21. Which type of force phenomenon is used in Sugar mills?
A. Centripetal force
B. Centrifugal force
C. Electrostatic force
D. Nuclear forces
Answer: B
In sugar mills, a centrifugal is used to separate sugar crystals from the syrup by the action of centrifugal forces. Centrifugal force acts away from the center.
22. The Speed control by variation of field flux results in _____________
A. Constant torque drive
B. zero speed
C. Variable torque drive
D. Variable power drive
Answer: C
The field flux control method is used to achieve the speed above the base speed. It provides a constant power drive and variable torque drive.
23. Calculate the compensator rating required for sin(Φ)=.8.
A. 0.9 P.U
B. 0.8 P.U
C. 0.7 P.U
D. 0.2 P.U
Answer: B
The compensator rating can be calculated using the relation
QP.U=√1-cos2(∅)=sin(∅)=.8.
This per unit value VAR compensator is required to improve the power factor of the system.
24. Calculate the heating time constant of the machine if the thermal capacity (C. of the machine is 16 watts/℃ and heat dissipation constant value (D. is 4 watts/℃.
A. 6 sec
B. 7 sec
C. 4 sec
D. 9 sec
Answer: C
The heating time constant of the machine is the ratio of the thermal capacity of the machine and the heat dissipation constant value.
τ = c÷D = 16÷4 = 4 sec.
25. Calculate the heat absorbed by a 20 Ω resistor when 40 V is applied across it.
A. 120 W
B. 100 W
C. 80 W
D. 110 W
Answer: C
The resistor always absorbs active power and dissipates it in the form of heat. Power absorbed by a 20 Ω resistor is
40×40÷20=80 W.
26. Full form of VFD is _____________
A. Variable frequency drive
B. Variable force drive
C. Value frequency drive
D. Variable force diverter
Answer: A
VFD stands for variable frequency drive. It is a controller for AC or DC motors to achieve the desired speed. It can perform the four-quadrant operation.
27. What is Load Equalisation?
A. Process of smoothing the fluctuating load
B. Process of removing the load
C. Process of changing the voltage level
D. Process of changing the speed
Answer: A
Load Equalisation is the process of smoothing the fluctuating load. Load fluctuation causes a large voltage dip in the system and can damage the device.
28. Which device is used to store the energy during load equalization?
A. Flywheel
B. Capacitor
C. Inductor
D. Resistor
Answer: A
The flywheel is used to store the energy during load equalization. It acts as a reservoir. It stores the energy during light load and utilizes the stored energy during peak load conditions.
29. Which test is used to determine the conditions where electric motors are being used?
A. Thermography
B. Geography
C. Seismography
D. Anthropology
Answer: A
Thermography is used to detect heat patterns. It uses an Infrared rays camera. This test is used to determine the conditions where electric motors are being used.
