Help me getting the the magnetizing circuit of a transformer

[ona2000]

I want to get the magnetizing circuit gm & bm of a transformer, If we have Ploss (no load loss) in watts and Ie (exciting current) in pu (based on nominal voltage and MVA base)

Here is the definition from PSSE documentations:
MAG1, MAG2 MAG1 is the no load loss in watts and MAG2 is the exciting current in pu on winding one to two base MVA (SBASE1-2) and nominal voltage (NOMV1).

Here is my derivation :

Ploss pu = Ploss/(MVAbase in watts)

Vpu * Vpu * gm = Ploss pu

Because V is the nominal voltage so Vpu = 1 pu, we get gm as Ploss pu

We have Y magnetizing circuit as gm + j bm
Yabs = sqrt(gm * gm + bm * bm) = Ipu/Vpu = Ipu (as Vpu = 1)

sqrt(gm * gm + bm * bm) = Ipu

Then bm = sqrt(Ipu * Ipu - gm * gm)

What is wrong with these calculations?

 

[alehman]

Is this a homework problem?

 

[ona2000]

No Sir, it is not a homework problem ... It is a work problem!

 

[7anoter4]

Hi ona2000
If we may neglect Z1=R1+jX1 , I'2o [and Z'2=R'2/s+jX'2] then
I1o=V1*(1/Rfe-j/Xmiu) ;gm=Zb/Rfe bm=Zb/Xmiu
[Zb=Vbase^2/MVAbase ]and then
Ipu=sqrt(gm^2+bm^2) indeed.
The total error may be 5-20% or more.See Attachment
Best Regards