Question

A standard 3-phase, 16-pole squirrel-cage induction motor is rated at 460 V,60 Hz. We ant the motor to run at a no-load speed of about 335 RPM while maintaining the same flux in the air gap. Calculate the voltage and frequency to be applied to the stator.

Answer 1

To run a 3-phase, 16-pole squirrel-cage induction motor at 335 RPM while maintaining the same flux, adjust the voltage to approximately 342.1 V and the frequency to 44.67 Hz.

Step-by-step explanation:

To calculate the voltage and frequency to be applied to the stator of a 3-phase, 16-pole squirrel-cage induction motor to run it at a no-load speed of about 335 RPM while maintaining the same flux in the air gap, we can use the following formulas:

1. First, we find the synchronous speed Ns, which is the speed at which the motor's magnetic field rotates. It's calculated by the formula Ns = (120 × f) / P, where f is the frequency in Hz and P is the number of poles.
2. For the original speed at 60 Hz, the synchronous speed is Nsoriginal = (120 × 60) / 16 = 450 RPM.
3. Since we want the motor to run at 335 RPM, we'll calculate the required frequency using the same formula, resulting in frequired = (P × Nsdesired) / 120. Inserting our values gives us frequired = (16 × 335) / 120 ≈ 44.67 Hz.
4. To maintain the same flux Φ in the air gap, the voltage V must also be adjusted in proportion to the frequency, according to Vnew / Voriginal = fnew / foriginal. Our original voltage is 460 V, so Vnew = (460 V × 44.67 Hz) / 60 Hz ≈ 342.1 V.

So, to have a no-load speed of about 335 RPM while maintaining the same flux in the air gap, the motor should be supplied with a voltage of approximately 342.1 V and a frequency of 44.67 Hz.