Types of CRGO - Cold Rolled Grain Oriented Electrical Steel

22 Nov 2023
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GNEE Cold Rolled Electrical Steel

Grain oriented electrical steel is an important material in the production of energy efficient transformers and large, high performance generators. In the form of laminated, wound or punched sheets, it is the essential core material of distribution transformers, power transformers and small transformers.
Grain-oriented electrical steel usually has a silicon level of 3% of the crystal orientation relative to the sheet. It is used for the cores of power and distribution transformers, cold-rolled grain-oriented steel is often abbreviated to CRGO.
Core laminations are the main part of an electrical transformer, and this attribute to 70% of a transformer cost. These core laminations are required to be cut from special steel called as Cold Rolled Grain Oriented Electrical Steel or popularly known as CRGO. The CRGO is a special quality of steel which have a special grain surface and comes in a thickness of 0.23 mm, 0.27 mm, 0.30 mm, 0.35 mm. (generally called M3, M4, M5 & M6). Lower the thickness of material better is the quality of material.
The Quality of CRGO is measured in terms of lower losses of electrical current, which flow in the core. The proper design of core and good quality of core material do a best job in combination. Mainly the core losses are measured in Watts per Kg.
Every type of steel has “grains” which consist of “domains”. These “domains” are nothing but electrical charges oriented in any random direction. Therefore if a transformer were to be made of Mild Steel used as core material, the core loss would be approx. 16 to 17 w/kg at 1.5T/50Hz and the size of the transformer would be approx. 18 to 20 times the size of a transformer manufactured with GO steels.

electrical steel coil

oriented electrical steel

Properties of CRGO Steel

It is a soft magnetic material and has the following properties: 

  • High magnetic permeability.
  • Reduced magnetostriction.
  • High resistivity.
  • High stacking or laminating factor allows compact core designs.
  • Low losses.

Grades of CRGO Steel

  • The early grades of steel were known as M7(0.7watts /lb at 1.5T/60Hz) and M6(.6watts/lb at 1.5T/60Hz).
  • Similarly, M5 M4 and M3 grades were developed in the late sixties.
  • A new material called Hi-B has a remarkable degree of orientation and is 2 - 3 grade better than conventional CRGO steel products.
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