Study of Artificial Water Tree Degradation Method for XLPE Power Cables

Abstract

In order to propose a method for producing water trees that measure a few millimeters in length in 20kV class to 60kV class XLPE cables, we discussed defect types and thermal conditions. First, surface roughness, needle protrusions, and line cracks were formed on the XLPE insulation surface of 6.6kV cables, and it was found that the water tree grew to a few millimeters in length from the needle protrusions and the line cracks. Second, water trees were generated in XLPE sheet and cable samples at room temperature and under a heat cycle and continuous elevated temperature conditions. Here, the longest water trees grew at room temperature. From these results, we selected needle protrusions and line cracks as defects and set room temperature as an artificial water tree degradation method. This method was applied with needle protrusions to a 22kV class XLPE cable, and we found that water tree length reached a few millimeters and AC breakdown voltage decreased to approximately 35% of the initial value.キーワード：電力用 CV ケーブル，水トリー，人工劣化，劣化診断 Keywords：XLPE power cables, water trees, artificial degradation, degradation diagnosis

Investigation of Water Tree Degradation in Dry‐Cured and Extruded Three‐Layer (E‐E Type) 6.6‐kV Removed XLPE Cables

“…α close to 1 has also been reported [15]. 8 shows the relationship between water tree length and 50-Hz equivalent years in the case of a needle defect formed on insulation surface of 6.6-kV XLPE cable by the authors [16]. 8 shows the relationship between water tree length and 50-Hz equivalent years in the case of a needle defect formed on insulation surface of 6.6-kV XLPE cable by the authors [16].…”

“…time, and α is expected to be greater as compared to bowtype water trees [14][15][16]. α close to 1 has also been reported [15].…”

“…As mentioned above, water trees in dry-cured E-E 6.6-kV XLPE cables are primarily bow-tie trees. Relationship between water tree length and period converted from that of 1000 Hz accelerated test with ratio of 1000 Hz to 50 Hz [16]. On the other hand, it has been reported that water trees originating from insulator surface lengthen over Fig.…”

“…8. Relationship between water tree length and period converted from that of 1000 Hz accelerated test with ratio of 1000 Hz to 50 Hz [16].…”

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

“…The thickness of the insulation was 4 mm. Its XLPE with a length of 5 m was degraded using the following procedure [33].…”