ELECTRICAL MACHINES QUIZ

A Shunt generator running at 1000 rpm has generated emf of 100 V. If the speed increases to 1200 rpm, the generated emf will be nearly

175 V

140 V

240 V

120 V

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A DC Shunt Motor having shunt field resistance of 250 Ω and armature resistance of 0.5 Ω is connected to 250 V supply and load current of 21 A. What is the back emf generated ?

210 V

230 V.

150 V.

240 V.

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In IM the rotor lamination can be ________________ than stator laminations.

sipper.

thicker.

rotor can not have any laminations.

thinner.

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For a single phase capacitor start induction motor which of the following is valid?

Direction of rotation cannot be changed.

Rotation can be changed by interchanging supply terminals.

None of these.

Rotation can be changed by reversing main winding terminals.

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Which motor cannot be started on no load?

series motors

cumulative compound motors

both B and C

shunt motors

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Which of these types of motor is self starting?

None of these.

Poly-phase synchronous machine.

Single phase induction motor.

Poly-phase induction motor.

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A 250 V DC generator in run at rated speed with no excitation. The open circuit voltage will be

very small, say about 2 or 3 V.

about 100 V.

zero.

250 V.

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The main purpose of providing tertiary winding in a three phase transformer is

None of these

to interconnect three voltage systems.

to carry extra load.

to suppress harmonic and unbalance in voltage.

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Short circuit test is performed on a transformer with a certain impressed voltage at rated frequency. If the short circuit test is now performed with the same magnitude of impressed voltage, but at frequency higher than the rated frequency then

The magnitude of current will decrease but the power factor will increase.

The magnitude will both increase.

The magnetude of current will increase, but power factor will decrease.

The magnitude of circuit as well as the power factor will decrease.

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A dc motor with armature resistance of 0.5 ohms connected directly to a 230 Volt supply. If the armature is stationary then the current flowing through armature is

570 A.

460 A.

340 A.

250 A.

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