Numerical Study On Rapeseed Oil As Cooling Fluid Of 800kV HVDC Converter Transformer

Power transformer is an important and expensive equipment in the profitable generation and electric power transmission,and their reliability and stability are the key to the safe operation of power systems.In addition,the high AC and DC voltages have begun to put forward new special requirements for the dielectric insulation medium inside the transformer,with the high-voltage direct current(HVDC)technology is becoming common in power grids worldwide in recent years.The related research has gradually become the key content in the electric power field.The majority of transformers depend on liquid dielectrics as insulating material.It prevents internal short circuits,protects the transformer from chemical attack and acts as a cooling agent when the transformer is energized.This work aims to evaluate the heat transfer effect of rapeseed oil in the HVDC converter transformer through numerical simulation,and provide a comprehensive analysis of the cooling performance of rapeseed oil while comparing it with the mineral oil response.A 2D cross sectional physical model of the converter transformer was designed using the software FLUENT,and the converter transformer’s technical data of the Fulong converter station of the Xiangjiaba-Shanghai project gave us the model’s required information.On this basis,this paper used Computational Fluid Dynamics(CFD)tools to simulate the internal convective heat transfer of the HVDC converter transformer under two working conditions found in the equipment representing the put-on service of the converter transformer and the action of the ODAF cooling system.The temperature and velocity fields at the critical points of the fluid domain were also calculated by CFD.At the same time,the temperature response of rapeseed oil and mineral oil insulation medium under two working conditions was compared,and then the overall cooling performance of the system was obtained in this paper.The results show that rapeseed oil requires more time to gain heat from the core and windings due to its lower thermal conductivity.However,the average temperature of rapeseed and mineral oils will not differ significantly once the channel temperature reaches a stable value.It indicates that the rapeseed oil could effectively replace the mineral oil as the insulation coolant of transformer under the same heating condition.Also,a slower flow of the rapeseed oil allows the fluid to enter the cooling channel smoothly.Hence,the rapeseed oil cools these channels by pushing the fluid in them and absorbs heat from the sources earlier than the mineral oil.The improvement in cooling indicates that rapeseed oil is better than mineral oil as a coolant and electrical insulating fluid for power transformers.