The power input to a 500 {V}, 50 {Hz}, 6-pole, 3-phase induction motor running at 975 {RPM} is 40 {kW}. The total stator losses are 1 {kW}. If the total friction and windage losses are 2.025 {kW}, then the efficiency is ________%

GATE Electrical Engineering (EE) 2021 Solved Papers

Question : 14 of 65

Marks: +1, -0

The power input to a

500 {V}, 50 {Hz}

, 6-pole, 3-phase induction motor running at

975 {RPM}

40 {kW}

. The total stator losses are

1 {kW}

. If the total friction and windage losses are

2.025 {kW}

, then the efficiency is ________%

Solution:

{S}=\;{ {N}_{s}- {N}_{r}}/{ {N}_{s}}=\;{1000-975}/{1000}

{s}=0.025

{P}_{ {gm}}=(1- {s}) {p}_{ {i}}=(1-0.025)( {P}_{ {in}}-

stator loss

)

η_{ {m}}=\;{P_{\;\text "out "\;}}/{P_{\;\text "in "\;}}=\;{P_{\;\text "gm "\;}-P_{\;\text "mech "\;}}/{40 {kW}}=\;{38.025-2.025}/{40}

η_{ {m}}=0.9

i.e.

90 \%

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