Grain-Oriented Silicon Steel: Advantages in Transformer Cores
Oct 16, 2025
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What Grain-Oriented Silicon Steel Is
Grain-oriented silicon steel, normally abbreviated to CRGO (cold-rolled grain-oriented electrical steel), is a soft magnetic material produced with a pronounced Goss texture. During cold rolling and the following high-temperature anneal the crystal grains grow so that their easy magnetisation axis lies parallel to the rolling direction of the strip. Magnetic performance is therefore excellent along that axis and clearly weaker across it.
That directional behaviour is what separates CRGO from non-grain-oriented electrical steel (CRNGO), whose grains are randomly distributed. CRNGO is essentially isotropic and is normally selected for rotating machines such as motors and generators. CRGO is selected for static apparatus such as transformers, where the flux path is fixed by the geometry of the laminated core.
Why the Core Decides Transformer Performance
The laminated core forms the magnetic circuit and performs two jobs:
Flux path: it gives the alternating flux produced by the primary winding a low-reluctance route to the secondary winding, so energy transfers with the smallest possible magnetising current.
Flux control: it guides the field so that most of it links the secondary turns and induces the required voltage.
Core material therefore sets no-load loss, magnetising current, temperature rise and physical size. Permeability, resistivity and hysteresis behaviour are the decisive properties, and these are exactly the areas in which grain-oriented strip outperforms ordinary structural steel.
Advantages of CRGO in Transformer Cores
| Property | Benefit in service |
|---|---|
| High permeability along the rolling direction | Lower magnetising current, so a smaller core carries the same power and runs cooler. |
| Low specific core loss | Grain orientation suppresses hysteresis and eddy-current loss, which lifts the whole-day efficiency of a distribution transformer. |
| Stable induction | Output voltage stays constant across a wide load range because the core needs little excitation. |
| Low magnetostriction | Less core vibration, so the familiar transformer hum and the acoustic signature of the installation are reduced. |
| Lower heat generation | Less loss means a lower temperature rise, longer insulation life and lower maintenance cost. |
| Compact laminations | Thin strip with a high stacking factor allows smaller and lighter cores for the same rating. |
Typical Applications of CRGO Cores
Grid distribution: step-up and step-down transformers from generating plant to end users, where loss is metered over the whole day.
Renewable generation: wind and solar farms raise voltage for transmission and lower it again at the point of use.
Industrial plants: voltage stability for large drives, furnaces and process machinery.
Traction and transport: on-board and trackside transformers for electric trains and trams.
Substations: voltage regulation and consistent supply quality for utility networks.
Grades, Thickness and Standards
Grain-oriented grades are designated by guaranteed specific loss at 1.7 T and 50 Hz, written P1.7/50, combined with a thickness code. A 0.23 mm grade with a guaranteed loss of 0.85 W/kg is therefore written 23QG085, while 30QG120 denotes a 0.30 mm grade at 1.20 W/kg. The specifications normally quoted in international trade are GB/T 2521, IEC 60404-8-7, ASTM A876 and JIS C 2553. Typical values for the three product families are summarised below.
| Product family | Example grade | Thickness (mm) | Nominal P1.7/50 (W/kg) | Typical actual P1.7/50 (W/kg) | Typical induction J800 (T) |
|---|---|---|---|---|---|
| Conventional CRGO | 23Q110 | 0.23 | 1.10 | 1.08 | 1.85 |
| Conventional CRGO | 27Q120 | 0.27 | 1.20 | 1.15 | 1.85 |
| Conventional CRGO | 30Q120 | 0.30 | 1.20 | 1.15 | 1.85 |
| Conventional CRGO | 35Q135 | 0.35 | 1.35 | 1.20 | 1.85 |
| Hi-B high permeability | 23G085 | 0.23 | 0.85 | 0.85 | 1.90 |
| Hi-B high permeability | 27G090 | 0.27 | 0.90 | 0.89 | 1.90 |
| Hi-B high permeability | 30G105 | 0.30 | 1.05 | 1.01 | 1.90 |
| Domain-refined Hi-B | 20GK070 | 0.20 | 0.70 | 0.69 | 1.88 |
| Domain-refined conventional | 23QK100 | 0.23 | 1.00 | 0.96 | 1.88 |
| Domain-refined conventional | 30GK095 | 0.30 | 0.95 | 0.92 | 1.88 |
Hi-B grades use tighter inhibitor control to raise induction and cut loss further, while laser domain-refined grades subdivide the magnetic domains with fine scribed lines so that loss falls again without changing the strip thickness. Both families are used in premium distribution transformers and large power transformers, where a small loss gain is worth a great deal over a service life of twenty-five to thirty years.
Frequently Asked Questions
Q: What does CRGO mean?
CRGO stands for cold-rolled grain-oriented electrical steel, a silicon steel strip whose grains are aligned with the rolling direction for low-loss transformer cores.
Q: What is the difference between CRGO and CRNGO?
CRGO has oriented grains and is used where the flux path is fixed, as in transformers. CRNGO has random grains, is isotropic, and is used for rotating machines such as motors and generators.
Q: How are grain-oriented grades designated?
By thickness and guaranteed specific loss at 1.7 T and 50 Hz. The grade 23QG085 is 0.23 mm thick with a guaranteed loss of 0.85 W/kg, and 30QG120 is 0.30 mm at 1.20 W/kg.
Q: Which standards cover grain-oriented electrical steel?
GB/T 2521 is the Chinese standard, IEC 60404-8-7 is the international one, ASTM A876 covers the American market and JIS C 2553 the Japanese market.
Q: Does grain orientation really reduce transformer noise?
Yes. Oriented grains lower magnetostriction, the dimensional change that occurs as the core magnetises, and that vibration is the main source of transformer hum.
Q: Why is 0.23 mm strip so common in distribution transformers?
Thinner strip cuts eddy-current loss, so a 0.23 mm grade usually shows lower specific loss than a 0.35 mm grade. It also needs careful handling because the stacking factor falls slightly as thickness decreases.
Q: Can CRGO be used in electric motors?
Normally not. A rotating field sweeps through every direction of the lamination, so the single-axis advantage of oriented steel cannot be used, and CRNGO is the economic choice.