 5%
C. 15 to 20%
B. 10 to 15%
D. 30 to 50%
125. A high starting torque can be obtained in a 3phase induction motor by
A. increasing rotor resistance
B. decreasing rotor resistance
C. increasing rotor reactance
D. none of the above
126. The starting torque of a 3-phase induction
motor is ____ supply.
A. independent of
B. directly proportional to
C. directly proportional to the square of
D. none of the above
127. The starting torque of an induction motor is
maximum when rotor resistance per phase is
____ rotor reactance/phase.
A. equal to
B. two times
C. four times
D. none of these
128. Under running conditions, the maximum torque
of 3-phase induction motor will occur at that
value of slip at which rotor resistance/phase is
____ rotor reactance/phase.
A. two times
B. four times
C. equal to
D. none of these
129. The maximum torque of a 3-phase induction
120. The rotor current in a 3-phase induction motor
is ____ slip.
A. inversely proportional to
B. directly proportional to
C. independent of
D. none of these
motor under running conditions is
A. inversely proportional to supply voltage
B. inversely proportional to rotor reactance at
standstill
C. directly proportional to rotor resistance
D. none of the above
121. At starting, rotor reactance of a 3-phase
130. If the supply voltage of a 3-phase induction
induction motor is ____ rotor resistance.
A. small as compared to
B. equal to that of
C. large as compared to
D. none of the above
motor is increased two times, then torque is
A. increased two times
B. decreased two times
C. increased four times
D. decreased four times
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
131. The 3-phase induction motor is so designed
that the rotor should have ____ under running
conditions.
A. high resistance
B. high reactance
C. large slip
D. low resistance
D. none of these
141. In a squirrel cage rotor, the bars are not placed
to the shaft but are skewed to have
A. greater mechanical strength
B. less rotor losses
C. uniform torque
D. none of the above
132. If a 3-phase induction motor is running at slip s
(in decimal) then rotor copper loss is equal to
A. (1 – s) x rotor input
B. (1 + s) x rotor input
C. s x rotor input
D. none of these
142. In a squirrel cage motor, the number of stator
slots is ____ rotor slots.
A. always equal to the number of
B. always greater than the number of
C. always less than the number of
D. either more or less than the number of
133. If an induction motor is running at slip s (in
decimal) then rotor output is equal to
A. (1 + s) x rotor input
B. (s - 1) x rotor input
C. s x rotor input
D. (1 – s) x rotor input
143. If the air gap between the rotor and stator of 3phase induction motor is increased then
A. no-load current is decreased
B. leakage reactances are decreased
C. leakage reactances are increased
D. none of the above
134. If Ns and Nr are the speeds of rotating field and
rotor respectively, the ratio rotor input/rotor
output is equal to
A. Nr/Ns
C. Ns - Nr
B. Ns/Nr
D. Nr – Ns
135. At no-load, the rotor core loss of a 3-phase
induction motor is
A. large
B. small
C. practically small
D. none of the above
136. Friction and windage loss of a 3-phase
induction motor are
A. maximum at no load
B. minimum at no load
C. remains the same at all loads
D. none of the above
137. For higher efficiency of 3-phase induction
motor, the slip should be
A. large
B. very large
C. as small as possible
D. 1
138. If a 3-phase induction motor is running at a slip
s (in decimal), then approximate efficiency of
the motor is
2
A. s
C. s - 1
B. 1 + s
D. 1 - s
144. If the slip of induction motor increases, then
current in the stator winding
A. is increased
B. is decreased
C. remains unchanged
D. none of the above
145. The conditions of an induction motor at no-load
resemble those of a transformer whose
secondary is
A. short-circuited
B. open-circuited
C. supplying a variable resistive load
D. none of the above
146. The conditions of an induction motor at
standstill resemble those of a transformer
whose secondary is
A. short-circuited
B. open-circuited
C. supplying a variable resistive load
D. none of the above
147. The conditions of an induction motor on load
resemble those of a transformer whose
secondary is
A. short-circuited
B. open-circuited
C. supplying a variable resistive load
D. none of the above
148. The speed of a squirrel cage induction motor is
139. A 3-phase induction motor is running at 2%
slip. If the input to rotor is 1000 W, then
mechanical power developed by the motor is
A. 20 W
C. 500 W
D. 200 W
B. 980 W
140. The approximate efficiency of a 3-phase 50 Hz,
4-pole induction motor running at 1350 rpm is
A. 90%
B. 40%
C. 65%
changed by
A. pole changing
B. rheostatic control
C. cascade control
D. none of these
149. One of the speeds of a 2-speed squirrel cage
induction motor is 800 rpm (lower speed). The
other speed would be
A. 400 rpm
C. 1600 rpm
B. 2400 rpm
D. 1200 rpm
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
150. A four speed squirrel cage induction motor
uses ____ stator windings.
A. four
B. three
C.
D.
one
two
A.
B.
C.
D.
squirrel cage
wound
either A or C
none of these
160. For the same rating, the size of a single-phase
151. In a double squirrel cage induction motor, the
outer cage winding has
A. high inductance
B. low resistance
C. high resistance
D. none of these
152. At starting of a double squirrel cage induction
motor
A. lower cage winding has low reactance
B. outer cage winding has good p.f.
C. lower winding is more effective
D. none of the above
induction motor is about ____ that of the
corresponding 3-phase induction motor.
A. 3 times
C. 1.5 times
B. the same as
D. 0.33 times
161. For the same rating, the p.f. of a single-phase
induction motor is about ____ that of the
corresponding 3-phase induction motor.
A. the same as
B. less than
C. more than
D. none of these
162. For the same rating, the efficiency of a single153. Very large 3-phase induction motors (> 25 HP)
are started
A. direct on line
B. star-delta starting
C. by autotransformer starting
D. none of the above
154. If the rotor slots are made deeper, rotor
resistance is
A. increased at starting
B. decreased at starting
C. increased under running condition
D. none of the above
155. In a squirrel cage induction motor, the number
of rotor bars is generally
A. even number
B. equal to stator poles
C. prime number
D. none of these
156. In a squirrel cage induction motor, the
maximum torque developed under running
conditions is
A. equal to starting torque
B. full-load torque
C. less than starting torque
D. much higher than full-load torque
157. In a wound rotor induction motor, the external
resistance is so adjusted in the rotor circuit that
maximum torque developed is
A. equal to its starting torque
B. equal to its full-load torque
C. less than its full-load torque
D. none of the above
158. For the same kVA rating, the leakage flux in
induction motor is ____ that of transformer.
A. more than
B. less than
C. about the same
D. none of these
159. A single-phase induction motor employs ____
rotor.
phase induction motor is about ____ that of the
corresponding 3-phase induction motor.
A. less than
B. the same as
C. more than
D. none of these
163. Three-phase induction motors are widely used
for industrial applications because
A. they are rugged in construction, requires
less maintenance and are less expensive
than other motors
B. their speed can be controlled very
smoothly over a wide range
C. their operating characteristics are superior
over other electrical motors
D. they can be manufactured easily for any hp
rating
164. In a three-phase induction motor
A. three-phase supply is to be given to stator
winding and dc supply to the rotor winding
B. only three-phase supply is to be given to
stator winding
C. three-phase supply is to be given to both
stator and rotor windings
D. three-phase supply is to be given to rotor
winding
165. The stator and rotor cores of an induction motor
are made up of laminated sheets
A. to reduce the hysteresis loss in the core
B. to reduce the eddy-current loss in the core
C. to make the rotor and stator mechanically
strong
D. to enable the stator and rotor cores
dissipate heat more effectively
166. The stator and rotor cores of an induction motor
are made up of magnetic material
A. to keep the cost of construction low
B. to reduce the magnetizing current
C. to make the parts strong
D. because the reluctance of the magnetic
material is strong
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
167. In wound-rotor type induction motors the rotor
terminals are brought out through slip rings
A. to enable extra resistance to be connected
across them during starting
B. to enable closing the rotor circuit externally
C. to enable three-phase supply to be applied
across the rotor winding through rush and
slip-ring arrangement
D. to enable connecting the rotor windings
either in star or in delta depending upon
the need
168. A pulsating (alternating) magnetic field will be
produced when
A. two-phase supply is applied across a twophase stator winding
B. three-phase supply is applied across a
three-phase stator winding
C. a polyphase supply is applied across a
polyphase stator winding
D. a single-phase supply is applied across a
single-phase stator winding
169. To make the simplest 6-pole stator winding, at
least
A. two coils are needed
B. one coil is needed
C. three coils are needed
D. six coils are needed
170. The direction of the rotating magnetic field
produced by the stator ampere-turns of a threephase induction motor changes if
A. the sequence of the supply to the stator
terminals is changed
B. a variable frequency voltage is applied
across the stator terminals
C. the supply voltage is changed
D. supply to any one phase is disconnected
171. A 400-V, 50-Hz, 4-pole, three-phase induction
motor cannot run at 1500 rpm because
A. at 1500 rpm there will be no emf induced in
the rotor circuit hence no torque will be
produced
B. an induction motor can run only at a speed
higher than its synchronous speed
C. at 1500 rpm, torque developed by the rotor
may not be sufficient to rotate the rotor
D. at 1500 rpm, the rotor will draw excessive
current and may be harmful to the motor
172. A 400-V, 50-Hz three-phase induction motor
rotates at 1440 rpm on full-load. The motor is
wound for
A. 2-poles
C. 6-poles
D. 8-poles
B. 4-poles
173. The slip of a 400-V, three-phase, 4-pole
induction motor when rotating at 1440 rpm is
A. 2 per cent
C. 4 per cent
B. 3 per cent
D. 5 per cent
174. The relation between synchronous speed,
stator supply frequency and stator number of
poles of a three-phase induction motor is given
by
A.
C.
B.
D.
175. When a 400-V, 50-Hz, 6-pole induction motor is
rotating at 960 rpm on no-load, its slip is
A. 1 per cent
C. 3 per cent
B. 2 per cent
D. 4 per cent
176. The torque-slip characteristic for a three-phase
induction motor is such that
A. for lower values of slip, torque is directly
proportional to slip and for higher values of
slip, torque is inversely proportional to slip
B. for lower values of slip, torque is inversely
proportional to slip and for higher values of
slip, torque is directly proportional to slip
C. for lower values of slip, torque is directly
proportional to the square of the slip and
for higher values of slip, torque is inversely
proportional to slip
D. for lower values of slip, torque is directly
proportional to the slip and for higher
values of slip, torque is inversely
proportional to square of slip
177. Torque developed by a three-phase, 400-V
induction motor is 100 N-m. If the applied
voltage is reduced to 200-V, the developed
torque will be
A. 50 N-m
C. 200 N-m
D. 62.5 N-m
B. 25 N-m
178. If the rotor circuit resistance of a three-phase
induction is increased
A. its starting torque will increase and the
maximum torque developed will also
increase
B. both the starting torque and maximum
torque will remain unchanged
C. its starting torque will increase but the
maximum torque developed will decrease
D. its starting torque will increase but the
maximum torque developed will remain
unchanged
179. To achieve higher starting torque in a threephase slip-ring type induction motor
A. extra resistance should be connected
across the slip-rings terminals
B. the phase sequence of the supply to the
motor should be reversed
C. the supply voltage should be increased
D. the windings should first be connected in
star and then in delta
180. For a three-phase induction motor having rotor
circuit resistance of 6 . Maximum torque occurs
at a slip of 0.6. The value of standstill rotor
circuit reactance is
A. 4.44
C. 1 Ω
B. 0.36
D. 10 Ω
181. While starting a three-phase induction motor, a
star-delta starter is used to
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
A. reduce the starting current to a safe value
B. achieve higher starting torque
C. enable the motor to start in the right
direction
D. be able to reverse the direction of rotation
of the rotor as and when necessary
182. A delta-connected 400-V, 50-Hz, three-phase
induction motor when started direct-on-line
takes a starting current of 30 A. When the
motor is started through a star-delta starter.
