ELECTRICAL MACHINES QUIZ

When flux density is constant in a transformer, hysteresis loss varies as

f²

V

V²

f

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In DC generators brushes are used for

reduce eddy current loss

convert ac armature current in to dc

collecting of current without any sparkings

collecting of voltage

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A 3 - ÃŽÂ¦ slip ring motor has

short-circuited rotor.

double cage rotor.

wound rotor.

any of the above.

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Two synchronous generators operating in parallel 200 MW and 400 MW respectively. The drooping characteristics of their governors are identical as 4% from no load to full load. Consider the governors operating at 50Hz on no load. What is the operating frequency, if the load is 600 MW?

45 HZ

50 Hz

48 Hz

48.5 Hz

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In DC machines shape of net flux density is?

peaky in nature

sine wave

flat tapped or trapezoidal

saddle shape

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Armature reaction depends on which of the following?

both 1 and 2

None of these

power factor of load

magnitude of load current

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In a stepper motor the detente torque means

maximum of the static torque with the phase winding excited.

maximum of the static torque with the phase winding unexcited.

minimum of the static torque with the phase winding excited.

minimum of the static torque with the phase winding unexcited.

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The emf induced in the dc generator armature winding is

DC

AC

None of these

AC and DC

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A generator may loose residual magnetism due to

heating.

any of these.

vibrations.

over excitation.

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Field divertor method of speed control of a DC series motor gives speed above rated one due to reduction of

Line current.

None of above.

Armature current.

Field current.

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