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Electrical machines miscellaneous

Electrical Machines

  1. The figure shows the per-phase equivalent circuit of a t wo-pol e t hr ee-phase i nduct i on mot or operating at 50 Hz. The “air-gap” voltage, Vg across the magnetizing inductance, is 210V rms, and the slip, is 0.05. The torque (in Nm) produced by the motor is _______.
    1. 200 – 303
    2. 303
    3. 400 – 403
    4. 40
Correct Option: C


VOC across j6.28 Ω = Vg = 210 V
Now from the given circuit,

Rth =
j6.28 × (0.4 + j0.22)
(0.04 + j0.22) + j6.28

= 0.216 ∠ 80.04
= 0.0375 + j0.2127
Now , I2 =
Vs
=
210
z(0.0375 + 1) + j(0.2127 + j0.22)

∴ |I2| = 186.81 A
τ =
3
× I22 .
r2
ωss

=
3
× 186.812 × 1 = 333.27 N-m
314.15



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