Understanding Oil Flow and Temperature Distribution in Power Transformers

In the realm of power transformer design, effective heat management is crucial for ensuring optimal performance and longevity. One essential component in this process is the oil flow guide washer, which plays a significant role in directing oil flow through winding horizontal ducts. This design ensures that the heat generated by the winding is adequately transferred to the oil, which can then dissipate the heat through convection. Without such a guide, the oil flow in horizontal ducts may become inconsistent, potentially leading to uneven temperature distribution across the winding.

Temperature distribution within transformer windings is generally assumed to be linear for the sake of simplifying calculations. This assumption stems from the fact that, in practice, temperature variation with winding height closely resembles a linear gradient, particularly with forced oil cooling systems. Although individual losses in each cable can differ due to the presence of eddy currents, the overall impact is often negligible when compared to I²R losses, thus justifying the uniform loss assumption in thermal analysis.

The winding temperature gradient, an important parameter in transformer design, comprises two significant components. The first is the temperature drop across the insulation paper of the winding cable, while the second refers to the drop from the insulation surface to the surrounding oil. Understanding these components is vital for accurate thermal modeling, as they influence the efficiency of heat transfer and the overall temperature rise of the winding.

The analysis further reveals that the temperature drop across the insulation paper is largely determined by the heat flux density per unit transfer surface, taking into account factors such as the thermal conductivity of the insulation material. Additionally, the convection from the insulation surface to the oil is defined by specific empirical formulas that enable designers to predict and manage thermal behavior effectively.

Thermal analysis of transformers aims to maintain both oil and winding temperatures within predefined limits. The winding hot spot temperature rise is particularly critical, as it serves as a key indicator of the transformer's anticipated service life. It's important that the temperature increases of lead cables, bushings, and switches remain lower than that of the windings, ensuring that the winding temperature is the primary factor affecting the unit's overall reliability.

By incorporating these thermal dynamics into the design, engineers can enhance the efficiency and durability of power transformers, ultimately leading to improved performance and extended operational life. Understanding the intricacies of oil flow and temperature gradients is essential for anyone involved in transformer design and maintenance.