Answer: a

Explanation: The term MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor. It is one of the most common transistors in digital electronics. It is a majority charge carrier device with the fastest switching because it does not have minority charge carriers which take more time in settling down.

Answer: b

Explanation: Snubber circuit refers to a kind of DV/dt protection circuit of the thyristor. It is used to limit the high rate of change of voltage from cathode to anode. It is usually used to protect SCR thyristor from high DV/dt and di/dt stress.

Answer: b

Explanation:

Answer: c

Explanation:

Given, ∅=30⁰

We know that,

Displacement factor = cos?∅ = cos30⁰ =

Answer: d

Explanation: The forward blocking mode of a silicon-controlled rectifier refers to a mode when the anode is made positive with respect to the cathode. It is also called off state.

Answer: c

Explanation: SCR stands for Silicon Controlled Rectifier. Once the SCR is turned on, it will remain in the same conducting state until the anode current becomes lower than the holding current.

Answer: b

Explanation: Once the SCR gets active or in on state, the gate current has no control over it. So the value of current remains unchanged.

Answer: b

Explanation: The term turns off means that it has changed its form from on to off state and capable of blocking the forward voltage.

Answer: b

Explanation: We know that for a single-phase full-wave rectifier

Answer: b

Explanation: TRIAC is an abbreviation for a three-terminal ac switch. If we divide TRIAC, we get TRI ana AC. “TRI,” as the name suggests that the device consists of three terminals, and “AC” means that the device controls the alternating current. It is a four-layer, 3 terminal bidirectional device.

Answer: a

Explanation:

Given;

Maximum input voltage = 10 V

We know that, for half wave rectifier circuit

And rms value of the output voltage

Answer: b

Explanation: Given;

EMF of a solar cell = 450 V

DC current I_dc = 10 A

Resistance of solar cell, R_cell = 1 ?

We know that, Voltage across the inverter = output voltage of the solar cell,

V_out = -(450 – 10 × 1) = -440 V

For three phase controlled bridge

Answer: c

Explanation:

Answer: b

Explanation: Most suitable power device for higher frequency (above 100 kHz) switching application is power MOSFET because it has lower switching losses. So, for lower frequency switching applications, BJT is used.

Answer:

Explanation: IGBT stands for Insulated Gate Bipolar Transistor. It includes the best features of power MOSFETS and power transistors(BJT). Same as a MOSFET, it has low input capacitance and high input impedance. In one state, it has low resistance and high current controlling capacity like a BJT.

Answer: b

Explanation: The thyristor is known as SCR because it is a silicon device used as a rectifier and that rectification can be controlled. It is made up of silicon only because the leakage current in silicon is less than that of germanium. If any device is used as a switch, it is necessary that leakage current must be minimum.

Answer: c

Explanation: The formula to caculate the even harmonics are given as

= 2f_S= 2 × 50 = 100 Hz

Answer: b

Explanation:

Given;

α = 30⁰

µ = 20⁰

We know that the fundamental power factor or displacement factor at input ac mains.

Answer: c

Explanation:

Given;

Firing angle α =

We know that the average output voltage of a semiconductor is given as

Answer: b

Explanation: Freewheeling diode is also called bypass diode or commutating diode. It is used to improve the waveform of the loaded current and power factor. It is connected across a realy, which is driven by a transistor. It enables for dissipation of energy stored in the inductance of the load in the circuit and provides a continuous flow of load current when the thyristor is blocked.

Answer: a

Explanation: In a three-phase bridge rectifier, the maximum conduction of each thyristor is 120⁰

Answer: b

Explanation: In a three-phase controlled bridge rectifier, the ripple frequency in the output voltage depends on supply frequency. The frequency of ripple in the output voltage

F_out = total number of pulses × supply frequency

In a 3-Ø controlled bridge rectifier, the ripple frequency in the output voltage is 6 times the supply frequency.

Answer: b

Explanation: We know that,

Answer: c

Explanation: A three-phase converter has an additional feature that it works as a 6 pulse converter for firing angle α <and as a three pulse converter for firing angle α ≥

Answer: c

Explanation: As we know, a three-phase full controlled converter operates in only two quadrants (First and Fourth).

