In the years to come, large power grid operators will operate and maintain an ever-increasing asset base. New innovative solutions are needed to increase the quality and efficiency of asset management to avoid corresponding growth in resources and cost. To this end, autonomous unmanned aerial vehicles (UAVs) provide a range of possibilities. Here, we present a novel prototype solution for autonomous and remotely operated inspection missions with resident drones on electrical substations, comprising: (1) an autonomous drone with sense and avoid and robustness to harsh weather capability; (2) a drone hangar for remote operations; and (3) drone operations and data acquisition management software. Further, we discuss the possibilities and challenges that such a system offers and give an overview of requirements that are key to realizing the potential of drones for improved asset management. These requirements are based on years of operational experience with electrical substations combined with the lessons learned during the development and testing of our drone system. We also experimentally investigate safety distances between the drone and high-voltage infrastructure. We demonstrate the usefulness of our autonomous inspection solution through extensive field testing at one of Statnett’s fully operational electrical substations.

Partial discharge measurements have been used for studying shrinkage voids in the insulation of mass-impregnated high voltage DC subsea power cables. Three 4.5-m long cable samples were subjected to ac partial discharge measurements at different ambient temperatures, both under isothermal conditions and after load current turn-offs. Two distinctly different phase resolved partial discharge patterns were observed, suggesting that two different "types" of cavities were created. The type causing by far the most powerful discharges appeared a few hours into the cooling period after load turn-off, which coincides in time with when load cycling breakdowns during type testing usually occur. Current loading has a significant effect on the cavities, as it leaves them-at least temporary-with a different dielectric strength afterwards. The mechanisms behind this change are not identified, but the associated time constants are of the order of days and weeks. Consequently, accurately determining the limitations of such cables with regard to their ability to withstand polarity reversals and rapid load changes may be more complicated than previously assumed.

Partial discharge measurements have been used for studying shrinkage voids in the insulation of mass-impregnated high voltage DC subsea power cables. Three 4.5-m long cable samples were subjected to ac partial discharge measurements at different ambient temperatures, both under isothermal conditions and after load current turn-offs. Two distinctly different phase resolved partial discharge patterns were observed, suggesting that two different "types" of cavities were created. The type causing by far the most powerful discharges appeared a few hours into the cooling period after load turn-off, which coincides in time with when load cycling breakdowns during type testing usually occur. Current loading has a significant effect on the cavities, as it leaves them -at least temporary -with a different dielectric strength afterwards. The mechanisms behind this change are not identified, but the associated time constants are of the order of days and weeks. Consequently, accurately determining the limitations of such cables with regard to their ability to withstand polarity reversals and rapid load changes may be more complicated than previously assumed.

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