Electrical Engineering Objective Questions { DC Motors }

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267. Which method for braking is generally used in Elevators?

B. Regenerative braking

C. Rheostatic braking

D. None of the above

268. 1n variable speed motor

A. a stronger commutating field is needed at los speed than at high speed

B. a weaker commutating field is needed at low speed than at high speed

C. same commutating field is needed at low speed than at high speed

D. None of the above

269. When the armature of rotates, e.m.f. induced is

A. self-induced e.m.f.

B. mutually induced e.m.f.

D. None of the above

270. Where D.C. motor of H.P. 12 requires frequent starting, stopping reversing and speed control

A. drum type controller is used

B. three point starter is used

C. four point starter is used

D. all above can be used

271. If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens

A. this will make armature to take heavy current, possibly burning it

B. this will result in excessive speed, possibly destroying armature due to

C. nothing will happen to motor

D. motor will come to stop

272. D.C. motor is to a drive a load which is almost zero for certain part of the load cycle and peak value for short short duration. We will prefer

A. series motor

C. compound motor

D. any of the above

273. Voltage equation for D.C. motor is

A. Eb = V + laRa

B. V = Eb + LaRa

C. Eb = V - la2Ra

D. V = Eb- laRa

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