Lets assume we have a 1 kg iron core, and a 100 kg iron core. Now saturation is defined as how much that core can absorb the magnetic field, since they are different sizes, don't they saturate at different fields?
Lets assume the 1kg core saturates at 1 Tesla, shouldn't the larger core saturate at a higher magnetic field?
Answer
Now saturation is defined as how much that core can absorb the magnetic field
Not quite. The saturation point of a ferromagnetic is roughly defined as the internal $\mathbf{B}$-field strength at which ferromagnetic amplification of the external $\mathbf{H}$-field stops. It doesn't really have anything to do with the size of the material.
A crude way of thinking of ferromagnetic materials is that (ignoring magnetic hysteresis) they act like "amplifiers" of external magnetic fields. This amplification factor is given by the relative permeability $\mu_r$; for example, iron typically has an amplification factor of 4000, meaning that it amplifies an externally-applied $\mathbf{H}$-field by a factor of 4000 relative to vacuum.
Unfortunately, this amplification stops past a certain point, typically on the order of several Tesla. This means that if $\mathbf{B}=\mu_r\mathbf{H}=2\text{Tesla}$ is the saturation maximum of the material, then increasing $\mathbf{H}$ by a factor of 2 will NOT result in $\mathbf{B}=4\text{Tesla}$, but in fact will be much less, maybe 2.1 Tesla.
One thing that does confuse me as far as the effect of size is concerned is this line on the Wiki page:
Saturation limits the maximum magnetic fields achievable in ferromagnetic-core electromagnets and transformers to around 2 T, which puts a limit on the minimum size of their cores.
Does anyone know what is meant when they say it puts a limit on the minimum core size?
No comments:
Post a Comment