# Power Electronics Expected MCQ PDF 1 For Coal India Limited (CIL) MT Exam 2017

1)   A rectifier with an external low pass filter is an example of
a. Indirect switch matrix circuits
b. Direct switch matrix circuits
c. Embedded converters
d. All of these

2)   In ac – dc conversion, when the switch is closed then the sum of voltages around the loop is
a. Zero
b. Non zero
c. Equal to the sum of voltage when switch is open
d. Twice of the voltage when switch is open

3)   An ideal switch is
a. Lossless
b. Carry current in any direction when it is on
c. Does not carry any current in any direction when it is off
d. All of these

4)   IGBT stands for
a. Insulated gate bipolar transistor
b. Insulated gate bidirectional transistor
c. Inductive gate bipolar transistor
d. Inductive gate bidirectional transistor

5)   Number of PN junction in an SCR is
a. Two
b. Three
c. Four
d. Five

6)   In a silicon controlled rectifier, the load is connected
a. Across anode
b. In series with anode
c. Across cathode
d. In series with cathode

7)   Anode of an operational SCR is
a. Always positive w.r.t cathode
b. Always negative w.r.t anode
c. Always positive w.r.t anode
d. Always negative w.r.t cathode

8)   If the gate voltage of an SCR is removed, then the
a. anode current decreases
b. anode current does not decrease at all
c. anode current increases
d. cathode current increases

 ANSWER: anode current does not decrease at all
9)   A single phase ac – dc converter is also known as
a. rectifier
b. inverter
c. chopper
d. regulator

10)   In a single phase full wave rectifier, during blocking state the peak inverse voltage of diode is
a. V m
b. 2 V m
c. V m / 2
d. 4 V m

11)   In a full wave rectifier, the rectification ratio is approximately equal to
a. 61%
b. 71%
c. 81%
d. 91%

12)   For power output higher than 15 kW, the suitable rectifier is
a. Single phase
b. 3 phase
c. Poly phase
d. Only (b) and (c)

13)   The sum of all phase current in a star connected primary winding with no neutral connection is equal to
a. Phase current
b. Three times the phase current
c. Three times the line current
d. Zero at all times

14)   In a 3 phase bridge rectifier the ripple frequency is
a. Equal to the input frequency
b. Twice the input frequency
c. Three times the input frequency
d. Six times the input frequency

 ANSWER: Six times the input frequency
15)   DIAC are specifically designed to trigger
a. TRIAC
b. SCR
c. GTO
d. Only (a) and (b)

16)   As the breakdown voltage reached, the DIAC exhibits
a. Negative resistance characteristics
b. Goes into avalanche condition
c. Voltage drop snaps back
d. All of these

17)   In BJT, the forward biased base emitter junction inject holes from base to emitter, the holes
a. Do not contribute to the collector current
b. Result in net current flow component into the base
c. Contribute to the collector current
d. Only (a) and (b)
e. Only (b) and (c)

18)   In BJT, switching losses occurs
a. Only at turn – on
b. Only at turn – off
c. Both at turn on and off
d. None of these

 ANSWER: Both at turn on and off
19)   Choppers is a
a. AC – DC converters
b. AC – AC converters
c. DC – AC converters
d. DC – DC converters

20)   The average value of the output voltage in a step – down dc chopper is given by
a. V 0 = V s
b. V 0 = D V s
c. V 0 = V s / D
d. V 0 = V s / ( 1 – D )

 ANSWER: V 0 = D V s
21)   The control method used for PWM dc – dc converter is
a. Voltage mode control
b. Current mode control
c. Hysteric control
d. All of these

22)   The main objective of static power converters is to
a. Obtain an dc output waveform from a dc power supply
b. Obtain an ac output waveform from a dc power supply
c. Obtain an dc output waveform from a dc power supply
d. Obtain an ac output waveform from a ac power supply

 ANSWER: Obtain an ac output waveform from a dc power supply
23)   A capacitive load in voltage source inverters generates
a. Small current spikes and can be reduced by using an inductive filter
b. Large current spikes and can be increased by using an inductive filter
c. Small current spikes and can be increased by using an inductive filter
d. Large current spikes and can be reduced by using an inductive filter

 ANSWER: Large current spikes and can be reduced by using an inductive filter
24)   The carrier which are commonly used in constant – frequency PWM is
a. Sawtooth carrier
b. Inverted sawtooth carrier
c. Triangle carrier
d. All of these

25)   Double edge modulation eliminates certain harmonics when the reference is a
a. Sine wave
b. Square wave
c. Triangular wave
d. Trapezoidal wave

26)   In a three phase voltage source inverters
a. Only amplitude of voltage is controllable
b. Only phase is controllable
c. Both amplitude and phase is controllable
d. Amplitude, phase and frequency of voltages should always be controllable

 ANSWER: Amplitude, phase and frequency of voltages should always be controllable
27)   In a 3 phase
VSI out of eight valid states, the number of valid states that produce
zero ac line voltages is/are

a. One
b. two
c. Three
d. Four

28)   In the
operation and control of both naturally commutated and forced commutated
SCR base converter, commutation plays an important role. The converters
is / are

a. AC – DC
b. DC – DC
c. DC – AC
d. All of these

29)   In commutation PAC stands for
a. Permanent angle converter
b. Phase angle converter
c. Phase angle commutation
d. Phase and commutation

30)   Any electrical signal present in a circuit other than the desired signal is known as
a. Noise
b. Distortion
c. Interference
d. All of these

31)   The man made noise sources is / are
a. Motors
c. Computers, digital electronics
d. All of these

32)   Due to non sinusoidal waveform of the input current, the power factor of the rectifier is
a. Negatively affected by firing angle
b. Negatively affected by distortion of the input current
c. Positively affected by both firing angle and distortion of the input current
d. Both (a) and (b)

33)   In rectifiers, load current flow is
a. Unidirectional
b. Bidirectional
c. Either (a) or (b)
d. Non directional

34)   Advantages of HVDC transmission over AC system is / are
a. Reversal of power can be controlled by firing angle
b. Very good dynamic behavior
c. They can link two AC system operating unsynchronized
d. All of these

35)   In dual converters,
a. Both rectifiers provides positive current to the load
b. Both rectifiers provide negative current to the load
c. One rectifiers provide positive current to the load and the other negative current
d. One rectifier provide positive current to the source and the other negative current to the load

36)   In a phase controlled 3 phase ac voltage controller, the harmonic present is
a. 2nd
b. 3rd
c. 5th
d. 7th

37)   The maximum firing angle in the half wave controlled regulator is
a. 180 degree
b. 190 degree
c. 200 degree
d. 210 degree

38)   The on – state voltage drop of IGBT consists of
a. Drop across the collector junction
b. Drop across the drift region
c. Drop across MOSFET portion
d. All of these

39)   To detect an over – current fault condition, the most reliable method is to connect a
a. Current sensor across IGBT
b. Voltage sensor across IGBT
c. Current sensor in series with IGBT
d. Voltage sensor in series with IGBT

 ANSWER: Current sensor in series with IGBT
40)   The IGBT resulted in higher switching speed and lower energy losses. It can be used for
a. Uninterruptible power supplies
b. Induction heating system
c. Constant voltage and frequency power supplies
d. All of these

1. amit singh chhonker March 9, 2017
• ALL EXAM REVIEW ADDA March 9, 2017
2. amit singh chhonker March 10, 2017
• ALL EXAM REVIEW ADDA March 10, 2017
• amit singh chhonker March 10, 2017
3. Chandra sekhar December 17, 2017
• Harikesh Yadav December 17, 2017