solved preview paper 3 (51-100)

Q.51. The phenomenon of squirrel cage motor some time showing a tendency to run at a very low speed is known as
a.) Cogging
b.) Crawling✔
c.) Damping
d.) Skewing

Q.52. A 5 H- HP 3 phase 400v star connected squirrel cage induction motor meant to drive a milling machine at starting takes about
a.) 40A✔
b.) 100A
c.) 150A
d.) 200A

Q.53. The starting torque of an induction motor can be increased by
a.) Increasing Rotor reactance
b.) Increasing the rotor resistance✔
c.) Increasing the supply frequency
d.) Giving supply through a star delta starter

Q.54. The span for full pitch coil wound for 6 poles is
a.) 180 degree mechanical
b.) 90 degree mechanical
c.) 60 degree mechanical✔
d.) 45 degree mechanical

Q.55. The armature flux opposes the main field flux when load power factor is
a.) Unity
b.) Zero lagging✔
c.) Zero leading
d.) 0.8 leading

Q.56. A commercial alternator has
a.) Rotating armature and stationary field
b.) Stationary armature and rotating field✔
c.) Both armature and field rotating
d.) Both armature and field stationary

Q.57. In alternator damper winding are used to
a.) Reduce Eddy current loss
b.) Prevent hunting✔
c.) Make the rotor dynamically balanced
d.) Reduce armature reaction

Q.58. The magnitude of the resultant magnetic field produced by a three phase current flowing through a three phase winding
a.) The maximum value of flux due to any one phase
b.) 1.5 time the maximum value of flux due to any one phase✔
c.) Half the value of maximum flux due to any one phase
d.) Twice tha maximum value of flux due to any one phase

Q.59. The pitch factor for 5/6 short pitch coil is
a.) 0.966✔
b.) 0.833
c.) 1.0
d.) 3.454

Q.60. Armature reaction in a electrical machine is the effect of
a.) Armature flux on the main field flux✔
b.) Heat produce on the armature winding
c.) Armature current on the output
d.) Armature flux on the output

Q.61. The speed regulation of synchronous motor is
a.) Unity
b.) Zero✔
c.) Infinity
d.) Always less then one

Q.62. The direction of the rotation of an ordinary shaded pole single phase induction motor
a.) Can be reversed by reversing the supply terminal connection to the stator winding
b.)can not be reversed✔
c.) Can be reversed by open circuiting the shading ring
d.) Can be reversed by short circuiting the shading ring

Q.63. In a single phase repulsion motor, torque is developed on the rotor when the brush axis is fixed
a.) At 90° 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 degree mechanical with the stator field axis

Q.64 . 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

Q.67. The armature of a DC machine is made up of laminated sheets to
a.) Reduce hysteresis loss
b.) Reduce Eddy current loss✔
c.) Reduce armature copper loss
d.) Increase dissipation of heat from the armature surface

Q.68. The function of a brush and commutator arrangement in a DC motor
a.) To produce uni-directional torque✔
b.) To produce unidirectional current in armature
c.) To help in changing the direction of rotation of armature
d.) To reduce parking

Q.69. The armature winding of a DC machine is made up of a number of coils distributed in a large number of armature slots instead of placing all the coil in two slots to
a.) Gets sinusoidal EMF at the output terminals
b.) Have minimum heat dissipation from the armature✔
c.) Make the armature dynamically balanced
d.) Get the maximum generated EMF in the armature

Q.70. The maximum permissible operating temperature of class-E insulating material is
a.)130 degree
b.)120 degree✔
c.)180 degree
d.)105 degree

Q.71. The number of parallel paths in the armature winding of a four pole wave connected DC Machine having 22 coil-sides is
a.) 4
b.) 22
c.) 2✔
d.) 11

Q.71. The direction of rotation of a DC motor can be reversed
a.) By reversing the connection of both the armature and the field winding with the supply
b.) By reversing the connection of either the armature or the field✔ winding connection with the supply
c.) By reducing the field flux
d.) By introducing an extra resistance in the armature circuit

Q.72. To have sparkless commutation the armature reaction effect in a DC machine is neutralized by
a.) Using compensating winding and commutating poles✔
b.) Shifting the brush Axis from the geometrical neutral axis to the magnetic neutral axis
c.) Fixing the processes in alignment with the main pole axis
d.) Increasing the field excitation

