What is the rotor current frequency of a 6-pole. 3-phase induction motor running at 950 rpm while connected to 50 Hz supply.

What is the rotor current frequency of a 6-pole. 3-phase induction motor running at 950 rpm while connected to 50 Hz supply.

Right Answer is:

2.5 Hz

SOLUTION

We have a 6-pole, 3-phase induction motor operating at 950 RPM when connected to a 50 Hz supply. We need to find the frequency of the rotor current.

Synchronous Speed (Ns):

  • Ns = (120 * f) / P

Where

Ns = Synchronous speed in RPM
f = Supply frequency in Hz
P = Number of poles

Ns = (120 * 50) / 6 = 1000 RPM

Slip (s):

  • Slip (s) = (Ns – Nr) / Ns
  • Where Nr = Rotor speed in RPM
  • s = (1000 – 950) / 1000 = 0.05

Rotor Current Frequency (fr):

  • fr = s * f
  • fr = 0.05 * 50 = 2.5 Hz

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