Fault Clearing Operation in Low-Frequency High-Voltage AC Systems

Low-frequency high-voltage ac (LF-HVac) system has been proposed as an alternative to HVdc and HVac systems for long-distance bulk power transmission. LF-HVac system employs back-to-back (BTB) converters to interconnect and control voltage and power interchange between two asynchronous power grids operating at different frequencies. While there are multiple studies on LF-HVac system available in the literature, fault clearing operation has not been analyzed. Therefore, this paper focuses on fault clearing operation in the LF-HVac system and proposes a novel method to reduce fault current by changing operating frequency of power source and converter during the fault condition. The performance of the proposed method is validated using detailed models of BTB converters developed in PSCAD/EMTDC. The ability to change operating frequency at the onset of a fault condition allows breakers to rapidly clear the fault and recloses. The results obtained using the proposed method substantially diminish the fault current.