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 3phase 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 onperiod and f is the chopping frequency, then output voltage in terms of input voltage is given by

V_{s}T_{on}/f

V_{a}f/T_{on}

V_{s}/fT_{on}

V_{s}f.T_{on}

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 3phase 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 toac 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: 3ph half wave converter
12.In a 3phase 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: T_{ON} /(T_{ON} + T_{OFF})
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.Stepup cyclo conveter operation is based on  commutation.
Answer: Forced
20.Stepdown cyclo conveter operation is based on  commutation.
Answer: Line