Q1. The EMF equation of a transformer is:
(A)
E = 4.44 f N phi_m
(B)
E = 2.22 f N phi_m
(C) E = f N phi_m
(D)
E = 4.44 N phi_m
Q2. In a transformer, the voltage ratio V1/V2 equals:
(A)
I1/I2
(B)
N2/N1
(C)
N1/N2
(D) sqrt(N1/N2)
Q3.
In a transformer, the current ratio I1/I2 equals:
(A)
N1/N2
(B)
N2/N1
(C)
(N1/N2)²
(D) 1
Q4. A transformer transfers
energy without changing
the:
(A)
Voltage
(B) Current
(C)
Frequency
(D) Power factor
Q5. The core of a transformer is laminated to reduce:
(A)
Hysteresis loss
(B)
Eddy-current loss
(C)
Copper loss
(D) Magnetising current
Q6. The flux in a transformer core is
set up by the:
(A)
Load current
(B)
No-load (magnetising) current
(C)
Secondary current
(D) Eddy current
Q7. For a 1100/220 V transformer with 50 primary turns, the secondary turns are:
(A)
10
(B) 100
(C) 250
(D)
500
Q8. A transformer with turns ratio 10:1 fed at 1000 V gives a secondary voltage of:
(A)
100 V
(B)
10 V
(C) 10000 V
(D)
1000 V
Q9 A step –up transformer
increases voltage and _____current
(A)
Increases
(B)
Decreases
(C)
Keeps same
(D) Doubles
Q10. The frequency of the secondary EMF of a transformer is the primary
frequency:
(A)
Twice
(B) Half
(C)
Equal to
(D) Zero
Q11. If a transformer is fed with DC, the result is:
(A)
Normal operation
(B)
Excessive current and overheating
(C)
Higher efficiency
(D) Step-up of voltage
Q12. In the EMF equation E = 4.44 f N phi_m, phi_m is the:
(A)
RMS flux
(B) Average flux
(C)
Maximum (peak) flux
(D)
Total flux
Q13. The all-day efficiency of a distribution transformer is based
on:
(A)
Output power only
(B)
Energy (kWh) over 24 hours
(C) Copper loss only
(D)
Iron loss only
Q14. An ideal transformer has efficiency:
(A)
50%
(B)
75%
(C) 90%
(D)
100%
Q15. The no-load current
of a transformer is mainly:
(A)
Resistive
(B)
Magnetising (reactive)
(C) Zero
(D)
Capacitive
Q16. The open-circuit test on a transformer gives the:
(A)
Copper loss
(B)
Iron (core)
loss
(C) Full-load regulation
(D)
Equivalent reactance
Q17. The short-circuit test on a transformer gives the:
(A)
Iron
loss
(B)
Copper loss and equivalent impedance
(C) Magnetising current
(D) No-load Pf
Q18. The open-circuit test is usually conducted on the:
(A)
HV side
(B)
LV side
(C)
Both sides
(D)
Neither side
Q19. The short-circuit
test is usually conducted
on the:
(A)
LV side
(B)
HV side
(C) Both sides
(D)
Tertiary side
Q20. Iron loss in a transformer is practically:
(A)
Proportional to load
(B)
Constant at all loads
(C) Zero at no load
(D)
Maximum at no load only
Q21. Copper loss in a transformer varies as the:
(A)
Load current
(B)
Square of load current
(C) Voltage
(D) Square of voltage
Q22. Maximum efficiency of a transformer occurs when:
(A)
Iron loss = 2 x copper loss
(B) Copper loss = iron loss
(C)
Copper loss = 0
(D) Iron loss = 0
Q23. A transformer has iron loss 400 W and full-load copper loss 900 W. Maximum
efficiency occurs at
of full load:
(A)
50%
(B) 66.7%
(C)
75%
(D) 100%
Q24. A
transformer has iron loss 100 W and full-load copper loss 400 W. Max efficiency
is at of full load:
(A)
25%
(B)
50%
(C)
75%
(D) 100%
Q25. Voltage regulation of a transformer is worst for a power factor load:
A)
Unity
(B) Leading
(C)
Lagging
(D) Zero leading
Q26. Voltage regulation of a transformer can be negative
for a power factor load:
(A)
Lagging
(B) Unity
(C)
Leading
(D)
Zero lagging
Q27. Zero Voltage regulation in a transformer occurs at
