Power Electronics Expected MCQ PDF 3 For Coal India Limited (CIL) MT Exam 2017


1)   Silicon controlled rectifier can be turned on
a. By applying a gate pulse and turned off only when current becomes zero
b. And turned off by applying gate pulse
c. By applying a gate pulse and turned off by removing the gate pulse
d. By making current non zero and turned off by making current zero

ANSWER: By applying a gate pulse and turned off only when current becomes zero
2)   TRIAC is a semiconductor power electronic device which contains
a. Two SCR’s connected in reverse parallel
b. Two SCR’s connected in parallel
c. Two SCR’s connected in series
d. Two BJT’s connected in series

ANSWER: Two SCR’s connected in reverse parallel
3)   An SCR can be used
a. as static conductor
b. for power control
c. for speed control of dc shunt motor
d. all of these

ANSWER: all of these
4)   A crowbar is a circuit which is used to protect a
a. voltage sensitive load from excessive dc power supply output voltages
b. current sensitive load from excessive dc power supply output voltages
c. voltage sensitive load from excessive ac power supply output voltages
d. current sensitive load from excessive ac power supply output voltages

ANSWER: voltage sensitive load from excessive dc power supply output voltages
5)   A full wave rectifier with resistive load produces
a. Second harmonic
b. Third harmonic
c. Fifth harmonic
d. Do not produce harmonics

ANSWER: Do not produce harmonics
6)   The input current waveform of a bridge controlled rectifier when the load is perfectly filtered is
a. Sine wave
b. Square wave
c. Saw – tooth wave
d. Trapezoidal wave

ANSWER: Square wave
7)   The advantage of using free – wheeling diode in half controlled bridge converter is that
a. There is always a path for the dc current independent of the ac line
b. There is always a path for the ac current independent of the ac line
c. There is always a path for the dc current dependent of the ac line
d. There is always a path for the ac current independent of the ac line

ANSWER: There is always a path for the dc current independent of the ac line
8)   Harmonics in 3 phase inverters can be reduced by using
a. Passive filter
b. Active filter
c. Both passive and active filters
d. None of these

ANSWER: Both passive and active filters
9)   The most suited gate pulses given to the AC regulator with R – L load can be in the form of
a. Continuous signal
b. Large isolating pulse transformer
c. A train of pulses
d. None of these

ANSWER: A train of pulses
10)   With increase in firing angle,
a. Both harmonic distortion and quality of input current increases
b. Harmonic distortion increases and quality of input current decreases
c. Harmonic distortion decreases and quality of input current increases
d. Both harmonic distortion and quality of input current decreases

ANSWER: Harmonic distortion increases and quality of input current decreases
11)   The power MOSFET device is a
a. Current controlled unipolar device
b. Voltage controlled unipolar device
c. Current controlled bipolar device
d. Voltage controlled bipolar device

ANSWER: Voltage controlled unipolar device
12)   The conduction losses in IGBT is
a. More than that of MOSFET
b. Lower than that of MOSFET
c. Equal to that of MOSFET
d. Equal to that of BJT

ANSWER: Lower than that of MOSFET
13)   For a buck converter to reduce the conduction losses in diode
a. A high on – resistance switch can be added in parallel
b. A low on – resistance switch can be added in parallel
c. A high on – resistance switch can be added in series
d. A low on – resistance switch can be added in series

ANSWER: A low on – resistance switch can be added in parallel
14)   For bidirectional operation of converters
a. A parallel combination of controllable switch and a diode is used
b. A parallel combination of controllable switch and capacitor is used
c. A series combination of controllable switch and a diode is used
d. A series combination of controllable switch and a capacitor is used

ANSWER: A parallel combination of controllable switch and a diode is used
15)   Single phase VSI are mainly used in
a. Power supplies
b. Ups
c. Multilevel configuration
d. All of these

ANSWER: All of these
16)   Very large values of modulation index (greater than 3.24) lead to
a. Square AC output voltage
b. Sine AC output voltage
c. Triangular AC output voltage
d. Trapezoidal AC output voltage

ANSWER: Square AC output voltage
17)   In single phase VSI, the harmonic which is not present is
a. 2nd
b. 3rd
c. 5th
d. 7th

ANSWER: 2nd
18)   Double fourier series analysis of PWM is
a. Two dimensional functions
b. Three dimensional functions
c. One dimensional functions
d. All of these

ANSWER: Two dimensional functions
19)   In bipolar modulation, the carrier is symmetric about zero with amplitude equal to Cm, the PWM output
a. Zero
b. Switches between – 1 / 2 and + 1 / 2
c. Switches between – 1 and + 1
d. Switches between 0 and + 1

ANSWER: Switches between – 1 / 2 and + 1 / 2
20)   Unipolar modulation is generally used in
a. AC – AC converters
b. AC – DC converters
c. DC – AC converters
d. DC – DC converters

ANSWER: DC – DC converters
21)   The square wave operation of 3 phase VSI lines contains the harmonics. The amplitudes are
a. Directly proportional to their harmonic order
b. Inversely proportional to their harmonic order
c. Not related to their harmonic order
d. None of these

