Study On The Relationship Between Energy Of Partial Discharge Pulse And The Development Of Electrical Tree In Oil-paper Insulation

Power transformer is typically oil-impregnated paper structure, carbonized traces produced during the development of partical discharge on the insulation paper of transformer. However, carbonized traces decreases the effective insulation distance of insulation paper. So there is a closely relationship between the severity of insulation defect and carbonized traces. By the method of artificially limit the discharge channel to get a single carbonized trace, and research on the influence of the development of the carbonized trace by a single partial discharge pulse energy.This test plate form of partial discharge of oil-paper insulation is built in a lab and needle-plate electrode is built on the basis of this model to simulate the nonuniform electric field in power transformers. And distributed potential measurement system is designed to measure the change of monitoring point potential distribution caused by partial discharge pulse. Many exploratory tests show that the measurement system of distributed potential has a good sensitivity and reliability. According to the the change of potential distribution on monitoring point, the position of space charge is ascertained and also get the calculation method of partial discharge energy based on the three capacitance method and the distributed potencial measurement system.Increasing the voltage step by step, partial discharge of needle-plate electrode model is studied. Broadband pulse current signal and potential distribution of the signal on the monitor points are acquired to contrastive analysis and calculation the relationship of partial discharge pulse energy with effective length of carbonized traces. Data processing results shows:the relationship between effective length of carbonized traces and total magnitude of partial discharge, total energy of partial discharge and total energy increment on Cs is piecewise linear relationship, and three kinds of relation curve has a trend of consistency. Based on layered dissection the tested insulation paper, observe the carbide morphology and the effective length of the carbonized trace under the magnifying glass.The results shows:carbonized traces under the needle tip seems like cloud cluster, and carbonized traces away from the needle tip are dendritic without a lot of branches. The growth direction of the whole carbonized trace is along the direction of electric field. Besides, there are many nodes along the carbonized trace, and two adjacent nodes are connected by a thin filaments carbonized trace.