A. Field-effect transistor
B. Field engages transistor
C. Field effect terminal
D. Fire engages transistor
Answer: A
FET stands for Field-effect transistor. It is a transistor that depends upon the electric field to control the conductivity of the channel.
102. Calculate the compensator rating required for sin(Φ) = .13.
A. 0.45 P.U
B. 0.12 P.U
C. 0.13 P.U
D. 0.82 P.U
Answer: C
The compensator rating can be calculated using the relation
QP.U = √1-cos2(∅) = sin(∅) = .13.
This per unit value VAR compensator is required to improve the power factor of the system.
103. Full form of DIAC is ________
A. Digital Alternating current
B. Discrete Alternating current
C. Diode for Alternating current
D. Digital Alternating counter
Answer: C
DIAC stands for Diode Alternating current. It is a bipolar switch. It will conduct when the voltage across it becomes greater than the break-over voltage.
104. Which harmonic is not present in 3-Φ fully controlled rectifier?
A. 81st harmonic
B. 15th harmonic
C. 17th harmonic
D. 11th harmonic
Answer: A
Triple harmonics are absent in the case of a 3-phase fully controlled rectifier. Because of the absence of triple harmonics, the THD of the rectifier is 31%.
15. Fifth lowest order harmonic present in 3-Φ fully controlled rectifier is __________
A. 15th
B. 17th
C. 13th
D. 12th
Answer: B
Only 6k±1 order harmonics are present in 3-Φ fully controlled rectifier. The fifth lowest order harmonic is the 17th harmonic for k = 3. Third-order harmonics are absent in 3-Φ fully controlled rectifier.
105. Choppers are used to control the DC voltage level.
A. True
B. False
Answer: A
Choppers are used to control the DC voltage level. They can increase, decrease or both the input DC voltage.
106. Which one of the following devices is uncontrolled?
A. SCR
B. MOSFET
C. Diode
D. TRIAC
Answer: C
A diode is an uncontrolled, unidirectional power electronic device. When the voltage across the diode becomes positive it starts conduction otherwise remains off.
107. Cuk-converter is better than the Buck converter in terms of the output voltage.
A. True
B. False
Answer: A
Cuk-converter is better than Buck converter in terms of the output voltage. The filter is present at the output and input side of the Cuk-converter whereas in Buck there is no filter circuit present on the input side.
108. What is the formula for output voltage for the Buck converter?
A. 8D×Vin
B. 5D×Vin
C. 2D×Vin
D. D×Vin
Answer: D
The output voltage of the buck converter is Vo = D×Vin. The value of the duty cycle is less than one which makes the Vo < Vin. The buck converter is used to step down voltage. Vin is a fixed voltage and Vo is a variable voltage.
109. What is the formula for output voltage for the Buck-Boost converter?
A. D×Vin
B. Vin ÷ (1-D)
C. D×Vin ÷ (1-D)
D. D×Vin ÷ (1+D)
Answer: C
The output voltage of the buck-boost converter is Vo = D×Vin ÷ (1-D).
It can step up and step down the voltage depending upon the value of the duty cycle.
If the value of the duty cycle is less than .5 it will work as a buck converter; for a duty cycle greater than .5 it will work as a boost converter.
110. What is the formula for output voltage for the Boost converter?
A. 8D×Vin
B. 5D×Vin
C. 2D×Vin
D. D×Vin
Answer: D
The output voltage of the boost converter is Vo = Vin ÷ (1-D. The value of the duty cycle is less than one which makes the Vo > Vin. The boost converter is used to step up the voltage. Vin is a fixed voltage and Vo is a variable voltage.
