Power Electronics Mid - II, November - 2014

1.In circulating current type of dual converter, the nature of voltage across reactor is
  • alternating
  • pulsating
  • direct
  • triangular
Answer: A
2.In a 3-phase semi converter frequency of the ripple in the output voltage may be
  • 3 time the supply frequency f for firing angle  < 60
  • 3 f for  > 60
  • 2f for  < 60
  • 6 f for  > 60
Answer: B
3.In a dual converter, converters1 and converters 2 work as under
  • 1 as rectifier, 2 as inverter
  • 1 as inverter, 2 as rectifier
  • both as rectifiers
  • both a&b
Answer: D
4.In dc chopper, if Ton is the on-period and f is the chopping frequency, then output voltage in terms of input voltage is given by
  • VsTon/f
  • Vaf/Ton
  • Vs/fTon
  • Vsf.Ton
Answer: D
5.In dc chopper, the waveforms for input and output voltages are respectively
  • discontinuous, continuous
  • both continuous
  • both discontinuous
  • continuous, discontinuous
Answer: D
6.The output voltage of 3-phase inverter contains
  • only even harmonics
  • both odd and even harmonics
  • only odd harmonics
  • only triple harmonics
Answer: C
7.An inverter converts
  • ac to dc
  • dc to ac
  • dc to dc
  • ac to ac
Answer: B
8.Which of the following is a PWM technique?
  • single pulse
  • multiple pulse
  • sinusoidal
  • All the above
Answer: D
9.An ac voltage regulator regulate the fixed ac signal to-------ac signal without changing its frequency
  • constant
  • fixed
  • variable
  • fluctuating
Answer: C
10.A device that converters ac to ac with variable frequency
  • rectifier
  • chopper
  • cycloconverter
  • inverter
Answer: C
11.Three phase ac to dc converter which requires neutral point connection is -----------------
Answer: 3-ph half wave converter
12.In a 3-phase half controlled converter each thyristor and diode conduct for -------------------- degrees.
Answer: 120
13.A Dc chopper Ton is 1msec and its frequency is 500Hz what will be its duty cycle -------------------
Answer: 50%
14.The most suitable switch used for dc to dc converter is ---------------------
Answer: GTO
15.Duty Cycle is defined as -------------------------
Answer: TON /(TON + TOFF)
16.In a single pulse modulation of PWM inverters, fifth harmonic can be eliminated if pulse width is equal to ----------------------
Answer: 72
17.In single pulse modulation of PWM inverter, the pulse width is 120 degrees. For an input voltage of 220V dc, the rms value of output voltage is --------------------
Answer: 179.63V
18.Cyclo converter is a frequency changer with ------------------ stage conversion.
Answer: One stage
19.Step-up cyclo conveter operation is based on ---------------------- commutation.
Answer: Forced
20.Step-down cyclo conveter operation is based on --------------------------- commutation.
Answer: Line