a__________Power factor:
(A)
Unity
(B)
Lagging
(C)
Certain leading
(D) Zero
Q28. The approximate voltage regulation is (I·R·cos(phi) +/- I·X·sin(phi))/V. The '+' sign is for load:
(A)
Leading PF
(B)
Lagging PF
(C)
Unity PF
(D) Resistive
Q29. The efficiency of a transformer is the ratio of:
(A)
Input to output
(B)
Output to input
(C)
Loss to output
(D) Copper to iron loss
Q30. Sumpner's (back-to-back) test on transformers determines:
(A)
Only iron loss
(B)
Both iron and copper losses together
(C) Only copper loss
(D)
Turns ratio
Q31. The main advantage
of an auto-transformer is:
(A)
Better isolation
(B)
Saving of copper, higher efficiency
(C) Lower voltage ratio
(D)
No core loss
Q32. The main disadvantage of an auto-transformer is:
(A)
High cost
(B)
Loss of electrical isolation
(C) Large size
(D)
Low efficiency
Q33. An 11000/2200 V, 100 kVA two-winding transformer reconnected as an auto-transformer (series) can give:
(A)
2200/13200 V; 120 kVA
(B)
11000/13200 V; 600 kVA
(C) 13200/2200 V; 120 kVA
(D)
2200/13200 V; 600 kVA
Q34. A 10-ohm load is impedance-matched to a 6250-ohm source
by a transformer. The turns ratio N1/N2 is:
(A)
10
(B)
15
(C) 20
(D)
25
Q35. Auto-transformers are
most economical when the two
voltage levels are:
(A)
Very different
(B)
Close to each other
(C)
Equal
Q36. Identify NOT correct:
(i) Delta-Y used at start of HV transmission (ii) open delta not possible
with Y-Y (iii) Y-Delta used in distribution (iv) oscillatory-neutral
absent in Y-Y:
(A)
(i)
and (ii) only
(B) (ii) and (iii)
only
(C)
(iii) and (iv) only
(D) (i) and (iv) only
Q37. The Delta-Star transformer connection is commonly
used for:
(A)
Stepping up at generating station
(B) Local lighting
(C)
Battery charging
(D) Rectification
Q38. The Star-Delta connection is commonly used for:
(A)
Stepping up
(B)
Stepping down at receiving end
(C)
Single-phase loads
(D) DC supply
Q39. The Y-Y connection of 3-phase transformers suffers from:
(A)
No problems
(B)
Oscillatory neutral and harmonics
(C) Excess copper
(D)
Low efficiency only
Q40. Open-delta (V-V) connection delivers
of the full delta-delta capacity:
(A)
100%
(B)
86.6%
(C) 57.7%
(D)
50%
Q41. The Scott connection is used to convert:
(A)
3-phase to 2-phase
(B)
2-phase to 1-phase
(C) 1-phase to 3-phase
(D)
DC
to AC
Q42. For parallel operation
of two transformers, they must have the same:
(A)
kVA rating
(B)
Voltage ratio and polarity
(C) Core material
(D)
Number of turns
Q43. The per-unit impedance
of two transformers in parallel
should be:
(A)
Different
(B)
Equal for proper load sharing
(C) Zero
(D)
Infinite
Q44. A 3-phase transformer bank using three single-phase units in delta-delta allows:
(A)
No fault tolerance
(B)
Open-delta operation if one fails
(C)
Only star output
Q45. Tap changing in a transformer is used to control the:
(A)
Frequency
(B)
Output voltage
(C)
Power factor
(D) Phase sequence
Q46. The EMF equation
of a DC machine is:
(A)
E = 4.44 f N phi
(B) E = phi Z N P/(60 A)
(C)
E = phi Z N/(60 P)
(D) E = phi N P A/60
Q47. In a lap winding, the number of parallel paths A equals:
(A)
2
(B)
P (number of poles)
(C)
Z
(D) P/2
Q48. In a wave winding, the number of parallel paths A equals:
(A)
P
(B)
2
(C) Z
(D)
P/2
Q49. A lap winding is used for current,
voltage
machines:
(A)
Low, high
(B)
High, low
(C) High, high
(D)
Low, low
Q50. A wave winding is used for voltage,
current machines:
(A)
