Power Electronics Mcqs - Set 2

1)   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. Multiple of two
b. Odd multiple of three
c. Odd multiple of five
d. Odd multiple of seven
Answer  Explanation 

ANSWER: Odd multiple of three

Explanation:
No explanation is available for this question!


2)   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 inductances
b. Three capacitances
c. Three resistance
d. Three transistors
Answer  Explanation 

ANSWER: Three inductances

Explanation:
No explanation is available for this question!


3)   If all the SCR’s of 3 phase PAC is replaced by diodes, they would be triggered_____________?

a. 120 degree after the zero crossing of the corresponding line voltages
b. 60 degree after the zero crossing of the corresponding line voltages
c. 120 degree before the zero crossing of the corresponding line voltages
d. 60 degree before the zero crossing of the corresponding line voltages
Answer  Explanation 

ANSWER: 60 degree after the zero crossing of the corresponding line voltages

Explanation:
No explanation is available for this question!


4)   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. Susceptibility
b. Emission
c. Interference
d. Electromagnetic compatibility
Answer  Explanation 

ANSWER: Electromagnetic compatibility

Explanation:
No explanation is available for this question!


5)   The opposite of susceptibility is___________?

a. Immunity
b. Emission
c. Interference
d. Electromagnetic compatibility
Answer  Explanation 

ANSWER: Immunity

Explanation:
No explanation is available for this question!


6)   The output current in PWM DC – DC converters is equal to___________?

a. Average value of the output inductor current
b. Product of an average inductor current and a function of duty ratio
c. Either A. or B.
d. None of these
Answer  Explanation 

ANSWER: Either A. or B.

Explanation:
No explanation is available for this question!


7)   A step – down choppers can be used in___________?

a. Electric traction
b. Electric vehicles
c. Machine tools
d. All of these
Answer  Explanation 

ANSWER: All of these

Explanation:
No explanation is available for this question!


8)   In a lossless inverter, the average power absorbed in one period by the load must be__________?

a. Equal to the average power supplied by the dc source
b. Greater than the average power supplied by the dc source
c. Lesser than the average power supplied by the dc source
d. Equal to the average power supplied by the ac source
Answer  Explanation 

ANSWER: Equal to the average power supplied by the dc source

Explanation:
No explanation is available for this question!


9)   The ac voltage controller can be used for ___________?

a. Lighting and heating control
b. On – line transformer tap changing
c. Soft starting
d. All of these
Answer  Explanation 

ANSWER: All of these

Explanation:
No explanation is available for this question!


10)   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. Top switch of each leg is on at any instant
b. Bottom switch of each leg is on at any instant
c. Either A. or B.
d. None of these
Answer  Explanation 

ANSWER: Either A. or B.

Explanation:
No explanation is available for this question!


11)   The phase angle of gate signal in TRIAC can be shifted by using_____________?

a. A capacitor
b. A variable resistor
c. An inductor
d. Only (a) and (b)
Answer  Explanation 

ANSWER: Only (a) and (b)

Explanation:
No explanation is available for this question!


12)   In the SPWM, the modulating signal is___________?

a. Square
b. Sinusoidal
c. Triangular
d. Saw – tooth
Answer  Explanation 

ANSWER: Sinusoidal

Explanation:
No explanation is available for this question!


13)   A TRIAC can be turned on with______________?

a. Positive voltage at the gate terminal
b. Negative voltage at the gate terminal
c. Either (a) or (b)
d. None of these
Answer  Explanation 

ANSWER: Either (a) or (b)

Explanation:
No explanation is available for this question!


14)   The transfer function of PWM is generally developed in______________?

a. Time domain
b. Frequency domain
c. Either A. or B.
d. None of these
Answer  Explanation 

ANSWER: Either A. or B.

Explanation:
No explanation is available for this question!


15)   DIAC and TRIAC both are semiconductors devices and conduct in____________________?

a. DIAC conducts in forward direction and TRIAC conducts in reverse direction
b. Both conducts in forward direction
c. Both conducts in reverse direction
d. Both conducts in either direction
Answer  Explanation 

ANSWER: Both conducts in either direction

Explanation:
No explanation is available for this question!


16)   The Graetz bridge makes excellent use of ______________?

a. Current transformer
b. Potential transformer
c. Power transformer
d. SCR
Answer  Explanation 

ANSWER: Power transformer

Explanation:
No explanation is available for this question!


17)   In constant frequency PWM, at perturbation the amplitude of the sinusoidal component is a___________?

a. Linear function
b. Non linear function
c. Constant function
d. None of these
Answer  Explanation 

ANSWER: None of these

Explanation:
No explanation is available for this question!


18)   If the firing angle becomes negative, then the rectifier begins to work as_______________?

a. A rectifier
b. An inverter
c. A chopper
d. A regulator
Answer  Explanation 

ANSWER: An inverter

Explanation:
No explanation is available for this question!


19)   In a 3 phase half wave rectifier, when firing angle is less than 90 degree, then the average dc output voltage becomes__________________?

a. Positive
b. Negative
c. Zero
d. None of these
Answer  Explanation 

ANSWER: Positive

Explanation:
No explanation is available for this question!


20)   Transformer utilization factor is a measure of the merit of a rectifier circuit. It is the ratio of_______________?

a. AC input power to the transformer volt – amp rating required by secondary
b. AC input power to the transformer volt – amp rating required by primary
c. DC output power to the transformer volt – amp rating required by secondary
d. DC output power to the transformer volt – amp rating required by primary
Answer  Explanation 

ANSWER: DC output power to the transformer volt – amp rating required by secondary

Explanation:
No explanation is available for this question!