Transformer Overload Management and Condition Monitoring

Thermal protection of power/distribution transformers is possible by using simple thermal models proposed by IEEE/IEC standards. These models are solved on-line and mainly supervise the hot spot temperature. From another point of view, there are many on-line monitoring systems working on chemical composition of insulating oil. These equipments can analyze the Degree of Polymerization (DP) and/or perform Dissolved Gas Analysis (DGA). Although, these equipments are not as fast as on-line thermal models that calculate the hot spot temperature or measure the hot spot directly, they can be effectively used to evaluate the condition of a transformer in a more realistic way. In this paper, a loss of life model is proposed that is not only based on the hot spot temperature, but also in terms of the several chemical dissociation effects (decomposition byproducts of cellulose). The proposed method can estimate the elapsed life in a more realistic manner based on more criteria relating to insulation aging.