Low, high
(B)
High, low
(C) High, high
(D)
Low, low
Q51. The commutator in a DC generator acts as a:
(A)
Rectifier
(B)
Inverter
(C) Amplifier
(D)
Filter
Q52. The commutator in a DC motor ensures
the:
(A)
Torque is unidirectional
(B)
EMF is AC
(C) Speed is zero
(D)
Field is removed
Q53. Brushes in a DC machine
are usually made
of:
(A)
Copper
(B)
Carbon
(C)
Aluminium
(D) Silver
Q 54 The field poles
of a DC machine produce the:
(A)
Armature current
(B)
Magnetic flux
(C)
Commutation
(D) Brush drop
Q55. Armature reaction in a DC machine causes:
(A)
Increase in flux
(B)
Distortion and weakening
of main flux
(C)
No effect
(D) Increase in speed
Q56. The effect of armature reaction
is minimised using:
(A)
Larger brushes
(B)
Interpoles and compensating windings
(C)
Higher speed
(D) More poles
only
Q57. The function of interpoles in a DC machine is to improve:
(A)
Efficiency
(B)
Commutation
(C) Speed
(D)
Power factor
Q58. The yoke of a DC machine provides:
(A)
Mechanical support and flux path
(B)
Cooling only
(C) Insulation
(D)
Commutation
Q59. A 4-pole lap-wound
DC generator has Z=400, phi=0.02
Wb, N=1500 rpm. EMF = phi Z N P/(60A) with A=P:
(A)
100 V
(B)
200 V
(C) 400 V
(D)
800 V
Q60. In the EMF equation, increasing the speed N while keeping flux constant will:
(A)
Decrease EMF
(B)
Increase EMF
(C) Not change
EMF
(D)
Reverse EMF
Q61. The residual magnetism in a DC generator is essential for:
(A)
Separately-excited type
(B)
Self-excited voltage build-up
(C) Reducing losses
(D)
Commutation
Q62. Equalizer rings are used in wound DC machines:
(A)
Wave
(B)
Lap
(C)
Both
(D) Neither
Q63.The direction of
DC shunt motor can be done by
(A)
Supply only
(B)
Either field or armature connections
(C)
Both field and
armature
(D) The brushes
Q64. Back-EMF in a DC
motor is
given by:
(A)
V + Ia·Ra
(B)
V - Ia·Ra
(C)
Ia·Ra
(D) V/Ia
Q65. A DC shunt motor runs at approximately:
(A)
Variable speed
(B)
Constant speed
(C)
Zero speed
(D) Synchronous speed
Q66. A DC series
motor should never
be run on:
(A)
Full load
(B) Half load
(C)
No load
(D)
Rated load
Q67. A DC series
motor is preferred for traction because
it gives:
(A)
Constant speed
(B)
High starting torque
(C) Low torque
(D)
Negative torque
Q68. In a DC motor, torque
is proportional to:
(A)
phi/Ia
(B)
phi·Ia
(C) Ia/phi
(D)
1/(phi·Ia)
Q69. In a DC motor, speed is proportional to:
(A)
Eb·phi
(B)
Eb/phi
(C) phi/Eb
(D)
1/(Eb·phi)
Q70. A DC series
motor on no-load
tends to:
(A)
Stop
(B)
Run at dangerously high speed
(C) Run at rated speed
(D)
Reverse
Q71. The speed of a DC shunt motor is controlled below base speed by:
(A)
Field control
(B)
Armature voltage (or resistance) control
(C) Increasing flux
(D) Adding load
Q72. Field control (flux
weakening) of a DC motor
gives speeds:
(B)
Above base speed
(C)
At base speed
only
(D)
Zero
Q73. A cumulatively-compounded DC motor combines
the features of:
(A)
Two series motors
(B)
Series and shunt
motors
(C) Two shunt motors
(D)
Induction and DC motors
Q74. A DC shunt motor is used for:
(A)
Cranes
(B)
Lathes, fans, pumps (constant speed)
(C) Traction
(D)
Hoists
Q75. A self-excited DC generator fails to build up if: (i) no residual magnetism (iv) field R > critical
R
(v) speed < critical
speed. Correct combination:
(A)
(i),(ii),(iii)
(B)
(i),(iii),(iv)
(C)
(i),(iv),(v)
(D) (i),(ii),(v)
Q76. A 250 V DC shunt motor takes 41 A at 800 rpm (Ra=0.2,
