Exploration Of Transformer Hot Spot Temperature Detection Technology Based On Ultrasonic Sensing

Converter transformer is the core equipment in UHVDC transmission systems.However,in recent years,insulation failures of converter transformers have occurred frequently.The partial discharge at weak insulation points is one of the main reasons for transformer insulation accidents.During the long-term operation of converter transformers,due to factors such as partial discharge,partial overheating,winding vibration,and human work,bubbles are inevitably introduced or generated in the transformer oil.Bubbles in the insulating oil or at the oil-pressboard interface can cause partial discharge at weak insulation points.The frequent partial discharges can lead to thermal effects,corona,and acoustic cavitation effects caused by voltage shocks,which can further generate bubbles in the insulating oil.As the number of bubbles increases,the movement and deformation of bubbles in the strong electric field region can easily accumulate into small bridges and generate bubble discharges,leading to breakdown of the oil gap.Therefore,the dynamic behavior of bubbles in transformer oil may be an important cause of gap discharge and breakdown.In order to prevent the risk of insulation failure in converter transformers caused by the development of bubbles,the dynamic behavior characteristics of bubbles under the action of partial discharge in oilpressboard insulated pinboard systems were deeply studied by combining experiments and simulations.By establishing a mechanical vibration aging platform and an electric heating combined aging experimental platform,and reasonably selecting the applied electric field strength,aging temperature,and oil-pressboard insulation vibration frequency,the aging effect of multiple physical fields such as electricity,heat,and force on oil-pressboard insulation can be comprehensively simulated.After pre-treatment,the insulating oil and pressboard are subjected to a joint aging test to obtain aged oil-pressboard insulation samples equivalent to the operating years of the converter transformer.Based on an oil-pressboard insulated needle board system,an image acquisition system,an electrical pressurization system,and an electrical measurement system,a bubble experimental observation platform under the action of partial discharge is established.A high-speed camera is set up to trigger simultaneously with an oscilloscope after delay correction,and the dynamic behavior characteristics of bubbles before and after partial discharge are collected and stored,and to simulate the phenomenon of partial discharge and bubble formation in the oil-pressboard insulation inside the converter transformer at a highly uneven electric field.Based on the experimental observation platform of bubbles under partial discharge,experimental research was conducted on oil-pressboard insulation samples at different aging stages.Based on the results of high-speed camera photography of bubble movement and development behavior before and after the occurrence of partial discharge in the platform,the generation process of bubbles in oil under the action of partial discharge is analyzed,and the number and evolution law of bubbles in oil are statistically analyzed and explored;Based on dynamics,the migration trajectory and deformation process of bubbles in oil are studied,and the migration and deformation characteristics of bubbles in oil at different aging stages are explored.A theoretical mechanism for the dynamic behavior of bubbles in oil is established.Build a simulation model of gas-liquid two-phase flow based on N-S equations to characterize the flow field distribution,study the complex dynamic process of bubbles under the combined action of alternating electric field,fluid phase field,and gravity field,and compare the bubble migration trajectory and deformation process obtained from experiments and simulations to verify the reliability of the model.Study the dynamic behavior characteristics of bubbles under different initial parameters and different application conditions,explore the effects of variables such as initial bubble position,initial radius,initial velocity,applied voltage,and oil temperature on bubble migration trajectory,bubble motion velocity,and bubble morphology changes,and improve the theoretical mechanism for dynamic behavior characteristics of bubbles in oil.