The relationship between electric tree aging degree and the equivalent time-frequency characteristic of PD pulses in high voltage cable

In the online monitoring on partial discharge of high voltage XLPE cable, severity of insulation electrical tree can be early warned through its partial discharge. This is an important measure to prevent sudden accident in high voltage cable and to ensure the normal operation of power system. This paper will apply the equivalent time-frequency analysis technology classified with PD pulses into the identification of electrical tree degradation of high voltage cable. The electrical tree in the whole insulation of 35kv cable slice is triggered by a tip under rated voltage, and electrical tree photos and PD pulses data are collected in real-time by microscope and PD broadband detection technology, then the relationship between different growth stages of electrical trees and the equivalent time-frequency figure of PD pulses are concluded. In addition, we used double-needle in different depth to trigger electrical trees of different extent in the insulation, concluded the relationship between the two electrical trees of different extent and the hybrid equivalent time-frequency figure of PD pulses, and found the method to distinguish the two electrical trees. Therefore it can provide criteria for the identification of electrical tree degradation of high voltage cable insulation.