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 windings but serves solely as a magnetic path is called the "yoke." A core is classified as shell-type when it surrounds the windings, whereas it is termed core-type when the windings surround the core legs. Both shell-type and core-type designs have their own distinct characteristics; however, the manufacturing processes dictated by the core structure differ significantly. Once a specific structural design is selected, it is very difficult to switch to another. In China, stacked core-type cores are predominantly used for transformers.

2. Single-phase and Three-phase Cores
There are five types of single-phase cores: the two-limb stacked core, the single-limb with side yokes four-limb core, the two-limb stacked core (with different arrangement), the double-limb stacked core, and the radial stacked core. For three-phase cores, there are four main types: the three-limb stacked core, the five-limb with side yokes core, the three-phase double-frame stacked core, and the three-phase reactor stacked core.

3. Spatial (Three-dimensional) and Planar Cores
In spatial cores, the core legs and yokes are not situated in the same plane. Common configurations include radial, involute, and symmetrical types. Because the magnetic flux distribution is more uniform, these designs help reduce power losses. In contrast, planar cores have their core legs and yokes lying in the same plane, which provides high mechanical strength and excellent manufacturability.

4. Stacked Cores and Wound Cores
Transformer cores are generally of the stacked type, assembled from individual laminations. Wound cores come in various forms. Involute wound cores have a relatively large air gap between the core leg and the yoke, which affects the no-load current; therefore, they cannot be manufactured in excessively small capacities. On the other hand, because leakage flux enters the lamination plane perpendicularly, it increases stray losses. Consequently, the width of the laminations should not be too large, meaning the capacity cannot be excessively high.

A transformer core primarily consists of the core body, fastening components, and insulating parts:

① Core Body / Magnetic Conductor: Made of electrical steel sheets (silicon steel).
② Fastening Components: Including structural clamps, tie rods, glass fiber binding tapes, steel binding straps, and spacing blocks.
③ Insulating Parts: Including clamp insulation, insulating tubes and pads, grounding straps, and supporting feet.