0.27mm 1.00 W/kg Grain-Oriented Silicon Steel for Transformer Cores

 

Grain-oriented silicon steel (GOES), also known as cold-rolled grain-oriented (CRGO) electrical steel, is a specialized ferromagnetic alloy containing 2.5–3.5% silicon, engineered with a highly aligned crystallographic texture known as the Goss orientation {110}<001>. This alignment allows magnetic flux to flow with minimal resistance along the rolling direction, making it the standard material for transformer core laminations.

The designation "0.27mm 1.00 W/kg" specifies two critical parameters: the nominal lamination thickness of 0.27 millimeters and the maximum specific total loss of 1.00 watts per kilogram measured at 1.7 tesla flux density and 50 hertz frequency. This corresponds to grade M100-27 under the EN 10107 European standard - a conventional grain-oriented (CGO) grade widely specified for distribution and power transformer cores.

 

Grain-oriented silicon steel is manufactured through a complex metallurgical process involving cold rolling with high reduction ratios, decarburization annealing, and high-temperature secondary recrystallization at approximately 1200°C. This process produces the distinctive Goss texture where nearly all grains are oriented with their easy-magnetization axis aligned in the rolling direction - a characteristic that distinguishes GOES from non-oriented electrical steel (CRNGO) and gives it superior magnetic permeability in one preferred direction.

 

 

Understanding the magnetic properties of grain-oriented silicon steel is essential for transformer core design. Four key parameters - core loss, magnetic polarization, stacking factor, and coating quality - collectively determine the energy efficiency, size, and cost of the final transformer.

Magnetic Property	Value & Test Condition	Why It Matters
Maximum Specific Total Loss	1.00 W/kg @ 1.7T, 50Hz	Determines no-load loss; lower = higher transformer efficiency
Minimum Magnetic Polarization (B₈₀₀)	1.88 T @ H = 800 A/m	Higher polarization allows a smaller core cross-section
Minimum Stacking Factor	0.95	95% of core volume is effective magnetic material
Core Loss Test Method	SST (Single Sheet Tester, IEC 60404-3)	Standardized, accurate full-sheet measurement
Approx. Density	7.65 kg/dm³	Used for weight calculation and core design

 

The production of grain-oriented silicon steel is one of the most sophisticated metallurgical processes in the steel industry. Each step is precisely controlled to develop the Goss crystal texture that gives GOES its superior magnetic properties along the rolling direction

   

 

Lamination thickness is one of the most critical design parameters in transformer core manufacturing. Eddy current losses - a major component of total core loss - are proportional to the square of lamination thickness. Thinner laminations reduce the eddy current loop area, directly reducing energy dissipation as heat.

 

The 0.27mm gauge represents the optimal balance for 50/60Hz power-frequency transformers:

• Lower eddy current loss than 0.30mm or 0.35mm gauges, improving transformer efficiency
• Better handling characteristics than ultra-thin 0.23mm gauges, which are more fragile and difficult to stamp/assemble
• High stacking factor (0.95 minimum) - thinner laminations have more coating/air interface per unit volume, but 0.27mm maintains excellent packing density
• Cost-effective - 0.27mm (M4 grade) is the most widely specified thickness for distribution transformers, offering the best price-to-performance ratio
• Meets efficiency mandates - helps transformers comply with EU Tier 2, US DOE 2016, and other global efficiency standards

 

 

Understanding the fundamental difference between oriented and non-oriented electrical steel

Property	Grain-Oriented (CRGO/GOES)	Non-Oriented (CRNGO)
Crystal Texture	Goss {110}<001> - anisotropic, aligned in rolling direction	Random/isotropic - uniform in all directions
Magnetic Permeability	Very high along rolling direction	Moderate, uniform in all directions
Core Loss	Low (0.85–1.35 W/kg @ 1.7T/50Hz)	Higher (varies by grade)
Primary Application	Transformer cores (flux flows in one direction)	Motors, generators (flux rotates)
Typical Thickness	0.23–0.35 mm	0.35–0.65 mm
Stacking Factor	0.95–0.97	0.95–0.98
Cost	Higher (complex manufacturing)	Lower (simpler process)
Standard	EN 10107	EN 10106

 

Power Transformers

3 MVA – 1000 MVA oil-immersed and dry-type units. CRGO cores minimize no-load losses in transmission and substation transformers.

Distribution Transformers

25 kVA – 2.5 MVA pole-mounted and pad-mounted units. 0.27mm (M4) is the most commonly specified grade for distribution networks.

Instrument Transformers

Current transformers (CT) and voltage transformers (PT/VT) requiring high permeability and low remanence for accurate measurement.

Traction Transformers

Railway and EV traction transformers requiring compact, high-efficiency cores with low losses under variable load conditions.

Reactors & Chokes

Shunt reactors, current-limiting reactors, and filter reactors using GOES cores for inductive components in power systems.

Specialty Transformers

Rectifier transformers, furnace transformers, and high-frequency power supply transformers for industrial applications.

 

  

 

What does 1.00 W/kg core loss mean for transformer performance?

1.00 W/kg at 1.7T/50Hz means the material dissipates 1 watt of energy per kilogram of core steel when magnetized to 1.7 tesla at 50 hertz. Lower core loss directly reduces the transformer's no-load losses, improving energy efficiency and reducing lifetime operating costs. This grade sits in the conventional GOES range, offering a balance of cost and performance.

 

Why is 0.27mm thickness preferred for transformer cores?

Eddy current losses are proportional to the square of lamination thickness. At 0.27mm, eddy current losses are significantly lower than thicker 0.35mm laminations while maintaining good handling characteristics and a high stacking factor of 0.95 minimum. It is the most widely used thickness for distribution transformers at 50/60Hz.

 

What is the EN 10107 standard for grain-oriented silicon steel?

EN 10107 is the European standard for grain-oriented electrical steel strip and sheet delivered in the fully processed state. It defines grade designations (e.g., M100-27), thicknesses from 0.20 to 0.35mm, and magnetic property requirements including core loss and magnetic polarization. The 0.27mm / 1.00 W/kg material corresponds to the M100-27 conventional grade.

 

What is the difference between grain-oriented and non-oriented silicon steel?

Grain-oriented (GOES/CRGO) steel has a Goss {110}<001> crystal texture that provides high magnetic permeability along the rolling direction, making it ideal for transformer cores where flux flows in one direction. Non-oriented (CRNGO) steel has isotropic properties suitable for rotating machines like motors and generators where flux direction changes.

 

What is the SST method for core loss testing?

The Single Sheet Tester (SST) method, defined by IEC 60404-3, measures AC magnetic properties using a single full-size sheet in a double-yoke magnetic circuit. It is preferred over the Epstein frame because it uses a single large sheet rather than many small strips, reducing cutting-stress effects and improving measurement accuracy for grain-oriented electrical steel.