What Are the Common Types of Transformer Cores?

1. Shell-Type and Core-Type Cores

The part of the core that houses the windings is called the "core leg," while the part that does not house the windings and serves solely as a magnetic path is called the "yoke." A core is referred to as shell-type when it encloses the windings, and core-type when the windings enclose the core legs. Both shell-type and core-type designs have their distinct characteristics; however, the manufacturing processes dictated by the core structure differ significantly. Once a specific structure is selected, it is difficult to switch to the other. In China, most transformer cores utilize the stacked core-type design.

2. Single-Phase and Three-Phase Cores

Single-phase cores are classified into five types: single-phase two-leg stacked cores, single-phase single-leg with side-yoke four-leg cores, single-phase two-leg stacked cores (dual-column), single-phase radial stacked cores, and single-phase double-leg stacked cores. Three-phase cores are classified into four types: three-phase leg-type stacked cores, three-phase five-leg with side-yoke cores, three-phase double-frame stacked cores, and three-phase reactor stacked cores.

3. Three-Dimensional (3D) and Planar (2D) Cores

In 3D cores, the core legs and yokes are not in the same plane. They include radial, involute, and symmetrical types. Due to a more uniform distribution of magnetic flux, they can reduce losses. In planar cores, the core legs and yokes lie in the same plane, offering high mechanical strength and excellent manufacturability.

4. Stacked Cores and Wound Cores

Most transformers utilize stacked cores, which are assembled from stacked laminations. Wound cores come in various forms. The involute core has a relatively large air gap between the core leg and the yoke, which affects the no-load current, meaning its capacity cannot be too small. However, because the leakage flux enters the plane of the core laminations perpendicularly, it increases additional losses; therefore, the lamination width should not be too large, meaning the capacity cannot be too high.

Core Composition:

The core assembly primarily consists of the core body, clamping hardware, and insulation components:

① Core Body (Magnetic Conductor): Made of electrical steel sheets (silicon steel laminations).

② Clamping Hardware: Includes clamps, tie rods, glass-bonded straps, steel binding straps, and spacer blocks.

③ Insulation Components: Includes clamp insulation, insulating tubes and pads, grounding shunts, and support feet.