Research On The Development Laws Of The Electrical Tree In Oil-paper

The core equipments of power grid,such as transformers,reactors and so on,is widely used oil-paper as insulating material.During the operation,the inherent or external defects of the insulating material may lead to partial discharge,which damage to oil-paper to produce electrical tree.Ultimately,the expansion of defects and equipment accidents will be caused to endanger the safe operation of power grid.Therefore,it is very important to explore the effect of partial discharge on the growth of electrical tree,and to find a reliable method for the insulation condition assessment of such equipments.In order to study the development of electrical tree in the oil-paper,in this paper,a large number of experiments had been done to realize the real-time monitoring of the growth of the electrical tree based on the distributed potential measurement system.Firstly,the measurement reliability of distributed measurement system was analyzed.Then,the measurement error of the experiment system was modified.Finally,the reliability of the measurement system was verified by experiments.Based on the constant voltage method,the voltage withstand experiments on oil-paper were carried out with different times.During the experiment,the space charge position change and the voltage amplitude of electrodes and the Q-? distribution of partial discharge were monitored on-line.Then the shape of the electrical tree in oil-paper was obtained after sample dissection.After experiment,integrated all these phenomena to study the development of the electrical tree in the insulation board.In addition,we explored the observation of the electrical tree in the insulation board with the XRT technology,for obtaining more realistic tree structure with nondestructive.It was found that,in the process of electrical tree growth,the space charge position accompanied with the growth of the electrical tree,and the amplitude of measuring electrodes increased with the growth of the electrical tree.So,they can be used as the characteristic of electrical tree growth.At the same time,the number and the capacity of partial discharge are closely related to the growth state of the electrical tree.In the growth stage,the PD quantity and PD number were maintained at a high level,and the discharge phase was relatively wide.With the growth of electrical tree,the electric field intensity of the end of the branch is decreased,and the PD quantity and discharge number gradually decrease or stop.From the perspective of tree shape,it contains three tree branches,such as mass branches and dendritic branches and double form branches.The oil-paper has a dense area and sparse structure in the surface.When the needle electrode is located at the junction of the two regions,it is easy to cause the dendritic branch.When it is located in a single structure area,it is easy to cause the mass branch,When it is located near the intersection of the two structures,it is easy to cause the double shape branches.Finally,the study found that XRT technology has good imaging effect on the electric tree and the micro void in the oil-paper.That is to say,it can be used as a method of observing the morphology of electrical tree in oil-paper.And it is still necessary to further study how to separate the electrical tree and the micro crack zone.