Electricity Power Electronics Part Two
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Attempt Free Electricity Power Electronics Part Two Here. Read The Important Electricity MCQ From Below.
1) The output current in PWM DC – DC converters is equal to
a. Average value of the output inductor current
b. Product of an average inductor current and a function of duty ratio
c. Either (a) or (b)
d. None of these
ANSWER: Either (a) or (b)
2) The opposite of susceptibility is
a. Immunity
b. Emission
c. Interference
d. Electromagnetic compatibility
ANSWER: Immunity
3) The ability of an electronic system to function properly in its intended electromagnetic environment and should not be a source of pollution to that electromagnetic environment is known as
a. Susceptibility
b. Emission
c. Interference
d. Electromagnetic compatibility
ANSWER: Electromagnetic compatibility
4) If all the SCR’s of 3 phase PAC is replaced by diodes, they would be triggered
a. 120 degree after the zero crossing of the corresponding line voltages
b. 60 degree after the zero crossing of the corresponding line voltages
c. 120 degree before the zero crossing of the corresponding line voltages
d. 60 degree before the zero crossing of the corresponding line voltages
ANSWER: 60 degree after the zero crossing of the corresponding line voltages
5) For commutation in three phase PAC, normally balanced three phase voltages VR, VY and VB are connected to the three legs of the converter via
a. Three inductances
b. Three capacitances
c. Three resistance
d. Three transistors
ANSWER: Three inductances
6) In square wave operation mode of 3 phase VSI, the VSI
a. Can control the load voltage
b. Cannot control the load voltage
c. Cannot control the load voltage except by means of dc link voltage
d. Cannot control the load voltage except by means of dc link current
ANSWER: Cannot control the load voltage except by means of dc link voltage
7) In a 3 phase VSI SPWM to use a single carrier signal and preserve the features of PWM technique, the normalized carrier frequency should be
a. Multiple of two
b. Odd multiple of three
c. Odd multiple of five
d. Odd multiple of seven
ANSWER: Odd multiple of three
Electricity Power Electronics Part Two
8) Regulator sampling PWM is usually used in
a. High power inverters
b. Rectifiers
c. Low power inverters
d. Only (a) and (b)
ANSWER: Only (a) and (b)
9) A combination of synchronized leading edge and trailing edge modulation has also been used to control a
a. Boost single – phase power factor converter
b. A buck dc – dc converter to reduce ripple in the intermediate dc bus capacitor
c. Both (a) and (b)
d. None f these
ANSWER: Both (a) and (b)
10) If energy is taken from the AC side of the inverter and sends it back into the DC side, then it is known as
a. Motoring mode operation
b. Braking mode operation
c. Regenerative mode operation
d. None of these
ANSWER: Regenerative mode operation
11) The ac output voltage waveform of VSI and AC output current waveform of CSI respectively is composed of
a. High dv / dt, low di / dt
b. Low dv / dt, low di / dt
c. Low dv / dt, high di / dt
d. High dv / dt, high di / dt
ANSWER: High dv / dt, high di / dt
12) Advantages of Cuk converter is / are
a. Large number of reactive component
b. Low stress on switch
c. Low stress on capacitor
d. None of these
ANSWER: None of these
13) In a flyback converter, the inductor of the buck-boost converter has been replaced by a
a. Flyback capacitor
b. Flyback resistor
c. Flyback transformer
d. Flyback transistor
ANSWER: Flyback transformer
14) In a push – pull converter, the filter capacitor can be obtained as
a. Cmin = V / ( Vr L f2 )
b. Cmin= ( 1 – D ) V / ( Vr L f2 )
c. Cmin= ( 1 – 2 D ) V / 32 ( Vr L f2 )
d. Cmin= ( 1 – 2 D ) V / 42 ( Vr L f2 )
ANSWER: Cmin= ( 1 – 2 D ) V / 32 ( Vr L f2 )
15) MOSFET stands for
a. Metal – oxide semiconductor field effect transistor
b. Molybdenum – oxide semiconductor field effect transistor
c. Metal – oxide silicon field effect transistor
d. Metal – oxide semiconductor field effect transmitter
ANSWER: Metal – oxide semiconductor field effect transistor
16) A MOSFET, for its conduction uses
a. Only minority carriers
b. Only majority carriers
c. Both minority and majority carriers
d. None of these
ANSWER: Only majority carriers
Electricity Power Electronics Part Two
17) An RC snubber network used in BJT
a. Divert the collector current during turn – off
b. Improves the reverse bias safe operating area
c. Dissipates a fair amount of switching power
d. All of these
ANSWER: All of these
18) The ac voltage controller can be used for
a. Lighting and heating control
b. On – line transformer tap changing
c. Soft starting
d. All of these
ANSWER: All of these
19) The phase angle of gate signal in TRIAC can be shifted by using
a. A capacitor
b. A variable resistor
c. An inductor
d. Only (a) and (b)
ANSWER: Only (a) and (b)
20) A TRIAC can be turned on with
a. Positive voltage at the gate terminal
b. Negative voltage at the gate terminal
c. Either (a) or (b)
d. None of these
ANSWER: Either (a) or (b)
21) DIAC and TRIAC both are semiconductors devices and conduct in
a. DIAC conducts in forward direction and TRIAC conducts in reverse direction
b. Both conducts in forward direction
c. Both conducts in reverse direction
d. Both conducts in either direction
ANSWER: Both conducts in either direction
22) The Graetz bridge makes excellent use of
a. Current transformer
b. Potential transformer
c. Power transformer
d. SCR
ANSWER: Power transformer
23) If the firing angle becomes negative, then the rectifier begins to work as
a. A rectifier
b. An inverter
c. A chopper
d. A regulator
ANSWER: An inverter
Electricity Power Electronics Part Two
24) In a 3 phase half wave rectifier, when firing angle is less than 90 degree, then the average dc output voltage becomes
a. Positive
b. Negative
c. Zero
d. None of these
ANSWER: Positive
25) Transformer utilization factor is a measure of the merit of a rectifier circuit. It is the ratio of
a. AC input power to the transformer volt – amp rating required by secondary
b. AC input power to the transformer volt – amp rating required by primary
