Water tree inception and its dependence upon electric field, voltage and frequency

1993 ◽  
Vol 140 (5) ◽  
pp. 397 ◽  
Author(s):  
J.C. Fothergill ◽  
A. Eccles ◽  
J.A. Houlgreave ◽  
L.A. Dissado
Keyword(s):  
Electric Field ◽  
Water Tree

scholarly journals Numerical Simulation for Void Coalescence (Water Treeing) in XLPE Insulation of Submarine Composite Power Cables

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5472
Author(s):  
Monssef Drissi-Habti ◽  
Das Raj-Jiyoti ◽  
Soumianarayanan Vijayaraghavan ◽  
Ech-Cheikh Fouad
Keyword(s):  
Electric Field ◽  
Applied Electric Field ◽  
Economic Consequences ◽  
Von Mises Stress ◽  
Void Coalescence ◽  
Power Cables ◽  
Premature Failure ◽  
Water Tree ◽  
Unit Cells ◽  
Von Mises

Due to the growing demand for offshore renewable energy, the development of durable submarine power cables is critical. Submarine power cables are expected to have a service life of over 20 years. However, it has been shown that these cables suffer from water-tree flaws that progressively extend to conductors and corrode copper, which may lead to premature failure. Water treeing is caused by the of interconnection of voids (of a few nanometers) that are present in the insulator after manufacturing or formed during operation. The economic consequences of a breakdown can be drastic due to the heavy maintenance required. In the current study, the insulator is modelled as cubic unit cells containing water voids in the form of ellipsoids. The displacement field of ellipsoids is found to be dependent on its distribution in the cubic cell and on the applied electric field. Von Mises stress and effective plastic strain at the tips of the ellipsoid are found to be significant when either the relative distance between the two ellipsoids is short or the applied electric field is high. The proposed model is intended to provide insights into the ageing of cross-linked polyethylene (XPLE), which is extremely difficult to predict experimentally due to the excessive time needed to achieve coalescence of voids.

scholarly journals Water Tree Propagation in a Wide Temperature Range: Insight into the Role of Mechanical Behaviors of Crosslinked Polyethylene (XLPE) Material

Polymers ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 40
Author(s):  
Siyan Lin ◽  
Kai Zhou ◽  
Yuan Li ◽  
Pengfei Meng
Keyword(s):  
Yield Strength ◽  
Electric Field ◽  
Wide Temperature Range ◽  
Mechanical Behaviors ◽  
Field Force ◽  
Temperature Range ◽  
Water Tree ◽  
Different Temperatures ◽  
Tree Length ◽  
Electric Field Force

To understand the propagation characteristics of water trees at a wide temperature range, this paper presents the effect of mechanical behaviors on the sizes of water trees. An accelerated water tree aging experiment was performed at −15 °C, 0 °C, 20 °C, 40 °C, 60 °C, and 80 °C for crosslinked polyethylene (XLPE) specimens, respectively. Depending on the micro observations of water tree slices, water tree length is not always increasing with the increase in temperature. From 0 °C to 60 °C, water tree length shows a trend from decline to rise. Above 60 °C, water tree length continues to reduce. Dynamic mechanical analysis (DMA) shows that the glass transition temperature of the new XLPE specimen is about −5 °C, and the α-relaxation is significant at about 60 °C. With the increase in temperature, the XLPE material presents different deformation. Meanwhile, according to the result of the yield strength of XLPE at different temperatures, with the increase in temperature, the yield strength decreases from 120 MPa to 75 MPa, which can promote the water tree propagation. According to the early stage in the water tree propagation, a water tree model was constructed with water tree branches like a string of pearls to calculate electric field force. According to the results of electric field force at different expansion conditions, with the increase in temperature, due to expansion of the water tree branches, the electric field force at water tree tips drops, which can suppress the water tree propagation. Regardless of high temperature or low temperature, the water tree propagation is closely related to the mechanical behaviors of the material. With the increase in temperature, the increased deformation will suppress the water tree propagation, whereas the decreased yield strength will promote water tree propagation. For this reason, at different temperatures, the promotion or suppression in water tree propagation is determined by who plays a dominant role.

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