[FEMM] Unexpected inductances values!

[Ahmad Eid <ahmad_m_eid@xxxxxxxxx>]

Dear all

I'm trying to find the inductances (self and mutual)
of four coils PM linear motor. 
I tried to folow the method that Dr David writes in
the manual, but I confused. If there are PM in the
design, I calculate the inductance with existing PM or
I should remove them first to calculate the
inductances.

My calculations as follows:
I applied 10 A in the fist coil only and each coil has
60 turns and using block integral and I don't remove
the permanent magnets from the model:

1) the self inductance of coil 1 = integral (A.J) dv =
-0.883457 Henry Amp^2 then dividing by current square:

	Lself = 8.8345 mH

2) the mutual inductance between coil 1 and 2
 	L12 = integral (A)dv
Integral of A over selection:
7.8108e-007 Henry Amp meter^2
Integral of A / selected area:
0.00150133 Henry Amp

L12 = 0.00150133 *Nturns/current=0.00150133*60/10 = 9
mH

3) L13 = L12 = integral (A)dv
Integral of A over selection:
-7.55774e-007 Henry Amp meter^2
Integral of A / selected area:
-0.00145268 Henry Amp

L13 = -0.00145268*60/10 = 8.716 mH

4) L14 =  L12 = integral (A)dv

Integral of A over selection:
9.24499e-007 Henry Amp meter^2
Integral of A / selected area:
0.00177699 Henry Amp

L14 = 0.00177699 *60/10 = 10.66194 mH

As shwon from the four results that the mutual
inductance is bigger than the self inductance and I
think this is wrong.

I don't know where are the mistakes

any suggestion will be appreciated
thanks all

ahmad




	
		
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