Optimization of Unbalanced Protection for AC Filter Capacitor Bank in UHV Converter Station

Taking the unbalanced protection action of the AC filter group at Changji converter station as the research object, this paper introduces the common structure and unbalanced protection principle of C1 capacitor, sorts out the handling and troubleshooting measures when the capacitor group fails, and verifies the consistency between the current unbalanced protection setting and logic and the initial design. In response to the problem of one or a small number of capacitor components failure within a single capacitor unit leading to the tripping of the entire capacitor group, the reasons for the deviation between the actual operating voltage and the design voltage, as well as the deviation between the power frequency current melting time and the tripping time of section III protection, resulting in insufficient internal fuse energy and ineffective melting, were identified. A set value and logic optimization method for capacitor group imbalance protection were proposed. The effectiveness of the proposed method was verified through PSCAD/EMTDC simulation modeling, avoiding frequent tripping of AC filter banks and improving equipment availability.