81. Shield bearings are used for ……….. machines.
(a) small size
(b) medium size
(c) large size
(d) small and medium size
Answer: (d) small and medium size
82. The slot leakage can be computed by assuming that
(a) the permanence of air paths is only considered, the reluctance of iron path being assumed as zero.
(b) the leakage path is straight across the slot and around the iron at the bottom.
(c) the current in the slot conductors is uniformly distributed over their cross section.
(d) all of the above.
Answer: (d) all of the above.
83. The magnitude of exciting current depends upon
(a) total mmf required.
(b) the number of turns in the exciting winding.
(c) the way in which the winding is distributed.
(d) all of the above.
Answer: (d) all of the above.
84.………. magnetic materials are used for construction of core of electromagnets.
(a) Soft
(b) Hard
(c) Either soft or hard
(d) None of these
Answer: (a) Soft
85. The design of electromagnets is based upon
(a) voltage equation.
(b) heating equation.
(c) force equation.
(d) magnetic circuit equation.
(e) all of the above.
Answer: (e) all of the above.
86. The force exerted by a lifting magnet varies with distance (D) as
(a) D2
(b) 1/D2
(c) D
(e) 1/D
Answer: (b) 1/D2
87. The winding where dummy coils are employed is sometimes called the winding.
(a) duplex
(b) triplex
(c) forced
(d) none of these
Answer: (c) forced
88. Dummy coils should not be employed in
(a) small machines.
(b) large machines.
(c) either (a) or (b).
(d) none of these.
Answer: (b) large machines.
89. The space factor is independent of
(a) density of the conductor.
(b) size of the conductor.
(c) insulation thickness.
(d) arrangement of the conductor.
Answer: (a) density of the conductor.
90. In a dc machine “contraction coefficient” is used to take into account the reduction of
(a) air-gap area due to armature slots.
(b) iron losses in the teeth due to lower tooth density.
(c) armature mmf due to armature slots.
(d) torque due to ventilating ducts. [U.P.S.C. I.E.S. E.E.-II, 1993]
Answer: (a) air-gap area due to armature slots.
91. Carter’s coefficient is applicable for estimating
(a) requirement of air-gap mmf.
(b) flux distribution in air gap.
(c) length of air gap.
(d) no-load loss. [A.M.I.E. Sec B. Electrical Design 1993]
Answer: (a) requirement of air-gap mmf.
92. A lap wound dc machine has 400 conductors and 8 poles. The voltage induced per conductor is 2 volts. The machine generates a voltage of
(a) 100 V
(b) 200 V
(c) 400 V
(d) 500 V [A.M.I.E. Sec B. Electrical Design 1954]
Answer: (a) 100 V
93. If the maximum flux density in the armature teeth at minimum section exceeds 2.2T, higher flux density
(a) causes increased iron losses, specially for a machine having high frequency of flux reversals.
(b) needs higher ampere-turns for passing the flux through armature teeth leading to increased field copper losses and increased cost of copper.
(c) both (a) and (b).
(d) none of these.
Answer: (c) both (a) and (b).
94. Specific electric loading is not governed by
(a) heating or temperature rise.
(b) speed of machine.
(c) magnetizing current.
(d) machine size.
(e) machine voltage.
(f) armature reaction and commutation.
Answer: (c) magnetizing current.
95. Specific magnetic loading is not governed by
(a) maximum flux density in the iron parts of the machine.
(b) armature reaction and commutation.
(c) iron losses.
(d) magnetizing current.
Answer: (b) armature reaction and commutation.
96. Use of higher specific electric loading is restricted due to problem of
(a) heat dissipation.
(b) commutation.
(c) armature reaction.
(d) all of these.
Answer: (d) all of these.
97. Use of more number of poles in a dc machine reduces
(a) weight of core and yoke.
(b) cost of copper in armature as well as field.
(c) overall diameter and length of the machine.
(d) length of commutator.
(e) all of the above.
Answer: (e) all of the above.
98. In dc machines the field mmf is made …………. that of armature mmf in order to prevent excessive distortion of field form due to armature reaction.
(a) lesser than
(b) much larger than
(c) equal to
(d) none of these
Answer: (b) much larger than
99. In dc machines the increase in field mmf causes
(a) increase in size and cost of the machine.
(b) reduction in size and cost of the machine.
(c) excessive sparking.
(d) none of the above.
Answer: (a) increase in size and cost of the machine.
100. The yoke of a dc machine
(a) must be made of magnetic material.
(b) should preferably be made of magnetic material but can be of non-magnetic material.
(c) must be made of non-magnetic material.
(d) is partially made of magnetic material and partially of non-magnetic material. [A.M.I.E Sec B. 2005]
Answer: (a) must be made of magnetic material.
Electrical Machine Design MCQ PDF Download
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