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Electrical Engineering Questions and Solutions Set 7

Electrical Engineering Questions and Solutions Set 7
Question:-
Option (A)
0.1,0.9
Option (B)
0.1,-0.9
Option (C)
0.1,1.9
Option (D)
0.1,-1.9
Correct Option:
C
Question Solution:
Nsf= (120 x f)/P = (120 x 50)/4 = 1500rpm
Nsr= -(120f/P) = -(120 x 50)/4 = -1500rpm
Slip w.r.t Nsf=Sf =(1500-1350)/1500 = 0.1
Slip w.r.t Nsr Sr =(-1500-1350)/-1500=1.9
Question:-
Option (A)
196 V
Option (B)
220 V
Option (C)
240 V
Option (D)
248 V
Correct Option:
D
Question Solution:
If = (220/220) = 1A : Ia = 12 A
Isupply = Ia + If = 12 + 1 = 13 A

As generator

Ia = 13 + 1 = 14 A
Emf = 220 + 2 × 14 = 248 V
Question:-
Option (A)
96.62%
Option (B)
97.08%
Option (C)
96.15%
Option (D)
97.88%
Correct Option:
A
Question Solution:
h=(0.8 x 25000)/(0.8 x 25000 + 300 + 400)
= 96.62%
Question:-
Option (A)
4156W
Option (B)
3885W
Option (C)
280W
Option (D)
3730W
Correct Option:
A
Question Solution:
Mechanical power developed in rotor =3.73KW


Ns= 120x50/6=1000 rpm


3730/rotor input=960/1000


So rotor input=3885 W


Stator input=rotor input stator loss=3885+280=4156W
Question:-
Option (A)
7.6%
Option (B)
6.7%
Option (C)
5.2%
Option (D)
10%
Correct Option:
A
Question Solution:
Cu loss will be 40 KW and percentage leakage reactance is 100%
Regulation=Vr cos j + Vxsin j = (2 x 0.8) + (10 x 0.6) = 7.6%
Question:-
Option (A)
Slip frequency
Option (B)
Supply frequency
Option (C)
Frequency corresponding to rotor speed
Option (D)
Zero
Correct Option:
A