I am a young electrical engineer and need to review the basics of transformer saturation: conceptually as well as the mathematics and theory behind it.
The flux density in a transformer core is limited in the case of iron alloys to an absolute maximum at about 1.5tesla(15000gauss).(for most small transformers 10,000 gauss is the norm) So the design criterion is based on the formula:- V(rms) (4.44*B*N*F*A)/ 10^8 Where B is the peak flux density(in gauss), N is the total of conductor turns on the core,f is frequency,A is core cross section in square cm. If this is adhered to the no load current in the primary coil will be limited to about 0.5 amperes per Kg of core.If the core peak flux exceeds this only slightly the no load current climbs very rapidly because the iron reluctance cannot grow and so the air flux must grow hugely(meaning that the primary current rises rapidly until it melts or the fuse melts)
Every magnetisable substance behaves like a collection of tiny compass needles, each of which can align itself with an externally-applied magnetic field. P.E. is stored in these compass needles and is released when the field collapses (and the compass needles spring back to their original positions). Since there are only so many of these tiny compass needles in a sample of magnetisable material, there is a limit to how much energy can be stored. Magnetic saturation occurs once all the compass needles are aligned with the external field. An inductor which has become saturated behaves as a simple resistor: it doesn't store energy, just convert it to heat. When a transformer core becomes saturated, the output waveform becomes distorted and the windings get very hot. Steel is generally good for a flux density of 1 - 1.6 Teslas (1 Tesla 1Weber per m?), the better grades being preferred for high-quality mains transformers as they allow cores to be made smaller. (Using a larger core would require more copper wire in the windings; there is a trade-off here.) Ferrites typically saturate at 0.2 - 0.5T, but are much preferred for high-frequency applications since the higher the frequency, the thinner each individual lamination would have to be to avoid eddy current losses.
