Electrical Test Demands in a HVDC Power Cable Life

Recent market trends towards power generation in remote renewable power plants such as concentrated solar power plants in desserts or off-shore wind parks, the economic interests for long distance power transmission as well as the negative public perception of overhead lines lead to an increasing attractiveness of power transmission via HVDC (High Voltage Direct Current) cables. This technology is not only space saving but also reaches at a certain distance economic benefits compared to HVAC (High Voltage Alternating Current) transmission when it comes to installation cost and transmission losses. However, HVDC cables require a) quality assurance as verification / validation of product developments and their market introduction, ongoing tests for confirmation of proper manufacturing, installation and commissioning and b) ageing monitoring respectively a quick fault location detection during their service life. The quality acceptance tests are standardized (e.g. according IEC, IEEE) with mostly fixed limits at repetitive, comparable conditions whereas diagnostic onsite tests allow more interpretation and application of experiences according individual boundary conditions but also some room for the risk management of the grid operator. Typical testing aspects on cables cover: . HVDC withstand tests . Partial discharge (PD) measurements . Quick, precise fault localization with limited harm on defect for the following root cause analysis Even though HVDC power transmission is applied in market since 1950s, the dielectric testing of extruded HVDC cables in the factory and on site is still challenging considering the increasing voltage levels, increasing cable lengths and earth or even offshore installation. The (long-term) validation of insulation coordination requires high voltages for quality assurance tests which represent typical expectable stresses during service life like transient wave shape, partial discharge behavior and dielectric field stress in the insulation medium. This contribution will discuss some of the latest technical solutions to generate the required testing voltages for HVDC cables to comply with current standards. Considering the above mentioned facts, important aspects will be shown to explain economical, physical and technical challenges of dielectric testing of extruded HVDC cables during their entire life time.