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GATE 2015 EE - SET 1 - Question 21

Solution :

$R_{a}$ = 0.152 , $E_{1}$= 200 V , Rate speed =$N_{1}$ , Rate flux = $\phi _{1}$

Half  rated speed =$N_{2}$ = $\frac{N_{1}}{2}$

Half rated flux =  $\phi _{2}$  ⇒  $\phi _{2}$ = $\frac{\phi _{1}}{2}$

$E\alpha$ = $\phi N$

$\frac{E_{1}}{E_{2}}$= $\frac{\phi _{1}N_{1}}{\phi _{2}N_{2}}$

$E_{2}$ = 200 /4 = 50 V

E =V $\left \lfloor 1 - e^\frac{-t}{RC}\right \rfloor$

25 = 50 $\left \lfloor 1 -e^\frac{-t}{0.1*1000*10^{-6}} \right \rfloor$

$\frac{1}{2}$  =$1- e^\frac{-t}{100*10^{-6}}$

t = 0.693 * 10 -4

t = 69.3 * 10 -6

t = 69.3μs

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