101. The stator voltage control method is a part of the slip changing technique.
A. True
B. False
Answer: A
The stator voltage control method comes under the slip changing technique. The load torque remains constant here. SV2=constant.
102. Calculate the value of the new slip using the given data: V1=12 V, S1=.1, V2=5.
A. 0.576
B. 0.247
C. 0.487
D. 0.987
Answer: A
This question is based on the concept of the stator voltage control method. The load torque remains constant.
S1V12=S2V22=constant.
S2=.576.
103. Calculate the average value of the sinusoidal waveform y(t)=4.56cos(77.64πt+4800π÷68).
A. 41 V
B. 0 V
C. 48 V
D. 78 V
Answer: B
The sinusoidal waveform is generally expressed in the form of V=Vmsin(ωt+α)
where
Vm represents peak value
ω represents angular frequency
α represents a phase difference.
The average value of a sine wave is zero because of equal and opposite lobes areas. Since sine wave is an odd function then the net area of the waveform over a period is a Net area
= A+(-A) = 0.
The average value is Net area÷Time=0.
104. R.M.S value of the periodic square waveform of amplitude 20 V is _______
A. 20 V
B. 18 V
C. 17 V
D. 13 V
Answer: A
R.M.S value of the periodic square waveform is Vm and r.m.s value of the trapezoidal waveform is Vm÷3½.
The peak value of the periodic square waveform is VM. Vm=20 V.
105. Calculate the time period of the waveform y(t)=sin(.1πt)+cos(.2πt).
A. 20 sec
B. 30 sec
C. 40 sec
D. 10 sec
Answer: A
The fundamental time period of the sine and cosine waves is 2π. The time period of y(t) is L.C.M {20,10}=20 sec.
The time period is independent of phase shifting and time-shifting.
106. The V/F control is a part of the synchronous speed changing technique.
A. True
B. False
Answer: B
V/F control comes under the synchronous speed changing technique. Speed above or below synchronous speed can be achieved using V/F control.
107. The slope of the V-I curve is 56.489°. Calculate the value of resistance. Assume the relationship between voltage and current is a straight line.
A. 1.5 Ω
B. 1.6 Ω
C. 2.5 Ω
D. 1.4 Ω
Answer: A
The slope of the V-I curve is resistance.
The slope given is 56.489° so R=tan(56.489°)=1.5 Ω.
The slope of the I-V curve is reciprocal to resistance.
108. If induction motor air gap power is 28.63 KW and gross developed power is 18.8 KW, then rotor ohmic loss will be _________ KW.
A. 9.83
B. 10.55
C. 15.54
D. 4.74
Answer: A
Rotor ohmic losses are due to the resistance of armature windings. Net
input power to the rotor is equal to the sum of rotor ohmic losses and mechanically developed power. Rotor ohmic losses=Air gap power-Mechanical developed power
=28.63-18.8=9.83 KW.
109. Calculate the value of inductive reactance if F=50 Hz and L=12 H.
A. 3768 Ω
B. 2578 Ω
C. 2477 Ω
D. 2456 Ω
Answer: A
Inductive reactance can be calculated using the relation
XL=2×3.14×f×L.
The value of inductive reactance is
XL=2×3.14×50×12=3768 Ω.
110. Calculate the value of capacitive reactance if F=60 Hz and C=14 H.
A. 189.5 mΩ
B. 252.4 mΩ
C. 244.5 mΩ
D. 244.8 mΩ
Answer: A
Capacitive reactance can be calculated using the relation