Rf=250). With 2 ohm added at stall, the
stalling-to-full-load torque ratio is about:
(A)
1.42
(B) 2.84
(C)
1.25
(D) 3.13
Q77. The Swinburne's test on a DC machine
is used to find:
(A)
Efficiency (no-load
test)
(B) Temperature rise
(C)
Full-load regulation
(D) Starting torque
Q78. The starter
is necessary for a DC motor to limit the high at starting:
(A)
Voltage
(B)
Armature current
(C)
Field current
(D) Flux
Q79. At the instant
of starting, a DC motor has back-EMF
equal to:
(A)
V
(B) V/2
(C)
Zero
(D) Maximum
Q80. A
three-point starter is used for a DC motor:
(A)
Series
(B)
Shunt/compound
(C) Induction
(D)
Synchronous
Q81. Critical field resistance of a DC shunt generator is the resistance which the generator fails to excite:
(A)
Below
(B)
Above
(C)
Equal to
(D) Twice
Q82. The Hopkinson's test on DC machines is a:
(A)
No-load test
(B)
Regenerative (back-to-back) full-load
test
(C)
Open-circuit test
(D) Brake test
Q83. In a level-compounded DC generator, the full-load voltage
equals the:
(A)
Half no-load voltage
(B)
No-load voltage
(C)
Zero
(D) Twice no-load voltage
Q84. The synchronous speed
of a 4-pole, 50 Hz machine is:
(A)
1000 rpm
(B)
1500 rpm
(C) 3000 rpm
(D)
750 rpm
Q85. The synchronous speed of a 6-pole, 50 Hz machine
is:
(A)
1500 rpm
(B)
1000 rpm
(C) 750 rpm
(D)
3000 rpm
Q86. The synchronous speed of a 2-pole, 50 Hz machine
is:
(A)
1500 rpm
(B)
3000 rpm
(C) 1000 rpm
(D)
750 rpm
Q87. The slip of an induction
motor is defined
as:
(A)
(N-Ns)/N
(B)
(Ns-N)/Ns
(C) Ns/N
(D)
N/Ns
Q88. The rotor frequency
of an induction motor equals:
(A)
f
(B)
s·f
(C) f/s
(D)
s²·f
Q89. A 4-pole, 50
Hz induction motor has rotor current period 200 ms. Its
slip speed is:
(A)
150 rpm
(B) 1350 rpm
(C)
75 rpm
(D) 1425 rpm
Q90. An induction motor runs at 1440 rpm on a 1500 rpm synchronous speed.
The slip is:
(A)
4%
(B) 6%
(C)
10%
(D) 2%
Q91. An induction motor can never run at synchronous speed because:
(A)
Friction is too high
(B)
At Ns there is no relative motion,
no torque
(C)
The slip is 1
(D) The rotor is open
Q92. At standstill, the slip of an induction motor is:
(A)
0
(B) 0.5
(C)
1
(D) Infinite
Q93. At synchronous speed, the
slip of an induction motor would be:
(A)
1
(B) 0.5
(C)
0
(D)
Infinite
Q94. The rotor EMF of an induction
motor at slip s is the standstill
rotor EMF:
(A)
s times
(B)
1/s
times
(C) s² times
(D)
equal to
Q95. The rotor
reactance at slip s is the standstill reactance:
(A)
1/s
times
(B)
s times
(C) s² times
(D)
equal to
Q96. A star-delta starter reduces the starting current
to of the DOL value:
(A)
One-half
(B)
One-third
(C) Twice
(D)
Equal
Q97. A slip-ring induction motor gives
high starting torque
by adding in the rotor:
(A)
Capacitance
(B)
External resistance
(C) Inductance
(D)
EMF
Q98. Speed control of an induction
motor by the modern method uses variation
of:
(A)
Resistance only
(B)
Supply frequency (V/f)
(C)
Brush position
(D) Core material
Q99.Starting torque at
s=1 is
(A)
Pull-out torque
(B)
Starting torque
(C)
Synchronous torque
(D) Zero torque
Q100. The maximum torque of an induction motor is the:
(A)
Starting torque
(B)
Breakdown (pull-out) torque
(C)
Running torque
(D) Slip torque
Q101. At maximum torque, the slip
of an induction motor equals:
(A)
1
(B)
R2/X2
(C)
X2/R2
(D) 0
Q102. The
maximum torque of an induction motor is of the rotor resistance:
(A)
Proportional to
(B) Inversely proportional to
(C)
Independent of
(D)
