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Silicon Steel Sheet Selection and Its Impact on Transformer Performance
A transformer is a core component in the power system responsible for voltage conversion, while the iron core is the key component that enables electromagnetic energy conversion. The performance of the core material directly affects the transformer’s no-load losses, operating efficiency, and service life. Among various core materials, silicon steel sheets have become the most widely used material in power transformer manufacturing due to their excellent soft magnetic properties.
The quality of silicon steel sheets is highly valued because it has a direct impact on the transformer’s energy efficiency level and life cycle cost. For power utilities, EPC contractors, and industrial project owners, understanding the key quality indicators of silicon steel sheets and their influence on transformer performance is an essential part of equipment selection.
As a professional power transformer manufacturer, Zisheng Electric provides a product portfolio covering oil immersed transformers, dry type transformers, amorphous alloy transformers, and switchgear equipment. The company has accumulated practical engineering experience in core material selection and energy-efficient transformer design. Based on the different energy efficiency requirements and operating conditions of target markets, including the Middle East, South America, Africa, and Russia, Zisheng Electric has developed systematic technical solutions in silicon steel sheet selection, core structure design, and loss control.
This article provides a comprehensive analysis of the application of silicon steel sheets in transformers from the perspectives of material characteristics, performance indicators, classification, and engineering applications.
Basic Characteristics and Classification of Silicon Steel Sheets
Silicon steel sheet, also known as electrical steel, is a low-carbon silicon-iron soft magnetic alloy with a silicon content generally ranging from 0.5% to 4.5%. Adding silicon to steel can increase the electrical resistivity and maximum magnetic permeability of iron while reducing coercivity, core losses, and magnetic aging.
The role of silicon in iron is mainly reflected in three aspects. First, it increases electrical resistivity, reduces the conductivity of steel sheets, and minimizes eddy current losses. Second, it improves magnetic permeability by reducing the magnetic crystalline anisotropy of steel. Third, it reduces hysteresis losses, making the magnetization process smoother and more efficient.
These characteristics enable silicon steel sheets to be rapidly magnetized and easily demagnetized under an alternating magnetic field, making them highly suitable for manufacturing transformer cores.
According to the difference in silicon content, silicon steel sheets can be divided into two categories:
Low silicon steel sheets: with a silicon content below 2.8%, mainly used in motor manufacturing.
High silicon steel sheets: with a silicon content between 2.8% and 4.8%, mainly used for transformer core manufacturing due to their lower core losses and better magnetic performance.
Main Evaluation Indicators of Silicon Steel Sheet Quality
The quality of silicon steel sheets is evaluated based on several key performance indicators, including iron loss, magnetic flux density, surface quality, and flatness.
1. Iron Loss (Specific Core Loss)
Iron loss is the most important indicator for evaluating the quality of silicon steel sheets. Generally, the lower the iron loss, the higher the grade of the silicon steel sheet.
Iron loss consists of two components: hysteresis loss and eddy current loss. Hysteresis loss is caused by the irreversible movement of magnetic domains during the magnetization process, while eddy current loss is generated by circulating currents induced in the steel sheet under an alternating magnetic field.
International silicon steel grade classification is mainly based on iron loss values. For example, the grade B20R060 has a specific core loss of 0.60 W/kg, which represents a reduction of more than 25% compared with traditional silicon steel sheets.
2. Magnetic Flux Density
A higher magnetic flux density means that a higher magnetic induction can be achieved under the same magnetic field strength. Using high magnetic induction silicon steel sheets for transformer cores can reduce the size and weight of the core, thereby saving silicon steel material, copper conductors, and insulation materials.
The magnetic flux density B₈₀₀A of conventional grain-oriented silicon steel is generally around 1.78T to 1.85T, while the value of high magnetic permeability grain-oriented silicon steel (Hi-B steel) can exceed 1.88T.
3. Surface Quality and Flatness
Silicon steel sheets require a smooth surface, good flatness, and uniform thickness to improve the core stacking factor. Silicon steel sheets with better flatness provide a higher stacking coefficient, better coating adhesion, and improved welding performance.
Currently, transformer manufacturers mainly use cold-rolled grain-oriented silicon steel sheets with high magnetic performance. The thickness of silicon steel sheets continues to decrease to reduce core losses. The traditional 0.35 mm specification has gradually been phased out, while the mainstream thicknesses are now 0.30 mm, 0.27 mm, and 0.23 mm.