Answer: b

Explanation:

Given;

V = 210

I = 90 A

α= 60⁰

We know that, Shunt compensation

= VI tan alpha;

Putting the value V , I, and αin above equation we get

= 210 × 90 tan 60⁰

= 72, 735 VAR = 72.8 KVAR

And power factor =

Cos α= Cos 60⁰ = 0.5

Answer: c

Explanation: Buck-boost regulator provides output voltage polarity reversal without a transformer. The buck-boost converter refers to a voltage regulator used to regulate dc power supplies. A negative polarity output may be required with respect to the same terminal of the input voltage. The output voltage can be either more or less than the input voltage.

Answer: d

Explanation: Choppers refer to a static switch used to provide Variable DC voltage from a constant DC voltage source. It is a DC to DC converters. It can be either step up or step down DC to DC converter. In Step up DC converter, the output voltage is less than the input voltage. It is also known as Buck converter. In step-up, DC converter, which is also called Boost Converter, is opposite to buck converter. There is also a converter based on the combination of these two; it works in both buck and boost mode depending upon operating conditions; this type of chopper is called Buck-Boost Converter.

Answer: c

Explanation:

Given;

V_out = 180 V

V_s = 220 V

f = 4 kHz = 4 × 10 ³

We know that,

Answer: b

Explanation: A cycloconverter is a kind of AC to AC converter based on thyristors that converts AC at one frequency to ac of another frequency without the involvement of a dc source. It is used primarily to increase or decrease the frequency of the output voltage(s) with respect to the frequency of the input voltage(s), without using any AC-DC nor DC-AC converters during the process. The supply side of the cycloconverter is considered as the input, while the load side is considered the output of it.

Answer: c

Explanation:

Given;

Source voltage= V

Duty cycle = α

We know that

The average value of output voltage of the step-up chopper is given as

Where

V is the voltage source, and α is the duty cycle.

Answer: c

Explanation: 18 switches are required to construct a three-phase to three-phase cycloconverter. Three phases of a three-phase cycloconverter need three sets of three-phase half-wave circuits, and each circuit needs 6 thyristors. So the total number of thyristors required is 18.

Answer: b

Explanation: A three-phase to three-phase cyclo converter requires 36 SCRs for 6 pulse devices.

Answer: d

Explanation:

Given;

Total number of pulses (m) = 6

Input phase voltage (V_P) = 220 V

We know that the fumdamental value of rms output voltage is given by

Answer: c

Explanation:

Given,

V_out(rms)= 240 V

m = 3 (for 3 phase)

We know that the fumdamental value of rms output voltage is given by

Answer: a

Explanation:

Given,

Vs = 60

We know that the fundamental component of the output voltage of a single-phase half-bridge inverter is given as

Answer: d

Explanation: PWM stands for Pulse Width Modulation. It is used in the voltage source inverter to control the output voltage and output harmonics. It is a method of controlling the average power of a signal over a continuous range by switching it between on and off states. It is a method of generating amplitude modulation. By increasing the number of pulses per half cycle, the order of harmonic frequency increases so that the filter’s size is reduced.

Answer: c

Explanation:

Given pulse duration (d) = 60⁰

Vs = 240 V

We know that pulse width is given as

2d = 60⁰

D = 30⁰

So the RMS value of the fundamental component of the output voltage is given as

Answer: a

Explanation:

Given,

Starting toque Test of the motor = 18 Nm

Load toque T_L= 9 Nm

Accelarating toque Ta = Tst- T_L = 18 Nm – 9 Nm = 9 Nm

Accelaration α =3 rad/sec²

We know thar moment of inertia is given as

Answer: b

Explanation: 3-∅ semiconverter drive only in a single quadrant; therefore, the moto can operate only in the first quadrant, which has positive speed and positive toque.

Answer: b

Explanation:

Given,

Rated speed (N₁) = 1200 rpm

Voltage across the armature (V_a1) = 240 V

Armature current (I_a) = 30 A

Armature resistance (R_a) = 3 ohm

Rated speed (N₂) = 700 rpm and V_s=280 V

We know that,

The rated speed of 1200 rpm voltage across the motor armature,

V_a1= E_b1+ I_a R_a

E_b1 = V_a1– I_a R_a

= 240 – 30 × 3

= 240 – 90 = 150 V

At 700 rpm,

At rated toque, armature current will also be rated that is 30 A because the current is directly proportional to the toque

