Reasons for Overheating of Dry-Type Transformer Cores

Reasons for Overheating of Dry-Type Transformer Cores

When a dry-type transformer is working, the magnetic field of the current in the electromagnetic coil causes the magnetic flux to change alternately. This changing magnetic flux induces an electromotive force (EMF) in the core. This induced EMF in the core forms an electric field in a plane perpendicular to the direction of the magnetic flux, hence the term “eddy current.” Eddy current losses also cause the core to overheat.

Most dry-type transformer cores are made of ferrite. In a typical transformer operating under alternating current conditions, power loss occurs not only in the resistance of the electromagnetic coil but also in the core, which is magnetized by the magnetic field of the current. This power loss in the core is generally called “iron loss,” which is caused by two factors: “hysteresis loss” and “eddy current loss.”

Hysteresis loss is the iron loss caused by eddy currents during the magnetization process. The magnitude of this loss is directly proportional to the area enclosed by the ferromagnetic material. The narrow ferromagnetic structure of silicon steel sheets results in lower hysteresis losses in transformer cores, significantly reducing heat generation. The block-shaped core also reduces another type of iron loss—eddy current loss.

To further reduce eddy current losses, transformer cores are made of ferrite cores with insulating layers, causing eddy currents to swirl within a narrow, elongated circuit. This smaller cross-section increases the resistance along the eddy current path. Additionally, the silicon in the silicon steel sheets increases the material’s resistance, further reducing eddy currents.

The core of a dry-type transformer is a crucial component. It provides strong control over voltage and current. Various transformers offer numerous advantages, and the design of transformer cores aims to comprehensively improve current and voltage stability and overall performance.