Comparison Item | Grain-Oriented Silicon Steel | Non-Oriented Silicon Steel |
|---|---|---|
Grain Orientation | Magnetic grains are mainly aligned in one direction | Magnetic grains are randomly distributed |
Magnetic Properties | Directional magnetic properties | Uniform magnetic properties in all directions (isotropic) |
Silicon Content | Generally above 3.0% | 0.5% to 3.0% |
Main Applications | Transformer cores | Motor and generator cores |
The magnetic flux in a transformer core mainly propagates along a specific direction, known as the rolling direction. Grain-oriented silicon steel has the lowest iron loss and the highest magnetic permeability along the rolling direction, which matches the operating characteristics of transformers.
Although non-oriented silicon steel has uniform magnetic properties in all directions and is suitable for rotating equipment such as motors, it cannot achieve optimal performance in transformer applications. Therefore, transformers generally use cold-rolled grain-oriented silicon steel sheets as the core material.
According to performance grades, grain-oriented silicon steel can be classified into the following categories:
Conventional Grain-Oriented Silicon Steel (CGO): The magnetic flux density B₈₀₀A is generally between 1.78T and 1.85T.
High Magnetic Induction Grain-Oriented Silicon Steel (Hi-B Steel): The magnetic flux density B₈₀₀A is generally not less than 1.85T. It has a more uniform grain orientation and lower iron loss.
Laser Scribed Silicon Steel Sheet: Based on Hi-B steel, laser treatment is applied to further refine magnetic domains, achieving even lower iron loss.
The quality of silicon steel sheets directly affects multiple transformer performance indicators.
The no-load loss of a transformer mainly consists of hysteresis loss and eddy current loss in the core. Using low-loss silicon steel sheets can directly reduce transformer no-load losses.
High-quality, low-loss, high magnetic induction silicon steel cores can effectively reduce no-load losses, while also minimizing magnetostriction, operating noise, and environmental impact caused by core vibration.
Taking 0.20 mm grain-oriented silicon steel as an example, the use of this material can reduce the no-load loss of high-efficiency transformers by approximately 28%.
With continuously increasing energy efficiency requirements worldwide, high-performance and low-loss grain-oriented silicon steel has become one of the key factors determining whether a transformer can achieve a higher energy efficiency class.
Silicon steel sheets with higher magnetic flux density can reduce the transformer core size under the same rated capacity. This helps reduce the consumption of silicon steel materials while also lowering the usage of copper conductors and insulation materials.
The flatness, coating quality, and corrosion resistance of silicon steel sheets directly affect the stacking quality, insulation performance, and long-term operational reliability of transformer cores.
A reasonable core stacking structure, assembly process, and tooling design can ensure stable performance of the transformer core during manufacturing and operation.
Zisheng Electric has been dedicated to the R&D and manufacturing of power equipment for many years. Its product range covers oil immersed transformers, dry type transformers, amorphous alloy transformers, and switchgear equipment. All products are custom-designed according to actual project requirements and can be manufactured in compliance with international standards such as IEC 60076 and GOST. The company currently owns 21 utility model patents and 3 software copyrights. Its products are exported to various regional markets including the Middle East, South America, Africa, and Russia. Since 2022, the company has developed and manufactured three-dimensional wound core liquid immersed transformers, which are applied in prefabricated substations and various distribution scenarios.
In terms of core material selection, Zisheng Electric selects different grades and specifications of grain-oriented silicon steel sheets according to the energy efficiency requirements and operating conditions of target markets. The specific selection criteria include: the energy efficiency standards of the project location (such as the A2 or A3 grade requirements of IEC 60076-12); the voltage level and capacity rating of the transformer; installation environment requirements for temperature rise and noise limitations; and customers’ preferences regarding initial investment and life cycle costs.
Zisheng Electric has accumulated extensive overseas engineering experience in the application of silicon steel sheets:
Saudi Arabia photovoltaic power plant step-up transformer project. The project is located in western Saudi Arabia, where the ambient temperature exceeds 45°C throughout the year and the ground surface temperature can reach above 60°C, placing high requirements on transformer temperature rise control and heat dissipation performance. Based on the project requirements, Zisheng Electric customized and designed several 33kV step-up transformers. The cores were made of 0.23 mm thick high magnetic induction grain-oriented silicon steel (Hi-B steel), with the designed magnetic flux density lower than conventional standards to reduce specific losses.
By optimizing the core joint structure and lamination process, the transformer’s no-load loss and operating temperature rise were effectively reduced. During the core design stage, Zisheng Electric fully considered the dual requirements of low loss and low noise. The final products successfully passed project acceptance and were put into stable operation.
Zambia steel plant power supply project. The project is located in Zambia’s Copperbelt Province, featuring a typical tropical plateau climate with an altitude of approximately 1,200 meters. The area experiences significant temperature differences between day and night, with frequent fluctuations in industrial loads. Zisheng Electric customized multiple 11/0.415kV distribution transformers for the project. The transformer cores adopted high magnetic induction grain-oriented silicon steel sheets, with the designed magnetic flux density set lower than conventional standards to provide additional temperature rise margins. Combined with the use of low-loss silicon steel sheets, the temperature rise and losses of the equipment were effectively controlled within the required standard limits under high-altitude conditions.
