Electricity Power Electronics Part One MCQ

Electricity Power Electronics Part One MCQ

1)   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 converter

2)   The quadrant operation of BJT is represented by

a. 1
b. 2
c. 3
d. 4

ANSWER: 2

3)   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

4)   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

5)   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

Electricity Power Electronics Part One MCQ

6)   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

7)   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

8)   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)

9)   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

10)   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

Electricity Power Electronics Part One MCQ

11)   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

12)   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

13)   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

14)   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

Electricity Power Electronics Part One MCQ

15)   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

16)   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

17)   In a three phase converter, the number of notches per cycle is
a. One
b. Three
c. Six
d. Nine

ANSWER: Six

18)   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

Electricity Power Electronics Part One MCQ

19)   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

20)   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

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)   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

Electricity Power Electronics Part One MCQ

23)   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

24)   In single phase VSI, the harmonic which is not present is
a. 2nd
b. 3rd
c. 5th
d. 7th

ANSWER: 2nd

25)   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

26)   Single phase VSI are mainly used in
a. Power supplies
b. Ups
c. Multilevel configuration
d. All of these

ANSWER: All of these

Electricity Power Electronics Part One MCQ

27)   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

28)   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

29)   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

30)   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

31)   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

32)   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

Electricity Power Electronics Part One MCQ

34)   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

35)   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

36)   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

37)   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

Electricity Power Electronics Part One MCQ

38)   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

39)   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

40)   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

 

41)   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

42)   In a square -wave operation of 3 phase CSIs, the power values are on for

a. 60 degree
b. 90 degree
c. 120 degree
d. 150 degree

ANSWER: 120 degree

Electricity Power Electronics Part One MCQ

43)   A carrier based PWM technique in CSI is composed of
a. A switching pulse generator and a shorting pulse generator
b. A shorting pulse distributor
c. A switching and shorting pulse combination
d. All of these

ANSWER: All of these

44)   In variable frequency, PWM gain
a. Phase lead helps to increase the mphase margin of the control loop
b. Phase lag helps to increase the phase margin of the control loop
c. Phase lead helps to decrease the phase margin of the control loop
d. Phase lag helps to decrease the phase margin of the control loop

ANSWER: Phase lead helps to increase the phase margin of the control loop

45)   In constant frequency PWM, at perturbation the amplitude of the sinusoidal component is a
a. Linear function
b. Non linear function
c. Constant function
d. None of these

ANSWER: None of these

46)   The transfer function of PWM is generally developed in
a. Time domain
b. Frequency domain
c. Either (a) or (b)
d. None of these

ANSWER: Either (a) or (b)

47)   In the SPWM, the modulating signal is
a. Square
b. Sinusoidal
c. Triangular
d. Saw – tooth

ANSWER: Sinusoidal

Electricity Power Electronics Part One MCQ

48)   In a full bridge VSI, in order to avoid the short circuit across the DC bus and the undefined AC output voltage condition, the modulating technique should ensure that
a. Top switch of each leg is on at any instant
b. Bottom switch of each leg is on at any instant
c. Either (a) or (b)
d. None of these

ANSWER: Either (a) or (b)

49)   In a lossless inverter, the average power absorbed in one period by the load must be
a. Equal to the average power supplied by the dc source
b. Greater than the average power supplied by the dc source
c. Lesser than the average power supplied by the dc source
d. Equal to the average power supplied by the ac source

ANSWER: Equal to the average power supplied by the dc source

50)   A step – down choppers can be used in
a. Electric traction
b. Electric vehicles
c. Machine tools
d. All of these

ANSWER: All of these

Electricity Power Electronics Part One MCQ

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