Real-Time Evaluation of the Dynamic Loading Capability of Indoor Distribution Transformers

With the integration of the renewable energy-based distributed small power plants, whose generated energies are uncertain, in addition to the increasing usage of the charging stations for electric vehicles, the determination of the dynamic loading of distribution transformers appears to be crucial. Therefore, the issues of the model-based online monitoring of distribution transformers may achieve acceptance, if a cost-benefit compromise is reached. In this paper, a new thermal model is proposed to calculate the top-oil temperature of indoor distribution transformers using calculated tank temperature which accounts for convection, radiation, conduction, and ventilation heat transfer phenomena. The model is validated using measurements during the in-service operation of two indoor distribution transformers. Moreover, a method for calculating the loading capability of indoor distribution transformers without sacrificing the transformer's life is presented which can be easily adjusted for other distribution transformers. Furthermore, the results of the hardware implementing the proposed model and method for a model-based online assessment of the loading capability during the in-service operation of an indoor distribution transformer are presented.