# Difference between Numerical calculating and FEA almost %10 error, Why?

I have a problem about flux density. If I use FEA programs (maxwell 2d) , I find 1.55-1.61 tesla at the stator yoke.

But if I use general formulas of total flux, which is E=4.44xfxɸxNxkdxkt, i find 1.71 tesla at the stator yoke.

This is why? All the other FEA result parameters phase current, torque, speed are confirmed with experiments. But yoke flux is not correct if I calculate the flux density with numerically.

We have motor, and motor specifications are:

Motor type: 3 phase squirrel cage induction motor, delta connection

40 turn for each phase

Frequency :50 Hz

Winding factor : 0.955

Voltage :383 Volt

I am calculating total flux and flux density as below.

Total flux = 383/(0.955x222x40)

= 0.0452 tesla

Stator length : 480 mm

Stator yoke width :27.4 mm

Flux density at yoke = 0.0452/(2x480x27.4x10^6)

= 1.717 tesla

As you see flux density is 1.717 tesla but FEA programs says 1.55- 1.61 tesla

About %10 percentage error appears.

At first I thought this is meshing problem, but there are good meshing in air gap. Please give me a answer?

Thanks a lot.