Understanding Axial Forces in Power Transformer Design

In power transformer design, axial forces play a significant role in the operational stability and efficiency of the unit. These forces arise from the interactions between the windings and can greatly influence the overall performance of transformers. A clear understanding of the factors contributing to these forces is essential for engineers and designers in the field.

The axial force, denoted as "ax," is measured in Newtons and is particularly impacted by the height of the windings. The average axial height of windings (Hwdg) directly correlates with the amount of axial force experienced. As the height of the windings decreases—often due to transportation constraints—the axial forces increase, leading to greater stress on the transformer structure. This is particularly relevant in large-rated power transformers, where the impedance affects both axial and radial forces generated during operation.

Further complicating the dynamics within a transformer are the varying ampere-turn distributions across windings. Unbalanced magneto-motive forces (mmf) between inner and outer windings can result in axial forces that tend to push the windings apart. For instance, if the inner low-voltage (LV) winding has no gap while the outer high-voltage (HV) winding has a tap gap, the resulting radial leakage flux generates additional axial forces. Designers must carefully balance the ampere-turns to mitigate these effects and enhance structural integrity.

Several strategies can be employed to manage axial forces effectively. One approach is to create a compensation gap in the LV winding to counterbalance the HV tap gap. Alternatively, the LV winding can be designed with fewer turns and thicker spacers, which can help in achieving a more balanced magnetic field and reducing excess axial force. Additionally, yoke laminations are used to direct leakage fluxes more axially, which can aid in diminishing axial forces at winding ends.

Despite efforts to achieve symmetry in winding designs, asymmetries due to manufacturing variances and tap positions are inevitable. These differences can lead to uneven ampere-turn distributions, generating challenges in maintaining equilibrium. Consequently, structural components like clamping rings may experience significant forces, which designers need to account for in the transformer’s overall structural design. Understanding these dynamics is crucial for ensuring reliable transformer operation and longevity.