Electrical steels are metals used in the manufacture of electrical equipment elements. The response to the question as to why the center of the transformer is made of electrical steel has properties that make it possible to reduce resistance. By-resistance, the transformer requires less energy for transmitting pulses.
Composition and production
Electrical steel is an alloy of iron and iron silicide (FeSi) in various proportions:
- Hot-rolled alloy up to 3.3% FeSi (E41, E42, E43).
- Cold-rolled alloy up to 4.5% FeSi (E310, E320, E3ZO).
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Silicide extracts oxygen from iron and reduces its magnetic properties. Iron is reduced by oxides, silicone oxide is formed, which is partially converted into slag. Around the same time, cementite (Fe3C) is being replaced by graphite. Often up to 0.5 percent of aluminum is applied during the manufacturing process. The finished products are supplied in the form of thin sheets.
Marking:
- E – Electrical.
- First digit (aluminium material):
- “1” – Lightly alloyed.
- “2” – Medium alloyed.
- “3” – High-alloyed.
- “4” – Highly alloyed.
- “A” – Small losses.
- 0 – Cold rolled.
Hot-rolled alloys are exposed to high temperatures at the end of manufacturing, allowing the desired thickness parameters to be defined. High temperature facilitates the re-arrangement of bonds between molecules, which results in a decrease in some properties.
A cold rolled alloy has a higher magnetic permeability when it matches the direction of the rolled product. The indicator is much lower throughout, so it is easier to make the core so that the lines close and use special assembly methods.
In addition, cold rolling increases the mechanical strength and surface consistency of the sheets by producing a crystallographic texture. Its consistency depends on the degree of reduction, the temperature of processing and the thickness of the sheet.
For these reasons, most manufacturers try to make cores from electrical steel, although its cost is 2 times higher than that of hot-rolled material.
Performance characteristics
When selecting an alloy for the manufacture of cores, the following shall be taken into account:
- Indicator of resistance (ability to maintain and transmit voltage).
- Coercive force (magnetic field voltage, tendency of the material to demagnetise).
- Coefficient of magnetic permeability (the ratio of induction to magnetic field voltage).
- Sheet thickness.
The magnetic circuit of the transformer concentrates the magnetic fluxes that cause eddy currents. The core of the transformer is made of electrical steel in order to minimize it. This goal can be accomplished if it is made of plates with a thickness of 0.35-0.5 mm.
Technical characteristics of cold rolled electrical steel:
- High magnetic permeability.
- High resistance, which reduces heating losses.
- Low losses for hysteresis (demagnetization) and eddy currents.
The sheets are well stamped, they are insulated with varnish in the magnetic circuit. This absolutely solves the question of why the steel is rolled cold.
Conclusion:
The magnetic cores of the transformers are made of electrical steel in order to enhance their performance. Adding to the silicon and cold rolled alloy, steel is almost the perfect material for the manufacture of electrical components.
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Contributor: Kiran Daware (is a junior electrical engineer at Nicore IndiaPvt. Ltd. He is in the development team of a silicon steel magnetic core and owns an electrical blog a electricaleasy).
