What is the saturation of a permanent magnet generator?

Answer 1

The term, 'saturation', applies to all ferromagnetic materials including the magnetic circuits used in machines. Saturation refers to a situation where a material's magnetic field has achieved its maximum intensity.

If a length of insulated wire is wound around a ferromagnetic material, and a current passed through it, that material will become magnetised. In the case of 'soft' materials, such as iron, this is only temporary and will disappear (almost) when the current is switched off. But with 'hard' materials, such as steel, the magnetism will be retained. In this sense, the terms 'soft' and 'hard' refer to the magnetic properties of the material, and not the literal sense!

So, when current is passed through the wire, we end up with what is called a magnetic field strength (symbol: H), defined in terms of the magnetomotive force (current times the number of turns) per unit length (in metres) for the magnetic circuit, and expressed in amperes per metre (usually spoken as 'ampere-turns per metre'). If the current is increased, then the intensity of the resulting magnetic field, i.e. its magnetic flux density (symbol: B) will also increase. But it will not increase indefinitely, rather it will reach a point called 'saturation' at which point any further increase in magnetic field strength will result in absolutely no further increase in the flux density of the field. This is the point at which saturationhas been reached.

If you think of a ferromagnetic material being made up of billions of molecules which behave like tiny, individual magnets (we call these 'domains'), in the unmagnetised state these are chaotically orientated and, so, the material is unmagnetised. When magnetised, these domains align in a north-south direction and, once aligned, the material has reached its maximum flux density and we say that it is 'saturated'.