ELECTRICAL MACHINES QUIZ

In a synchronous machine, if φ is the flux per pole and f is the frequency of the emf induced E then

E ∝ f/φ

E ∝ φf

E ∝ φ/f

E ∝ 1/(φf)

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As compared to an induction motor, the air gap in a DC motor is

between 50% and 90%.

more.

same.

less than 50%.

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In which of the following generators negative voltage regulation can occur?

series generators

shunt generator

over compound generator

both B and C

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

V

V²

f

f²

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In synchronous generator V curve is drawn between

field current on Y-axis and armature current on X-axis.

either of these.

field current on X-axis and armature current on Y-axis.

field current on X-axis and power factor on Y-axis.

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At slip s = 1 torque developed in machine is

starting torque.

maximum torque.

none.

electromagnetic torque.

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Two synchronous generators operating in parallel 200 MW and 400 MW respectively. The drooping characteristics of their governors are 4% and 5% from no load to full load. Consider the governors operating at 50Hz on no load. How will the machine share, if the load is 600 MW?

None of these

generator 1 gets over load

generator 2 gets over load

200 MW and 400MW

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The speed of a 50 Hz three phase induction motor under full load condition is 725 rpm the number of poles of the motor are ______________.

8.

2.

4.

6.

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For high current and low voltage rating which winding is employed to DC machine?

No wave and lap winding.

Both wave and lap winding.

Lap winding.

Wave winding.

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The reduced air gap results in an increase

cost of operation.

power factor.

starting torque.

breaking torque.

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