power electronics MCQs – Page 7

Practise focused power electronics questions with marked answers for exam preparation and subject revision.

power electronics Mcqs

121. The ac voltage controller can be used for ___________?
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A. On line transformer tap changing

B. Lighting and heating control

C. All of these

D. Soft starting

122. Thyristor can be protected from over voltages by using____________?
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A. fuse.

B. heat sink.

C. voltage clamping device.

D. snubber circuit.

123. Form factor of a rectifier is the ratio of ______________?
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A. Peak value of current and voltage to its root mean square value

B. Average value of current and voltage to its root mean square value

C. Root mean square value of voltage and current to its peak value

D. Root mean square value of voltage and current to its average value

124. If holding current of a thyristor is 2 mA then latching current should be_____?
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A. 0.009 A.

B. 0.002 A.

C. 0.004 A.

D. 0.01 A.

125. In reverse blocking mode of a thyristor______?
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A. junction J3 is in forward bias and J1, J2 in reverse bias.

B. junction J1, J3 is in reverse bias and J2 is in forward bias.

C. junction J1 and J2 is in forward bias and J3 is in reverse bias.

D. junction J2 is in reverse bias and J1, J3 is in forward bias.

126. For bidirectional operation of converters____________?
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A. A series 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 capacitor is used

D. A parallel combination of controllable switch and a diode is used

127. For power output higher than 15 kW, the suitable rectifier is________________?
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A. Poly phase

B. 3 phase

C. Single phase

D. Only (b) and (c)

128. The IGBT resulted in higher switching speed and lower energy losses. It can be used for___________?
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A. Induction heating system

B. All of these

C. Constant voltage and frequency power supplies

D. Uninterruptible power supplies

129. In bipolar modulation, the carrier is symmetric about zero with amplitude equal to Cm, the PWM output
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A. Switches between 1 and + 1

B. Switches between 1 / 2 and + 1 / 2

C. Switches between 0 and + 1

D. Zero

130. The typical value of SCR for modern alternator is____________?
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A. 1.2.

B. 1.0.

C. 1.5.

D. 0.5.

131. Bidirectional semiconductor device is___________?
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A. BJT

B. SCR

C. TRIAC

D. Diode

132. The man made noise sources is / are_____________?
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A. Computers, digital electronics

B. All of these

C. Switches, radio interferences

D. Motors

133. Due to non sinusoidal waveform of the input current, the power factor of the rectifier is____________?
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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)

134. Voltage commutation circuit can be converted into a current commutation by interchanging the positions of____________?
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A. Capacitor and SCR

B. Diode and capacitor

C. Capacitor and load

D. Inductor and capacitor

135. To meet high current demand we use SCRs in______________?
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A. series connection.

B. parallel connection.

C. anti parallel connection.

D. both B and C.

136. Switching frequency of SITH is____________?
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A. 5 KHz

B. 60 KHz

C. 100 KHz

D. 10 KHz

137. The switching function of semiconductor devices can be characterized with____________?
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A. Duty ratio, frequency and time delay

B. Duty ratio only

C. Duty ratio and frequency

D. Frequency only

138. The power demand can be estimated approximately by___________?
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A. Statistical method

B. Mathematical method

C. Load survey method

D. Economic parameters

139. A modern power semiconductor device that combines the characteristic of BJT and MOSFET is_____________?
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A. GTO

B. IGBT

C. MCT

D. FCT

140. In the SPWM, the modulating signal is___________?
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A. Saw tooth

B. Sinusoidal

C. Square

D. Triangular

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