Application Research On Transformer Insulation Status Diagnosis Based On RVM Curve

The insulation problem of large-scale power transformers is a key factor affecting the safe and stable operation of the power system.With the development of UHV,the voltage level and capacity of the transformer will increase significantly.Once a transformer fails to withdraw from the grid due to an insulation failure,a large area of power supply interruption will be caused.It is extremely troublesome for the economy and life of the people.Therefore,it is of great significance to make accurate detection and evaluation of the insulation state of the power transformers.The recovery voltage method(RVM)based on the medium response theory is a new type of detection method in recent years.It has the outstanding advantages of carrying information,strong anti-interference ability and non-destructive measurement.It uses oil-paper insulation structure under the action of high voltage DC.The polarization characteristics are measured and the polarization curves are measured to obtain the characteristic parameters,so as to diagnose the state of moisture and aging of the transformer insulation.This paper summarizes the research results of insulation aging detection using the recovery voltage method at home and abroad,uses the basic principles of circuit theory to derive the expression of the multi-branch Debye polarization model,and simulates the aging model of the oil-paper insulation structure based on the Debye model and Cole model under the MATLAB/simulink module.The results show that different charging voltages and chargedischarge times do not affect the changing trend of the recovery voltage curve,and the change of the insulation resistance value changes the trend of the curve.The fitting rule of the change law of the maximum value,the center time,and the initial slope of the three characteristic parameters on the recovery voltage curve with the insulation resistance was analyzed,which provided a theoretical basis for the evaluation of the insulation status of the transformer.In view of the lack of mature recovery voltage test system in China,this paper designs and builds a recovery voltage test system based on the basic RVM test principle,which mainly includes a high voltage DC power supply,a switching action unit,a filtering module,and a data acquisition part to achieve the collection of field test data.Experiments on the oil-paper insulation were carried out in the laboratory.Correspondences and fitting curves between different test temperatures and recovery voltage characteristics were obtained,indicating that measurement results at different ambient temperatures must be calculated.Finally,a fitting relationship between the micro-water content of the insulation structure and the characteristic parameters of the recovery voltage is found.The fitting relationship between the degree of polymerization of the insulation board and the peak value of the recovery voltage,which provides an accurate assessment of the insulation state of the transformer and an approximate calculation of the remaining life.