Relative permeabilities in steel datasheets

[Steradiant]

TL;DR

How to interpret the data in an electric steel datasheet?

Hello,
I have a question regarding BH-curves and relative permeabilities from electrical steel datasheets. When e.g. looking at the datasheet from the isovac 330-35A there is the data for the J/H-curve. I calculated B=mu_0*H + J and mu_r=B/(mu_0*H). When evaluating this calculation pointwise with the the data from the table, I don't get the same mu_r/J curve as shown in the datasheet. My maximum mu_r is 7.07e3 instead of 8.23e3. What am I not considering?

 

[cmb]

(2nd edit ... hmmm ... on second thoughts I agree that doesn't look quite right in the data sheet)

 

[alan123hk]

I took a preliminary look at this specification sheet. The first thing that confuses me is that it seems to use the "J/H magnetization curve" instead of the "B/H magnetization curve". People usually use B to represent the magnetic flux density, but in this specification use J to represent.

 

[cmb]

I took a preliminary look at this specification sheet. The first thing that confuses me is that it seems to use the "J/H magnetization curve" instead of the "B/H magnetization curve". People usually use B to represent the magnetic flux density, but in this specification use J to represent.

It's giving AC values. B is usually a letter for DC flux. I assume they are using J to denote it is an AC flux.

I originally looked at that thinking they'd plotted initial (DC) permeability on the first graph (and labelled it wrong) and assumed the OP was talking about that (which is ALSO a difference with the graphs). But the data itself in that table doesn't calculate through.

If they have in mind that there is some sort of adjustment for AC then I am not sure what that is. They seem to have used a value for uo of about 1.1e-6 instead of 1.25e-6 to arrive at their permeability values. I don't know maybe there is some sort of adjustment for this sort of AC calculation but I have never heard of it.

At this point I'd be contacting the vendors for a clarification.

 

[alan123hk]

I calculated B=mu_0*H + J and mu_r=B/(mu_0*H)

I can understand that $~u_r = \frac B {u_0H}$, but I don't quite understand why $~~B=u_0H+J$.

Do you think $J$ is related to the vector current density and magnetization vector $M$ of ferromagnetic materials ? But according to the specification, the unit of $J$ is mt (millitesla), so it should represent the magnetic flux density.

My maximum mu_r is 7.07e3 instead of 8.23e3. What am I not considering?

Could you please elaborate on how you calculated this result ?

 

[Steradiant]

In table on page 2 they list the magnetic polarization in Tesla. Therefore I assumed, that J in the Table is the magnetic polarization (https://en.wikipedia.org/wiki/Magnetization#Magnetic_polarization). As far as I know it's pretty common to use the magnetic polarization instead of the magnetic flux density in the material characterization.

mu_r = 1+J/(mu_0*H) = 1+0.8/(mu_0*90) = 7074.55