General overview of AC and DC current injection on high voltage potential for HVDC long-term tests

HVDC transmission systems like cables or gas insulated systems are of great interest for future grid expansions. They are usually type tested in one-year long-term tests, to ensure lifetimes up to 40 years and more. HVDC equipment always has to be tested with voltage and current at the same time to investigate temperature dependent space charge effects inside the insulation material. Even though the HVDC equipment in the grid is operated with DC current and DC voltage, laboratory tests often have to be performed with AC current heating due to laboratory limitations. The following report shows the technical limits of AC current injection and presents solutions for DC current injection on high voltage potential. The solutions are described and compared to each other. Furthermore, the report shows the status of actual research and prototyping for this new generator type.