So the applied voltage

V_a2= E_b2+ I_a R_a

= 87.5 + 30 × 3

= 177.5 V

So the duty ratio,

Answer: c

Explanation:

Given,

The back emf constant of the motor E_b = 0.30 V/rpm

Armature current (I_a) = 8 A

Armature resistance (R_a) = 3 ohm

V_max = 240 V

Firing angle α = 60⁰

We know that,

The average output voltage of a single phase half controlled rectifier is given as

Answer: a

Explanation: Ripple frequency refers to a frequency of the residual AC voltage. After that, it has been rectified to DC in a power supply. Because of higher ripple content in the converter output motor, heating and commutating problems arise. It works on high DC voltage. For a half-wave rectifier, the value of ripple frequency i the same as the AC frequency, and for a full-wave, the value of ripple frequency is twice the original AC frequency.

Answer: c

Explanation: We know that the voltage is directly proportional to the speed. Therefore smoother voltage shape is achieved at a higher speed.

Answer: c

Explanation: Single-phase induction motors work on single-phase AC supply. It has two windings; Main windings and auxiliary winding. For speed control of a single-phase induction motor by an ac voltage controller, and only a fundamental component of current is required to develop a toque. The harmonics in the motor current may cause power losses resulting in heating of the motor.

Answer: b

Explanation:

Given,

Normally a 4-ohm resistor is connected to the rotor circuit during off periods; r = 8 ohm is additional

T_off = 6 ms

f = 200 Hz

We know that frequency is reciprocal of a period

So,

Answer: c

Explanation:

As we know,

The synchronous motor always runs at synchronous speed

Where,

f = frequency

p = number of poles.

So the rotor speed is decided by the stator frequency supply.

Answer: b

Explanation:

Given,

DC link current I_d = Constant

DC link voltage V_d = 450 V

P = 60×10³

So, the power supllied to the motor is given as

P = V_d I_d

Answer: b

Explanation: Cycloconverters are mainly used where precise speed control is needed. It means cycloconverter is not suitable for cement mill drive as well as compressor drive. Papermill requires constant speed drive. So cycloconverter fed induction motor drive is widely used for machine tool drive.

Answer: d

Explanation: Two quadrant chopper is used for both regenerative and motoring breaking.

Answer: d

Explanation:

:

Given,

V_out = 400 V

Duty cycle α = 0.6

Armature current I_S = 80 A

We know that for regenerative mode, chopper os worked as a step-up chopper

Therefore,

= 600(1 – 0.6) = 240 V

Now the power supplier back to the supply

= V_S I_S = 240 × 80 = 19200 W

Answer: a

Explanation: A power diode refers to a semiconductor device that is used to convert alternating current to direct current. It consists of two terminals, cathode and anode, the same as that of a normal diode. A power diode is nothing but a signal diode with an extra layer.

Answer: d

Explanation: V- I characteristics of diode lies in the first and third quadrant. The first quadrant works in the forward region, and the third quadrant works in reverse biased mode.

Answer: b

Explanation:

In a six-phase half-wave rectifier, usually six diodes are used. Since the supply frequency is 50 z, therefor the ripple frequency is six-time that of the power supply

= 50 × 6 = 300 Hz

Answer: b

Explanation: Displacement factor refers to the power factor due to the phase shift between voltage and current at fundamental line frequency.

SO,

The displacement power factor is given as = Cos?

? is 60⁰

Therefore, Cos60⁰ = 0.5

Answer: b

Explanation: PN junction diode refers to a diode that is formed when a p-type semiconductor is fused with an n-type semiconductor. It creates a potential barrier across the diode junction. In forward biasing conditions, the PN junction diode acts as a closed switch.

Answer: b

Explanation:

Given,

Current Gain β = 400

Base current I_B = 8mA

The dc current gain β_dc refers to the collector current ratio to base current at constant V_CE under dc biasing conditions.

Answer: b

Explanation: The two-transistor models of an SCR are obtained by bisecting the SCRs top and bottom two layers. SCR is a unidirectional device that works like a diode. It enables current to flow in a single direction only.

Answer: c

Explanation:

Given,

Slope = 160

We know that

Power is defined as the product of voltage and current

Therefore,

P = V_g× I_g = 0.8

Slope V_g / I_g = 160

V_g = 160 × I_g

160 I²_g = 0.8

I_g = 71 mA