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Test: SCR Commutation Techniques


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20 Questions MCQ Test Power Electronics | Test: SCR Commutation Techniques

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

The thyristor turn-off requires that the anode current

Detailed Solution for Test: SCR Commutation Techniques - Question 1

 For effective turn-off of the SCR the anode current must fall below the holding current value.

Test: SCR Commutation Techniques - Question 2

 In case of class A type commutation or load commutation with low value of R load the

Detailed Solution for Test: SCR Commutation Techniques - Question 2

In case of Class A commutation the requirement is that the circuit should be an under-damped RLC circuit.

Test: SCR Commutation Techniques - Question 3

The class A commutation or load commutation is possible in case of

Detailed Solution for Test: SCR Commutation Techniques - Question 3

 The nature of the circuit should be such that when energized from the source, current must a a natural tendency to decay to zero for load commutation to occur in a SCR circuit.

Test: SCR Commutation Techniques - Question 4

In case of class B commutation or resonant-pulse commutation with L = 5 μH and C = 20 μC with initial voltage across the capacitor (Vs) = 230 V. Find the peak value of resonant current.

Detailed Solution for Test: SCR Commutation Techniques - Question 4

Ip = Vs x √C/L.

Test: SCR Commutation Techniques - Question 5

 In case of class B commutation or resonant-pulse commutation with L = 5 μH and C = 20 μC with the initial voltage across the capacitor (Vs) = 230 V. Find the conduction time for auxiliary thyristor.

Detailed Solution for Test: SCR Commutation Techniques - Question 5

Ip = Vs x √C/L
ω = 1/√LC
t = π/ω.

Test: SCR Commutation Techniques - Question 6

An SCR is connected in series with L = 5 mH and C = 20 μF. Find the resonant frequency of the circuit.

Detailed Solution for Test: SCR Commutation Techniques - Question 6

ω = 1/√LC.

Test: SCR Commutation Techniques - Question 7

The type of commutation when the load is commutated by transferring its load current to another incoming thyristor is

Detailed Solution for Test: SCR Commutation Techniques - Question 7

In the Class C type commutation also called as complementary commutation the load is commutated by transferring the current th another device.

Test: SCR Commutation Techniques - Question 8

The type of commutation in which the pulse to turn off the SCR is obtained by separate voltage source is

Detailed Solution for Test: SCR Commutation Techniques - Question 8

In class E commutation, another voltage source is used. It is also called as external pulse commutation.

Test: SCR Commutation Techniques - Question 9

The natural reversal of ac supply voltage commutates the SCR in case of

Detailed Solution for Test: SCR Commutation Techniques - Question 9

 Both line and natural commuataion are used in converters.

Test: SCR Commutation Techniques - Question 10

 ___________ commutation technique is commonly employed in series inverters.

Detailed Solution for Test: SCR Commutation Techniques - Question 10

Load commuation is used in inverter in which L and C are connected in series with the load or C in parallel with the load such that overall load circuit is under damped.

Test: SCR Commutation Techniques - Question 11

 For the circuit shown in the figure below,

C = 4 pF
L = 16 μH
Vs = 200V
The capacitor voltage after the SCR is self commutated is

Detailed Solution for Test: SCR Commutation Techniques - Question 11

It is simply the negative of Vs as it is a series circuit & after turn off the whole voltage appears across the thyristor.

Test: SCR Commutation Techniques - Question 12

 For the circuit shown below,

The maximum value of current through thyristors T1 & TA can be given by

Detailed Solution for Test: SCR Commutation Techniques - Question 12

 I1 = (Vs/R)
T2 = (Vs√C/L).

Test: SCR Commutation Techniques - Question 13

For the circuit shown in the figure below,

C = 4 pF
L = 16 μH
Vs = 200 V
The peak thyristor current is

Detailed Solution for Test: SCR Commutation Techniques - Question 13

The peak SCR current is Vs/2.

Test: SCR Commutation Techniques - Question 14

For the circuit shown in the figure below, ___ type of commutation would take place for the SCR (THY1)

Detailed Solution for Test: SCR Commutation Techniques - Question 14

The given figure is that of a class B commutation or resonant-pulse commutation, which is a type of forced commutation technique.

Test: SCR Commutation Techniques - Question 15

For the circuit shown in the figure below

R1 = 50 Ω, R2 = 100 Ω, Vs = 100 V. At the time of turn-on of the SCR, initial thyristor current is

Detailed Solution for Test: SCR Commutation Techniques - Question 15

 Io = Vs x [(2/R1)+(1/R2)].

Test: SCR Commutation Techniques - Question 16

 Natural commutation of an SCR takes place when

Detailed Solution for Test: SCR Commutation Techniques - Question 16

Anode current (load current) becomes zero and turns off the device, hence the name line commutation.

Test: SCR Commutation Techniques - Question 17

 ___________ commutation is usually used in phase-controlled rectifiers

Detailed Solution for Test: SCR Commutation Techniques - Question 17

 Line commuataion is used in converters.

Test: SCR Commutation Techniques - Question 18

Parallel-capacitor commutation is

Detailed Solution for Test: SCR Commutation Techniques - Question 18

 Parallel capacitor is another name for forced commutation.

Test: SCR Commutation Techniques - Question 19

Class E commutation is a/an

Detailed Solution for Test: SCR Commutation Techniques - Question 19

As an external source is used it is a external-pulse commutation technique.

Test: SCR Commutation Techniques - Question 20

Below is the circuit of a resonant-pulse commutation, the maximum voltage to which the capacitor C charges is

Detailed Solution for Test: SCR Commutation Techniques - Question 20

 The capacitor charges from 0 to Vs with the right side plate positive.

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