Development of a thermal performance indicator based on a thermal model for oil-immersed distribution transformers with two-stage cooling

This paper introduces a model to estimate the top-oil temperature in Oil Directed Air Forced (ODAF) power transformers, focusing on two-stage cooling systems. Controlling top-oil temperature is vital for assessing thermal performance and load capacity, crucial for reliable power distribution. This model targets the rated top-oil temperature under standardized (rated) conditions (full load, maximum cooling, and 20°C ambient temperature). A significant contribution is its application to distribution transformers, less explored compared to larger transformers. The model uses an algorithm based on the rated top-oil temperature, allowing comprehensive evaluation under varying conditions. This ensures safe operation and serves as a benchmark for long-term thermal performance, aiding utility companies like Enedis in optimizing transformer loading, extending asset lifespan, and preventing failures. Additionally, this model detects cooling capacity degradation, particularly from air cooler fouling. By identifying increases in rated top-oil temperature due to clogged coolers, it facilitates timely maintenance to prevent severe issues. Extensive validation across diverse conditions confirms model's accuracy and reliability, making it a valuable tool for optimizing transformer operation and maintenance.