HVDC switchgears are key equipment in the control of power and protection against faults in large offshore HVDC systems. With the continuous increases in the size of wind farms and in the capacity of wind turbines, the operating voltage of wind farm power systems is also being increased to keep power transmission losses as low as possible.
In this respect, KEMA Labs (the CESI Testing, Inspection and Certification Division) demonstrated the testing of two types of new switchgear for offshore: HVDC circuit breakers and HVDC gas-insulated switchgear (GIS).
Specifically, all demonstrations were conducted by the KEMA Labs experts within the framework of the European PROMOTioN project on offshore transmission grids, which was completed in 2020. The challenge for KEMA Labs was to validate components of future HVDC grids.
KEMA Labs, as a project founding father, was in fact a partner of choice because of its reputation in innovative testing technologies. Three HVDC circuit breaker technologies, rated 80 to 350 kV, were tested in our high-power laboratory, and one long-duration high-voltage withstand test of an HVDC GIS (320 kV) was performed in a high-voltage laboratory of KEMA Labs site in Arnhem, The Netherlands.
The system studies led to understand the impact of transients on switchgear in a faulted grid. A key duty for HVDC circuit breakers is massive energy absorption: by operating ac short-circuit generators in low frequency, for the first time ever, tests could be performed covering the complete interrupting cycle of a fault current up to 20 kA in a meshed HVDC grid. For the largest circuit breakers, six short-circuit generators were needed. This means that, unlike earlier tests elsewhere, all breaking functionalities can now be tested in a single "shot" as in service, leaving no doubt to the end-user.
Industrial partners supplied the three different technologies of circuit breakers: Mitsubishi Electric (Japan) provided an active current injection HVDC circuit breaker based on high-voltage vacuum circuit breakers. Hitachi ABB Power Grids (Sweden, Switzerland) provided a hybrid HVDC circuit breaker based on semiconductors as well as a HVDC GIS. SciBreak (Sweden) brought in a new type of converter-assisted vacuum arc-based dc circuit breaker.