The starting current will be
A. 3 A
C. 15 A
D. 30 A
B. 10 A
183. The magnetizing current a three-phase
induction motor is much higher than the
equivalent transformer because
A. the size of an induction motor is higher
than an equivalent transformer
B. of the presence of air-gap between stator
and rotor in an induction motor
C. grain oriented magnetic material is used for
the core of an induction motor
D. inferior magnetic material is used for the
core of an induction motor
184. Smooth speed control of a three-phase
induction motor over a wide range is possible,
by
A. pole changing method
B. frequency control method
C. using consequent pole technique
D. by voltage control method
185. The power input in blocked-rotor test performed
on a three-phase induction motor is
approximately equal to
A. hysteresis loss in the core
2
B. I R loss in the windings
C. eddy-current loss in the core
D. iron-loss in the core
186. The power input in no-load test performed on a
three-phase induction motor is approximately
equal to
A. hysteresis loss in the core
2
B. I R loss in the windings
C. eddy-current loss in the core
D. iron-loss in the core
187. In the equivalent circuit of a three-phase
induction motor the mechanical load on the
motor can be represented by a resistance of
value
A.
C.
B.
D.
188. The phenomenon of squirrel-cage motors
sometime showing tendency to run at a very
low speed is known as
A. cogging
C. damping
B. crawling
D. skewing
189. The speed of revolving field for a 50-Hz, 8-pole
machine will be
A. 1500 rpm
B. 1440 rpm
C.
D.
1000 rpm
750 rpm
190. The torque developed by an induction motor is
A. directly proportional to the square of the
rotor resistance
B. directly proportional to the square of the
supply voltage
C. inversely proportional to the supply voltage
D. inversely proportional to the slip
191. The power factor of an induction motor will be
high when
A. running at no-load
B. running at full-load
C. rotor is blocked
D. the rotor is crawling
192. A 5-hp, three-phase, 400-V star-connected
squirrel-cage induction motor meant to drive a
milling machine, at starting takes about
C. 150 A
A. 40 A
B. 100 A
D. 200 A
193. The starting torque of an induction motor can
be increased by
A. increasing the rotor reactance
B. increasing the rotor resistance
C. increasing the supply frequency
D. giving supply through star-delta starter
194. For a given three-phase induction motor,
maximum torque will be developed at starting if
the rotor parameters are as follows:
A. R2 = 2 , X2 = 8
B. R2 = 4 , X2 = 8
C. R2 = 8 , X2 = 8
D. R2 = 16 , X2 = 8
195. The speed of a three-phase induction motor will
increase if the
A. number of poles of the stator winding is
increased
B. number of poles of the stator winding is
decreased
C. frequency of the stator supply is decreased
D. resistance of the rotor circuit is increased
196. Induction motors now-a-days use die-cast
aluminum rotor because
A. aluminum is lighter than copper
B. aluminum is cheaper than copper
C. aluminum is easy to cast because of low
melting point and is easily available
D. aluminum has less resistivity than copper
197. When the rotor circuit resistance of a polyphase
induction motor is increased
A. the staring torque increases
B. the maximum value of torque decreases
C. the slip at which maximum torque occurs
remains unchanged
D. maximum torque is developed at starting
198. In an induction motor the rotor resistance and
reactance are 0.2 ohm and 5 ohm respectively.
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
In order that the torque of the motor may be a
maximum, the value of slip should be equal to
A. 10%
C. 4%
B. 8%
D. 1%
199. What will happen if the air gap in an induction
motor is increased?
A. the windage losses will increase
B. the magnetizing current of the rotor will
decrease
C. the power factor will decrease
D. the speed of the motor will increase
200. An induction motor is said to be crawling if
A.
B.
C.
D.
it accelerates too fast
it is started on full load
it is subjected to fluctuating load
it runs at 10 to 15 percent of rated speed
201.
D.
parallel with starting
208. The purpose of starting winding in a singlephase induction motor is to
A. reduce losses
B. limit temperature rise of the machine
C. produce rotating flux in conjunction with
main winding
D. none of the above
209. If Im and Is are the current in the main and
starting windings respectively and α is the
angle between Im and Is, then motor torque T
is given by
A. T α Im Is cos α
B. T α Im Is sin α
C. T α Im Is
D. none of these
210. In the resistance split-phase induction motor
A.
B.
C.
D.
SINGLE PHASE MOTORS
202. Most of single-phase induction motors are ____
machines.
A. 2 pole
C. 8 pole
B. 6 pole
D. 4 pole
203. The main winding and starting winding of a
single -phase induction motor are connected in
____ across the supply.
A. series
B. parallel
C. series-parallel
D. none of these
204. The starting winding of a single-phase
induction motor has ____ that of the main
winding.
A. more poles than
B. less poles than
C. same number of poles
D. none of the above
205. A 50 Hz, 4 pole single-phase induction motor
will have a synchronous speed of
A. 1500 rpm
B. 750 rpm
C. 1200 rpm
D. none of these
206. A 4 pole, 50 Hz single-phase induction motor
has a slip of 5%. The speed of the motor will be
A. 1500 rpm
B. 1425 rpm
C. 1200 rpm
D. none of these
207. In a single-phase induction motor, speed
sensitive centrifugal switch is connected in
____ winding.
A. parallel with main
B. series with main
C. series with starting
shown in Fig. 1, the angle α between Im and Is
is about
A. 80 degrees
B. 65 degrees
C.
D.
75 degrees
25 degrees
211. The starting winding of a split-phase induction
motor shown in Fig. 1 is disconnected when the
motor attains about ____ of synchronous
speed.
A. 75%
C. 25%
B. 50%
D. 100%
212. In the resistance split-phase induction motor
shown in Fig. 1, the main windings has
A. high resistance and high inductance
B. high resistance and low inductance
C. low resistance and high inductance
D. low resistance and low inductance
213. At starting, the current Is in the starting winding
shown in Fig. 1
A. lags V by 90 degrees
B. leads V by 90 degrees
C. is nearly in phase with V
D. leads V by 75 degrees
214. A resistance split-phase induction motor is
used for
A. low inertia loads
B. high inertia loads
C. very high inertia loads
D. none of the above
215. The direction of split-phase induction motor can
be reversed by interchanging the connections
of supply of
A. either main or starting winding
B. both main and starting winding
C. rotor winding
D. none of the above
216. The resistance split-phase induction motor has
____ starting torque.
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
A.
B.
C.
D.
high
moderate
very low
none of these
225. The capacitor-start, capacitor-run induction
motor acts as a true 2-phase motor at
A. starting
C. all loads
B. no load
D. full load
217. The resistance split-phase induction motor is
C.
used in those applications where
A. starting is frequent
B. starting period is long
starting is infrequent
D. none of the above
226. The capacitor-start, capacitor-run motor is used
in those applications where
A. highly starting torque is required
B. silence is important
C. noisy operation is not important
D. none of the above
218. The resistance split-phase induction motors are
the most popular single-phase induction motors
because of
A. their low cost
B. their high starting torque
C. the long starting period
D. none of the above
219. In the capacitor start induction motor shown in
Fig. 2, the angle α between Im and Is is
227. The capacitor-start, capacitor-run motor has
A.
B.
C.
D.
no centrifugal switch
low power factor
noisy operation
low efficiency
228. Capacitor motors ____ resistance split-phase
induction motors.
A. are costlier than
B. are less costly than
C. cost about the same as
D. poor starting torque than
229. Most of the troubles of single-phase induction
A. exactly 90°
B. about 30°
C.
D.
about 40°
about 75°
220. The value of Is in capacitor-start motor shown
in Fig. 2 is ____ the current Im.
A. equal to
B. less than that of
C. more than that of
D. none of the above
230. The single-phase shaded pole motor has
A.
B.
C.
D.
221. The capacitor C used in the capacitor-start
motor shown in Fig. 2 is always a ____
capacitor.
A. paper
B. ceramic
C.
D.
mica
electrolytic
222. At starting, the line current of a capacitor-start
induction motor is ____ normal full-load current.
A. 8 to 10 times
B. 4 to 5 times
C. equal to
D. 7 to 8 times
223. In a capacitor-start, capacitor-run motor, ____
winding is cut-out after starting.
A. starting
B. main
C. neither A or B
D. none of these
224. A capacitor-start, capacitor-run motor has
A.
B.
C.
D.
low power factor
high power factor
low efficiency
high starting torque
motor are traceable to the
A. rotor bars
B. main winding
C. shaft bearings
D. starting switch
squirrel cage rotor
wound rotor
high power factor
high starting torque
231. The direction of rotation of shaded pole motor
depends upon
A. supply frequency
B. number of poles on the stator
C. which half of the pole is shaded
D. supply voltage
232. The full-load efficiency of a shaded pole motor
is about
A. 70 to 80%
B. 60 to 70%
C.
D.
30 to 35%
5 to 10%
233. The single-phase series motor can operate on
A.
B.
C.
D.
ac only
dc only
both ac and dc
none of these
234. For the same rating, a dc series motor costs
___ single phase series motor.
A. about the same as
B. more than
C. less than
D. none of these
235. A 2 HP dc series motor will weigh ___ 2 HP
single-phase series motor.
A. about the same as
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
B. less than
C. more than
D. none of these
B.
C.
D.
236. A vacuum cleaner employs ____ motor.
A.
B.
C.
D.
resistance split-phase
capacitor start
shaded-pole
single-phase series
reversing connections of starting winding
using a reversing switch
reversing supply connections
246. If a single-phase induction motor runs slower
than normal, the more likely defect is
A. improper fuses
B. shorted running winding
C. open starting winding
D. worn bearing
237. The best suited motor to drive a 1/4 HP fan in a
247. The capacitor in a capacitor-start induction run
hospital would be ____ motor.
A. shaded pole
B. single-phase series
C. capacitor run
D. hysteresis
238. The washing machine generally employs ____
motor.
A. single-phase series motor
B. resistance split-phase
C. shaded-pole
D. hysteresis
248. A permanent-split single-phase capacitor motor
239. The best suited motor to drive a 3/4 HP air
compressor would be ____ motor.
A. capacitor start
B. single-phase series
C. shaded pole
D. resistance split-phase
C.
D.
split phase
ac series
241. The starting winding of a single-phase motor is
placed in the
A. rotor
B. stator
C.
D.
does not have
A. centrifugal switch
B. starting winding
C. squirrel-cage rotor
D. high power factor
249. The starting torque of a capacitor-start
240. The least expensive fractional horsepower
motor is
A. shaded pole
B. capacitor-start
ac motor is connected in series with ____
winding.
A. starting
B. squirrel-cage
C. running
D. compensating
armature
field
induction-run motor is directly related to the
angle or between its two winding currents by
the relation
A. cos
C. tan
B. sin
D. sin /2
250. In a two-value capacitor motor, the capacitor
used for running purposes is a/an
A. dry-type ac electrolytic capacitor
B. paper-spaced oil filled type
C. air-capacitor
D. ceramic type
251. If the centrifugal switch of a two-value capacitor
242. One of the characteristics of a single-phase
motor is that it
A. is self-starting
B. is not self-starting
C. requires only one winding
D. can rotate in one direction only
243. After the starting winding of a single phase
induction motor is disconnected from supply, it
continues to run only on ____ winding.
