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Test: Power Electronics - 1


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25 Questions MCQ Test Power Electronics | Test: Power Electronics - 1

Test: Power Electronics - 1 for Electrical Engineering (EE) 2023 is part of Power Electronics preparation. The Test: Power Electronics - 1 questions and answers have been prepared according to the Electrical Engineering (EE) exam syllabus.The Test: Power Electronics - 1 MCQs are made for Electrical Engineering (EE) 2023 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Test: Power Electronics - 1 below.
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Test: Power Electronics - 1 - Question 1

A cycloconverter can be

Detailed Solution for Test: Power Electronics - 1 - Question 1

The output frequency can be more or less than input frequency.

Test: Power Electronics - 1 - Question 2

In the below figure the average load current is 15 A. The rms value of transformer secondary current is

Detailed Solution for Test: Power Electronics - 1 - Question 2

RMS secondary current = = 15/1.414 = 10.608 A.

Test: Power Electronics - 1 - Question 3

In a 3 phase fully controlled converter the firing frequency is

Detailed Solution for Test: Power Electronics - 1 - Question 3

It is a 6 pulse converter.

Test: Power Electronics - 1 - Question 4

Two thyristor of same rating and same specifications

Detailed Solution for Test: Power Electronics - 1 - Question 4

Turn on and turn off times of similar SCRs may not be same.

Test: Power Electronics - 1 - Question 5

The amount of dielectric heating is inversely proportional to frequency.

Detailed Solution for Test: Power Electronics - 1 - Question 5

It is proportional to frequency.

Test: Power Electronics - 1 - Question 6

A semiconverter feeding an RLE load operates in

Detailed Solution for Test: Power Electronics - 1 - Question 6

Semiconvertor operates only in first quadrant.

Test: Power Electronics - 1 - Question 7

The phenomenon of overlap in converter operation due to

Detailed Solution for Test: Power Electronics - 1 - Question 7

Source inductance delays turn off and hence causes overlap.

Test: Power Electronics - 1 - Question 8

A thyristor has a maximum allowable junction temperature of 120ºC and the ambient temperature is 40ºC. If thermal resistance is 1.6º C/W, the maximum allowable internal power dissipation is

Detailed Solution for Test: Power Electronics - 1 - Question 8

.

Test: Power Electronics - 1 - Question 9

For a 12 pulse operation, the two 6 pulse units are fed by

Detailed Solution for Test: Power Electronics - 1 - Question 9

30� phase difference is necessary.

Test: Power Electronics - 1 - Question 10

In a single phase full wave converter (M - 2 connection) feeding a highly inductive load, the firing angle for each thyristor is a in the respective half cycle. The period of conduction of each thyristor is

Detailed Solution for Test: Power Electronics - 1 - Question 10

Since conduction is from a to p + a, period of conduction is p in each half cycle.

Test: Power Electronics - 1 - Question 11

An SCR is triggered at 40ºin the positive half cycle only. The average anode current is 50 A. If the firing angle is changed to 80º, the average anode current is likely to be

Detailed Solution for Test: Power Electronics - 1 - Question 11

.

Test: Power Electronics - 1 - Question 12

The characteristics of a non-linear resistance is i = kv4. If i becomes 100 times, v becomes

Detailed Solution for Test: Power Electronics - 1 - Question 12

v ∝ (i)1/4 ∝ (100)1/4 ≈ 3.

Test: Power Electronics - 1 - Question 13

In a step down chopper using pulse width modulation, Ton = 3 x 10-3 and Toff = 1 x 10-3 s. The chopping frequency is

Detailed Solution for Test: Power Electronics - 1 - Question 13

.

Test: Power Electronics - 1 - Question 14

Thyristors are suitable for dc circuit breakers but not for ac circuit breakers.

Detailed Solution for Test: Power Electronics - 1 - Question 14

They are suitable for both dc and ac circuit breakers.

Test: Power Electronics - 1 - Question 15

Assertion (A): Inverters and choppers use fast switching thyristors

Reason (R): Fast switching SCR has low turn off time.

Detailed Solution for Test: Power Electronics - 1 - Question 15

Low turn off time enables fast switching.

Test: Power Electronics - 1 - Question 16

The value of capacitor C for dynamic equalising circuit of series connected thyristors is determined by

Detailed Solution for Test: Power Electronics - 1 - Question 16

Value of C is proportional to maximum difference between reverse charge of SCRs in series.

Test: Power Electronics - 1 - Question 17

A chopper

Detailed Solution for Test: Power Electronics - 1 - Question 17

A chopper is a dc-ac converter. It converts a fixed dc voltage into a variable dc voltage.

Test: Power Electronics - 1 - Question 18

Assertion (A): If the duty cycle of chopper is low the current would not become discontinuous

Reason (R): If the time constant L/R of the load in chopper is low the current may become discontinuous.

Detailed Solution for Test: Power Electronics - 1 - Question 18

If duty cycle is low, current may become discontinuous.

Test: Power Electronics - 1 - Question 19

In a single phase full wave regulator, the firing angles in the positive and negative half cycles are generally

Detailed Solution for Test: Power Electronics - 1 - Question 19

Firing angles are kept equal to get symmetrical output voltage.

Test: Power Electronics - 1 - Question 20

An electric heater is controlled by thyristors through on-off control. If a = 0.4, the heating is

Detailed Solution for Test: Power Electronics - 1 - Question 20

Vl = V a. Therefore Vl2 - V2 (a). Heating is proportional to a.

Test: Power Electronics - 1 - Question 21

A two winding transformer is feeding a single phase half wave rectifier circuit. The load is purely resistive. The rms value of transformer secondary current is Is and rms value of load current in Irms. Then

Detailed Solution for Test: Power Electronics - 1 - Question 21

.

Test: Power Electronics - 1 - Question 22

The terminals of a power BJT are called

Detailed Solution for Test: Power Electronics - 1 - Question 22

In a BJT terminals are emitter, base and collector irrespective of rating.

Test: Power Electronics - 1 - Question 23

In single phase half wave regulator, the average current over one full cycle

Detailed Solution for Test: Power Electronics - 1 - Question 23

The input current during positive half cycle is less than that during negative half cycle.

Test: Power Electronics - 1 - Question 24

The dynamic equalising circuit consists of a series combination of capacitor C and resistor RC across each thyristor. This resistance RC (along with parallel connected diode)

Detailed Solution for Test: Power Electronics - 1 - Question 24

Discharge current flows through Re .

Test: Power Electronics - 1 - Question 25

A single phase semiconverter is feeding a highly inductive load and has freewheeling diode across the load. The waveshapes of output voltage and output current

Detailed Solution for Test: Power Electronics - 1 - Question 25

When freewheeling diode conducts output current exists but output voltage is zero.

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