Transformer cores are predominantly built using transformer steel sheets, particularly cold-rolled grain-oriented silicon steel. This guide offers a detailed exploration of transformer steel—how it reduces energy loss and where it's used across industries and everyday life.

What Is Transformer Steel?

Transformer steel, commonly known as silicon steel, typically contains 0.8% to 4.8% silicon. Thanks to its high magnetic permeability, this material becomes the go-to choice for transformer cores. With the advancement of advanced precision control systems (PCS), transformer steel allows higher magnetic induction in energized coils, enabling more compact transformer designs.

Commonly used grain-oriented grades:
For 0.23 mm thickness: B23G095, 23QG095, 23JGH095
For 0.27 mm thickness: B27G100, 27QG100, 27JGH100
For 0.30 mm thickness: B30G100, 30QG100, 30JGH100

1. Transformer Power Losses

The transformer always works in the AC state, and the power loss is not only in the resistance of the coil, but also in the iron core magnetized by the alternating current. The power loss in the iron core is usually called "iron loss". Iron loss is caused by two reasons, one is hysteresis loss, and the other is eddy current loss.

Hysteresis loss is the iron loss caused by the hysteresis phenomenon during the magnetization process of the iron core. The size of this loss is proportional to the area surrounded by the hysteresis loop of the material. The hysteresis loop of silicon steel is narrow, and the hysteresis loss of the core of a transformer made of silicon steel is small, which can greatly reduce the heat generation.

Since silicon steel has the advantages above, why not use a whole piece of silicon steel as the iron core but process it into sheets? This is because the sheet core can reduce another type of iron loss - eddy current loss. ​

2.What is eddy current loss？

When the transformer is working, there is alternating current in the coil, and the magnetic flux it generates is also alternating. This changing magnetic flux produces an induced current in the iron core. The induced current generated in the iron core circulates in a plane perpendicular to the direction of the magnetic flux, so it is called eddy current.

Eddy current losses also heat the core. In order to reduce eddy current losses, the core of the transformer is stacked with silicon steel sheets that are insulated from each other, so that the eddy currents pass through a smaller cross-section in a long and narrow circuit to increase the resistance on the eddy current paths; at the same time, the silicon in the silicon steel increased the resistivity of the material, which also plays a role in reducing eddy currents.

For the iron core of the transformer, 0.35mm cold-rolled silicon steel sheet is generally used. It is cut into long pieces according to the required size of the iron core, and then overlapped into a shape like the picture below. Theoretically, in order to reduce eddy currents, the thinner the silicon steel sheets and the narrower the spliced sheets, the better the effect. This design helps reduce eddy current losses and heat generation, while also optimizing material usage and production efficiency.

But when actually making silicon steel cores. It is not just based on the above-mentioned favorable factors, because making the iron core in that way will greatly increase the manufacturing hours and also reduce the effective cross-section of the iron core. Therefore, when using silicon steel sheets to make transformer cores, you must start from the specific situation, consider the pros and cons, and choose the best size.

Transformers are made based on the principle of electromagnetic induction. There are two windings wound on the closed iron core column, a primary winding and a secondary winding. When the original winding is connected to the AC power supply voltage. There is an alternating current flowing through the original component, and a magnetic potential is established. Under the action of the magnetic potential, an alternating main magnetic flux is generated in the iron core.

So why can it boost and reduce the voltage? We’ll need to use Lenz's law to explain it. The magnetic flux generated by the induced current always hinders the change of the circular magnetic flux. When the original magnetic flux increases, the magnetic flux generated by the induced current is opposite to the original magnetic flux, that is to say, the secondary magnetic flux.

According to Lenz’s Law, the induced magnetic field in the secondary winding opposes the change in magnetic flux from the primary, resulting in an induced alternating voltage proportional to the turns ratio. Therefore, the iron core is the magnetic circuit part of the transformer.

3. Performance Metrics of Transformer Steel

The performance of transformer steel sheets is determined by several key properties:

Low iron loss: Grades like B27G100 or B30G120 offer reduced iron loss, boosting transformer efficiency.

High magnetic induction: Grades such as B23G090 or 23JG090 enable lighter and more compact transformer cores.

High stacking factor: Uniform thickness and smooth surfaces improve core assembly.

Excellent coating and welding characteristics: Particularly important in small motor applications.

Magnetic aging resistance and annealing stability before shipment.