A. rotor
B. field
C. compensating
D. running
244. If starting winding of a single-phase induction
motor is left in the circuit, it will
A. draw excessive current and overheat
B. run slower
C. run faster
D. spark at light loads
245. The direction of rotation of a single-phase
motor can be reversed by
A. reversing connections of both windings
motor using two capacitors fails to open, then
A. electrolytic capacitor will, in all probability,
suffer breakdown
B. motor will not carry the load
C. motor will draw excessively high current
D. motor will not come up to the rated speed
252. Each of the following statements regarding a
shaded-pole motor is true except
A. its direction of rotation is from un-shaded
to shaded portion of the poles
B. it has very poor efficiency
C. it has very poor p.f.
D. it has high starting torque
253. Compensating winding is employed in an ac
series motor in order to
A. compensate for decrease in field flux
B. increase the total torque
C. reduce the sparking at brushes
D. reduce effects of armature reaction
254. A universal motor is one which
A.
B.
is available universally
can be marked internationally
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
C.
D.
can be operated either on de or ac supply
runs at dangerously high speed on no-load
255. In a single-phase series motor the main
purpose of inductively-wound compensating
windings is to reduce the
A. reactance emf of commutation
B. rotational emf of commutation
C. transformer emf of commutation
D. none of the above
C.
D.
stepper motor
shaded-pole motor
264. Usually, large motors are more efficient than
small ones. The efficiency of the tiny motor is
used in a wrist watch is approximately ____ per
cent.
A. 1
C. 50
B. 10
D. 80
265. For production of a rotating magnetic field
256. A repulsion motor is equipped with
A.
B.
C.
D.
a commutator
slip-rings
a repeller
neither A nor B
257. A repulsion-start induction-run single-phase
motor runs as an induction motor only when
A. brushes are shifted to neutral plane
B. short-circuiter is disconnected
C. commutator segments are short-circuited
D. stator winding is reversed
258. If a dc series motor is operated on ac supply, it
will
A.
B.
C.
D.
have poor efficiency
have poor power factor
spark excessively
all of the above
259. An outstanding feature of a universal motor is
its
A.
B.
C.
D.
best performance at 50 Hz supply
slow speed at all loads
excellent performance on d.c. supply
highest output kW/kg ratio
260. The direction of rotation of a hysteresis motor is
determined by the
A. retentivity of the rotor material
B. amount of hysteresis loss
C. permeability of rotor material
D. position of shaded pole with respect to the
main pole
261. Speed of the universal motor is
A.
B.
C.
D.
dependent on frequency of supply
proportional to frequency of supply
independent of frequency of supply
none of the above
262. In the shaded pole squirrel cage-induction
motor, the flux in the unshaded part always
A. leads the flux in the unshaded pole
segment
B. is in phase with the flux in the unshaded
pole segment
C. lags the flux in the unshaded pole segment
D. none of the above
263. Which of the following motor is an interesting
example of beneficially utilizing a phenomenon
that is often considered undesirable?
A. hysteresis motor
B. reluctance motor
A. a single-phase supply is to be connected
across a single-phase winding
B. a two-phase supply should be connected
across a two-phase winding
C. a dc supply is to be connected across a
single-phase winding
D. the polarities of a dc supply connected
across a single-phase winding should be
continuously reversed through a suitable
switching-device
266. When a single-phase supply is connected
across a single-phase winding, the nature of
magnetic field produced is
A. pulsating in nature
B. rotating in nature
C. constant in magnitude but rotating at
synchronous speed
D. constant in magnitude and direction
267. In a resistance split-phase type single-phase
induction motor, a time-phase difference
between the currents in the main and auxiliary
winding is achieved by
A. placing the two-windings at an angle of 90
degrees electrical in the stator slots
B. applying two-phase supply across the two
windings
C. having different ratio of resistance to
inductive reactance for the two windings
supplied from a single-phase supply
system
D. connecting the two windings in series
across a single phase supply
268. In a split-phase capacitor-start induction motor,
a time-phase difference between the currents in
the main and auxiliary winding is achieved by
A. placing the two-windings at an angle of 90
degrees electrical in the stator slots
B. applying two-phase supply across the two
windings
C. introducing capacitive reactance in the
auxiliary winding circuit
D. connecting the two windings in series
across a single phase supply
269. The direction of rotation of an ordinary shaded
pole single-phase induction motor
A. can be reversed by reversing the supply
terminal connections to the stator winding
B. cannot be reversed
C. can be reversed by open-circuiting the
shading rings
D. can be reversed by short-circuiting the
shading rings
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
270. Direction of rotation of split-phase type singlephase induction motor can be reversed by
A. reversing the supply terminals connections
B. reversing the connection of only the
auxiliary winding across the supply
C. reversing the connections of either the
main winding or the auxiliary winding
terminals
D. reversing the connections of only the main
winding across the supply terminals
271. In a single-phase repulsion motor, torque is
developed on the rotor when the brush axis is
fixed
A. at 90 degrees electrical with the stator field
axis
B. in alignment with the stator field axis
C. at an acute angle with the stator field axis
D. at 90 degrees mechanical with the stator
field axis
272. If the centrifugal switch of a resistance splitphase induction motor fails to close when the
motor is de-energized, then
A. no starting torque will be developed when
supply is connected again across the motor
terminals
B. a dangerously high current will flow through
the main winding when supply is connected
again across the motor terminals
C. starting torque developed may not be
sufficient to enable the motor to restart
D. the motor will develop high starting torque
when an attempt is made to restart
273. A dc series motor when connected across an
ac supply will
A. develop torque in the same direction
B. not develop any torque
C. draw dangerously high current
D. develop a pulsating torque
274. To enable a dc series motor work satisfactorily
with an ac supply, the following modifications
should be done
A. The yoke and the poles should be
completely laminated
B. Only the poles should be made of
laminated steel
C. The air-gap between the stator and the
rotor be reduced
D. Compensating poles should be introduced
SYNCHRONOUS MOTORS
275. EE Board Exam April 1993
A single phase synchronous motor gives an
output of 9.46 kW at 0.9 lagging p.f. at 600volts. If the stray power loss is 600 watts and
the field loss is 900 watts, while the effective
armature resistance is 0.6-ohm, calculate the
efficiency of the synchronous motor.
A. 82.35%
C. 85.25%
B. 81.24%
D. 84.64%
276. EE Board Exam April 1991
A three-phase synchronous motor is measured
by two wattmeters A and B. Wattmeter A reads
28.6 kW and wattmeter B reads 46.5 kW. The
input power of the motor is under excited and
assumed constant. What are the readings of
wattmeters A and B if the power factor is 85%
and the motor is over-excited?
A. 48.6 kW, 26.5 kW
B. 42.5 kW, 32.6 kW
C. 52.6 kW, 22.5 kW
D. 51 kW, 24.1 kW
277. EE Board Exam October 1991
A 3,600 volts three-phase star connected turbo
synchronous generator of synchronous
reactance of 0.5 ohm per phase and negligible
resistance is supplying 30,000 kVA at 0.8 pf
lagging to a large power system. If the steam
supply is cut-off, calculate the amount of
current that the generator will then carry
assuming negligible losses.
A. 3901 A
C. 3094 A
B. 3823 A
D. 3870 A
278. REE Board Exam October 1994
A wye-connected turbo alternator having a
synchronous reactance of 0.5 ohm and
negligible resistance is connected to a large
power system having a busbar voltage of 13.8
kV supplying a load of 15,000 kVA at 0.80
lagging power factor. If the steam supply is cutoff, the armature current will the machine carry
assuming negligible losses?
A. 256.55 A
C. 384.26 A
B. 525.62 A
D. 627.55 A
279. REE Board Exam October 1994
A 1,000 kVA, 6,600 V wye-connected threephase alternator having a reactance of 8.8
ohms and a negligible resistance is supplying
power to a constant frequency bus bar. The
open-circuit emf at this instance is 4,311 V per
phase. If steam supply is suddenly cut-off, the
armature current in amperes is nearest to
A. 57
C. 59
B. 60
D. 56
280. EE Board Exam October 1985
An inductive load consumes 10 kW at 0.75 pf
lagging. A synchronous motor with a pf of 0.9
leading is connected in parallel with the
inductive load. What is the minimum required
kW size of the synchronous motor so that the
combined load will have a pf of 0.8 lagging?
C. 1.075 kW
A. 1.068 kW
B. 1.203 kW
D. 1.109 kW
281. EE Board Exam April 1980, April 1992
An industrial plant draws 500 kW at 0.6 power
factor from a 3-phase system. In order to raise
the power factor to 0.866 lagging and to supply
needed additional power, a synchronous motor
is added. This motor draws 300 kW, bringing
the new total plant load to 800 kW. Neglecting
the losses of the synchronous motor, calculate
its exact required kVA rating.
A. 363.24 kVA
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
B. 345.23 kVA
C. 393.34 kVA
D. 307.35 kVA
289. An electric motor in which both the rotor and
282. EE Board Exam April 1988
An existing industrial plant has an average load
of 900 kW at 0.6 pg lagging. To raise the
overall power factor to 0.92, a synchronous
motor driving a DC generator is to be installed.
If the input of the synchronous motor will be
250 kW, calculate its kVA input rating.
C. 723 kVA
A. 753 kVA
B. 788 kVA
D. 715 kVA
283. EE Board Exam October 1994
Power factor improvement may be achieved by
the use of
A. synchronous motor
B. synchronous converter
C. long transmission line
D. induction motor
284. EE Board Exam October 1993
A synchronous motor
A. will have a low power factor when run
below rated speed
B. may have its speed varied by inserting a
rheostat in the DC field current
C. will slow down with an increase in load
within the limits of its pull out torque
D. will take minimum line current at any load
when operating at unity power factor
285. EE Board Exam October 1990
In starting a 500 HP, 2,300 volts, 3-phase
synchronous motor the field winding is initially
short circuited so as to
A. provide better flux distribution in the air gap
B. increase induced voltage in fild winding
C. produce much larger starting torque
D. lower voltage produced between layers of
the field
286. EE Board Exam April 1990
A synchronous motor running without load is
A. synchronous converter
B. synchronous condenser
C. capacitor motor
D. induction motor
287. In a synchronous motor, damper winding is
provided in order to
A. stabilized rotor motion
B. suppressed rotor oscillations
C. develop necessary starting torque
D. both B and C
288. In a synchronous motor, the magnitude of
stator back e.m.f. Eb depends on
A. speed of the motor
B. load on the motor
C. both the speed and rotor flux
D. d.c. excitation only
stator fields rotate with the same speed is
called a/an ____ motor.
A. d.c.
B. Schrage
C. synchronous
D. universal
290. While running, a synchronous motor is
compelled to run at synchronous speed
because of
A. damping winding in its pole faces
B. magnetic locking between stator and rotor
poles
C. included e.m.f. in rotor field winding by
stator flux
D. compulsion due to Lenz’s law
291. The direction of rotation of a synchronous
motor can be reserved by reversing
A. current to the field winding
B. supply phase sequence
C. polarity of rotor poles
D. none of the above
292. When running under no-load condition and with
normal excitation, armature current Ia drawn by
a synchronous motor
A. leads the back e.m.f. Eb by a small angle
B. is large
C. lags the applied voltage V by a small angle
D. lags the resultant voltage ER by 90˚
293. The angle between the synchronously rotating
stator flux and rotor poles of a synchronous
motor is called ____ angle.
A. synchronizing
B. torque
C. power factor
D. slip
294. If load angle of a 4 pole synchronous motor is
8˚ (elect.), its value in mechanical degree is
____.
A. 4
C. 0.5
B. 2
D. 0.25
295. The maximum value of torque angle in a
synchronous motor is ____ degrees electrical.
A. 45
B. 90
C. between 45 and 90
D. below 60
296. A synchronous motor running with normal
excitation adjusts to load essentially by
increases in its
A. power factor
B. torque angle
C. back e.m.f.
D. armature current
297. When load on a synchronous motor running
with normal excitation is increased, armature
current drawn by it increases because
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
A.
B.
C.
