Understanding Core Losses in Electrical Transformers

Core losses are a critical aspect of transformer efficiency, impacting their overall performance. These losses primarily arise from the magnetic properties of the core material and the design of the transformer itself. Two major types of core losses are hysteresis and eddy current losses, which together contribute to what is termed no-load loss. Understanding the factors influencing these losses can lead to more efficient transformer designs.

One significant factor affecting core losses is the gap at the core joint. Research indicates that smaller gaps yield better core performance, with a noticeable impact on no-load losses. A 1.5 mm gap can increase losses by 1 to 2%, while a 3 mm gap may lead to losses rising by 8 to 12%. This underscores the importance of minimizing gaps at core joints to enhance efficiency.

Another important design element is the number of laminations per layer in the core. Fewer laminations per layer typically result in lower core losses. For instance, using two laminations per layer can provide a 3 to 4% advantage in loss reduction compared to four laminations. Although reducing the number of laminations can increase manufacturing time, the two-lamination design is often the preferred choice due to its efficiency benefits.

The geometry of transformer cores also plays a crucial role in core losses. Single-phase two-limb and three-limb cores tend to have more uniform flux distributions and lower total harmonic distortions than their four-limb and five-limb counterparts. Additionally, the construction method is pivotal; step-lap joints are increasingly favored over traditional mitered joints due to their ability to minimize flux density in the air gap, thus enhancing overall performance.

The building factor, which typically ranges from 1.1 to 1.25 for three-phase, three-limb cores, reflects the proportion of joint weight to total core weight. Higher height-to-width ratios in core windows can reduce core loss by minimizing joint weight. This relationship illustrates how meticulous attention to design can lead to significant reductions in energy losses, optimizing transformer efficiency for various applications.