DC Motors MCQs

Question 1

Compansating winding are used in D.C. generators

Accepted Answer

none of the above

Answer

mainly to reduce the eddy currents by providing local short-circuits

Answer

to provide path for the circulation of cooling air

Answer

to neutralise the cross-magnetising effect ofthe armature reaction

Question 2

Which of the following components of a D.C. generator plays vital role for providing direct current of a D.C. generator?

Accepted Answer

Dummy coils

Answer

Commutator

Answer

Eye bolt

Answer

Equilizer rings

Question 3

In a D.C. generator the ripples in the direct e.m.f. generated are reduced by

Accepted Answer

using carbon brushes of superios quality

Answer

using conductor of annealed copper

Answer

using commutator with large number of segments

Answer

using equiliser rings

Question 4

D.C. generator varies significantly with the load current?

Accepted Answer

None of the above

Answer

Field copper loss

Answer

Windage loss

Answer

Armature copper loss

Question 5

The match between the control method needed and the speed/torque regime is as follows P Field Control, Q Armature Control1. Below base speed2. Above base speed3. Above base torque4. Below base torque

Accepted Answer

P-1; Q-3

Answer

P-2; Q-1

Answer

P-2; Q-3

Answer

P-1; Q-4

Question 6

motor draws 1.5 A from a supply voltage of 25 V and runs at 1500 rpm. The efficiency of the motor while it is operating on load at 1500 rpm drawing a current of 3.5 A from the motor may result in same source

Accepted Answer

88.80%

Answer

48.00%

Answer

57,1%

Answer

59.20%

Question 7

D.C. generators are installed near the load centres to reduce

Accepted Answer

corona losses

Answer

iron losses

Answer

line losses

Answer

sparking

Question 8

The purpose of retardation test on D.C. shunt machines is to find out

Accepted Answer

stray losses

Answer

eddy current losses

Answer

field copper losse

Answer

windage losse

Question 9

During Rheostat braking of D.C. series motors

Accepted Answer

motor is run as a generator

Answer

motor is reversed in direction

Answer

motor is run at reduced speed

Answer

motor runs in toggle mode