The project had high requirements for transformer overload capacity and operational reliability. In the core structure design, Zisheng Electric adopted a three-dimensional wound core structure combined with high magnetic induction grain-oriented silicon steel sheets. By optimizing the magnetic flux density design of the core yoke, the no-load loss was reduced, achieving low-energy-consumption operation of the transformer throughout its life cycle.
Brazzaville city center substation project in the Republic of Congo. The project is located in Brazzaville, the capital of the Republic of Congo. The local power grid infrastructure is relatively outdated, with significant voltage fluctuations. The local climate is tropical rainforest, with distinct rainy and dry seasons. The equipment needs to adapt to high temperature, high humidity, and frequent lightning conditions.
Zisheng Electric customized multiple 33/0.4kV distribution transformers for the project. The cores adopted high magnetic induction grain-oriented silicon steel sheets, and moisture-resistant treatment was applied to the core insulation coating to ensure stable insulation performance in high-humidity environments.
The three-dimensional wound core structure ensures a completely symmetrical three-phase magnetic circuit, eliminating additional losses at the joints of traditional laminated cores. Combined with the low-loss characteristics of high-grade silicon steel sheets, the no-load loss of the transformers was effectively reduced. The transformers have demonstrated strong resistance to grid fluctuations and excellent moisture protection performance during operation and have been running stably for more than 18 months.
Russia industrial park power distribution project. The project is located in the Siberian region of Russia, where the minimum winter temperature can reach -45°C, placing special requirements on the low-temperature performance of transformer core materials and the reliability of the insulation system.
Based on the project requirements, Zisheng Electric customized multiple 10kV oil immersed distribution transformers. The cores adopted low-loss grain-oriented silicon steel sheets, and the core insulation coating formulation was optimized for low-temperature environments to ensure that the coating would not crack or peel off under extreme cold conditions.
For severe cold climates, Zisheng Electric also adjusted the designed magnetic flux density of the core. While maintaining efficiency, this reduced specific losses and heat generation, enabling the transformers to start normally and operate stably in extremely cold environments.
Africa off-grid photovoltaic energy storage project. The project uses a photovoltaic and energy storage system to supply power to remote areas, with significant load fluctuations and strict requirements for equipment efficiency and reliability. For this project, Zisheng Electric customized multiple amorphous alloy transformers, combining amorphous alloy materials with a three-dimensional wound core structure.
The amorphous alloy core adopts a new type of magnetic conductive material. Compared with traditional silicon steel sheet core transformers, the no-load loss is reduced by approximately 70%, and the no-load current is reduced by approximately 80%. This technology provides significant energy-saving advantages in low-load operating conditions and is well suited to the operating characteristics of photovoltaic power plants, such as low loads during nighttime and cloudy or rainy days.
Zisheng Electric has carried out continuous R&D and process development in this technical field, forming customized manufacturing capabilities for high-efficiency amorphous alloy transformers.
Zisheng Electric can assist customers with the following selection and confirmation processes:
Recommend suitable silicon steel sheet grades according to energy efficiency requirements;
Determine the core cross-section and lamination thickness based on voltage level and capacity;
Confirm whether the calculated core loss meets project technical specifications;
For special operating conditions in target markets, confirm coating types and protection requirements.
Before delivery, all equipment undergoes complete factory tests according to the IEC 60076 standard. The test items include no-load loss measurement and no-load current measurement, and bilingual Chinese-English test reports are provided.
The quality of silicon steel sheets directly affects the key performance indicators of transformers: iron loss determines energy efficiency, magnetic flux density determines transformer size and material consumption, while surface quality and coating performance determine long-term operational reliability.
With continuously increasing energy efficiency standards and growing attention to life cycle cost management, high-performance and low-loss grain-oriented silicon steel has become a key consideration in transformer selection.
For transformer purchasers and designers, understanding the quality indicators of silicon steel sheets and their impact on transformer performance helps them make more reasonable equipment selection decisions during the project design stage. We provide comprehensive technical support covering core material selection, customized transformer design, and factory testing.
Zisheng Electric — Years of experience in power equipment R&D and manufacturing. Our products cover dry type transformers, oil immersed transformers, amorphous alloy transformers, and switchgear equipment. We provide customized manufacturing according to international standards such as IEC 60076 and GOST, serving markets including the Middle East, South America, Africa, and Russia.
For transformer core selection or energy efficiency solution support for specific projects, please send project parameters through Zisheng Electric’s official channels to obtain technical feedback.
