Cold Rolled Grain Oriented (CRGO) silicon steels are used for laminations of the Power Transformers. Cold Rolled Grain Oriented (CRGO) sheets will have superior magnetic properties in the direction of rolling. The crystals are aligned in the direction by cold rolling followed by heat treatment process. Magnetic properties of the CRGO steel Sheets are dependent on the magnetic properties of the individual crystals of the material and the direction of orientation of the crystal. The properties of the CRGO silicon steels are improved by composition, manufacturing process, heat treatment, laser irradiation etc.
When alloying, the concentration levels of carbon, sulfur, oxygen and nitrogen must be kept low, as these elements indicate the presence of carbides, sulfides, oxides and nitrides. These compounds, even in particles as small as one micrometer in diameter, increase hysteresis losses while also decreasing magnetic permeability. Larger the size of grains lesser the losses and hence grain size of CRGO steel is made larger than normal steel.
Thickness of the CRGO sheets will be of the order of 0.33mm to 0.25mm. These CRGO Steel Laminations are stacked together to form a magnetic core for the Transformer.The Commercially available CRGO steel sheets will have 3% of Silicon. Higher the Silicon content increases the resistivity and reduces the eddy current losses. But Silicon Content above 3.5% makes the CRGO silicon steel sheets brittle.
Hysteresis Loss
When a magnetic field is applied, all the grains of the magnetic material will orient in the direction of magnetizing force. In another cycle this grains will orient in opposite direction in the direction of magnetizing force. The energy required to change the orientation of the magnetic grains in the direction of the magnetic field is lost in the form of heat. This loss is called hysteresis loss which make it non reversal.
Magnetic permeability
In electromagnetism, permeability is the measure of the ability of a material to support the formation of a magnetic field within itself. In other words, it is the degree of magnetization that a material obtains in response to an applied magnetic field. In general, permeability is not a constant, as it can vary with the position in the medium, the frequency of the field applied, humidity, temperature, and other parameters.