Dynamic thermal model of kiosk oil immersed transformers based on the thermal buoyancy driven air flow

This paper presents a dynamic thermal model of an indoor transformer station - transformer, high voltage and low voltage compartments are placed in a kiosk with inlet and outlet ventilation openings. The well-known dynamic thermal model of an oil immersed power transformer is extended with thermal models of walls and ceiling of the kiosk and natural air ventilation through the ventilation holes. The influence of wind velocity and the direction to convective heat transfer on each of the outer surfaces is taken into account. The solar calculator is developed and applied to determine the sun irradiation on each of the kiosk surfaces, taking into account shadows on some of the walls. The natural ventilation is modeled using equilibrium of pressure produced due to thermal buoyancy and pressure drop on the air path. The model is validated by comparing calculation results with the results of measurements on the transformer kiosk, with different surfaces of ventilation inlet and outlet openings. The model can be used in design phase to optimize ventilation openings (jalousies). Another application of the model is the estimation of the maximum possible load in forecasted ambient conditions, possible being applied in scope of smart grid concept.