Hello folks,
Let us talk something about the soul of the power system – Transformers.
The core of the transformer is a very important component of transformer and governs the operating character of it. As we always say, it is not made up of silicon steel (electrical steel). It is made up of material called - CRGO steel (Cold Rolled Grain Oriented Steel). CRGO is silicon steel but treated specially.
Features of Si Steel are Ferromagnetic material, High permeability to the flow of flux (magnetization is easy), Low hysteresis coefficient and so hysteresis loss is low.
If core is made up of pure steel, it has good magnetic properties but it has more conductivity. Strength of eddy current inside core depends on conductivity of steel. There exists a large circulating current (eddy current) as conductivity of core is more. About 4-5% silica is added to pure steel, to reduce eddy current loss. Conductivity of steel is reduced without affecting its magnetic strength. Yet eddy current is not reduced to that extended which is needed. So we go for CRGO.
Addition of silicon to iron is important as it significantly increases the electrical resistivity of the steel, which decreases the induced eddy currents and narrows the hysteresis loop (area under B-H curve is proportional to the losses) of the material, thus lowering the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability of the material.
So this Si-steel has BCC structure - Body centered cubic structure (Google it to know about it). This crystal, when subjected to magnetic field, can undergo magnetization in 3 ways (directions)
1. Along the shorted edge of the cube
2. Along the face diagonal of the cube
3. Along the through diagonal of the cube
Shorter the length of axis of magnetization, lower is the reluctance offered. To reduce magnetizing current, permeability should be very high and reluctance offered should be very low. So we take special efforts to magnetize every crystal (almost) along the shortest axis that is the edge of the cube.
This texture is developed by a series of careful working and annealing operations. It involves heating a material to above its critical temperature, maintaining a suitable temperature, and then cooling. Transformer core is laminated to reduce eddy current loss.
Order of flux density of core in its increasing order is
Cast iron > Cast steel > Mild steel > Silicon Steel > CRGO
Thank you for your time and do comment about your areas of interest. We can have a two-way discussion on that topic.
Let us talk something about the soul of the power system – Transformers.
The core of the transformer is a very important component of transformer and governs the operating character of it. As we always say, it is not made up of silicon steel (electrical steel). It is made up of material called - CRGO steel (Cold Rolled Grain Oriented Steel). CRGO is silicon steel but treated specially.
Features of Si Steel are Ferromagnetic material, High permeability to the flow of flux (magnetization is easy), Low hysteresis coefficient and so hysteresis loss is low.
If core is made up of pure steel, it has good magnetic properties but it has more conductivity. Strength of eddy current inside core depends on conductivity of steel. There exists a large circulating current (eddy current) as conductivity of core is more. About 4-5% silica is added to pure steel, to reduce eddy current loss. Conductivity of steel is reduced without affecting its magnetic strength. Yet eddy current is not reduced to that extended which is needed. So we go for CRGO.
Addition of silicon to iron is important as it significantly increases the electrical resistivity of the steel, which decreases the induced eddy currents and narrows the hysteresis loop (area under B-H curve is proportional to the losses) of the material, thus lowering the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability of the material.
So this Si-steel has BCC structure - Body centered cubic structure (Google it to know about it). This crystal, when subjected to magnetic field, can undergo magnetization in 3 ways (directions)
1. Along the shorted edge of the cube
2. Along the face diagonal of the cube
3. Along the through diagonal of the cube
Shorter the length of axis of magnetization, lower is the reluctance offered. To reduce magnetizing current, permeability should be very high and reluctance offered should be very low. So we take special efforts to magnetize every crystal (almost) along the shortest axis that is the edge of the cube.
This texture is developed by a series of careful working and annealing operations. It involves heating a material to above its critical temperature, maintaining a suitable temperature, and then cooling. Transformer core is laminated to reduce eddy current loss.
Order of flux density of core in its increasing order is
Cast iron > Cast steel > Mild steel > Silicon Steel > CRGO
Thank you for your time and do comment about your areas of interest. We can have a two-way discussion on that topic.
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