Equal to
Q103. The crawling of an induction motor is due to:
(A)
Harmonics in the air-gap flux
(B)
High slip
(C) DC supply
(D)
Low voltage
Q104. Cogging (magnetic locking)
in an induction motor is avoided by:
(A)
Equal stator and rotor slots
(B)
Skewing the rotor slots
(C) Adding resistance
(D)
Increasing voltage
Q105. A single-phase induction motor is not self-starting because it produces
a field:
(A)
Rotating
(B)
Pulsating
(C) Constant
(D)
Zero
Q106. A capacitor-start single-phase induction motor has high:
(A)
Running speed
(B)
Starting torque
(C) Efficiency
(D)
Slip
Q107. A shaded-pole motor
is used for:
(A)
Heavy loads
(B)
Small fans and toys (low torque)
(C) Traction
(D) Cranes
Q108. The rotor power input, rotor copper loss and mechanical power are in the ratio:
(A)
s : 1 : (1-s)
(B) 1:s: (1-s)
(C) (1-s) : s : 1
(D) 1 : (1-s) : s
Q109. The efficiency of an induction
motor is approximately equal to:
(A)
Slip
(B)
(1 - slip)
(C) 2·slip
(D)
1/slip
Q110. A double-cage induction motor is used to obtain:
(A)
Low starting torque
(B)
High starting torque with low current
(C) Constant speed
(D)
Leading PF
Q111. The power factor
of an induction motor at no load is:
(A)
High
(near unity)
(B)
Very low (lagging)
(C) Leading
(D) Zero
Q112. The no-load test on an induction motor gives the:
(A)
Copper loss
(B)
Friction, windage and core losses
(C)
Full-load slip
(D) Starting torque
Q113. The blocked-rotor test on an induction motor is similar
to the test of a
transformer:
(A)
Open-circuit
(B)
Short-circuit
(C)
No-load
(D) Polarity
Q114. A synchronous motor runs at:
(A)
Variable speed
(B)
Synchronous speed always
(C)
Slip speed
(D) Zero speed
Q115. The rotor of a synchronous machine is supplied
with:
(A)
AC
(B)
DC
(C)
Pulsed DC
(D) No supply
Q116. The EMF generated in a synchronous machine is given by:
(A)
E = 4.44 f N phi Kp Kd
(B) E = phi Z N P/60A
(C)
E = V - IRa
(D) E = 2.22 f N phi
Q117. The pitch factor (Kp) of a winding
is always:
(A) Greater than 1
(B) Less than or equal to 1
(C) Equal to 2
(D) Zero
Q118. The distribution factor
(Kd) accounts for coils being:
(A)
Full-pitch
(B)
Spread over slots
(C)
Short-pitched
(D) Series-connected
Q119. An over-excited synchronous motor on no load behaves
as a:
(A)
Resistor
(B) Inductor
(C)
Capacitor (synchronous condenser)
(D) Battery
Q120. An under-excited synchronous motor draws a current:
(A)
Leading
(B)
Lagging
(C)
Zero
(D) DC
Q121. The V-curve of
a synchronous motor is a plot of armature current versus:
(A)
Speed
(B)
Field excitation
(C) Load angle
(D)
Frequency
Q122. A synchronous motor is started
using a:
(A)
Commutator
(B)
Damper (amortisseur) winding
(C) Capacitor
(D)
Slip ring only
Q123. The power developed by
a synchronous machine is
proportional to:
(A)
cos(delta)
(B)
sin(delta)
(C) tan(delta)
(D)
delta²
Q124. Maximum power of a synchronous machine occurs at a load angle
of:
(A)
0 deg
(B)
45 deg
(C)
90 deg
(D)
180
deg
Q125. In a round-rotor synchronous motor, reactive
power is maximum at a load angle of:
(A)
0 deg
(B)
45 deg
(C)
90 deg
(D)
180
deg
Q126. A short-shunt compound
generator supplies 100 A at 250 V (shunt 130, armature 0.1, series 0.1 ohm, brush drop 1V/brush). EMF is:
(A) 270.2 V
(C)
262.2 V
(D)
272.2 V
Q127. The slip test on a salient-pole
synchronous machine is used to find:
(A)
Synchronous impedance
(B)
Xd and Xq
(C)
Armature resistance
(D) Field current
