C ₅ F ₁₀ O/CO ₂ gas mixture is one of the most promising alternatives to SF ₆ as an insulating gas in high‐voltage switchgear. As a key performance index in product design, the temperature rise characteristics are rarely reported. In this paper, the thermodynamic parameters of C ₅ F ₁₀ O/CO ₂ gas mixture were calculated first. Then, the calculation model of transient temperature rise was constructed for a 252 kV/3150 A bus, and a temperature rise experimental platform was built to verify the reliability of the proposed calculation model. On this basis, the influence of different factors such as load current, charging pressure, mixing ratio, and structure size on the temperature rise of the bus was further analysed, and it is found that increasing the charging pressure and the mixing ratio of C ₅ F ₁₀ O could effectively reduce the bus temperature rise but it still could not reach the level of SF ₆ . The main structure size that affects the temperature rise of the bus is the outer diameter of the conductor, which increases by 10.2%, and the temperature rise is the same as that of the original SF ₆ bus. Finally, a high‐precision bus temperature rise surrogate model, which combined with the Latin hypercube model, the coefficient of prognosis, and the Kriging fitting method was established to facilitate the structural design.

The traditional canned electric valve consists of an induction motor and a reducer, which need to be matched with the position sensor to achieve precise control of valve position. The position sensor and reducer are not only easily damaged in high-temperature liquids, but also the slip rate of the induction motor is greatly affected by the liquid temperature, which makes it difficult to achieve accurate control. To address the above problems, this paper introduces a new topology of canned electric valve permanent magnet synchronous motor (CEV-PMSM), and a new maximum torque per ampere (MTPA) model is proposed. The new MTPA control equation considering the canned sleeve parameters is derived theoretically. By comparing it with i_d = 0 control and ideal MTPA control strategy, it is proved that the new MTPA model reflects the electric valve operation characteristics more realistically. In order to achieve sensorless control of the electric valve, and to achieve fast response and high-precision control under external disturbances and parameter uncertainties, the proposed control scheme combines sensorless control and two-degree-of-freedom (2-DOF) control. Consequently, the proposed control scheme can effectively improve the static and dynamic performances of the CEV-PMSM, as well as adjust the tracking and anti-disturbance performances independently. Finally, a 2 kW 100 r/min prototype was manufactured and corresponding experiments were conducted to verify the accuracy of the analysis.

The C₅F₁₀O/CO₂ gas mixture is one of the most promising SF₆ alternative gases at the present stage, which was initially applied in high-voltage electrical equipment. This paper mainly studies the interruption performance of 3%C₅F₁₀O/97%CO₂ gas mixture (k = 3%) with a charging pressure of 0.6 MPa in high-voltage circuit breakers. First, the thermodynamic parameters, transport coefficient, and net radiation coefficient were calculated for k = 3%. On this basis, a 40.5 kV circuit breaker was used as a prototype to establish the magnetohydrody-namic model for breaking 20 kA short-circuit current, and the arc temperature and pressure distribution in the arc extinguishing chamber of the circuit breaker were calculated. The LC oscillation circuit was used to build an arc-extinguishing characteristic test platform to verify the accuracy of the numerical calculation. Finally, based on the Mayr arc model and the critical electric field strength, the post-arc thermal breakdown and electrical breakdown characteristics of SF₆, CO₂, and k = 3% were quantitatively analyzed. The results show that under 0.6 MPa, the thermal breakdown performance of k = 3% is about 89.7% of SF₆, which is nearly twice higher than that of CO₂ and has better thermal breaking ability. The electrical breakdown performance of k = 3% is about 20.4% of SF₆, and the probability of electrical breakdown in the front end of the fixed contact is high. This problem should be paid attention to in the design of high-voltage circuit breakers. This study can provide a reference for the development and optimization of environmentally friendly high-voltage circuit breakers.

Recently, perfluoromethyl vinyl ether (CF₃OCF = CF₂) has been proposed to have the potential to replace SF₆, but its arc-extinguishing ability is still unknown. To provide the necessary basic parameters for further study of arc extinguishing characteristics, this series of papers focuses on the physical and chemical properties of CF₃OCF = CF₂ arc plasma. The research content of this paper is decomposition characteristics and thermodynamic parameters. The geometric configuration, rotational inertia, and vibration frequency characteristics of CF₃OCF = CF₂ and its decomposition products were obtained at the B3LYP/6–311G(d,p) level. The energy of each particle was calculated at the CCSD(T)/cc-pVTZ level. The most likely decomposition path was CF₃OCF = CF₂→CF₃+CF₂CFO→CF₂+CFO. The equilibrium compositions of arc plasma were calculated by the mass action law model. The main components of pure CF₃OCF = CF₂ after arc were C₃F₈, C₃F₆, C₂F₆, CF₄, and CO. When CO₂ was mixed in CF₃OCF = CF₂, with the increase of CO₂ content, the main components after arc gradually became CF₂O, CF₄, CO₂, and CO. The thermodynamic parameters such as density, specific enthalpy, and specific heat at constant pressure were obtained by thermodynamic relationship. Through ρC _p and ρh, it can be inferred that the radial heat transfer capacity of CF₃OCF = CF₂ is not as good as SF₆, but the energy dissipation capacity of axial heat convection is stronger than SF₆, and the arc presents the characteristics of large radius and long length.

In order to solve the problem that it is difficult to take into account the performance constraints between the core functions of insulation, current flow and arc extinguishing of high-voltage vacuum circuit breakers at the same time, this paper proposes a flexible control strategy for the motor operating mechanism of high-voltage vacuum circuit breakers. The relationship between the rotation angle of the motor and the linear displacement of the moving contact of the circuit breaker is analyzed, and the ideal dynamic curve is planned. The motor drive control device is designed, and the phase-shifted full-bridge circuit is used as the boost converter. The voltage and current double closed-loop sliding mode control strategy is used to simulate and verify the realization of multi-stage and stable boost. The experimental platform is built and the experiment is carried out. The results show that under the voltage conditions of 180 V and 150 V, the control range of closing speed and opening speed is increased by 31.7% and 25.9% respectively, and the speed tracking error is reduced by 51.2%. It is verified that the flexible control strategy can meet the ideal action curve of the operating mechanism, realize the precise control of the opening and closing process and expand the control range. The research provides a theoretical basis for the flexible control strategy of the high-voltage vacuum circuit breaker operating mechanism, and provides new ideas for the intelligent operation technology of power transmission and transformation projects.

Temperature monitoring is the main indicator to ensure the safe operation of the coal mine explosion-proof box. In this study, a three-way flameproof cable box was considered for coal mines. A three-dimensional transient temperature field simulation model was constructed for magnetic–thermal coupling and subsequently used to conduct temperature field simulation for the failure of the flameproof cable box for coal mines. An experimental platform was developed to test the temperature characteristics of failure flameproof cable boxes for coal mines and obtain temperature curves at various failure currents. Using the experimental results of temperature characteristics and temperature field simulation outcomes, we analyzed the time responses and spatial distribution characteristics of the temperature rise of flameproof cable boxes for coal mines. The error between simulation and experimental results does not exceed 1 K, and the upper limit of time to ensure safe operation under different failure modes is determined. Thus, the acquired temperature distribution characteristics in a failure mode can be used as a reference for the design, inspection, and status warning of flameproof cable boxes for coal mines.