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Common Data for Questions 71,72,73: A three phase squirrel cage induction motor has a starting current of seven times the full load current and full load slip of 5%.
If an autotransformer is used for reduced voltage starting to provide 1.5 per unit starting torque, the autotransformer ratio (%) should be
- 57.77%
- 72.56%
- 78.25%
- 81.33%
Correct answer: 78.25%
Solution
Using Tst/Tfl = x^2 (Isc/Ifl)^2 * sfl with Isc/Ifl=7, sfl=0.05: 1.5 = x^2 * 49 * 0.05 = 2.45 x^2, so x^2=0.6122 and x=0.7825. The autotransformer ratio is 78.25%, not 72.56%.
Related GATE Technical questions
- Consider the following C code segment.
int a, b, c = 0;
void prtFun(void);
main()
{
static int a = 1; /* Line 1 */
prtFun();
a += 1;
prtFun();
printf("
%d %d ", a, b);
}
void prtFun(void)
{
static int a = 2; /* Line 2 */
int b = 1;
a += ++b;
printf("
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}
What output will be generated by the given code segment?
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