Perfluoroisobutyronitrile (C₄F₇N) 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 C₄F₇N/CO₂ 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 C₄F₇N caused by arcing can be suppressed. Whole process arc model describing the arcing stage and 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, influences of the arcing time on internal and external characteristics of the arc, current zero characteristics and post-arc re-ignition characteristics are theoretically analyzed. Reasonable phase-controlled arcing range (PCAR) is calculated and evaluated. According to IEC 62271-103: 2011 and GB/T 3804-2017 standard, synthesis tests are carried out under different arcing times. Results show evaluated PCAR can improve characteristics of the arcing stage and reduce average arcing time. Probability of successful breaking is increased. Effectiveness of phase-controlled technology and evaluation method of arcing range under slightly positive pressure is further verified.

For phase-controlled vacuum breakers, the acting time of Permanent Magnetic Actuator (PMA) should be precise. Variation of capacitor voltage, jamming, temperature, etc. (called disturbance factors) impact dispersion of closing time seriously. Tracking control is used to suppress this dispersion. However, PMA is a nonlinear, high-order complex system. The control process is dynamic following control. Therefore, the dispersion suppression capability of conventional controllers faces challenges. In order to solve this problem, a new technology has been put forward in this paper. By using this technology, response speed and anti-interference ability of the control system are improved. Time scatter is better suppressed. A current-displacement double closed-loop controller (CDCC) based on inverse system method is proposed. During the motion stage, the dynamic characteristics of the controller can be optimized by using the inverse systems to correct output of the automatic displacement regulator (ADR) and the automatic current regulator (ACR). A simulation system is established and performance of different control methods commonly used in phase control is compared. Based on the aforementioned theory, many experiments have been performed when disturbance factors change, such as capacitor voltage, environment temperature, and so on. Results prove that current deviation and displacement deviation can be corrected under severe conditions and closing time can be stabilized within ±0.5 ms. Therefore, anti-interference ability and dynamic performance of PMA are ensured when external factors change drastically, which will increase accuracy of the phase-controlled operation and prolong the lifespan of circuit breakers.