c. DC output power to the transformer volt – amp rating required by secondary
d. DC output power to the transformer volt – amp rating required by primary
ANSWER: DC output power to the transformer volt – amp rating required by secondary
26) Ripple factor is the ratio of
a. Rms value of the ac component of load voltage to the dc voltage
b. Average value of the ac component of load voltage to the peak value of voltage
c. Average value of the dc component of load voltage to the ac voltage
d. Peak value of the dc component of load voltage to the ac voltage
ANSWER: Rms value of the ac component of load voltage to the dc voltage
27) Form factor of a rectifier is the ratio of
a. Root mean square value of voltage and current to its peak value
b. Root mean square value of voltage and current to its average value
c. Average value of current and voltage to its root mean square value
d. Peak value of current and voltage to its root mean square value
ANSWER: Root mean square value of voltage and current to its average value
28) The curve between V and I of SCR when anode is positive w.r.t cathode and when anode is negative w.r.t cathode are known as
a. both as forward characteristics
b. both as reverse characteristics
c. former as forward characteristics and later as reverse characteristics
d. former as reverse characteristics and later as forward characteristics
ANSWER: former as forward characteristics and later as reverse characteristics
29) With gate open, the maximum anode current at which SCR is turned off from ON condition is called
a. breakdown voltage
b. peak reverse voltage
c. holding current
d. latching current
ANSWER: holding current
Electricity Power Electronics Part Two
30) Bidirectional semiconductor device is
a. Diode
b. BJT
c. SCR
d. TRIAC
ANSWER: TRIAC
31) An ideal diode is
a. Unidirectional
b. Bidirectional
c. Fixed voltage polarity
d. Only (a) and (c)
ANSWER: Only (a) and (c)
32) 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
ANSWER: All of these
33) 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
34) 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
ANSWER: All of these
35) The maximum firing angle in the half wave controlled regulator is
a. 180 degree
b. 190 degree
c. 200 degree
d. 210 degree
ANSWER: 210 degree
Electricity Power Electronics Part Two
36) In a phase controlled 3 phase ac voltage controller, the harmonic present is
a. 2nd
b. 3rd
c. 5th
d. 7th
ANSWER: 2nd
37) 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
ANSWER: Both rectifiers provides positive current to the load
38) 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 un synchronized
d. All of these
ANSWER: All of these
39) In rectifiers, load current flow is
a. Unidirectional
b. Bidirectional
c. Either (a) or (b)
d. Non directional
ANSWER: Unidirectional
40) 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)
ANSWER: Both (a) and (b)
41) The man made noise sources is / are
a. Motors
b. Switches, radio interferences
c. Computers, digital electronics
d. All of these
ANSWER: All of these
Electricity Power Electronics Part Two
42) 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
ANSWER: Noise
43) In commutation PAC stands for
a. Permanent angle converter
b. Phase angle converter
c. Phase angle commutation
d. Phase and commutation
ANSWER: Phase angle converter
44) 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
ANSWER: All of these
45) 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
ANSWER: two
46) 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
47) Double edge modulation eliminates certain harmonics when the reference is a
a. Sine wave
b. Square wave
c. Triangular wave
d. Trapezoidal wave
ANSWER: Sine wave
Electricity Power Electronics Part Two
48) 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
ANSWER: All of these
49) 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
50) 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
51) 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
ANSWER: All of these
52) 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
Electricity Power Electronics Part Two
53) Choppers is a
a. AC – DC converters
b. AC – AC converters
c. DC – AC converters
d. DC – DC converters
ANSWER: DC – DC converters
54) In BJT, switching losses occur
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
55) 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)
ANSWER: Only (a) and (b)
56) 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
ANSWER: All of these
57) DIAC are specifically designed to trigger
a. TRIAC
b. SCR
c. GTO
d. Only (a) and (b)
ANSWER: Only (a) and (b)
Electricity Power Electronics Part Two
58) 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
59) 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
ANSWER: Zero at all times
60) 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)
ANSWER: Only (b) and (c)
61) In a full wave rectifier, the rectification ratio is approximately equal to
a. 61%
b. 71%
c. 81%
d. 91%
ANSWER: 81%
62) In a single phase full wave rectifier, during blocking state the pea inverse voltage of diode is
a. V m
b. 2 V m
c. V m / 2
d. 4 V m
ANSWER: 2 V m
63) A single phase ac – dc converter is also known as
a. rectifier
b. inverter
c. chopper
d. regulator
ANSWER: rectifier
Electricity Power Electronics Part Two
64) 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
65) 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
ANSWER: Always positive w.r.t cathode
66) 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
ANSWER: In series with anode
67) Number of PN junction in an SCR is
a. Two
b. Three
c. Four
d. Five
ANSWER: Three
Electricity Power Electronics Part Two
68) IGBT stands for
a. Insulated gate bipolar transistor
b. Insulated gate bidirectional transistor
c. Inductive gate bipolar transistor
d. Inductive gate bidirectional transistor
ANSWER: Insulated gate bipolar transistor
69) 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
ANSWER: All of these
70) 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
ANSWER: Non zero
71) 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
ANSWER: Direct switch matrix circuits
Electricity Power Electronics Part Two
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