Tuesday, October 14, 2025

For high voltage DC transmission, the preferred converter is

 71. The converter that operates in all four quadrants is

A) Single converter
B) Dual converter
C) Cycloconverter
D) Full-wave rectifier
Answer: B) Dual converter

72. The ripple factor of a full-wave rectifier is

A) 1.21
B) 0.482
C) 0.707
D) 0.2
Answer: B) 0.482

73. In a converter, if the firing angle α increases, the average output voltage

A) Increases
B) Decreases
C) Remains same
D) Becomes zero
Answer: B) Decreases

74. The firing angle of a fully controlled converter can vary between

A) 0°–90°
B) 0°–180°
C) 0°–120°
D) 0°–150°
Answer: B) 0°–180°

75. The output voltage of a step-down chopper is equal to

A) Supply voltage × Duty ratio
B) Supply voltage / Duty ratio
C) Supply voltage × (1 – Duty ratio)
D) Constant value
Answer: A) Supply voltage × Duty ratio

76. In an SCR, turn-on time decreases with

A) Increase in gate current
B) Decrease in gate current
C) Decrease in anode voltage
D) Increase in holding current
Answer: A) Increase in gate current

77. A TRIAC conducts when

A) Positive gate current
B) Negative gate current
C) Both positive and negative gate current
D) Only when AC voltage is zero
Answer: C) Both positive and negative gate current

78. For a MOSFET, the body diode conducts during

A) Forward blocking
B) Reverse conduction
C) Gate off condition
D) Switching
Answer: B) Reverse conduction

79. In a 3-phase full converter, maximum DC voltage =

A) 1.17×VL−L1.17 \times V_{L-L}
B) 1.35×VL−L1.35 \times V_{L-L}
C) 1.57×VL−L1.57 \times V_{L-L}
D) 0.9×VL−L0.9 \times V_{L-L}
Answer: B) 1.35×VL−L1.35 \times V_{L-L}

80. The lowest order harmonic in a 6-pulse converter is

A) 5th
B) 7th
C) 11th
D) 13th
Answer: A) 5th

81. In a 3-phase inverter, the line-to-line voltage waveform is

A) Sinusoidal
B) Square
C) Quasi-square
D) Pulse width modulated
Answer: C) Quasi-square

82. The control strategy of PWM inverter is based on

A) Frequency ratio
B) Voltage ratio
C) Amplitude and frequency ratio
D) None of these
Answer: C) Amplitude and frequency ratio

83. The average output voltage of a semi-converter is

A) Vmπ(1+cos⁡α)\frac{Vm}{\pi}(1 + \cos α)
B) Vm2π(1+cos⁡α)\frac{Vm}{2π}(1 + \cos α)
C) Vmπcos⁡α\frac{Vm}{π}\cos α
D) Vm2πsin⁡α\frac{Vm}{2π}\sin α
Answer: A) Vmπ(1+cos⁡α)\frac{Vm}{\pi}(1 + \cos α)

84. The maximum firing angle for a semi-converter is

A) 60°
B) 90°
C) 120°
D) 150°
Answer: B) 90°

85. The turn-off time of an SCR is least affected by

A) Temperature
B) Gate current
C) Forward current
D) Supply voltage
Answer: D) Supply voltage

86. The power factor of a converter becomes leading when

A) α > 90°
B) α < 90°
C) α = 90°
D) At zero load
Answer: A) α > 90°

87. In a Class E commutation, the SCR is turned off by

A) Resonant circuit
B) Load inductance
C) Line current
D) Reverse voltage
Answer: A) Resonant circuit

88. The conduction angle of a diode in a full converter is

A) 90°
B) 120°
C) 180°
D) 270°
Answer: C) 180°

89. The form factor of a single-phase full converter output is

A) 1.11
B) 1.57
C) 0.9
D) 1.2
Answer: A) 1.11

90. The average output current of a converter feeding R load is

A) Constant
B) Pulsating
C) DC
D) AC
Answer: C) DC

91. The harmonic elimination technique in inverters uses

A) Selective harmonic elimination (SHE)
B) Phase control
C) Current commutation
D) PWM
Answer: A) Selective harmonic elimination (SHE)

92. In voltage source inverter, the input voltage should be

A) Constant
B) Variable
C) Rippled
D) Sinusoidal
Answer: A) Constant

93. In current source inverter, the output current is

A) Constant
B) Variable
C) Pulsating
D) Sinusoidal
Answer: A) Constant

94. The advantage of 3-phase inverter over single-phase inverter is

A) Lower ripple content
B) Higher losses
C) More devices
D) Poor efficiency
Answer: A) Lower ripple content

95. The device used in regenerative braking of DC motor is

A) Chopper
B) Converter
C) Inverter
D) Cycloconverter
Answer: A) Chopper

96. The effect of increasing load inductance in a converter is

A) Smooth current
B) More ripple
C) High switching loss
D) Lower efficiency
Answer: A) Smooth current

97. The gate signal for SCR must be removed

A) Immediately after triggering
B) Throughout conduction
C) During commutation
D) During reverse bias
Answer: A) Immediately after triggering

98. The commutation class suitable for DC choppers is

A) Class A
B) Class B
C) Class C
D) Class D
Answer: D) Class D

99. In a converter, the overlap angle is caused by

A) Source inductance
B) Load inductance
C) Gate delay
D) Temperature
Answer: A) Source inductance

