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Power Electronics

Answer: A

UJT relaxation oscillator is used to provide gate pulses to SCR for triggering.

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2.

The rated current of a thyristor is 40 A. The holding current will be about :

Answer: D

The holding current is much less then 1% of rated current.

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Answer: B

Natural commutation is possible only in ac circuits.

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4.

A single phase full wave regulator feeds R-L load. The best gating signal is

Answer: C

To ensure proper triggering pulse train in necessary because load is R - L.

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5.

The number of gates in an SCR is

Answer: A

No answer description available for this question.

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6.

In a 3 phase semiconverter, the dc output voltage for a certain firing angle is 50% of the maximum possible value. The firing angle is

Answer: C

Vdc ∝ (1 + cos a). Maximum possible output voltage occurs when a = 0.

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7.

A 3 phase induction motor is fed by a 3 phase ac regulator to change the stator voltage. The variation in speed will be more if

Answer: B

If load torque is constant, the change in speed is very small.

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8.

Assertion (A): A GTO circuit is more compact than SCR circuit

Reason (R): A GTO can be turned off by negative gate pulse.

Answer: A

Since commutation circuit is not required, GTO circuit is compact.

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9.

The two modes of operation of three phase bridge inverters are known as

Answer: C

In 180° mode each thyristor conducts for 180° and in 120° mode each thyristor conducts for 120°.

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10.

A silicon controlled switch has :

Answer: C

Anode, cathode, anode gate and cathode gate.

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