power electronics MCQs – Page 8

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

power electronics Mcqs
141. The effects of EMI can be reduced by_____________?
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A. Reducing the efficiency of the coupling path

B. Suppressing emissions

C. Reducing the susceptibility of the receptor

D. All of these
142. The ac output voltage waveform of VSI and AC output current waveform of CSI respectively is composed of___________?
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A. High dv / dt, high di / dt

B. High dv / dt, low di / dt

C. Low dv / dt, low di / dt

D. Low dv / dt, high di / dt

143. 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______________?
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A. Three resistance

B. Three inductances

C. Three transistors

D. Three capacitances

144. A single phase full bridge inverter can operated in load commutation mode in case load consist of______?
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A. RLC overdamped.

B. RL.

C. RLC underdamped.

D. RLC critically damped

145. The transfer function of PWM is generally developed in______________?
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A. None of these

B. Frequency domain

C. Either A. or B.

D. Time domain

146. Ripple factor is the ratio of______________________?
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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. Peak value of the dc component of load voltage to the ac voltage

D. Average value of the dc component of load voltage to the ac voltage

147. A thyristor can termed as__________?
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A. AC switch

B. DC switch

C. Both a and B

D. Square wave switch

148. Double fourier series analysis of PWM is_____________?
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A. Two dimensional functions

B. Three dimensional functions

C. All of these

D. One dimensional functions

149. The capacitance of reversed bised junction J2 in a thyristor is CJ2 = 20 pF and can be assumed to be independant of the off state voltage. The limiting value of the charging current to turn on the thyristor is 16 mA. What is the critical value of dv/dt?
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A. 600 V/s

B. 1000 V/s

C. 800 V/s

D. 1200 V/s

150. Why resistor is used in Snubber circuit_________________ ?
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A. To minimize the discharging current

B. All of these

C. To minimize the loss

D. To minimize the charging current

151. Practical way of obtaining static voltage equalization in series connected SCRs is by the use of____________?
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A. Resistors of the same value across each SCR

B. One resistor across the string

C. Resistors of different values across each SCR

D. One resistor in series with each SCR

152. The maximum firing angle in the half wave controlled regulator is_____________?
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A. 190 degree

B. 210 degree

C. 180 degree

D. 200 degree

153. Anode current in an SCR consists of____________?
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A. holes only

B. electrons only

C. either electron or holes

D. Both electron and holes

154. In a 3 phase bridge rectifier the ripple frequency is _____________?
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A. Twice the input frequency

B. Three times the input frequency

C. Six times the input frequency

D. Equal to the input frequency

155. Leakage current flows through the thyristor in_________?
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A. forward blocking mode

B. reverse blocking mode

C. both forward and reverse blocking mode

D. forward conduction mode

156. By which one of the following we can measure the reliability of a string_____________?
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A. Derating factor

B. Reliability factor

C. Factor of safety

D. String efficient

157. In single phase VSI, the harmonic which is not present is____________?
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A. 2nd

B. 5th

C. 3rd

D. 7th

158. 60 thyrsistors are connected in series and parallel to form a 10 KV and 5.5 KA switch. Each thyristor is rated for 1.2 KV, 1 KA. The no. of parallel path are 6. The efficiency of the switch is______________________?
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A. 76.3 %

B. 83.30%

C. 91.60%

D. 90.90%

159. Which of following is normally ON device?
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A. IGBT

B. BJT

C. TRIAC

D. SIT
160. 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____________?
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A. Odd multiple of seven

B. Odd multiple of three

C. Multiple of two

D. Odd multiple of five