D.
back e.m.f. Eb becomes less than applied
voltage V
power factor is decreased
net resultant voltage ER in armature is
increased
motor speed is reduced
298. When load on a normally-excited synchronous
motor is increased, its power factor tends to
A. approach unity
B. become increasingly lagging
C. become increasingly leading
D. remain unchanged
299. The effect of increasing load on a synchronous
motor running with normal excitation is to
A. increase both its Ia and p.f.
B. decrease Ia but increase p.f.
C. increase Ia but decrease p.f.
D. decrease both Ia and p.f.
300. Ignoring the effects of armature reaction if
excitation of a synchronous motor running with
constant load is increased, its torque angle
must necessarily
A. decrease
B. increase
C. remain constant
D. become twice the no-load value
301. If the field of a synchronous motor is underexcited, the power factor will be
A. lagging
B. leading
C. unity
D. more than unity
302. Ignoring the effects of armature reaction, if
excitation of a synchronous motor running with
constant load is decreased from its normal
value it leads to
A. increase in but decrease in Eb
B. increase in Eb but decrease in Ia
C. increase in both Ia and p.f. which is lagging
D. increase in both Ia and
303. A synchronous motor connected to infinite busbars at constant full-load, 100% excitation and
unity p.f. On changing the excitation only, the
armature current will have
A. leading p.f. with under-excitation
B. leading p.f. with over-excitation
C. lagging p.f. with over-excitation
D. no change of p.f.
304. The V-curves of a synchronous motor show
relationship between
A. excitation current and back emf
B. field current and p.f.
C. dc field current and ac armature current
D. armature current and supply voltage
305. When a load on a synchronous motor is
increased, its armature currents is increased
provided it is
A. normally excited
B.
C.
D.
over-excited
under-excited
all of the above
306. If main field current of a salient-pole
synchronous motor fed from an infinite bus and
running at no-load is reduced to zero, it would
A. come to a stop
B. continue running at synchronous speed
C. run at sub-synchronous speed
D. run at super-synchronous speed
307. In a synchronous machine when the rotor
speed becomes more than the synchronous
speed during hunting, the damping bars
develop
A. synchronous motor torque
B. d.c. motor torque
C. induction motor torque
D. induction generator torque
308. In a synchronous motor, the rotor Cu losses are
met by
A. motor input
B. armature input
C. supply lines
D. d.c. source
309. A synchronous machine is called a doublyexcited machine because
A. it can be overexcited
B. it has two sets of rotor poles
C. both its rotor and stator are excited
D. it needs twice the normal exciting current
310. Synchronous capacitor is
A.
B.
C.
D.
an ordinary static capacitor bank
an over-excited synchronous motor driving
mechanical load
an over-excited synchronous motor
running when mechanical load
none of the above
Unsolved problems
311. REE Board Exam September 2004
What is the percent slip of the synchronous
motor when running?
A. 3
C. 1
B. 2.5
D. 0
312. The speed regulation of as synchronous motor
is
A.
B.
C.
D.
unity
zero
infinity
always less than one
313. Synchronous motors are to be used in situation
where
A. the load is constant
B. the load is required to be driven at very
high speeds
C. the load is to be driven at constant speed
D. the starting torque requirement of the load
is very high
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
SYNCHRONOUS CONVERTERS
314. EE Board Exam April 1994
In a three phase synchronous converter, the
ratio of the AC voltage to DC voltage is
C. 0.50
A. 0.612
B. 1.0
D. 0.707
315. EE Board Exam April 1992
A 500 kW, 600-V DC, 12-phase synchronous
converter operates as a direct converter at a full
load efficiency of 92% and a power factor of
0.93. Calculate the AC voltage between slip
rings and the AC current drawn from a 12phase transformer fed supply.
A. 112 V, 229 A
B. 112 V, 215 A
C. 110 V, 229 A
D. 110 V, 215 A
316. EE Board Exam April 1992
A generator is rated 600 kVA, 240 V, 60 cycles,
3-phase, 6 poles and wye-connected. What will
be the speed of the driving pulley if the driven
and driving pulleys are 1 ft and 2 ft in diameter
respectively?
A. 2400 rpm
C. 600 rpm
B. 1200 rpm
D. 900 rpm
317. REE Board Exam October 1998
The pulley of an old gen-set has a diameter of
20 inches. The belt exerts a pull of 353 pounds
on the pulley. The gen-set runs at 900 rpm.
What is the approximate kW rating of the genset?
A. 75
C. 200
B. 250
D. 37.5
318. The speed of a motor-generator set consisting
of a 6-pole induction motor and a 4-pole dc
generator fed from a 3-phase.
A. 1000
C. 1500
D. 3000
B. 600
319. A rotary converter generally
A.
B.
C.
D.
combines the functions of an induction
motor and a d.c. generator
has a set of slip – rings at both ends
has one armature and two fields
is a synchronous motor and a d.c.
generator combined
322. One unique advantage of employing induction
regulator method for controlling the dc output
voltage of a rotary converter is that it
A. is extremely simple and relatively cheaper
B. responds instantaneously to changes in
load
C. can be used for inverters
D. gives voltage changes in exact jumps
323. The most commonly used connection for
joining the six secondaries of a transformer
used for 3-phase to 6-phase conversion is
A. diametrical
B. zig-zag
C. double star
D. double-delta
324. The function of a cycloconverter is to convert
A.
B.
C.
D.
ac power into dc power
direct current into alternating current
high ac frequency directly to low ac
frequency
a sine wave into a rectangular wave
325. Major disadvantage of using three sets of
SCRs for variable voltage speed control of a
SCIM is the
2
A. considerable I R loss
B. poor power factor
C. long delay of thyristor firing pulses
D. necessity of using a processor
326. In the current fed frequency converter
arrangement for controlling the speed of an
individual SCIM, the direction of rotation can be
reversed by
A. changing the output frequency of the
inverter
B. altering the phase sequence of pulses that
trigger the d.c link current
C. interchanging any two line leads
D. reversing the d.c link current
327. In the chopper uses speed control method for a
WRIM the motor speed inversely depends on
A. fixed resistor across the rectifier
B. chopper switching frequency
C. chopper ON time TON
D. both B and C
328. In the synchronous motor drive using current
320. The a.c. line current at slip-rings in a 6-phase,
6-ring, rotary converter having 100% efficiency
and unity p.f. is ____ times the d.c. current.
A. 0.943
C. 0.236
B. 0.472
D. 1.414
321. A 3-phase supply can be converted into a 6phase supply by joining the secondaries of the
3-phase transformer in
A. double delta
B. double star
C. diametrical
D. any of the above
fed dc link
A. converter-2 functions as a self commutated
inverter
B. converter-1 works as uncontrolled rectifier
C. converter-3 is a controlled rectifier
D. gate triggering of converter 2 is done at
motor frequency
329. In the three cycloconverter drive of a
synchronous motor
A. each cycloconverter produces a 3-phase
output
B. all cycloconverters act as voltage sources
C. a 3-phase controlled rectifier produces
field-exciting current
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
D.
air-gap flux is kept constant by controlling
stator currents only
SPECIAL MACHINES
330. A single – stack, 4 – phase, 6 – pole VR stepper
motor will have a step angle of
A. 15º
C. 45°
B. 30º
D. 90º
331. In a three-stack 12/8 pole VR motor, the rotor
pole pitch is
A. 15º
B. 30º
C.
D.
45°
60º
332. A three-stack VR stepper motor has a step
angle of 10º. What is the number of rotor teeth
in each stack?
A. 36º
C. 18°
B. 24º
D. 12°
333. If a hybrid stepper motor has a rotor pitch of 36º
and a step angle of 9º, the number of its
phases must be
A. 4
C. 3
B. 2
D. 6
334. What is the step angle of a permanent-magnet
stepper motor having 8 stator poles and 4 rotor
poles?
A. 60º
C. 30°
B. 45º
D. 15º
340. The rotor of a stepper motor has no
A.
B.
C.
D.
windings
commutator
brushes
all of the above
341. Wave excitation of a stepper motor results in
A.
B.
C.
D.
microstepping
half – stepping
increased step angle
reduced resolution
342. A stepper motor having a resolution of 300
steps/rev and running at 2400 rpm has a pulse
rate of ____ pps.
A. 4000
C. 6000
B. 8000
D. 10,000
343. The torque exerted by the rotor magnetic field
of a PM stepping motor with unexcited stator is
called ____ torque.
A. reluctance
B. detent
C. holding
D. either B or C
344. A variable reluctance stepper motor is
constructed of ____ material with salient poles.
A. paramagnetic
B. ferromagnetic
C. diamagnetic
D. non–magnetic
335. A stepping motor is a ____ device.
A.
B.
C.
D.
345. Though structurally similar to a control
mechanical
electrical
analogue
incremental
336. Operation of stepping motors at high speed is
referred to as
A. fast forward
B. slewing
C.
D.
inching
jogging
337. Which of the following phase switching
sequence represents half-step operation of a
VR stepper motor?
A. A, B, C, A ………
B. A, C, B, A ……….
C. AB, BC, CA, AB ………
D. A, AB, B, BC …….
338. The rotational speed of a given stepper motor
is determined solely by the
A. shaft load
B. step pulse frequency
C. polarity of stator current
D. magnitude of stator current
339. A stepper motor may be considered as a ____
converter.
A. dc to ac
B. ac to ac
C. dc to ac
D. digital-to-analogue
transmitter, a control receiver differs from it in
the following way
A. it has 3-phase stator winding
B. it has a rotor of dumbbell construction
C. it has a mechanical damper on its shaft
D. it has a single-phase rotor excitation
346. The control ____ synchro has three-phase
winding both on its stator and rotor
C. receiver
A. differential
B. transformer
D. transmitter
347. Regarding voltages induced in the three stator
windings of a synchro, which statement is
false?
A. they depend on rotor position
B. they are in phase
C. they differ in magnitude
D. they are polyphase voltages
348. The low-torque synchros cannot be used for
A.
B.
C.
D.
torque transmission
error detection
instrument servos
robot arm positioning
349. Which of the following synchros are used for
error detection in a servo control system?
A. control transmitter
B. control transformer
C. control receiver
D. both A and B
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
350. For torque transmission over a long distance
with the help of electrical wires, which of the
following two switches are used?
A. CX and CT
B. CX and CR
C. CX and CD
D. CT and CD
359. Squirrel-cage induction motor is finding
increasing application in high-power servo
systems because new methods have been
found to
A. increased its rotor resistance
B. control its torque
C. decrease its inertia
D. decouple its torque and flux
351. The arrangement required for producing a
rotation equal to the sum or difference of the
rotation of two shafts consist of the following
coupled synchros.
A. control transmitter
B. control receiver
C. control differential transmitter
D. all of the above
352. Which of the following motor would suit
applications where constant speed is
absolutely essential to ensure a consistent
product?
A. brushes dc motor
B. disk motor
C. permanent-magnet synchronous motor
D. stepper motor
360. A six-pole, three-phase squirrel-cage induction
motor is connected to a 60-cps supply. At fullload, the rotor’s induced emf makes 72
complete cycles in 1 minute. Find the rotor
speed.
C. 1054 rpm
A. 1176 rpm
B. 1200 rpm
D. 1124 rpm
361. A 50 HP, 440 V, 3-phase, 60 Hz, 6-pole squirrel
cage induction motor is operating at full-load
and 0.8 pf. The full-load efficiency is 85% and
the percentage slip is 5%. Determine the fullload torque.
A. 214.55 N-m
B. 206.72 N-m
C. 312.47 N-m
D. 323.24 N-m
353. A switched reluctance motor differs from a VR
stepper motor in the sense that it
A. has rotor poles of ferromagnetic material
B. rotates continuously
C. is designed for open – loop operation only
D. has lower efficiency
354. The electrical displacement between the two
stator windings of a resolver is
A. 120º
C.
B. 90º
D.
60°
45º
355. Which of the following motor runs from a low dc
supply and has permanently magnetized
salient poles on its rotor?
