Evaluation Method Of Damp And Aging State Of Transformer Main Insulation Based On Cole-cole Model Dielectric Parameters

Power transformer is the critical equipment to ensure the reliability of the power supply,of which the operating conditions directly related to the safe operation of the power system.Utilizing valid measurement techniques and analytical methods can be in favor of the transformer oil-paper insulation condition assessment and reduce the incidence of transformer accidents,which plays an important role in the condition evaluation of power transformers.Traditional methods to assess the deterioration of transformer oil-paper insulation including the degree of polymerization measurement,oil micro-water content analysis,which is hard to take samples and may cause misjudgment.The new techniques based on theory of dielectric polarization and relaxation is introduced to evaluate the insulation condition of transformer oil-impregnated paper(OIP)system owing to the strong anti-jamming capability and nondestructive ability of such techniques.In this paper,the aging and moisture status of the oil-paper insulation is evaluated by dielectric response technique and a group of characteristic parameters was extracted from the dielectric response curves.Firstly,a series of single-layer oil-paper insulation samples with different aging degree and moisture content are prepared in the laboratory.Then,the effects of aging,moisture,temperature and the combination of various factors on the dielectric response characteristics in the frequency domain were analyzed.The aging state and the moisture content are then combined to classify the evaluated target state.Also,the frequency domain dielectric parameters and the chemical characteristic parameters which can effectively characterize the aging and damp state of oil-paper insulation samples are extracted.Moreover,a standard model library was established and this paper presented several Fuzzy judgment methods to distinguish the effect of aging and moisture on oil-paper insulation.Finally,in order to verify its effectiveness,the oil-impregnated pressboards prepared in lab and four actual transformers were used to perform the FDS measurements.The main achievements made in the paper are as follows:(1)The dielectric properties and regularity of oil-paper insulating samples under different factors were studied.The influence of moisture and aging on the dielectric properties of oil-paper insulation in the frequency domain is similar.When the moisture content is low,moisture and aging can be distinguished by the different impact bands of the measured frequency.When the moisture content is high,the influence of aging action will be covered by water.The test temperature does not change the shape of the frequency domain spectrum and only moves the curves in the horizontal direction.The average activation energy factor can be used to eliminate the effect of temperature on the dielectric response of oil-paper insulation better.(2)The fuzzy evaluation method of aging and moistened state under laboratory was presented.Considering the coupling of aging and moisture,the aging and moistened state of the oil-paper insulation are recombined into 15 new evaluation target states for diagnostic identification.The dielectric characteristic parameters and the chemical parameters of the insulating oil are extracted as the state feature vector,and the standard model library of fuzzy evaluation is established,which realizes the accurate evaluation of the state of laboratory made oil-paper insulation samples.(3)It is verified that the XY model can connect the dielectric data of the main insulation of the field transformer with the standard model library of laboratory.The frequency domain spectrum of the oil–paper combination insulation model calculated by the XY model is compared with the measured frequency domain spectrum.It was found that the measured curve and the simulation curves are kept in good agreement,with regardless of the X,Y value and the conductivity of the insulating oil change in the whole frequency range.The experimental results show that the XY model can realize the effective conversion between the frequency domain spectrum of the single layer and the oil–paper combination insulation system.(4)The methods and processes for the evaluation of the aging and moisture status of a field transformer's main insulation are put forward.Based on the evaluation method of single layer insulating paperboard,the aging and damp state of four different voltage classes transformers were evaluated in combination with XY model.The results show that the aging results are consistent with the operating life of the transformer,and the moisture results are consistent with the results of the software in the dielectric test equipment,which proves that the evaluation method can realize the effective diagnosis of the main insulation state of the transformer.