21. Energy is stored in Flywheel in the form of __________
A. Kinetic energy
B. Electrical energy
C. Solar energy
D. Wind energy
Answer: A
Energy is stored in Flywheel in the form of kinetic energy. It stores rotational kinetic energy.
22. Calculate the coefficient of fluctuation of speed using the data: Vmax(Fluctuation)=25 m/sec, Vmean=12 m/sec.
A. 2.08
B. 2.16
C. 2.34
D. 2.74
Answer: A
The coefficient of fluctuation of speed is the ratio of the maximum fluctuation speed and mean speed.
C.F = Vmax(Fluctuation) ÷ Vmean = 25÷12 = 2.08.
23. Calculate the maximum fluctuation of speed using the data: Vmax=23 m/sec, Vmin=13 m/sec.
A. 12
B. 10
C. 14
D. 15
Answer: B
The maximum fluctuation of speed is the difference between the maximum speed and minimum speed. Maximum fluctuation of speed
= Vmax – Vmin = 23 – 13 = 10.
24. Calculate the Kinetic energy of the object of mass = 7 Kg moving in a straight line with a velocity of 12 m/s.
A. 504 J
B. 502 J
C. 503 J
D. 509 J
Answer: A
The Kinetic energy of the object of mass = 7 Kg moving in a straight line with a velocity of 12 m/s is
.5×m×v2 = .5×7×12×12 = 504 J.
25. Calculate the rotational kinetic energy of the object using the data: I=5 Kg-m2, ω=25 rad/sec.
A. 1.46 KJ
B. 1.56 KJ
C. 2.58 KJ
D. 3.15 KJ
Answer: B
The Kinetic energy of the object having a moment of inertia=5 kg-m2 rotating with an angular velocity equal to 25 rad/sec is
.5×I×ω2 = .5×5×25×25 = 1.56 KJ.
26. Calculate the line voltage for 3-∅ 120° VSI if the value of DC supply is 96 V.
A. 68.25 V
B. 67.87 V
C. 66.25 V
D. 62.14 V
Answer: B
The line voltage for 3-∅ 120° VSI is
(VDC÷√2)=.707×96=67.87 V.
In 3-phase 120° VSI each phase conducts for 120° and only three switches from different phases conduct at a single time.
27. Calculate the phase voltage for 3-∅ 120° VSI if the value of DC supply is 78 V.
A. 30.45 V
B. 15.18 V
C. 31.84 V
D. 48.15 V
Answer: C
The line voltage for 3-∅ 120° VSI is (VDC÷√6)=31.84 V.
In 3-phase 120° VSI each phase conducts for 120° and only three switches from different phases conduct at a single time.
28. Calculate the r.m.s value of thyristor current in 3-Φ Full-wave converter for the load current=2 A and α=59°.
A. 1.15 A
B. 2.55 A
C. 2.07 A
D. 2.89 A
Answer: A
The r.m.s value of thyristor current in a 3-Φ Full-wave converter is Io√1÷3. It is the r.m.s value of the thyristor current.
I(r.m.s) = Io√1÷3=1.15 A.
29. Calculate the average value of thyristor current ia n 3-Φ Full-wave converter for the load current=729 A and α=3°.
A. 254 A
B. 285 A
C. 247 A
D. 243 A
Answer: D
The average value of thyristor current in a 3-Φ Full-wave converter is Io÷3. It is the average value of the thyristor current.
I(r.m.s) = Io÷3=243 A.
30. 1600 V rated 8 SCRs are connected in series. The operation voltage of the string is 4400. Calculate the string efficiency.
A. 34.37 %
B. 30.15 %
C. 38.48 %
D. 35.84 %
Answer: A
The string efficiency can be calculated using the formula
operation voltage ÷ (Number of SCRs×Rated voltage)
= 4400÷(1600×8) = 34.37 %.