DC Cable Short Circuit Fault Protection in VSC-MTDC
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- Institutt for elkraftteknikk 
With the development of offshore wind farms, Voltage Source Converter based High Voltage Direct Current or Multi-terminal High Voltage Direct Current Technology (VSC-HVDC/MTDC) is becoming promising in the field of large-capacity and long-distance power transmission. However, its extreme vulnerability to DC contingencies remains a challenge in both research and practice. DC cable short circuit faults, or cable pole-to-pole faults, though less common than DC cable ground faults, can cause the most severe damage to the VSC as well as the whole system. In this thesis work, firstly a simple 3-terminal MTDC system is built and validated in PSCAD/EMTDC. Afterwards, based on the self-built MTDC system, DC cable short circuit faults with different locations are studied and analyzed in both theory and numerical simulation. Finally, a comprehensive protection scheme is proposed against such DC cable short circuit faults in the target MTDC system, combining the sub-schemes in fault detecting/locating principles, fault isolating tools and fault current limiting technologies. The coordination among the three parts is also taken into consideration. The scheme is later proven to be fast, selective, reliable, sensitive and robust in general. Moreover, the specific design procedure is further extended into a general design philosophy for DC cable short circuit fault protection in VSC-MTDC systems.