Flexible Solution CRGO Silicon Steel Transformer Iron Core

Core Functions

• Magnetic Circuit Carrier: The iron core provides a low-reluctance path for magnetic flux, allowing the alternating current in the primary winding to generate magnetic flux that efficiently links with the secondary winding, enabling voltage transformation through electromagnetic induction.

• Reduction of Magnetic Loss: By using high-permeability materials and optimizing the structure, the iron core minimizes eddy current loss and hysteresis loss (collectively called "iron loss"), which are the main sources of transformer energy loss.

• Mechanical Support: The iron core acts as a skeleton to support the windings, ensuring the relative position stability of the primary and secondary windings during operation, short circuits, or transportation.

Structural Composition

The transformer iron core is typically composed of the following parts:

• Iron Yoke: The horizontal part at the top and bottom of the iron core, which connects the iron limbs and closes the magnetic circuit.

• Iron Limb: The vertical part of the iron core, around which the primary and secondary windings are wound. The number of iron limbs depends on the transformer type: three-phase transformers usually have three limbs (to balance the three-phase magnetic flux), while single-phase transformers have two limbs.

• Clamping Structure: Including upper and lower clamps, tension bolts, and pull plates (as mentioned in the transformer clamp introduction), which fasten the iron core laminations to prevent loosening or deformation.

Material Selection

The material of the iron core directly affects the transformer’s efficiency and loss. The most commonly used materials are:

• Grain-Oriented Silicon Steel Sheets:

• Characteristics: High magnetic permeability in the rolling direction, low hysteresis loss, and thin thickness (typically 0.23mm, 0.27mm, or 0.30mm). The grain orientation ensures that magnetic flux flows along the optimal path, reducing loss.

• Application: Widely used in power transformers and distribution transformers due to its excellent magnetic properties.

• Non-Oriented Silicon Steel Sheets:

• Characteristics: Magnetic properties are relatively uniform in all directions, making them suitable for applications where magnetic flux changes direction (e.g., rotating electrical machines). However, their loss is higher than grain-oriented silicon steel, so they are rarely used in high-efficiency transformers.

• Amorphous Alloy Sheets:

• Characteristics: Extremely low iron loss (about 1/3 of grain-oriented silicon steel) due to their non-crystalline structure. They are ideal for energy-saving transformers but have lower mechanical strength and higher cost.

Lamination and Stacking Technology

To reduce eddy current loss (caused by induced currents in the iron core), the iron core is made by stacking thin silicon steel sheets, with each sheet insulated by a thin oxide layer or coating. Common stacking methods include:

• Step-Lap Stacking: The joints of adjacent laminations are staggered in steps, reducing magnetic resistance at the joints and minimizing flux leakage and loss.

• Butt-Joint Stacking: Laminations are directly butted at the joints. This method is simpler but has higher magnetic resistance, so it is mostly used in low-power transformers.

Key Performance Indicators

• Iron Loss: Measured under rated voltage and frequency, it reflects the energy loss caused by hysteresis and eddy currents. Lower iron loss indicates higher efficiency.

• Magnetic Permeability: A higher value means the material can conduct magnetic flux more easily, reducing the excitation current required to generate magnetic flux.

• Mechanical Strength: The lamination structure and clamping system must withstand the electromagnetic force generated during short circuits to avoid deformation or damage.

Development Trends

With the demand for energy conservation and high efficiency, transformer iron cores are developing toward:

• Thinner Silicon Steel Sheets: Reducing eddy current loss (loss is proportional to the square of sheet thickness).

• High-Grade Grain-Oriented Steel: Such as HiB (High Magnetic Induction) silicon steel, which further reduces loss.

• Amorphous Alloy Cores: Increasingly used in distribution transformers for their ultra-low loss, despite higher material costs.