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Model Questions for SSC Junior Engineer EXAM - Electrical Engg set-6

1. The output current in PWM DC - DC converters is equal to

(a) Product of an average inductor current and a function of duty ratio
(b) Average value of the output inductor current
(c) Either (a) or (b)
(d) None of these

2. In square wave operation mode of 3 phase VSI, the VSI

(a) Cannot control the load voltage except by means of dc link voltage
(b) Cannot control the load voltage
(c) Cannot control the load voltage except by means of dc link current
(d) Can control the load voltage

3. In a lossless inverter, the average power absorbed in one period by the load must be

(a) Greater than the average power supplied by the dc source
(b) Lesser than the average power supplied by the dc source
(c) Equal to the average power supplied by the dc source
(d) Equal to the average power supplied by the ac source

4. The opposite of susceptibility is

(a) Interference
(b) Immunity
(c) Electromagnetic compatibility
(d) Emission

5. A step - down choppers can be used in

(a) Machine tools
(b) Electric vehicles
(c) Electric traction
(d) All of these

Study Kit for SSC Junior Engineer EXAM (Paper-1) 2017-2018

6. In a full bridge VSI, in order to avoid the short circuit across the DC bus and the undefined AC output voltage condition, the modulating technique should ensure that

(a) Bottom switch of each leg is on at any instant
(b) Top switch of each leg is on at any instant
(c) Either (a) or (b)
(d) None of these

7. The ability of an electronic system to function properly in its intended electromagnetic environment and should not be a source of pollution to that electromagnetic environment is known as

(a) Interference
(b) Emission
(c) Electromagnetic compatibility
(d) Susceptibility

8. 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

(a) Odd multiple of five
(b) Multiple of two
(c) Odd multiple of seven
(d) Odd multiple of three

9. If all the SCR's of 3 phase PAC is replaced by diodes, they would be triggered

(a) 120 degree before the zero crossing of the corresponding line voltages
(b) 60 degree after the zero crossing of the corresponding line voltages
(c) 60 degree before the zero crossing of the corresponding line voltages
(d) 120 degree after the zero crossing of the corresponding line voltages

10. 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

(a) Three resistance
(b) Three inductances
(c) Three transistors
(d) Three capacitances