A. permanent magnet dc motor
B. disk dc motor
C. permanent magnet synchronous motor
D. brushless dc motor
356. A dc servomotor is similar to a regular dc motor
except that its design is modified to cope with
A. electronic switching
B. slow speeds
C. static conditions
D. both B and C
357. One of the basic requirements of a servomotor
is that it must produce high torque at all
A. loads
C. speeds
B. frequencies
D. voltages
358. The most common two-phase ac servomotor
differs from the standard ac induction motor
because it has
A. higher rotor resistance
B. higher power rating
C. motor stator windings
D. greater inertia
362. A synchronous motor is drawing 60 kW is
connected in parallel with a load drawing 250
kW at a lagging power factor of 0.8. If the
combined load has a power factor of 0.9, at
what power factor is the synchronous motor
operating?
A. 0.862 leading
B. 0.849 leading
C. 0.868 leading
D. 0.874 leading
363. A three-phase Y-connected synchronous motor
with a line-to-line voltage of 440 V and a
synchronous speed of 900 rpm operates with a
power of 9 kW and a lagging power factor of
0.8. The synchronous reactance per phase is
10 ohms. Determine the torque angle in
electrical degrees.
A. 36.33°
C. 35.51°
B. 33.51°
D. 38.46°
364. A 10-hp, 230-V, three-phase Y-connected
synchronous motor has a reactance of 3 ohms
per phase and a negligible resistance. To what
voltage must the motor is excited in order to
deliver full load at unity power factor and 90%
efficiency?
A. 262 V
C. 248 V
D. 242 V
B. 254 V
365. A three-phase, star connected synchronous
motor takes 50 kW at 660 V, the power factor
being 0.8 lagging. This machine has a
synchronous reactance of 1 ohm per phase
with a negligible resistance. If the emf is
increased by 30%, the power taken remaining
the same, find the new leading current.
A. 94.1 A
C. 90.3 A
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
B. 85.2 A
D.
88.6 A
366. A 6.6 kV, Y-connected synchronous motor has
a synchronous reactance per phase of 10 ohms
and a negligible resistance. For a certain load,
the motor draws 990 kW at normal voltage. At
this load, the induced emf per phase is 5160 V.
Determine operating pf.
C. 0.462
A. 0.478
B. 0.502
D. 0.518
B. 85.30%
D.
83.20%
373. A 15-hp, 230 V, single phase synchronous
motor is taking a current of 50 A at a power
factor of 0.85 leading. Effective resistance is
0.2 ohm. If this motor drives a mechanical load
of 12 hp, determine its rotational losses.
C. 376 W
A. 323 W
B. 340 W
D. 314 W
374. A single-phase rotary converter has an output
367. A 75-hp, 600-volt, 1000-rpm, three-phase Yconnected synchronous motor has an armature
resistance of 0.05 ohm per phase and a
leakage reactance of 0.45 ohm per phase. The
efficiency at rated load, 80% pf leading is 92%.
Determine mechanical power developed within
the armature.
A. 64 kW
C. 60 kW
B. 62 kW
D. 67 kW
368. A 230 V, 60 Hz, 3-phase, Y-connected
synchronous motor draws a current of 20 A and
delivers 8 bhp. Armature resistance per phase
is 0.5 Ω. If the iron and friction losses amount
to 300 W, determine the operating power factor
of the motor.
A. 0.809
C. 0.866
B. 0.807
D. 0.862
voltage of 110 volts. Determine the line current
in the AC side when the machine delivers a DC
output of 50 A. Assume the machine is
operating with a pf of 0.85 and efficiency of
95%.
A. 70.71 A
C. 87.57 A
B. 90.34 A
D. 82.23 A
375. Three single-phase transformers connected
delta-delta fed a three-phase rotary converter
at 2,300 V. This converter supplies power to a
DC load that draws 100 kW at 250 V. If the
rotary converter operates at an efficiency of
95% at unity pf, calculate the current in the
secondary windings of the transformer bank.
A. 397 A
C. 229 A
B. 355 A
D. 249 A
376. A 4-phase star connected rotary converter
369. A 2200 V, 200 hp, 3-phase mesh connected
synchronous motor is working on full load at an
efficiency of 0.88 and 0.8 pf leading. The
armature reactance per phase is 5 ohms.
Determine the induced emf per phase. Neglect
resistance.
A. 2377 V
C. 2380 V
B. 2345 V
D. 2307 V
370. A 500-hp, 2200 V, 3-phase, star-connected
synchronous motor has a synchronous
impedance of 0.3 + j3 Ω per phase. Determine
the induced emf per phase if the motor works
on full load with an efficiency of 94% and a
power factor of 0.8 leading.
C. 1402 V
A. 1360 V
B. 1354 V
D. 1522 V
371. An alternator rated 530-kVA, is operating at
0.60 pf lagging. A synchronous condenser is in
parallel to improve the pf to 90% lagging.
Determine the operating power factor of the
synchronous condenser. Assume the alternator
is not supposed to be overloaded.
A. 0.546 leading
B. 0.447 leading
C. 0.643 leading
D. 0.593 leading
372. A 230-V, 60-Hz, single-phase synchronous
motor is taking a current of 20 A at 0.866
lagging p.f. Effective armature resistance is 0.3
ohm. Iron and friction losses amount to 450 W.
Determine the efficiency of the motor at this
load. Neglect losses in the excitation.
A. 86.15%
C. 88.52%
operating at 0.90 efficiency and 0.85 power
factor is connected across a 220 V, 60 Hz
mains and draws 50 A. Determine the DC load
current.
A. 208.46 A
C. 216.37 A
B. 220.54 A
D. 212.25 A
377. The dc output of a six-phase star-connected
converter is 500 kW at 400 V. If the pf and
efficiency of the machine is 0.866 and 0.92
respectively, determine the ac current drawn
from the supply.
A. 762 A
C. 732 A
B. 740 A
D. 729 A
378. A 600 kW, 6-phase, Y-connected, 18-pole,
synchronous converter has simplex lap wound
armature with 1000 conductors. The flux per
pole is 60 mWb. The machine runs at 600 rpm
at rated load. Determine the ac current in the
slip rings. Assume the operating power factor
and efficiency of the machine equal to 1.0 and
0.9 respectively.
C. 462.25 A
A. 496.21 A
B. 488.42 A
D. 472.07 A
379. A 4-pole 230-V, 60 Hz, three-phase induction
motor directly drives a 6-pole alternator.
Determine the output frequency. Assume a slip
of 3% in the motor.
A. 90.0 Hz
C. 86.6 Hz
B. 88.4 Hz
D. 87.3 Hz
380. A three-phase rotary converter delivers 150 A
at 500 V dc. Determine the current on the AC
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
side if the operating power factor of the
machine is 0.8 and the efficiency is 90%
A. 179 A
C. 189 A
B. 157 A
D. 196 A
and a reactance of 25 ohms per phase.
Determine the induced emf when fully loaded at
0.8 power factor lagging.
A. 5521 V
C. 5475 V
B. 5362 V
D. 5582 V
381. An open delta bank is serving a three-phase
rotary converter. The converter supplies 175 A
of current to 1.4 ohm dc resistive load. If the
machine draws an AC current of 100 A at 0.8 pf
lagging, determine minimum size of
transformer needed.
C. 25.9 kVA
A. 15.0 kVA
B. 24.7 kVA
D. 19.4 kVA
382. The percent slip of an induction motor is the
ratio
A. rotor copper loss / rotor power input
B. stator copper loss / stator power input
C. stator copper loss / rotor power output
D. rotor copper loss / stator copper loss
389. If Ns is the synchronous speed and s the slip,
then actual running speed of an induction motor
will be
A. Ns
C. (1 – s)Ns
B. sNs
D. (Ns – 1)s
390. When the synchronous motor has a leading
power factor, the generated emf is ____ than
the applied voltage.
A. equal
B. greater
C. lesser
D. none of these
391. The word TEFC stands for
383. An 80 kW, 440 volts, 3-phase Y connected, 60
Hz, 4-pole synchronous motor has a
synchronous reactance of 3-ohm per phase.
Calculate the torque in Newton-meter if it is
operating at rated condition at 92% efficiency.
A. 714
C. 571
B. 135
D. 461
384. A 220 volts single phase induction motor draws
current of 10 amps at 0.75 pf. A capacitor of 50
F is connected in order to improve the power
factor. What is the new power factor?
A. 0. 866 leading
B. 0.866 lagging
C. 0.95 lagging
D. 0.95 leading
A.
B.
C.
D.
totally enclosed frequency controlled
torque, energy, frequency controlled
totally enclosed fused cooled
totally enclosed fan cooled
392. Synchronous motor are
A.
B.
C.
D.
self-starting
not self-starting
essentially self-starting
none of these
393. The motor in which stator and rotor magnetic
field rotate at the same speed is
A. induction motor
B. universal motor
C. reduction motor
D. synchronous motor
385. A test is performed on a 230 volts, delta
connected synchronous motor having 92%
efficiency and 85% power factor. With 6 volts
dc impressed across its terminals, the current
reading is 90 amperes. Determine the ohmic
resistance per phase.
A. 0.067 /phase
B. 0.44 /phase
C. 0.1 /phase
D. 0.15 /phase
386. A synchronous motor operates continuously on
the following duty cycle: 50 hp for 10 sec, 100
hp for 10 sec, 150 hp for 5 sec, 120 hp for 20
sec, idling for 14 sec. What would be the size of
motor to be used?
A. 90 hp
C. 150 hp
D. 120 hp
B. 100 hp
387. A polyphase motor may be protected against
reversal of rotation by using a
A. reverse speed relay
B. reverse power relay
C. reverse phase relay
D. reverse current relay
388. A 1000 kVA, 11 kV, 3-phase, Y-connected
394. An over-excited synchronous motor takes
A.
B.
C.
D.
lagging current
leading current
lagging and leading current
none of these
395. In a synchronous motor, which loss does not
vary with load?
A. copper losses
B. hysteresis losses
C. windage losses
D. none of the above
396. Squirrel cage induction motor differs from the
slip ring type in that it has no
A. slip rings
B. windings on the stator
C. rotor winding
D. rotating part
397. A 3- synchronous motor runs at full-load speed
of 1200 rpm. If the load is reduced to one-half
of rated, calculate its speed regulation.
A. 100%
C. 0%
B. 50%
D. 86.6%
synchronous motor has a resistance of 3 ohms
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
398. An industrial load is taking 500 kW at 0.6
lagging p.f. is desired to raise the p.f. to 0.866
lagging using a synchronous machine whose
power input is 300 kW. Calculate the kVA rating
of the motor required for such operation and
the power factor at whuch the motor will
operate.
A. 365 kVA, 0.826 leading
B. 365 kVA, 0.778 leading
C. 305 kVA, 0.826 leading
D. 380 kVA, 0.866 leading
399. A 3–phase, 440-volts, 50 Hz induction motor
has 4% slip. What is the frequency of the rotor
induced emf?
A. 200 Hz
C. 2 Hz
B. 50 Hz
D. 0.2 Hz
400. What is the ratio of maximum to full-load torque
in a motor having a slip of 5% at full-load and
25% at maximum torque?
A. 15
C. 3
B. 2.6
D. 5.2
401. A 3Φ 6-pole induction motor has a nameplate
speed of 1160 rpm, what is its full-load slip?
A. 2.58%
C. 3.59%
D. 1.4%
B. 3.3%
402. A 3Φ, induction motor is wound for 4 poles and
is supplied from a 50 Hz system. What is the
rotor frequency when rotor runs at 1410 rpm?
A. 3 Hz
C. 2.9 Hz
B. 2.5 Hz
D. 3.5 Hz
403.
A.
B.
C.
D.
404.
A.
B.
C.
D.
405.
A.
B.
C.
D.
Question Bank in AC GENERATORS
406. EE Board Exam October 1990
What is the speed of a 100 kW, 230-volt, threephase, four-pole, 60 Hz alternator?
