GATE Electrical Engineering (EE) 2018 Solved Paper

Question : 51 of 65

Marks: +1, -0

A 200 V DC series motor, when operating from rated voltage while driving a certain load, draws 10 A current and runs at 1000 rpm. The total series resistance is 1Ω The magnetic circuit is assumed to be linear. At the same supply voltage, the load torque is increased by 44%. The speed of the motor in rpm (rounded to the nearest integer) is ________________.

Your Answer:

Validate

Solution:

Given,

I_{a 1}=10 {A}

N_{1}=1000 {rpm}

( {R}_{ {a}}+ {R}_{ {se}})=1 Ω

{T}_{2}=1.44 {T}_{1}

In series motor,

T ∝ I_{a}^{2}

\;{T_{1}}/{T_{2}}=\;{I_{a_{1}}^{2}}/{I_{a_{2}}^{2}}

\;{T_{1}}/{1.44 T_{1}}=\;{10^{2}}/{I_{a_{2}}^{2}}

I_{a 2}=12 {A}

Also,

E_{b} ∝ I_{a} N

\;{E_{b 1}}/{E_{b 2}}=\;{I_{a 1} N_{1}}/{I_{a 2} N_{2}}

\;{200-10(1)}/{200-12(1)}=\;{10 × 1000}/{12 × N}

N=824.56 {rpm}

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