Experimental investigation on the cause of harmfulness of the blue water tree to XLPE cable insulation

Abstract

Through investigations made on crosslinked polyethylene (XLPE) insulated power cables that had experienced failures, blue-colored water trees were observed in addition to ordinary white water trees. The blue water tree was found to be much more harmful than the white water tree, since more electrical trees started at the blue trees. Elemental analysis revealed that iron and sulfur exist in the blue tree. In the case of this blue water tree, space charge exists abundantly but only at the tree tip, while no charge signal is observed on the electrode from which the tree starts. This indicates that the conductivity of the blue tree is very high. This is considered to be the main reason of the harmfulness of this tree.

A new dielectric response model for water tree degraded XLPE insulation - part a: model development with small sample verification

“…Also in equations (2) and (3), σ w and ε w are the water tree channel conductivity and permittivity respectively and σ p and ε p are the XLPE conductivity and permittivity respectively. The ranges of these values considered in this study are [15][16][17]:…”

A novel characterization method for water trees based on the transmission characteristics of complementary split ring resonators

“…Hvidsten et al found that the tangent value of dielectric loss angle of insulating material increased with water tree ageing and showed strong non-linear characteristics [14]. The existence of water trees can also increase the dielectric constant and conductivity of polyethylene [15][16][17]. So, there is a strong connection between water tree and dielectric properties, which implies that water trees can be detected by means of testing the change in dielectric properties.…”

Study on electrical characteristics of XLPE insulation of high voltage cable

“…The blue tree was found to be much more harmful than the white water tree, since more electrical trees started at the blue trees which probably involve some specific highly catalytic impurity. The main reason of the harmfulness of the blue tree is its very high electrical conductivity, which is confirmed from the fact that the space charge accumulates only at the interface between the treed and the un-treed regions [39].…”

“…#$ % & distribution cables rated from 6.6 kV to 33 kV [46]. Compared to distribution cables, there have been a smaller number of reports on water tree deterioration in HV transmission cables rated 66 kV [39]. Since manufacturing techniques are stricter for HV XLPE cables (rated 110~220kV) and the cables normally apply the configuration with a metallic radial waterproof layer, water treeing is not an issue any more.…”