Question:-
The full-load efficiency and power factor of a 16 h.p., 440 V, 3 phase induction motor are 85% and 0.8 (lag) respectively. The short circuit current (line value) is 45 A at 220 V. Calculate the ratio of starting to full-load current if the motor is provided with a star-delta starter. Neglect magnetizing current.
Option (A)
0.5
Option (B)
0.8
Option(C)
1.23
Option(D)
1.3
Correct Option:
(D)
Question Solution:
Ift = (16 x 746) /( √3 x 440 x 0.8 x 0.85) =23.0 A . (line value)
Line value of short circuit current on normal voltage,
ISC = 45 x (440/220) =90A
So phase value of short circuit current
=(90/ √3) = 51.96A
Now line value of starting current in star I1y
= phase value of starting current in star
=(51.96/ √3) = 30.0A
(I1y/Ift) = (30.0/23.0) = 1.304
question-answer-faq-1642