Study On Loss And Temperature Of ±400kV Forced Water Cooling Based Dry Bushing At Valve Side Of Converter Transformer

High voltage direct current(HVDC)transmission is an important way of energy allocation in modern power system.Converter transformer is one of its important equipments,whose valve side bushing plays an important role in the safety and stability of the whole converter station.In the actual operation,the transformer bushing bears all current and voltage loads and mechanical loads with certain strength,and there are complex electrical,thermal and mechanical effects inside.With the increase of transmission energy,overheating has become a serious hidden danger of safe and stable operation of converter valve side bushing.Therefore,it is necessary to study the internal loss and temperature distribution of bushing,understand the heating mechanism,improve the structure of bushing,and increase the service life of bushing,which is of great significance to break the monopoly of bushing technology at home and abroad and improve the reliability of DC transmission.In this paper,a new type of forced water cooling bushing structure is proposed for the first time.The aluminum alloy water pipe is added into the current carrying conductor,and the deionized water from the valve hall of the converter valve is selected as the coolant to reduce the temperature of the epoxy core and the current carrying conductor.Based on Maxwell’s equations and Poynting’s theorem,according to the symmetry of each field,the analytical form of current carrying conductor loss is derived,and compared with the numerical simulation results,the total error is 0.378%.A three-dimensional electromagnetic thermal fluid multi physical field coupling simulation model is established,the temperature distribution and heat flux distribution inside the bushing are calculated,and the cooling mechanism of deionized water in the bushing is analyzed.The highest temperature inside the bushing is at the contact position between the bushing and oil.In transformer oil,the temperature gradually decreases along the axial direction.The highest temperature of regin impregnated paper(RIP)is 90℃.Except for the flange height,the temperature of other parts of the RIP gradually increases from the inside to the outside along the radial direction with small temperature gradient.The temperature of RIP on the air side is 40-50℃,which is far lower than the temperature of material insulation failure.The new structure can reduce the insulation failure caused by overheating of the bushing,meet the requirements of long-term operation of the bushing,and help to extend its service life.The surface temperature of the current carrying conductor of the valve side forced water cooling dry bushing prototype of 400kV converter transformer is measured experimentally,and the temperature results under the same working condition are compared with the simulation results.The error is mostly within±5%,which verifies the accuracy of the simulation results and proves that the forced water cooling structure plays a key role in the heat dissipation of the bushing.