Q128. In a salient-pole machine,
the direct-axis reactance Xd is the quadrature-axis reactance
Xq:
(A)
Less than
(B)
Greater than
(C)
Equal to
(D) Unrelated to
Q129. A synchronous condenser is an
over-excited synchronous motor:
(A)
Driving a mechanical load
(B)
Running on no mechanical load
(C)
Acting as a generator
(D) With reversed
field
Q130. Identify incorrect: (ii) damper winding gives starting
torque to synchronous motor (iv) synchronous condenser
drives a mechanical load. The incorrect
statement is:
(A)
(ii)
only
(B)
(iv) only
(C) Both
(D)
Neither
Q131. Two alternators in parallel share active power by adjusting
their:
(A)
Excitation
(B)
Prime-mover input (governor)
(C) Frequency only
(D)
Phase sequence
Q132. Two alternators in parallel share reactive power by adjusting
their:
(A)
Prime-mover input
(B)
Field excitation
(C) Speed only
(D)
Load angle
Q133. The synchronising power of an alternator is maximum at a load angle of:
(A)
90 deg
(B)
0 deg
(C) 45 deg
(D)
180
deg
Q134. The
synchronous impedance method of finding regulation gives a value:
(A)
Exact
(B)
Pessimistic (higher)
(C) Optimistic (lower)
(D) Zero
Q135. Hunting in a synchronous machine is reduced by the:
(A) Field winding
(B) Damper Winding
(B)
(C) Armature winding
(D) Commutator
Q136. A synchronous machine connected to an infinite
bus has constant:
(A)
Speed and voltage
(B) Current only
(C)
Torque only
(D) Excitation only
Q137. The voltage
regulation of an alternator is negative for a power factor load:
(A)
Lagging
(B) Unity
(C)
Leading
(D) Zero lagging
Q138. Three conditions for paralleling alternators include same voltage,
same frequency and same:
(A)
Power
(B)
Phase sequence
(C)
Current
(D) kVA
Q139. The area of a B-H hysteresis loop represents:
(A)
Copper loss
(B)
Hysteresis loss per cycle
(C) Eddy loss
(D)
Friction loss
Q140. A hard magnetic material
has coercivity compared
to a soft material:
(A)
Lower
(B)
Higher
(C) Equal
(D)
Zero
Q141. Soft magnetic materials
are used for transformer cores because they have:
A)
Large loop area
(B)
Small loop area (low loss)
(C) High coercivity
(D)
High retentivity
Q142. Retentivity is the flux density remaining when the:
(A)
Current is maximum
(B)
Magnetising force is removed
(C) Core is saturated
(D)
Frequency is zero
Q143. Coercivity is the reverse magnetising force needed to reduce the flux density
to:
(A)
Maximum
(B)
Zero
(C) Retentivity
(D)
Saturation
Q144. Eddy-current loss in a core is reduced
by:
(A)
Using thick laminations
(B)
Using thin laminations
(D) Removing the core
Q145. Hysteresis loss is proportional to (Steinmetz):
(A)
f
(B)
f²
(C) Bmax only
(D)
f x Bmax^1.6
Q146. Permanent magnets
are made from magnetic materials:
(A)
Soft
(B)
Hard
(C) Diamagnetic
(D)
Paramagnetic
Q147. Silicon steel is used in transformer cores because it has:
(A)
High hysteresis loss
(B)
Low hysteresis loss and high resistivity
(C) High conductivity
(D)
Low permeability
Q148. The ceramic insulating material Steatite is composed of:
(A)
Clay, quartz, feldspar
(B)
Clay, talc, magnesite
(C)
Clay, quartz, barium
carbonate
(D) Talc, magnesite, quartz
Q149. The maximum efficiency
of a transformer is independent of:
(A)
Iron
loss
(B) Copper loss
(C)
Power factor of the load
(D) Load current
Q150. The damper winding in a synchronous machine also helps to suppress:
(A)
Voltage
(B)
Hunting and oscillations
(C)
Frequency
(D) Excitation
