Study of conductor corrosion in wet-design high voltage cables

Wet-design HVAC cables, now qualified up to 72 kV, are often used as inter-array cables in wind farms. Benefits of omitting the traditional lead sheath include significant weight and cost reduction, improved fatigue properties and increased maximum laying depth. For HVDC the use of wet design is almost non-existent but on-going research efforts may lead to the development of such products in the future. Metallic return conductors for HVDC links are, however, sometimes manufactured without lead sheath and often with large conductor cross-sections which may raise the need to include a conductor tape in the design. The aim of this study is to investigate the compatibility between cable conductors and several commercial cable tapes with regards to corrosion. Three types of ageing experiments were performed. The first was wet ageing of aluminium strips in contact with tape sandwiched between XLPE semicon plates at $80^{\circ} \mathrm{C}$. The second was wet ageing of several different full-scale high voltage cable core samples in a climate chamber at 40 and $90{ }^{\circ} \mathrm{C}$, and the third a two-year wet-AC test. Visual inspection showed that most tested tapes drastically increase the rate of corrosion, compared to reference tests without tapes. Corrosion studies of full-size cable demonstrated the effect of conductor tape - but also the resilience of a normal wet-design AC cable. Samples retrieved after a two-year thermoelectric wet-ageing HVAC test were inspected without finding any trace of conductor corrosion.