Research On Relationship Between Electrical Tree Length And Partial Discharge In Polyethylene

The insulation state of power equipment is one of the key factors affecting its reliability,and the electrical tree,as an important defect in the insulation system of power equipment,has been a bottleneck to improve the reliability of power equipment.Especially the electrical tree defect in the insulation system of high-voltage cables,transformers and other equipment under field conditions,the generation mechanism and the development law of which are still not clear enough,and the relationship between the detection amount and the state of electrical tree defect is also not clear.What’s more,the local pulse signal is often the only highly relevant information that can be detected under field conditions.Therefore,this paper starts from the partial discharge of electrical trees,and estimates the scale of electrical trees in insulation materials to evaluate the insulation state of field equipment.Firstly,based on the correlation between electrical tree growth characteristics and partial discharge in polymers,a test platform for electrical tree growth and partial discharge detection is established,and electrical tree growth tests under the needle plate electrode in polyethylene materials are carried out.Regarding the detection results,the main factors affecting electrical tree growth and the partial discharge characteristics at different stages of development are discussed and analyzed.It is found that the rapid voltage boost will promote the initiation and growth of electrical trees,and the secondary voltage will trigger the secondary growth of electrical trees.By analyzing the partial discharge spectra of electrical trees at different stages of development,it is found that the discharge patterns during the growth period of electrical trees are generally wing-like or feather-like,while the hump-like,turtlelike and sparse scattered cloud-like patterns generally appear in the stagnant growth period of electrical trees,indicating different degrees of air-gap discharge in the material.According to the phase distribution of partial discharge,it is found that the phase distribution during the growth period of electrical trees is wider than that of other stages,and the discharge frequencies and average discharge amount of positive and negative half-cycles are more symmetrical.Under the condition of increasing voltage,the growth curve of electrical trees and the general trend of partial discharge development remain consistent,which verifies the thermodynamic formulation of electrical trees growth,that is,energy is the fundamental cause that drives the growth of electrical trees.Therefore,from the perspective of energy conservation and combined with the fractal theory of electrical trees,this paper proposes a method for estimating the length of electrical trees in polymers based on the partial discharge energy,the feasibility of which is verified by calculating the length of electrical trees in PE/XLPE,epoxy resin and silicone rubber materials.