Abstract
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.
Highlights
Offshore energy is a potentially promising source of renewable energy and extensive work has been devoted to suggest reliable structures that can withstand harsh environments while ensuring reliable delivery of electricity to onshore electric power stations [1,2,3,4,5]
The growth of these ellipsoids and the merging of neighboring ellipsoids is the cause of degradation of the insulator material in the form of water treeing, and the material’s breakdown
The initiation and propagation of water trees in insulators of submarine power cables poses a serious threat to the lifetime of the cables
Summary
Offshore energy is a potentially promising source of renewable energy and extensive work has been devoted to suggest reliable structures that can withstand harsh environments while ensuring reliable delivery of electricity to onshore electric power stations [1,2,3,4,5]. Submarine power cables are deployed to work in extreme environmental conditions for a lifetime of 20 to 25 years [5]. A large number of elements are required to form the complex structure of a submarine power cable (Figure 1, [6]). The investment required for operation and maintenance of submarine power cables is substantial. Efficient methods are necessary to predict the lifetime of cables [5]. Among the various constituents of a submarine power cable, the insulator surrounding the conductor is an integral component and regular monitoring of the insulator is important to prevent a breakdown. At the advent of submarine power cables, oil–paper insulation was initially used.
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