A. 450 rpm
C. 1200 rpm
B. 900 rpm
D. 1800 rpm
407. REE Board Exam April 1997
A six-pole, 3-phase AC generator has 72 slots,
the coil span is 12. What is the pitch factor?
C. 0.985
A. 1.000
B. 0.939
D. 0.966
408. REE Board Exam October 1994
A 30 MVA, 15 kV three-phase alternator will
have a per phase nominal impedance of ____.
A.
B.
C.
D.
7.5 ohms
9 ohms
15 ohms
none of these
409. EE Board Exam April 1990
A 6-pole, 3-phase, 60 cycle alternator has 12
slots per pole and four conductors per slot. The
winding is 5/6 pitch. There are 2,500,000
Maxwells entering the armature from each
North Pole, and this flux is sinusoidally
distributed along the air gap. The armature coils
are all-connected in series. The winding is wyeconnected. Determine the open circuit emf of
the alternator.
A. 532.1 V
C. 512.4 V
B. 504.2 V
D. 572.4 V
410. EE Board Exam April 1995
A 1200 kVA, 6600 volt, 3-phase, Y-connected
alternator has an effective resistance of 0.40
ohm and a reactance of 6 ohms per phase. It
delivers full load current of 0.80 lagging power
factor at rated voltage. What will be the terminal
voltage for the same excitation and load current
if the power factor is 0.80 leading?
A. 4560 V
C. 7898 V
B. 9878 V
D. 4250 V
411. REE Board Exam March 1998
A generator is rated 100 MW, 13.8 kV and 90%
power factor. The effective resistance is 1.5
times the ohmic resistance. The ohmic
resistance is obtained by connecting two
terminals to a DC source. The current and
voltage are 87.6 A and 6 V respectively. What
is the effective resistance per phase?The
generator is wye-connected.
A. 0.0513 ohm
C. 0.342 ohm
B. 0.0685 ohm
D. 0.0617
ohm
412. REE Board Exam October 1997
To get the armature resistance of a 100 MW,
13.89 kV and 90% power factor generator, two
terminals are connected to a DC source. The
measured current and voltage are 87.6
amperes and 6 volts respectively. What is the
DC resistance per phase?
A. 0.0223 ohm
C. 0.0685
ohm
B. 0.0342 ohm
D. 0.0617
ohm
413. EE Board Exam October 1991
Determine the efficiency of a 1500 kVA, 2300
V, 3-phase, Y-connected alternator, which
operates at rated output with a power factor of
80%. The DC armature resistance at 70°C
between terminals is 0.08 ohm. The field takes
70 A at 120 V from the exciter equipment.
Friction and windage losses are 15 kW, iron
loss is 35 kW and stray load losses are 1.5 kW.
Assume the effective armature winding
resistance is 1.5 times the DC value.
A. 94.56%
C. 93.35%
B. 90.31%
D. 92.62%
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
414. EE Board Exam April 1994
A three-phase, 11-kV wye-connected
synchronous alternator has a synchronous
reactance of 8 ohms per phase but negligible
resistance. If the excitation is such that the
open circuit voltage is 14 kV, determine the
power factor at the maximum output.
C. 0.793
A. 0.786
B. 0.772
D. 0.708
420. EE Board Exam October 1981
Two alternators are operating in parallel
supplying a common load of 425 kW at 0.85
power factor lagging. Alternator A contributes
600 kVAR at 0.92 power factor lagging. Solve
for the power factor of alternator B.
A. 0.813 lagging
B. 0.834 lagging
C. 0.804 lagging
D. 0.820 lagging
415. EE Board Exam April 1994
A three-phase AC generator is supplying power
to a load of 3200 kW at 230 volts and a power
factor of 60%. Assume that the loss of the line,
the generator armature and the load is equal to
the 10% of the load, what would be the savings
in watts if the power factor were raised to 80%?
A. 100,000
C. 80,000
D. 230,000
B. 140,000
416. EE Board Exam April 1992
A three-phase turbo alternator has a reactance
of 15 ohms and negligible resistance, the
machine draws an armature current of 250
amperes at 0.8 pf lagging when running on
12,000 volts infinite bus-bars. If the steam
admission is constant but the emf is raised by
20%, calculate the new operating pf.
A. 0.547
C. 0.509
B. 0.586
D. 0.575
417. EE Board Exam April 1980
A standby Diesel generator set will have the
following loads: inductive load drawing 50 kVA
at 0.8 power factor; Lighting load drawing 20
kVA at 1.0 power factor. At what power factor
will the generator operate?
A. 0.855 lagging
B. 0.872 lagging
C. 0.821 lagging
D. 0.894 lagging
418. EE Board Exam April 1992
A 250 V, 30 Hz generator supplies power to a
parallel circuit consisting of a 20 hp motor
whose efficiency is 90% at 0.80 pf lagging and
a second load that draws an apparent power of
7 kVA at unity pf. Determine the system
reactive power.
A. 23.582 kVAR
C. 10.341
kVAR
D. 20.384
B. 12.435 kVAR
kVAR
419. EE Board Exam October 1980
Two alternators A and B are operating in
parallel supplying a load drawing 1000 kVA at
0.80 power factor lagging. If alternator A
contributes 500 kVA at 0.60 power factor
lagging, determine the power factor of
alternator B.
A. 0.928 lagging
B. 0.852 lagging
C. 0.901 lagging
D. 0.977 lagging
421. EE Board Exam April 1988
SipalayMines, has two 3-phase, 60 H AC
generators operating in parallel. The first unit
has a capacity of 1000 kVA and the second unit
has a capacity of 1500 kVA. The first is driven
by a prime mover so adjusted that the
frequency falls from 61 Hz at no-load to 59.6 Hz
at full-load. The second has a different speedload characteristics, the frequency falls from
61.4 Hz at no-load to 59.2 Hz at full-load. When
these alternators are jointly delivering 2000 kW,
what is the load of each generator?
A. 884 kW, 1116 kW
B. 867 kW, 1133 kW
C. 915 kW, 1085 kW
D. 804 kW, 1196 kW
422. REE Board Exam March 1998
Two alternators are driven by shunt motors.
The shunt motors have speed-load droop
characteristics of 3% and 4% respectively. The
alternators are in parallel and each carrying 50
kW. There is no automatic speed-load control.
An additional 50 kW is switched on. What are
the resulting loads of the alternators assuming
that the speed-load control of each is not
adjusted?
A. 78.57 kW, 71.43 kW
B. 82.51 kW, 67.49 kW
C. 75 kW, 75 kW
D. 80.31 kW, 69.69 kW
423. EE Board Exam April 1989
There are two alternators, 100 kW, 3-phase in
parallel are driven by shunt motors whose
speed-load droop characteristics are as follows:
Alternator no. 1: no-load speed 600 rpm and
the full-load speed 530 rpm; while alternator no.
2: no-load speed 590 rpm and the full-load 550
rpm. For what load will the alternators divide
the load equally?
A. 62.45 kW
C. 67.54 kW
B. 68.78 kW
D. 64.67 kW
424. EE Board Exam April 1989
There are two alternators, 100 kW, 3-phase in
parallel are driven by shunt motors whose
speed-load droop characteristics are as follows:
Alternator no. 1: no-load speed 600 rpm and
the full-load speed 530 rpm; while alternator no.
2: no-load speed 590 rpm and the full-load 550
rpm. What is the greatest load that can be
delivered without overloading either alternator?
A. 171.43 kW
C. 177.54 kW
B. 168.78 kW
D. 164.67 kW
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
431. The frequency of voltage generated by an
425. ECE Board Exam April 1998
Find the frequency in kilocyles per second in
the armature of a 10 pole, 1,200 rpm generator.
A. 1000.0
C. 10.00
B. 100.0
D. 0.100
426. A certain 3-phase, star-connected, 1,000 kVA,
11,000 volt alternator has rated current of 52.5
amperes. The dc resistance of the winding per
phase is 0.3 ohm. The test results are given
below:
Field current
Line voltage
OC Test
12.5 A
422 volts
SC Test
12.5 A
52.5 A
Determine the full-load voltage regulation at
unity power factor
A. 0.44%
C. 0.64%
B.
0.54%
D.
0.74%
427. A 10 MVA, 10 kV, 3-phase, 50 Hz, 1,500 rpm
alternator is parallel with each other much
greater capacity. The moment of inertia of the
5
2
rotor is 2 x 10 kg-m and the synchronous
reactance of the machine is 40%. Calculate the
natural time of oscillation.
A. 8.3 ms
C. 10.3 ms
alternator having 4-poles and rotating at 1800
r.p.m. is ____ Hertz.
A. 60
C. 120
B. 7200
D. 450
432. A 50-Hz alternator will run at the greatest
possible speed if it is wound for ____ poles.
A. 8
C. 4
B. 6
D. 2
433. The main disadvantage of using short-pitch in
alternators is that it
A. reduces harmonics in the generated
voltage
B. reduces the total voltage around the
armature coils
C. produces asymmetry in the three phase
windings
D. increases Cu of end connections
434. Three-phase alternators are invariably Yconnected because
A. magnetic losses are minimized
B. less turns of wire are required
C. smaller conductors can be used
D. higher terminal voltage is obtained
435. The winding of a 4-pole alternator having 36
B.
9.3 ms
D.
11.3 ms
428. A 6.6 kV, Y-connected, 3-phase alternator has
a synchronous reactance of 6 ohms per phase
and a negligible resistance. At a certain field
current the armature is known to induce 5.8 kV
per phase. At this excitation, calculate the
maximum power that can be produced.
A. 12 MW
C. 11 MW
slots and a coil span of 1 to 8 is short-pitched
by ___ degrees.
A. 140
C. 20
B. 80
D. 40
436. If an alternator winding has a fractional pitch of
5/6, the coil span is ____ degrees.
A. 300
C. 30
D. 60
B. 150
437. The harmonic which would be totally eliminated
B.
10 MW
D.
9.8 MW
429. A 6.6 kV, Y-connected, 3-phase alternator has
from the alternator e.m.f. using a fractional
pitch of 4/5 is
rd
th
A. 3
C. 5
th
th
B. 7
D. 9
a synchronous reactance of 6 ohms per phase
and a negligible resistance. At a certain field
current the armature is known to induce 5.8 kV
per phase. At this excitation, calculate the
maximum current.
C. 4.83 kA
A. 2.83 kA
438. For eliminating 7th harmonic from the e.m.f.
B.
439. If, in an alternator, chording angle for
3.83 kA
D.
5.83 kA
430. A 6.6 kV, Y-connected, 3-phase alternator has
a synchronous reactance of 6 ohms per phase
and a negligible resistance. At a certain field
current the armature is known to induce 5.8 kV
per phase. At this excitation, calculate the
power factor at maximum power.
A. 0.853
C. 0.873
B.
0.863
D.
0.843
wave of an alternator, the fractional-pitch must
be ____.
A. 2/3
C. 7/8
B. 5/6
D. 6/7
fundamental flux wave is α, its value for 5
harmonic is
A. 5α
C. 25α
B. α/5
D. α/25
th
440. Regarding distribution factor of an armature
winding of an alternator which is statement is
false?
A. it decreases the distribution of coils
(slot/pole) increases
B. higher its value, higher the induced e.m.f
per phase
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
C.
