Grain-Oriented Electrical Steel Coil CRGO: Grades, Losses and Core Design

What Is CRGO Electrical Steel?

CRGO stands for cold-rolled grain-oriented electrical steel. It is an iron-silicon alloy processed so that the crystal grains align in the rolling direction, giving low core loss and high permeability in that direction. It is the standard material for the cores of power and distribution transformers, reactors, and large rotating machines. Magnetic testing follows IEC 60404-2, and grade classification follows GB/T 2521 or ASTM A876/A876M depending on the project.

Production Route

Hot rolling: the silicon steel slab is hot-rolled to strip thickness.

Cold rolling: two-stage cold rolling with intermediate annealing builds the desired texture.

Decarburization annealing: carbon is removed to avoid magnetic aging.

Final annealing: the material develops the Goss orientation at high temperature in a controlled atmosphere.

Coating: an insulating coating is applied to provide interlaminar insulation and stress protection.

Key Properties

Grain orientation: magnetization is easiest along the rolling direction.

Low core loss: hysteresis and eddy-current losses are minimized at 50 Hz and 60 Hz.

High permeability: a strong Goss texture lowers the magnetizing current.

High lamination factor: flat strip with a thin coating packs tightly, raising the effective core cross-section.

Grade Families and Typical Loss Values

Family	Designation examples	Thickness (mm)	Max core loss P1.7/50 (W/kg)
Common	23SQ110	0.23	1.10
Common	27SQ120 / 27SQ130 / 27SQ140	0.27	1.20 / 1.30 / 1.40
Common	30SQ120 / 30SQ130 / 30SQ140	0.30	1.20 / 1.30 / 1.40
High magnetic induction	27SQG090 / 27SQG095 / 27SQG100 / 27SQG110	0.27	0.90 / 0.95 / 1.00 / 1.10
High magnetic induction	30SQG100 / 30SQG105 / 30SQG120	0.30	1.00 / 1.05 / 1.20
Domain refined	23SQGD080 / 23SQGD085 / 23SQGD090	0.23	0.80 / 0.85 / 0.90
Domain refined	27SQGD085 / 27SQGD090 / 27SQGD095	0.27	0.85 / 0.90 / 0.95
Domain refined	30SQGD095 / 30SQGD100 / 30SQGD105	0.30	0.95 / 1.00 / 1.05

The number after the thickness digits is the maximum core loss in watts per kilogram at 1.7 T and 50 Hz. Equivalent designations from other suppliers may use different prefixes, so compare guaranteed loss values rather than prefixes.

Design Considerations for Transformer Cores

Loss evaluation: choose the grade so the transformer meets the specified no-load loss with the smallest core.

Core construction: step-lap joints reduce no-load current and noise.

Flux density: running at 1.7 T at rated voltage is typical for distribution transformers; higher induction requires better grades.

Cutting: match the slitting width to the blank layout to maximize yield.

Handling Notes

Keep coils dry and store them on their edges.

Protect cut edges from rust after slitting.

Avoid sharp bends across the rolling direction.

If stress-relief annealing is required, follow the recommended temperature window for coated CRGO to protect the insulation coating.

Frequently Asked Questions

What is the difference between CRGO and non-oriented steel?

CRGO has grains aligned in the rolling direction for low loss in a defined flux path; non-oriented steel has random grains and is used where flux changes direction, such as motor cores.

What is the lamination factor of CRGO coils?

Typical values are 96-97.5% depending on thickness and coating, measured per IEC 60404-13.

Which CRGO grade is best for a 50 Hz distribution transformer?

Grades around 27Q120 or 30Q130 give a good balance of loss and cost; low-loss projects use 23Q110, 27Q110, or domain-refined grades.

Can CRGO be used at 60 Hz?

Yes, core loss scales with frequency; the same grade shows a higher loss at 60 Hz, so the design flux density may be adjusted accordingly.

Why is the insulating coating important?

The coating provides interlaminar insulation that blocks eddy currents between sheets; damage to the coating increases core loss and can overheat the core.

What width and weight are typical for CRGO coils?

Common coil widths are 800-1200 mm, with inside diameters around 508 mm and weights of 2-5 t; narrower widths are produced by slitting.