The transformer core is the core component of a power transformer. As the carrier of the magnetic circuit for electromagnetic induction, it directly affects the efficiency, volume and operational stability of the transformer. ​

In terms of materials, modern transformer cores are mostly made by laminating silicon steel sheets (with a silicon content of approximately 3% to 5%). The addition of silicon can significantly increase the resistivity of iron and reduce eddy current losses - this is the useless power consumption caused by electromagnetic induction of current in the iron core. Silicon steel sheets are usually rolled into thin sheets of 0.3mm or 0.23mm. After being coated with an insulating layer on the surface, they are stacked layer by layer to further reduce the influence of eddy currents.

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Its structure is divided into two types: core-type and shell-type. In the core-type, the windings of the core wrap around the core column and are mostly used in power transformers. Shell-type cores are wound around and are commonly found in small transformers. The geometric design of the core needs to be precisely calculated to ensure the unobstructed magnetic circuit and avoid magnetic saturation at the same time. ​

Efficient core design is the key to energy conservation in transformers. Nowadays, the application of new materials such as ultrafine crystalline alloys is driving cores towards lower losses and higher magnetic permeability, providing core support for the construction of green power grids.

The transformer core (also known as the magnetic core) is the central magnetic circuit component of a transformer. Its material selection directly affects the transformer's efficiency, losses, and applicable scenarios. Based on operating frequency, power requirements, and cost factors, core materials can be categorized into the following types:

 

1. Traditional Silicon Steel Sheets (Fe-Si Alloy):​​

Composition:

Cold-rolled steel sheets with silicon content ranging from 0.8% to 4.8% , typically with a thickness of  0.35mm or thinner​.

Characteristics:

High saturation magnetic induction (Bs≈1.6–1.7T), suitable for high-power scenarios at power frequencies (50/60 Hz).

Laminated stacking: Insulating coatings are applied between layers to reduce eddy current losses. However, losses increase significantly at high frequencies​.

Applications:

Primarily used in power transformers and motor cores for low-frequency, high-power electrical equipment.

 

2. Ferrite Core​

Composition:

Manganese-zinc (MnZn) or nickel-zinc (NiZn) ferrite, classified as sintered magnetic metal oxides.

Characteristics:

High resistivity: Significantly reduces eddy current losses at high frequencies, suitable for a ​frequency range of 1 kHz——1 MHz​ .

Low saturation flux density (Bs ≈<0.5T), weak DC bias capability, and prone to magnetic saturation.

Applications:

Widely used in electronic devices such as switch-mode power supplies (SMPS)​, ​high-frequency transformers, and inductors.

 

3. Metal Magnetic Powder Cores

Types:

Iron powder cores

Iron-silicon-aluminum powder cores (FeSiAl)

High-flux powder cores (HighFlux)

Molybdenum permalloy powder cores (MPP) .

Characteristics:

Strong anti-saturation capability: Reduces eddy currents through insulation-coated dispersed magnetic particles, making it suitable for DC superposition scenarios .

Medium permeability (μe≈10—125) with a frequency range of 10 kHz - 100 kHz​ .

Applications:

Widely used in medium-to-high-frequency power devices such as:

​PFC inductors (Power Factor Correction)

​Filter inductors.

 

4. Novel Alloy Materials​

Amorphous Alloys​

Composition:

Iron-based (e.g., Fe₈₀B₁₀Si₁₀) or cobalt-based amorphous ribbons, characterized by disordered atomic arrangement​ .

​Advantages:

​Ultra-low core losses (only 1/5 of silicon steel), enabling significant energy savings .

Limitation:

Significant magnetostriction (resulting in higher operating noise) .

​Applications:

Energy-efficient distribution transformers.

 

Nanocrystalline Alloys​

​Structure:

​Nano-scale crystalline grains (<50 nm) embedded in an amorphous matrix .

​Advantages:

​High permeability & low losses (superior to ferrites at 50 kHz) .

​Strong harmonic resistance and excellent thermal stability (operating range: -40–120°C) .

​Applications:

​High-frequency transformers and PV inverters​ .

​EV electric drive systems (e.g., integrated OBC/DC-DC modules）

 

Key Factors in Material Selection​

​Operating Frequency​

​Low Frequency (≤1 kHz) :

​Silicon Steel or Amorphous Alloys (e.g., Fe₈₀B₁₀Si₁₀).

High Frequency (>10 kHz) :

​Ferrite Cores (MnZn/NiZn) or Nanocrystalline Alloys.

 

Loss Requirements​

​Lowest Core Loss:

​Amorphous/Nanocrystalline Alloys.

High-Frequency Loss Optimization:

​Ferrites.

 

Cost and Process

​Cost-Effectiveness & Maturity:

​Silicon Steel.

High Initial Cost with Long-Term ROI:

​Amorphous/Nanocrystalline Alloys.​