D.
it is not affected by the type of winding
either lap or wave
its not affected the number of turns per coil
2400 V and rated terminal voltage of 3000 V is
____.
A. 20
C. 150
B. -20
D. -26.7
441. When speed of alternator is changed from 3600
r.p.m. to 1800 r.p.m. the generated
e.m.f./phase will become
A. one-half
C. four times
B. twice
D. one-fourth
442. The magnitude of the three voltages drops in
an alternator due to armature resistance,
leakage reactance and armature reaction is
solely determined by
A. load current, Ia
B. p.f. of the load
C. whether it is a lagging or leading p.f. load
D. field construction of the alternator
443. Armature reaction in an alternator primarily
affects
A. rotor speed
B. terminal voltage
C. frequency of armature current
D. generated voltage per phase
444. Under no-load condition, power drawn by the
prime mover of an alternator goes to
A. produce induced e.m.f in armature winding
B. meet no load loss
C. produce power in the armature
D. meet Cu losses both in armature and rotor
windings
445. As load p.f of an alternator becomes more
leading, the value of generated voltage
required to give rated terminal voltage
A. increases
B. remains unchanged
C. decreases
D. varies with rotor speed
446. With a load p.f. of unity, the effect of armature
reaction on the main-field flux of an alternator is
A. distortional
B. magnetizing
C. demagnetizing
D. nominal
447. At lagging loads, armature reaction in an
alternator is
A. cross-magnetizing
B. demagnetizing
C. non-effective
D. magnetizing
448. At leading p.f., the armature flux in an alternator
____ the rotor flux.
A. opposes
B. aids
C. distorts
D. does not affect
450. If, in a 3-Ф alternator, a field current of 50 A
produces a full-load armature current of 200 A
on short-circuit and 1730 V on open circuit,
then its synchronous impedance is ____ ohm.
A. 8.66
C. 5
B. 4
D. 34.6
451. The power factor of an alternator is determined
by its
A. speed
B. load
C. excitation
D. prime mover
452. For proper parallel operation a.c. polyphase
alternators must have the same
A. speed
C.
B. voltage rating
D.
kVA rating
excitation
453. Of the following conditions, the one which does
NOT have to be met by the alternators working
in parallel is
A. terminal voltage of each machine must be
the same
B. the machine must have the same phase
rotation
C. the machine must operate at the same
frequency
D. the machine must have equal rating
454. After wiring up two 3-Ф alternators, you
checked their frequency and voltage and found
them to be equal. Before connecting them in
parallel, you would
A. check turbine phase
B. check phase rotation
C. lubricate everything
D. check steam pressure
455. Zero power factor method of an alternator is
used to find its
A. efficiency
B. voltage regulation
C. armature resistance
D. synchronous impedance
456. Some engineers prefer ‘lamps bright’
synchronization to ‘lamps dark’ synchronization
because
A. brightness of lamps can be judged easily
B. it gives sharper and more accurate
synchronization
C. flicker is more pronounced
D. it can be performed quickly
457. It is never advisable to connect a stationary
449. The voltage regulation of an alternator having
0.75 leading p.f. load, no-load induced e.m.f of
alternatorto live bus-bars because it
A. is likely to run as synchronous motor
B. will get short-circuited
C. will decrease bus-bar voltage through
momentarily
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
D. will disturb generated e.m.fs. of other
alternators connected in parallel
B. ac
C. both dc and ac
D. none of these
458. Two identical alternators are running in parallel
and carry equal loads. If excitation of one
alternator is increased without changing its
steam supply , then
A. it will keepsupplying almost the same load
B. kVAR supplied by it would decrease
C. its p.f. will increase
D. kVA supplied by it would decrease
467. The ac armature winding of an alternator
operates at ____ the field winding.
A. the same as
B. much lesser voltage than
C. much higher voltage than
D. none of the above
468. The salient-pole construction for field structure
459. Keeping its excitation constant, if steam supply
of an alternator running in parallel with another
identical alternator is increased, then
A. it would over-run the other alternator
B. its rotor will fall back in phase with respect
to the other machine
C. it will supply greater portion of the load
D. its power factor would be decreased
460. The load sharing between two steam-driven
alternators operating in parallel may be
adjusted by varying the
A. field strengths of the alternators
B. power factors of the alternators
C. steam supply to their prime movers
D. speed of the alternators
461. Squirrel-cage bars placed in the rotor pole
faces of an alternator help reduce hunting
A. above synchronous speed only
B. below synchronous speed only
C. above and below synchronous speed both
D. none of the above
462. For a machine on infinite bus active power can
be varied by
A. changing field excitation
B. changing of prime mover speed
C. both A and B above
D. none of the above
463. Majority of alternators in the use have
A.
B.
C.
D.
revolving ac armature winding
stationary field type construction
revolving field type construction
none of the above
464. The stator of an alternator is identical to that of
a
A.
B.
C.
D.
dc generator
3-phase induction motor
1-phase induction motor
Rosenberg generator
of an alternator is generally used for ____
machine.
A. 2-pole
B. 4-pole
C. 8-pole
D. none of these
469. An alternator is sometimes called ____
generator.
A. synchronous
B. asynchronous
C. Rosenberg
D. none of these
470. A turbo-alternator uses
A. salient-pole field structure
B. non-salient-pole field structure
C. rotating ac armature winding
D. none of the above
471. The non-salient pole field construction is used
for ____ generator.
A. low-speed
B. medium-speed
C. high-speed
D. none of these
472. The ac armature winding of an alternator is
A.
B.
C.
D.
always star-connected
generally delta-connected
star-delta connected
none of the above
473. Low-speed alternators are driven by
A.
B.
C.
D.
hydraulic turbines
steam engines
steam turbines
none of these
474. High-speed alternators are driven by
A.
B.
C.
D.
diesel engines
hydraulic turbines
steam turbines
none of these
465. The stator of an alternator rarely uses ____
slots.
A. wide-open type
B. semi-closed type
C. closed type
D. none of these
475. The air-gap in an alternator is ____ in an
induction machine.
A. much shorter than
B. much longer than
C. about the same as
D. none of these
466. The field winding of an alternator is ____
excited.
A. dc
476. The stator of an alternator is wound for ____ on
the rotor.
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
A.
B.
C.
D.
more number of poles than
less number of poles than
the same number of poles as
none of the above
477. Turbo-alternators have rotors of
A.
B.
C.
D.
small diameter and long axial length
large diameter and long axial length
large diameter and small axial length
same diameter and axial length
478. The rotor of a turbo-alternator is made
cylindrical in order to reduce ____.
A. eddy current loss
B. hysteresis loss
C. windage losses
D. none of these
479. The number of cycles generated in a 6-pole
alternator in one revolution is
A. 3
B. 6
C. 50
D. none of these
480. The speed at which a 6-pole alternator should
be driven to generator 50 cycles per second is
A. 1,500 rpm
B. 1,000 rpm
C. 500 rpm
D. none of these
481. The frequency of emf generated in an 8-pole
alternator running at 900 rpm is
A. 50 Hz
B. 60 Hz
C. 120 Hz
D. none of these
482. In case of a 4-pole machine, 1 mechanical
degree corresponds to ____ electrical degree.
A. 2
B. 4
C. 8
D. none of these
483. For the same rating, the size of low-speed
alternator is ____ that of high-speed alternator.
A. about the same
B. more than
C. less than
D. none of these
484. The synchronous reactance of an alternator is
due to ____.
A. leakage flux
B. d.c. field excitation
C. armature reaction
D. none of the above
485. The synchronous reactance of an alternator is
generally ____ armature resistance.
A. 5 times smaller than
B. 5 times greater than
C. 10 to 100 times greater than
D. 10 times smaller than
486. The synchronous reactance of an alternator
____ as the iron is saturated.
A. decreases
B. increases
C. remains unchanged
D. none of the above
487. In an alternator, the effect of armature reaction
is minimum at power factor of ____.
A. 0.866 lagging
B. 0.866 leading
C.
D.
0.5 lagging
unity
488. If the lagging load p.f. of an alternator is
decreased, the demagnetizing effect of
armature reaction ____.
A. remains the same
B. is decreased
C. is increased
D. none of these
489. A 3-phase alternator generates an open-circuit
phase voltage of 4000 V when exciting current
is 50 A; the short-circuit current for the same
excitation being 800 A. The synchronous
reactance per phase is
A. 80 ohms
B. 5 ohms
C. 15 ohms
D. none of these
490. A 30 MVA, 15 kV alternator will have a per
phase nominal impedance of
A. 9 ohms
B. 15 ohms
C. 7.5 ohms
D. none of these
491. When load on an alternator is increased, the
terminal voltage increases if the load pf is
A. unity
C. leading
B. lagging
D. zero
492. The efficiency of the turbo-alternator ____ with
increase in speed.
A. decreases
B. increases
C. remains unchanged
D. none of the above
493. The full-load efficiency of the alternator ____
with the size of the machine.
A. increases
B. decreases
C. remains unchanged
D. none of the above
494. For the same power rating, an alternator is
____ that of a dc generator.
A. larger in size than
B. smaller in size than
C. of the same size as
D. none of the above
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
495. In the armature winding of an alternator, the
coil span falls short of full-pitch by 60°
(electrical). The pitch factor is
A. 0.866
B. 0.5
C. 0.25
D. none of these
496. A 3-phase alternator has 3 slots per pole. The
distribution factor of the winding is
A. 0.866
B. 0.5
C. 1
D. none of these
497. The disadvantage of a short-pitched coil is that
A.
B.
C.
D.
harmonics are introduced
waveform becomes non-sinusoidal
voltage round the coil is reduced
none of the above
498. The voltage regulation of an alternator for a pf
of 0.8 lagging is ____ at unity pf.
A. greater than
B. smaller than
C. the same as
D. none of these
499. The voltage regulation of an alternator is larger
than that of a dc generator because of
A. larger armature resistance
B. large leakage reactance
C. complex effects of armature reaction
D. none of the above
C. output kW will change
D. none of the above
505. The distribution of load between two alternators
operating in parallel can be changed by
changing
A. phase sequence
B. field excitation of alternators
C. driving torques of prime movers
D. none of the above
506. When a number of alternators are operating in
parallel, the power factor at which each
operates is determined by
A. power factor of the load
B. driving torque of the prime mover
C. its field excitation
D. none of the above
507. If the excitation of an alternator operating in
parallel with other alternators is increased
above the normal value of excitation, its
A.
B.
C.
D.
pf becomes more lagging
pf becomes more leading
output current decreases
output kW decreases
508. The voltage of the bus-bar to which several
alternators are paralleled may be raised by
simultaneously ____ of all alternators.
A. increasing field excitation
B. decreasing field excitation
C. increasing input to prime movers
D. decreasing input to prime movers
500. The per phase dc armature resistance of an
alternator is 0.5 ohm. The effective ac armature
resistance would be about
A. 0.5 ohm
C. 4 ohms
D. 0.25 ohm
B. 0.75 ohm
501. The dc armature resistance of a Y-connected
alternator measured across its two terminals is
0.5 ohm. The per phase resistance is
A. 0.5 ohm
C. 0.25 ohm
B. 1 ohm
D. 1.5 ohms
502. The dc armature resistance of a deltaconnected alternator measured across its two
terminals is 1 ohm. The per phase dc
resistance is
A. 3 ohms
B. 1.5 ohms
C. 0.33 ohm
D. none of these
509. The frequency of the system with which several
alternators are paralleled can be increased by
simultaneously ____ of all generators.
A. increasing field excitation
B. decreasing field excitation
C. increasing the speed of prime movers
D. decreasing the speed of prime movers
510. The alternators driven by ____ do not have a
tendency to hunt.
A. diesel engines
B. water turbines
C. steam turbines
D. none of these
511. Damper windings are used in alternators to
A.
B.
C.
D.
prevent hunting
reduce windage losses
achieve synchronism
none of the above
503. The under excited alternator supplies ____.
A.
B.
C.
D.
lagging VAR
leading VAR
no reactive power
none of the above
512. The rating of an alternator is expressed in
A. kW
B. HP
C.
