The ceramic insulating material Steatite is composed of:

 

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