Q.73. Which type of motor is preferred for traction work?
a.) DC series motor✔
b.) Three phase induction motor
c.) Universal motor
d.) Synchronous motor

Q.74. A solid angle is expressed in terms of
a.) Radians
b.) Degrees
c.) Radian/metre
d.) Steradian✔

Q.75. Glare is reduced by
a.) Increasing lamp height
b.) Using reflectors
c.) Using diffuser
d.) All of the above✔

Q.76. In induction heating which of the following is high
a.) Current✔
b.) Voltage
c.) Frequency
d.) Power

Q.77. The electrodes used for direct resistance heating are made of
a.) Mild steel✔
b.) Copper
c.) Carbon
d.) None of the above

Q.78. In which type of welding current is passed through the metal piece to be joint
a.) Arc
b.) TIG
c.) Resistance✔
d.) MIG

Q.79. In transmission line sag depends upon
a.) Conductor material
b.) Length of span
c.) The tension in conductor
d.) All of the above✔

Q.80. Electroplating is the process of
a.) Removing 1 metal from the other
b.) Coverings superior metal over the inferior metal✔
c.) Refining of metals
d.) All of the above

Q.81. Which of the following motor is used in household refrigerator?
a.) AC series motor
b.) DC shunt motor
c.) Reluctance motor
d.) Single phase induction motor✔

Q.82. Voltage regulator are used to _________the voltage
a.) Increase
b.) Stabilize✔
c.) Decrease
d.) None of the above

Q.83. The direct current system employed for tramways operates on
a.) 3000 V
b.) 1500 V
c.) 750 V✔
d.) 440 V

Q.84. Low frequency operation of overhead line in traction system
a.) Reduce the spacing between substation
b.) Increase the spacing between substation✔
c.) All of the above
d.) None of the above

Q.85. In electrolytic process the electrical energy is converted into
a.) Mechanical energy
b.) Heat energy
c.) Chemical energy✔
d.) None of the above

Q.86. Ajax Wyatt furnace is started when
a.) Field below core level
b.) Fully filled
c.) Field above core level✔
d.) All of the above

Q.87. The output of full wave rectifier contains
a.) Only even harmonics
b.) Only odd harmonics✔
c.) Both odd and even harmonics
d.) No harmonics

Q.88. Which of the following has negative temperature co-efficient
a.) Electrolyte✔
b.) Brass
c.) Silver
d.) Mercury

Q.89. A wire of resistance R has its length and area of cross section doubled heat resistance becomes
a.) R✔
b.) R/4
c.) 2R
d.) 4R

Q.90. The unit of retentivity is
a.) Ampere return
b.) Weber
c.) Ampere turn/metre
d.) Weber/metersquare✔

Q.91. Which material has least specific resistance
a.) Mercury✔
b.) Zinc
c.) Copper
d.) Lead

Q.92. In an a.c. circuit M.I. metres measure
a.) Mean value
b.) Peak value
c.) R.M.S. value✔
d.) Average value

Q.93. Economisers are used to heat
a.) Air
b.) Steam
c.) Feedwater✔
d.) None

Q.94. A coil has 1000 turns and current of 8 ampere causes a flux of 5 milli-weber to it .The inductance of coil will be
a.) 1.0 H
b.) 2.15 H
c.) 1.5 H✔
d.) 2.0 H

Q.95. Internal resistance of dry cell is
a.) 1-15 ohm
b.) 2-5 ohm
c.) 1-1.5 ohm
d.) 0.2-0.4 ohm✔

Q.96. Bronze is an alloy of
a.) Copper and Zinc
b.) Copper zinc and Tin
c.) Copper and Tin✔
d.) None

Q.97. Suitable turbine used for harnessing tidal power is
a.) Francis turbine
b.) Pelton wheel
c.) Kaplan turbine✔
d.) None

Q.98. Advantage of hydropower over Thermal Power is
a.) Low initial cost
b.) Low operatinng cost✔
c.) Continuous power
d.) None

Q.99. Impedance relay can be used for
a.) Earth fault
b.) Phase fault only
c.) Both Earth and phase fault✔
d.) None

Q.100. For energy efficient Motors which of the following is correct
a.) Use more power
b.) Used low quality material
c.) High reliability✔
d.) Less cost