Design And Analysis Of Evaluation System For Transformer Insulation With Recovery Voltage Method

Oil-immersed power transformers are still the main products of transformers due to their excellent insulation capacity,heat dissipation performance,stability and low cost.The stable operation of the transformer is one of the important prerequisites for the safety and reliability of the power system.With the economic development,the transmission distance of the power grid has increased significantly,the transmission voltage has developed to ultra-high voltage,and the transformer has changed to ultra-high voltage and large capacity in response to the needs of the power grid.The insulation accident of transformer will lead to power system failure,which may cause a wide range of power outage,and have a great negative impact on the economy and production life.Therefore,it is significant to accurately assess the insulation status of power transformers.At present,insulation evaluation methods mainly include frequency domain spectroscopy,polarization / depolarization current method and recovery voltage method(RVM).RVM is a research hotspot in recent years.This paper has conducted research on the achievements in the field of transformer insulation testing at home and abroad,and analyzed related theories and insulation testing products.Based on the dielectric response theory,the equivalent extended Debye model of transformer oil-paper insulation system is established.The parameters of the model are derived by the branch fitting method with the maximum time constant,and the extended Debye model is simulated by Simulink.The relevant laws of RVM characteristics,circuit parameters and test parameters are summarized to provide theoretical support for RVM characteristics to evaluate the insulation state of transformer.At present,there is a lack of mature recovery voltage test systems in China.In order to solve this situation,this paper designs and builds a recovery voltage test device based on the RVM principle,which mainly includes an HVDC charging module,a recovery voltage measurement / acquisition module,a main controller module,and corresponding Anti-interference module.The device has the advantages of extremely low bias current,high input impedance,strong antiinterference ability,high accuracy and simple compact structure.In this paper,the transformer insulation status grading strategy and an insulation evaluation algorithm based on Long ShortTerm Memory(LSTM)are constructed,and the equipment can make accurate insulation status assessment.The test device and evaluation method form the insulation evaluation test system of the transformer,which solves the lack of the recovery voltage test system to a certain extent.Based on the established insulation evaluation system,the relevant tests and researches on oil paper insulation are carried out in the laboratory.Firstly,the recovery voltage of oil paper insulation model is tested to verify the feasibility and effectiveness of the design of recovery voltage test device,and the accuracy of the evaluation algorithm is verified according to the field test data.Secondly,the relationship between the number of layers of insulating paper and the characteristic value of the recovery voltage is studied in the laboratory,which provides a reference for the accurate evaluation of the actual insulation state and the estimation of the residual life of the transformer.