ANSWER: Inversely proportional to their harmonic order
22)   Under harmonic free load voltages, the 3 phase VSI
a. Does not contains second harmonic
b. Does not contains third harmonic
c. Does not contains fifth harmonic
d. Does not contains seventh harmonic

ANSWER: Does not contains second harmonic
23)   For similar carrier and modulating signals, the line current used in CSI is
a. Identical to line voltage in a VSI
b. Identical to line current in VSI
c. Identical to phase voltage in VSI
d. Identical to phase voltage in CSI

ANSWER: Identical to line voltage in a VSI
24)   In a 3 phase
CSI, if the required line output voltages are balanced and 120 degree
out of phase, then the chopping angles are used to eliminate only the
harmonics at frequencies

a. 5
b. 7
c. 11
d. All of these

ANSWER: All of these
25)   In a three phase converter, the number of notches per cycle is
a. One
b. Three
c. Six
d. Nine

ANSWER: Six
26)   During the commutation period in 3 phase converter, overlap time is
a. Dependent on the load current
b. Dependent on the voltage
c. Dependent on both the load current and load voltage behind the short circuit current
d. Independent on both the load current and load voltage

ANSWER: Dependent on both the load current and load voltage behind the short circuit current
27)   Between the incoming and outgoing devices in voltage commutation
a. Large overlapping takes place
b. Small overlapping operation
c. No overlapping operation
d. None of these

ANSWER: No overlapping operation
28)   The effects of EMI can be reduced by
a. Suppressing emissions
b. Reducing the efficiency of the coupling path
c. Reducing the susceptibility of the receptor
d. All of these

ANSWER: All of these
29)   In radiative coupling, the emitter radiation field
a. Decays as 1 / R, where R is the separation distance between the emitter and the receptor
b. Decays as R, where R is the separation distance between the emitter and the receptor
c. Decays as 1 / 2 R, where R is the separation distance between the emitter and the receptor
d. Decays as 2R, where R is the separation distance between the emitter and the receptor

ANSWER: Decays as 1 / R, where R is the separation distance between the emitter and the receptor
30)   In EMC
signal, the source delivers maximum power to the input of transmission
line when the transmission line input impedance

a. Is equal to the source resistance
b. Greater than the source resistance
c. Smaller than the source resistance
d. None of these

ANSWER: Is equal to the source resistance
31)   For swept
frequency measurements, the input impedance of the mismatched
transmission line would vary with frequency as the electrical length of
the transmission line would

a. Decrease with frequency
b. Remains same with change in frequency
c. Increase with frequency
d. Either (a) or (b)

ANSWER: Increase with frequency
32)   Voltage commutation circuit can be converted into a current commutation by interchanging the positions of
a. Diode and capacitor
b. Capacitor and SCR
c. Inductor and capacitor
d. Capacitor and load

ANSWER: Diode and capacitor
33)   In a load commutated DC – DC chopper, the capacitor has a
a. Symmetric triangular voltage across itself
b. Symmetric rectangular voltage across itself
c. Symmetric trapezoidal voltage across itself
d. Symmetric sinusoidal voltage across itself

ANSWER: Symmetric trapezoidal voltage across itself
34)   In current commutated DC-DC choppers, the voltage spike appears across the load when
a. Voltage across the commutating inductances collapses
b. The capacitance voltage adds to the supply voltage
c. Both (a) and (b)
d. None of these

ANSWER: Both (a) and (b)
35)   LISN is a device used to measure conducted emissions. LISN stands for
a. Line integrated stabilization network
b. Line impedance stabilization network
c. Line integrated stored network
d. Laser integrated stabilization networking

ANSWER: Line impedance stabilization network
36)   The output power of the cascaded amplifier / attenuator system can be determined using
a. Actual gain of amplifier
b. Actual gain of amplifier and attenuator
c. Gain in dB of amplifier and attenuator
d. Actual gain of attenuator

ANSWER: Actual gain of amplifier and attenuator
37)   An SCR is made up of silicon because
a. silicon has large leakage current than germanium
b. silicon has small leakage current than germanium
c. silicon has small leakage voltage than germanium
d. silicon has large leakage voltage than germanium

ANSWER: silicon has small leakage current than germanium
38)   AC power in a load can be controlled by using
a. two SCR’s in parallel opposition
b. two SCR’s in series
c. three SCR’s in series
d. four SCR’s in series

ANSWER: two SCR’s in parallel opposition
39)   The switching function of semiconductor devices can be characterized with
a. Duty ratio only
b. Frequency only
c. Duty ratio and frequency
d. Duty ratio, frequency and time delay

ANSWER: Duty ratio, frequency and time delay
40)   The quadrant operation of BJT is represented by

a. 1
b. 2
c. 3
d. 4

ANSWER: 2

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Power Electronics Expected MCQ PDF 2 For Coal India Limited (CIL) MT Exam 2017

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