Research on phase-controlled arcing range of ring main unit filled with C4F7N/CO2 mixed gas under slightly positive pressure

Perfluoroisobutyronitrile (C
4
F
7
N) and its mixed gas are being widely studied as one of the most potential gases to replace SF6. Focusing on the breaking process of ring main unit (RMU) filled with C
4
F
7
N/CO
2
mixed gas under slightly positive pressure, the phase-controlled technology is used to improve the breaking capacity of the interrupter in this paper. The decomposition and consumption of C
4
F
7
N caused by arcing can be suppressed. The whole process arc model describing the arcing stage and the current zero stage is established based on magnetohydrodynamics (MHD) and black box model (BBM). During the opening process in which both the current and the opening distance are time-varying, the influence of the arcing time on the internal and external characteristics of the arc, the current zero characteristics and the post-arc re-ignition characteristics is theoretically analyzed. The reasonable phase-controlled arcing range (PCAR) are calculated and evaluated. According to IEC 62271-103: 2011 and GB/T 3804-2017 standard, synthesis tests are carried out under different arcing times. The results show that the evaluated PCAR can improve the characteristics of the arcing stage and reduce the average arcing time. The probability of successful breaking is increased. The effectiveness of the phase-controlled technology and the evaluation method of the arcing range under the slightly positive pressure is further verified.