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QUESTION: 1

The below shown single phase controlled rectifier configuration is a

Solution:

It is a two pulse i.e full wave M-2 connection.

QUESTION: 2

In the below shown circuit, considering the load to be purely R load, the thyristor T2 would conduct from ωt =

Solution:

The bottom winding forward biases the SCR T2 at π, conduction starts after the pulse is given at α & stops when T2 is naturally commutated at 2π.

QUESTION: 3

For a single pulse M-2 rectifier with RL load and firing angle α >0°, the value of the inductance L is such that the load current is continuous.

Choose the correct statement.

Solution:

As mentioned, L is such that the load current is continuous. Hence, it never falls below a predefined positive value.

QUESTION: 4

For the circuit below, the transformer ratio is 1:1 and Vs = Vm sinωt. When T1 is forward biased and is triggered at α than T2 is

Solution:

When T1 is gated, the other SCR T2 is reversed biased due to the windings so connected.

QUESTION: 5

The circuit turn-off time of M-2 type connection is

Solution:

When T1 is gated, SCR T2 is off from ωt = α to π

Thus t = π-α(offtime)/ω

Same can be said when T2 is gated and T2 is off.

QUESTION: 6

Find the expression for the average value of the output voltage for the below given circuit. Consider the load current to be continuous, firing angle = α, transformer ration 1:1 and Vs = Vm sinωt.

Solution:

As the load current is continues, the voltage is positive from α to π and negative from π to π+α and so on. Thus,

Vavg = 1/Period ∫ Vm sinωt d(ωt)

Where period = π

And the integral runs from α to α+π.

QUESTION: 7

A fully controlled converter uses

Solution:

Fully controlled implys that all the elements are “fully controlled” hence, it uses SCRs only except the FD.

QUESTION: 8

A single phase full-converter using R load is a _________ quadrant converter and that using an RL load without FD is a __________ quadrant converter

Solution:

In R load both V and I are positive, in RL load the voltage can be negative but current is always positive.

QUESTION: 9

A single phase full controlled bridge converter (B-2) uses

Solution:

4 SCR’s are connected in a bridge fashion.

QUESTION: 10

In a B-2 type full controlled bridge converter

Solution:

B-2 is the bridge type controller, in which 2 devices conduct at a time. One acting as the current supplying path and other acts as a return path.

QUESTION: 11

For the below given circuit,

Solution:

T1-T2 are gated together at a time and T3-T4 are gated together at a time.

QUESTION: 12

With respect to the below given circuit, from ωt = 0 to α, ____ thyristor(s) block the forward voltage

Solution:

T1 and T2 are not yet gated, hence they block the forward voltage.

QUESTION: 13

With respect to the below given circuit, from ωt = 0 to α,

Solution:

T1 and T2 are not yet gated, hence they block the forward voltage where as no voltage exists across T3 and T4.

QUESTION: 14

For the below given circuit, when the devices T1 and T2 are conducting from ωt = α till they are naturally commutated at π voltage across the other two pair of devices is

Solution:

When T1 and T2 are conducting they act like S.C’s and the other pair of devices i.e. T3 and T4 has to take care of the reverse voltage.

QUESTION: 15

A single-phase full converter B-2 type connection has a RLE type of motor load connected. The minimum requirement to turn-on the device is

Solution:

Device will not turn on until the supply voltage exceeds the motor back emf E.

QUESTION: 16

For the below shown circuit with continuous load current.

Each thyristor pair conducts for

Solution:

As the load current is continuous each pair conducts from π to π+α i.e π radians.

QUESTION: 17

For the below given circuit

Solution:

T1-T2 are gated together at a time and T3-T4 are gated together at a time.

QUESTION: 18

For the below shown circuit has dis-continuous load current waveform.

Each thyristor pair conducts for

Solution:

Load current is discontinues than SCR pair conducts for less than 90° depending on the value of the inductor L.

QUESTION: 19

A single-phase full converter with B-2 type of connection has a continuous load current waveform. The thyristor pairs T3, T4 is triggered at ωt =

Solution:

First, at α T1-T2 conduct, then after π+α the next pair is excited i.e. T3-T4 and likewise.

QUESTION: 20

The PIV for each diode in a single-phase, full converter with B-2 type of controlled rectifier is

Consider supply voltage as Vs = Vm sinωt.

Solution:

The peak inverse voltage handled by each device is Vm in case of B-2 type of configuration.

QUESTION: 21

A motor load is connected to a single-phase full converter B-2 type controlled rectifier. The net energy is transferred from ac source to the motor (dc load) when

Solution:

Converter will work as a line commuted inverter when π-α > α.

QUESTION: 22

The below shown rectifier configuration has continues load current, find the expression for the average value of output voltage when the supply Vs = Vm sinωt is connected.

Solution:

Vo = 1/π x [∫ Vm sinωt d(ωt)] Where the integration runs from α to π+α.

QUESTION: 23

Find the expression of the rms value of output voltage for a single-phase M-2 type rectifier with RL load and continues load current. Transformer ratio is 1:1 with supply voltage Vs = Vm sinωt

Solution:

Vor^{2} = 1/π x [∫ Vm^{2} sin^{2}ωt d(ωt)], Where the integration runs from α to π+α

Vor = Vm^{2}/2 = Vs.

QUESTION: 24

A single-phase full controlled converted with RLE load will act like a line-commutated inverter when the firing angle α

Solution:

It will act like a inverter i.e. most of the current would flow from the battery or back emf E to the source. For α=90° it will not act like a converter nor an inverter.

QUESTION: 25

In converter operation, with output voltage = Vo and RLE load.

Solution:

The output voltage obtained by a converter is always greater than the counter or back emf E.

Vo = IR + E.

QUESTION: 26

In inverter operation, with output voltage = Vo and a RLE load connected

Solution:

In inverter operation Vo < E.

QUESTION: 27

A motor load is connected to a single-phase full converter B-2 type controlled rectifier, the net energy is transferred from ac source to the motor (dc load) when

Solution:

It works as a converter when π-α < α.

QUESTION: 28

The below shown rectifier configuration has continues load current, find the expression of the RMS value of output voltage when the supply Vs = Vm sinωt

Solution:

Vor^{2} = 1/π x [∫Vm^{2} sin^{2}ωt d(ωt)] Where the integration runs from α to π+α

Vor = Vm^{2}/2 = Vs.

QUESTION: 29

Choose the correct statement

Solution:

The PIV of diodes in M-2 is 2Vm, whereas that in B-2 type of connection is Vm.

QUESTION: 30

An SCR has the peak forward voltage = 1000 V. Find the maximum voltage that the SCR can handle if employed in a M-2 type full controlled converter circuit. Use factor of safety (FOS) = 2.5

Solution:

In M-2 type configuration maximum voltage handled is 2Vm

Therefore, 1000/2×2.5 = 200 V.

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