MCQ Questions DC Machines

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MCQ Questions DC Machines: Test your knowledge of DC Machines .

MCQ Questions DC Machines

1.The armature reaction mmf in a dc machine has a shape.
(a) sinusoidal (b) trapezoidal
(c) rectangular (d) triangular

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2. A dc series motor has linear magnetisation and negligible armature resistance. The motor speed is
(a) directly proportional to T , T = load torque (b) inversely proportional to T
(c) directly proportional to T (d) inversely proportional to T

3.The power drawn by a dc shunt motor on no-load comprises
(a) iron loss only (b) mechanical less only
(c) iron loss and mechanical loss (d) copper loss only

4. A series motor must not be run at light/no load because
(a) it will draw a dangerously large current
(b) it will run at dangerously high speed
(c) it will draw dangerously high current and run at dangerously high speed
(d) it will stall

5. PC machine poles are constructed of thick laminations
(a) to reduce iron loss in pole body and pale shoes
(b) to reduce iron loss in pole body comfort and ease of construction.
(c) to reduce pulsation loss in pole shoes and for ease of construction.
(d) for ease of construction.

6. A differentially compound motor under high overload conditions will behave like a/an
(a) shunt motor (b) series motor
(c) cumulative compound motor (d) ac synchronous motor

7. A 6-pole, lap-wound, dc armature with 720 conductors draws 50A from the mains. Its armature reaction
people is
(a) 1000 AT peak, triangular wave shape (b) 500 AT peak, triangular wave shape
(c) 1000 AT peak, sinusoidal wave shape (d) 500 AT peak, sinusoidal wave shape

8. The process of current communication in a dc machine is opposed by the
(a) emf induced in the commutating coil because of the interpose fl ux
(b) reactance emf
(c) coil resistance
(d) brush resistance

9. In Hopkinson’s test on two identical dc shunt machines,
(a) iron losses in both machines are equal
(b) iron loss in the generating machine is more than that in the motoring machine
(c) iron loss in the motoring machine is more than that in the generating machine
(d) only starry-tool components of iron loss in both machines are equal.

10. In a separately excited dc motor, the motor back emf
(a) reduces the effective motor time constant.
(b) increases the effective motor time constant
(c) does not affect the motor time constant
(d) reduces the effective motor time constant to zero

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MCQ Answers

1 (d) 2. (b) 3. (c) 4. (b) 5. (c) 6. (b) 7. (b) 8. (b) 9. (b) 10. (a)

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