4. Types of Transformer Steel Sheets

Silicon steel sheets for electrical purposes are commonly known as silicon steel sheets or silicon steel sheets. As the name suggests, it is electrical silicon steel with a silicon content of up to 0.8%-4.8%, which is made by hot and cold rolling.

Generally, the thickness is less than 1mm, so it is called thin plate. Silicon steel sheets belong to the plate category and are an independent branch due to their special uses. Silicon steel sheets for electrical purposes have excellent electromagnetic properties and are indispensable and important magnetic materials in the power, telecommunications and instrument industries.

There are mainly two kinds of classifications of silicon steel sheets:

Silicon steel sheets can be divided into low silicon and high silicon according to their silicon content. Low silicon wafers contain less than 2.8% silicon.

They have a certain mechanical strength and are mainly used to make motors, commonly known as motor silicon steel sheets. High silicon wafers contain 2.8%-4.8% silicon. They have good magnetism but are brittle and are mainly used for manufacturing transformer cores, commonly known as transformer silicon steel sheets. There is no strict boundary between the two in actual use, and high-silicon wafers are commonly used to manufacture large motors such as those work with trolling motor battery.

According to the production and processing technology, it can be divided into hot rolling and cold rolling.

Cold rolling can be divided into two types: grain non-oriented and grain oriented. Among cold-rolled silicon steel, grain-oriented transformer steel is particularly critical for high-efficiency transformer cores, gradually replacing hot-rolled and non-oriented types in power applications.

5. Applications of Transformer Steel Sheets

Hot-rolled silicon steel sheet for electrical purposes (GB5212-85)

Hot-rolled silicon steel sheets for electrical purposes are made of ferrosilicon soft magnetic alloy with low carbon loss, and are hot-rolled into sheets with a thickness of less than 1mm. Hot-rolled silicon steel sheets can be divided into low silicon (Si≤2.8%) and high silicon (Si≤4.8%) steel sheets according to their silicon content. ​

Cold-rolled silicon steel sheet for electrical purposes (GB2521-88)

This kind of silicon steel sheet is made of electrical silicon steel containing 0.8%-4.8% silicon and is made by cold rolling. Cold-rolled silicon steel sheets are divided into two types: grain-non-oriented and grain-oriented steel sheets. Cold-rolled electrical steel sheet has the characteristics of smooth surface, uniform thickness, high stacking coefficient, and good punching performance.

It has higher magnetic induction and lower iron loss than hot-rolled electrical steel sheets. Using cold-rolled sheets instead of hot-rolled sheets to manufacture motors or transformers can reduce its weight and volume by 0%-25%. If cold-rolled oriented sheet is used, the performance will be better. Using it instead of hot-rolled sheet or low-grade cold-rolled sheet can reduce the power consumption of the transformer by 45%-50%, and the transformer performance will be more reliable.

While non-oriented silicon steel is typically used in motors or low-frequency transformers, grain-oriented transformer steel remains the preferred material for high-performance power transformers, ensuring minimal core loss and superior magnetic flux guidance, pulse transformers, magnetic amplifiers, etc. Steel plate specifications and dimensions: thickness is 0.35mm, 0.50mm, 0.65mm, width is 800-1000mm, length is≤2.0m.​

Hot-rolled silicon steel sheet for home appliances (GBH46002-90)

The grade of hot-rolled silicon steel sheet for home appliances or home solar power system is represented by JDR. The number after JDR is the iron loss value *100, and the number after the horizontal line is the steel plate thickness (mm) * 100.

Hot-rolled silicon steel sheets for home appliances can have slightly lower electromagnetic performance requirements, and the minimum iron loss value (P15/50) is 5.40W/kg. Generally delivered without washing. This kind of silicon steel sheets are used on differential motors used in electric fans, washing machines, vacuum cleaners, range hoods and other household appliances.

Whether you're manufacturing distribution transformers, pulse transformers, or industrial-grade magnetic amplifiers, the right choice of transformer steel significantly impacts performance, size, and energy efficiency.

MOOPEC provides a comprehensive selection of Baosteel-oriented transformer steel grades, including B23G095, B27G100, and B30G120, with rapid delivery, small-batch customization, and expert support throughout the material selection and core lamination process. We ensure fast quoting within 12 hours and delivery in 7 days for global orders.

Looking for reliable, low-loss, high-performance transformer steel sheets?
Choose MOOPEC – your trusted transformer steel solution partner.