On-site application and improvement of water tree deterioration diagnosis for XLPE cable by residual charge method

Abstract

Residual charge method", which has been developed for detection of non-bridged water tree, is well known as a high reliability water tree deterioration diagnosis technique for XLPE cable, and it has been applied for on-site cable system diagnosis.Traditional residual charge method measures the amount of electrical charge, and the information of cable length is required to evaluate the result. In this paper, we would like to introduce our development of the new technique of residual charge method which does not need the information of cable length to evaluate the deterioration degree.

Measurement of residual charge using pulse voltages for water tree degraded xLPE cables diagnosis

“…A negative DC voltage was applied to the cable for 7 minutes, and the cable was grounded. The time duration of the DC voltage application was selected according to the data in [30]. Then, an AC voltage of 6 kVrms was applied, and the DC current component was measured.…”

“…Other water tree diagnostic techniques are based on the polarization and depolarization processes due to water tree degradation [24][25][26][27][28][29][30]. One such technique is called the residual charge method [25][26][27][28][29][30].…”

“…One such technique is called the residual charge method [25][26][27][28][29][30]. In this method, a DC voltage is applied to a water tree-degraded XLPE cable in order to accumulate space charges in water tree parts, and after it is grounded, an AC voltage is applied to it to release deeply trapped space charges, i.e., residual charges.…”

Relationship between residual charge signals and AC breakdown voltages of removed 6.6 kV XLPE cables using residual charge detection method with pulse voltages

“…The residual charge method is a main diagnostic method used for the water tree degradation of cross-linked polyethylene (XLPE) cables in Japan [1]- [6]. In this method, space charges are accumulated at water tree degraded part of an XLPE cable by an application of a DC voltage, and after the cable is grounded in a certain time, deeply trapped space charges, i.e., residual charges are released by an application of an AC voltage.…”