D.
kVA
kVAR
Unsolved problems
504. If the excitation of an alternator operating in
parallel with other alternators is decreased, its
A. pf becomes more leading
B. pf becomes more lagging
513. REE Board Exam September 2004
A 3,600 V, 500 kVA, 60 Hz, 3-phase Yconnected generator on test yields the following
results: Mechanical and iron losses is 10 kW;
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
field current at full load 100% p.f. is 50 A; field
current at full-load 80% p.f. is 70 A; resistance
per phase of armature winding is 0.4 ohm. The
exciter voltage is constant at 120 volts and
voltage current is control is done by means of
rheostat. Determine the full-load armature
current at 80% lagging p.f.
A. 96.5 A
C. 64.2 A
B. 99.8 A
D. 80.2 A
514. A 4-pole, 1200 rpm alternator will generate emf
at
A. 50 Hz
B. 40 Hz
C.
D.
60 Hz
25 Hz
515. The span for a full-pitch coil wound for six poles
is
A.
B.
C.
D.
A. 750 rpm
B. 1500 rpm
C.
D.
3000 rpm
1440 rpm
523. The magnitude of the resultant magnetic field
produced by a three-phase current flowing
through a three-phase winding is equal to
A. the maximum value of flux due to any one
phase
B. 1.5 times the maximum value of flux due to
any one phase
C. half the value of maximum flux due to any
one phase
D. twice the maximum value of flux due to any
one phase
524. Voltage regulation of an alternator may be
negative when
A. the load power factor is lagging
B. the load power factor is leading
C. it is loaded beyond its full-load capacity
D. the machine is run at very low speeds
180 degrees mechanical
90 degrees mechanical
60 degrees mechanical
45 degrees mechanical
516. The pitch factor for a two-thirds short-pitch coil
is
A. 0.5
B. 0.66
525. Pitch factor for 5/6 short pitch coil is
C.
D.
0.866
0.707
517. The armature flux opposes the main field flux
when the load power factor is
A. unity
C.
leading
B. zero lagging
D.
zero
0.8 leading
518. The armature flux helps the main field flux
when the load power factor is
A. unity
C.
B. zero lagging
D.
leading
0.8 lagging
zero
519. A commercial alternator has
A. 0.966
B. 0.833
C.
D.
1.0
3.454
526. Distribution factor for a winding having 3
slots/pole/phase and a slot angle of 20 degrees
is
A. 0.96
C. 0.5
B. 1.0
D. 0.707
527. Armature reaction in an electrical machine is
the effect of
A. armature flux on the main flux
B. heat produced on the armature windings
C. armature current on the output
D. armature flux on the output
A. rotating armature and stationary field
528. An infinite bus-bar should maintain
B. stationary armature and rotating field
A. infinite frequency and infinite voltage
C. both armature and field rotating
D. both armature and field stationary
B. constant frequency and constant voltage
C. constant frequency but variable voltage
D. variable frequency and variable voltage
520. The stator core of a synchronous machine is
made up of laminated sheets to
A. increase the magnitude of flux produced
B. make the machine lighter in weight
C. minimize the eddy current loss
D. minimize the hysteresis loss
521. In alternators damper windings are used to
A.
B.
C.
D.
reduce eddy current loss
prevent hunting
make the rotor dynamically balanced
reduce armature reaction
522. A 4 –pole 50-Hz synchronous machine runs at
529. ______ refers to an AC generator.
A. Commutator
B. Motor (AC)
C.
D.
Rotor
Alternator
530. In huge alternators, the moving part is
A.
B.
C.
D.
brushes
armature
poles
none of the above
531. In case of alternator, the stator frame serves
A.
to protect the whole machine
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
B.
C.
D.
as a return path for the flux
to hold the armature stampings
to ventilate the armature
541. Steam turbo-alternators are much smaller in
532. Alternators mostly wotk on rotating field type
principle which is different from d.c. machines
where the field is stationary. Therefore
alternators
A. don’t obey Faraday’s law
B. work on Faraday’s law
C. do not obey Lenz’s law
D. obey Lenz’s law
533. High speed alternators have a rotor
construction
A. similar to d.c. machines
B. of non-salient type
C. of salient-type
D. none of the above
cylindrical rotor type alternators is
A. high d.c. voltage
B. high a.c. voltage
C. low d.c. voltage
D. low a.c. voltage
coil span factor is
A. 0.8
B. 0.866
C.
D.
0.786
0.966
variable frequency
definite currents
definite frequencies
definite power factor
536. The standard practice, nowadays in alternators
is to have
A. rotating field
B. rotating armature
C. either rotating field or rotating armature
D. none of the above
537. In power generating stations (thermal stations)
the usual number of poles employed in
alternators are
A. twenty four
B. forty eight
C. thirty two
D. none of the above
538. The diameter of high speed turbo alternators as
compared to hydroelectric ones are
A. smaller because speed is high
B. smaller because speed is less
C. larger because speed is high
D. none of the above
less weight of the entire armature
increased of generated emf per phase
544. When the power factor of load is unity, the
armature flux of an alternator will be
A. demagnetizing
B. square wave form
C. cross-magnetizing
D. none of the above
545. An alternator is capable of delivering power at a
particular frequency. The frequency can be
increased by
A. increasing armature speed
B. reversing the armature rotation
C. increasing the current supplied in the field
electromagnets
D. reversing the field polarity
546. If the input of the prime mover of an alternator
is kept constant but the excitation is increased
then
A. kVA will be leading
B. kVA will be lagging
C. kW will be changed
D. the power factor of the load will remain
constant
547. For two alternators operating in parallel, if the
539. The slip rings employed in a three-phase
alternators in hydrostation are insulated for
A. extra high tension voltage
B. low voltage
C. full armature voltage
D. very high voltage
540. When the speed of alternator increases, the
C.
D.
is more than one number of slots per pole per
phase results in
A. reduction of irregularities produced in the
waveform
B. economy of materials used in the winding
C.
D.
535. Alternators are generally designed to generate
frequency
A. decreases
B. remains the same
542. For a coil having a span of 2/3 or pole pitch, the
543. Distributing the armature winding in alternators
534. The voltage applied to the field of a rotating
A.
B.
C.
D.
size than water-turbine alternators for a given
output. This is so because
A. steam turbo alternators are built with
smaller capacities
B. steam turbo alternators run at high speed
C. steam turbo alternators have long rotors
D. all of these
increases
changes
load shared by one of them is to be increased,
its field excitation is
A. to be strengthened keeping input torque
same
B. to be weakened keeping input torque same
C.
D.
to be kept constant but input torque should
increase
none of the above
548. A four-pole, three-phase, 50-Hz star connected
AC generator has 24 stator slots. There are 6
conductors per slot and a sinusoidally
distributed flux per pole of 65mWb. Find the
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
terminal voltage on open circuit, if the coil span
factor is unity.
A. 546.05 V
C. 568.48 V
B. 579.44 V
D. 558.62 V
555. A 100 MVA 10 kV turbo-alternator has a current
limiting reactor of 0.162 ohms in its neutral. The
per unit voltage of the reactor reactance based
on the generator rating is
A. 0.05
C. 0.025
B. 0.5
D. 0.25
549. A 2,500 kVA, three-phase, 60-Hz, 6.6 kV wyeconnected alternator has a field resistance of
0.45 Ω and an armature resistance of 0.05 Ω
per phase. The field current at full load 0.85
power factor is 200 A. The stray power losses
amount to 82 kW. Calculate the efficiency of
the alternator at full-load, 0.85 power factor
lagging.
A. 93.7%
C. 95.2%
B. 94.8%
D. 96.3%
556. A three-phase, 6-pole, 72-slot armature of a
synchronous generator is wound using a two
layer lap coil having 20 conductors per coil with
a pitch of 83.33%. The flux per pole is
4,800,000 Maxwells. If the rotor of the
generator is driven at a speed of 1200 rpm,
calculate the induced emf per phase. Note:
There are 2 coils in 1 slot.
C. 5,564 V
A. 5,680 V
B. 5,390 V
D. 5,854 V
550. A 6.6 kV, Y-connected, 3-phase alternator has
a synchronous reactance of 6 Ω per phase and
a negligible resistance. At a certain field current
the armature is known to induce 5.8 kV per
phase. Calculate the maximum power that can
be developed by the alternator at this
excitation.
A. 12 MW
C. 9.8 MW
D. 10 MW
B. 11 MW
557. A 2-pole three phase 50 Hz Y-connected AC
generator has 9 slots per pole and 6
conductors per slot. What is the flux per pole if
the voltage on open circuit is 1.1 kV line-toline? Assume a coil span of unity.
C. 0.1507 Wb
A. 0.1657 Wb
B. 0.1742 Wb
D. 0.1728 Wb
558. A 1 MVA, 11 kV, three-phase Y-connected
551. A three-phase alternator has 6 slots per pole
per phase. Determine the distribution factor.
A. 0.977
C. 0.963
B. 0.956
D. 0.948
552. A three-phase star connected AC generator is
rated at 2.5 MVA, 11 kV, 60 Hz. The generator
has a negligible resistance and a synchronous
reactance of 20 ohms per phase. To what value
will the terminal voltage rise when full load at
80% pf lagging is switched-off?
C. 15.3 kV
A. 14.2 kV
B. 13.5 kV
D. 12.7 kV
553. A 5000 kVA, 3-, 10 kV, 50 Hz alternator runs at
1500 rpm connected to constant frequency,
constant voltage busbars. If the moment of
4
inertia of entire rotating system is 1.5 x 10 kg2
m and the steady short circuit current is 5
times the normal full load current. Calculate the
natural time period of oscillation.
A. 1.5 sec
C. 1.3 sec
D. 1.2 sec
B. 1.4 sec
554. A three phase wye connected ac generator is
rated 1500 kVA, 11000 V. The effective
resistance and synchronous reactance per
phase are 1.5 ohms and 30 ohms respectively.
To what value will the terminal voltage rise
when full-load at 0.8 pf lagging is switch off.
A. 14 kV
C. 15 kV
B. 13 kV
D. 12 kV
synchronous generator has a synchronous
reactance of 5 ohms and a negligible
resistance per phase. At a certain field current
the generator delivers rated load at 0.9 lagging
power factor at 11 kV. For the same excitation,
what is the terminal voltage at 0.9 leading
power factor full-load?
A. 11.6 kV
C. 11.3 kV
B. 11.4 kV
D. 11.5 kV
559. A 2500 kVA, 6600 V synchronous turbo
alternator is operating at full load and 0.8 pf
lagging. This machine has a synchronous
reactance per phase of 10.4 ohms and
negligible resistance. Calculate the percentage
voltage regulation.
A. 48.56%
C. 45.84%
B. 42.35%
D. 43.96%
560. Two alternators are connected in parallel. The
total load is 4250 kW at 0.85 power factor
lagging. Alternator operates with a load of 2125
kW at 0.707 power factor lagging. Determine
the kVA load of alternator B.
A. 2245 kVA
C. 2185 kVA
B. 2078 kVA
D. 2410 kVA
561. The best and the most accurate method for
determining the voltage regulation is
A. synchronous impedance method
B. mmf method
C. emf method
D. Pottier triangle method
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)
lOMoARcPSD|12936282
562. A 3-phase, 8-pole generator is delta connected.
The terminal voltage is 2400 V while the line
current is 500 amperes. If the machine is
converted to wye, what will be the terminal
voltage in volts?
A. 4800 V
C. 4600 V
B.
4157 V
D.
3800 V
563. A 3-phase, 8-pole delta connected generator
has a line current of 500 amperes. If converted
in wye, what is the tolerable current?
A. 371.5 A
C. 245.1 A
B. 288.7 A
D. 315.2 A
564. A single-phase alternator gives 250 amperes at
1,200 volts. What is the output of the machine
in KVA?
C. 400
A. 300
B. 450
D. 350
565.
A.
B.
C.
D.
566.
A.
B.
C.
D.
567.
A.
B.
C.
D.
Downloaded by PINAY TICKTOCKERISZTS (salluum.pwet@gmail.com)