The efficiency of a 60 Hz, 6-pole, 1000 rpm 3-phase induction motor is _______.

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SSC JE Electrical 07 Jun 2024 Shift 3 Official Paper - 1
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  1. 69.3%
  2. 83.4%
  3. 75.5%
  4. 94.2%

Answer (Detailed Solution Below)

Option 2 : 83.4%
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Concept

 The slip 's' is given by:

\(s={N_s-N_r\over N_s}\)

The power relation for an induction motor is given by: 

\(P_g:P_c:P_d=1:s:1-s\)

The efficiency of a 3ϕ induction motor is given by:

% η \(={P_d\over P_g}\times 100\)

% η \(={1-s\over 1}\times 100\)

where, s = Slip

Ns = Synchronous speed

Nr = Rotor speed

Calculation

Given, Nr = 1000 rpm

P = 6

\(N_s={120\times 60\over 6}=1200\space rpm\)

\(s={1200-1000\over 1200}=0.167\)

% η \(={1-0.167\over 1}\times 100\)

%η = 83.4%

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