100. The converter efficiency decreases due to

A) Commutation loss
B) Switching loss
C) Conduction loss
D) All of the above
Answer: D) All of the above

101. The total harmonic distortion (THD) is least in

A) Single pulse inverter
B) Sinusoidal PWM inverter
C) Square wave inverter
D) Multilevel inverter
Answer: D) Multilevel inverter

102. The principle of ZVS and ZCS converter is to

A) Reduce switching loss
B) Increase conduction loss
C) Reduce voltage rating
D) Increase current ripple
Answer: A) Reduce switching loss

103. The IGBT has

A) Positive temperature coefficient
B) Negative temperature coefficient
C) Zero coefficient
D) Nonlinear coefficient
Answer: A) Positive temperature coefficient

104. The turn-off time of GTO is

A) Greater than SCR
B) Less than SCR
C) Equal to SCR
D) Negligible
Answer: B) Less than SCR

105. For MOSFET, RDS(on) increases with

A) Increase in temperature
B) Decrease in temperature
C) Increase in gate voltage
D) Decrease in drain current
Answer: A) Increase in temperature

106. A forced commutation circuit is required in

A) DC choppers
B) AC converters
C) Natural commutated circuits
D) DC motors only
Answer: A) DC choppers

107. The device most suitable for frequency control is

A) Inverter
B) Converter
C) Chopper
D) Cycloconverter
Answer: D) Cycloconverter

108. The frequency ratio (mf) in PWM inverter is

A) Carrier frequency / Reference frequency
B) Reference frequency / Carrier frequency
C) Output / Input frequency
D) None of these
Answer: A) Carrier frequency / Reference frequency

109. In a 6-pulse converter, for α = 0°, the output voltage is

A) Maximum
B) Zero
C) Minimum
D) Negative
Answer: A) Maximum

110. The harmonic order for 12-pulse converter is

A) 6n ± 1
B) 12n ± 1
C) 24n ± 1
D) 3n ± 1
Answer: B) 12n ± 1

111. The converter that produces variable DC from fixed DC is

A) Inverter
B) Chopper
C) Cycloconverter
D) Rectifier
Answer: B) Chopper

112. The main disadvantage of IGBT over MOSFET is

A) Lower switching speed
B) Higher switching speed
C) Higher frequency
D) Higher efficiency
Answer: A) Lower switching speed

113. In a buck converter, when duty ratio = 0.75, output voltage is

A) 75% of input
B) 25% of input
C) Equal to input
D) Zero
Answer: A) 75% of input

114. The maximum theoretical efficiency of any converter is

A) 95%
B) 98%
C) 100%
D) 80%
Answer: C) 100%

115. In inverter, the commutation circuit provides

A) Turn off current
B) Turn on voltage
C) Current limiting
D) Voltage limiting
Answer: A) Turn off current

116. The inductor current in a buck converter is continuous when

A) Load current > critical current
B) Load current < critical current
C) Voltage ripple = 0
D) Duty cycle = 1
Answer: A) Load current > critical current

117. The ripple current in inductor depends on

A) Duty ratio
B) Switching frequency
C) Inductance value
D) All of the above
Answer: D) All of the above

118. The main function of isolation transformer in converter is

A) Electrical isolation
B) Voltage regulation
C) Current control
D) Harmonic reduction
Answer: A) Electrical isolation

119. The main advantage of multilevel inverter is

A) Low harmonic distortion
B) High losses
C) High cost
D) Complex control
Answer: A) Low harmonic distortion

120. In 3-level inverter, the number of switches required per phase is

A) 2
B) 4
C) 6
D) 8
Answer: B) 4

121. The conduction loss in MOSFET is given by

A) I2RDS(on)I^2 R_{DS(on)}
B) V×IV \times I
C) V2/RDS(on)V^2 / R_{DS(on)}
D) I/RDS(on)I / R_{DS(on)}
Answer: A) I2RDS(on)I^2 R_{DS(on)}

122. The loss due to capacitor charging and discharging during switching is

A) Conduction loss
B) Switching loss
C) Commutation loss
D) Snubber loss
Answer: B) Switching loss

123. A diode reverse recovery time should be

A) Short
B) Long
C) Infinite
D) Medium
Answer: A) Short

124. For high voltage DC transmission, the preferred converter is

A) 6-pulse
B) 12-pulse
C) 18-pulse
D) 3-pulse
Answer: B) 12-pulse

125. A GTO is preferred in

A) Medium voltage, high current
B) Low voltage, low current
C) High frequency, low power
D) Very high frequency applications
Answer: A) Medium voltage, high current

126. The effect of increasing switching frequency is

A) Reduced ripple
B) Increased losses
C) Better waveform
D) All of the above
Answer: D) All of the above

127. The conduction interval in a Class C chopper is

A) 0 to T/2
B) 0 to T
C) Variable
D) Fixed
Answer: C) Variable

128. In an inverter, the dead-time is used to

A) Prevent shoot-through
B) Reduce ripple
C) Increase frequency
D) Improve waveform
Answer: A) Prevent shoot-through

129. The most efficient switching occurs when

A) Voltage = 0 or Current = 0 during switching
B) Both V and I high
C) Gate voltage large
D) Duty ratio low
Answer: A) Voltage = 0 or Current = 0 during switching

130. The main limitation of PWM inverter is

A) High switching loss
B) Poor waveform
C) High ripple
D) High conduction loss
Answer: A) High switching loss

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