In order to meet the fast operation demands of DC circuit breakers, a high-speed vacuum mechanical switch (VMS) driven by a repulsive force actuator is focused. To improve the drive speed and energy conversion efficiency (ECE) of the actuators, the dynamic characteristics of the double sided coil repulsive force actuators are investigated, and two generalized optimization design methods focusing on the aspect ratio of the driving coils (defined as ARF) and the electrical parameters (defined as EF) are developed. FEM simulation models’ simulation and tests of VMS prototypes are conducted to verify the optimization methods. Results prove that the ARF method could improve the ECE of a VMS from 1.05% to 7.55%, and EF method could improve ECE of the same VMS from 1.05% to 6.61%, the combination of ARF and EF could improve the value of VMS’s ECE to 10.50%, thus proving the validity and accuracy of the optimization methods.

Transition is an important issue in rail electromagnetic launches; it limits the performance of electromagnetic launch systems. In launch progresses, wear on the contact surface of armature significantly affects the contact surface morphology and armature structure. Studying wear, contact resistance, and sliding friction coefficient of the contact surface between the armature and the rail is important to understand and suppress transitions. In this paper, specially designed armatures, which make the wear on armature contact surface all melt wear, are used in rail launch experiments, to measure the wear rate of melt wear and observe how it is affect by loading. In the experimental results, average wear rate is represented by the average thickness of aluminum debris left on the rails: the average wear rate is within 0.6-2 mm/m and the average debris thickness is in a range of 3-10 μm . Based on the idea that melt wearing is the main mechanism, the heat balance of contact surface is analyzed. It is concluded that melt wear absorbs much of the heat generated in the surface, and the remainder goes into the rails. Equations based on this heat balance based are then derived to establish relationship among melt wear, launch parameters, and material parameters. According to the equations and the experimental results, the contact resistance of armatures with 80 mm ² contact areas is 2.56 μΩ, the contact resistance of armatures with 50 mm ² contact areas is 4.09 μΩ and the sliding friction coefficient is 0.11.

In the process of electromagnetic launch, the nonuniform contact pressure distribution on the armature-rail interface kept changing with the armature moving forward. At first, the contact pressure was mainly provided by the deformation of the trailing arm, from which it could keep a good metal-metal contact at the armature-rail interface. After the pulse current was constructed, the magnetic pressure would dominate the contact pressure because it was much larger than the mechanical interference pressure. In this paper, the 3-D modeling of contact pressure distribution was carried out with the finite-element method. In the simulation of 3-D contact calculations, the current entered the armature from the trailing edge. The electromagnetic force perpendicular to the armature trailing arm was equivalent to the uniform load on the inner surface of the trailing arm. A typical contour pattern of nonuniform contact pressure distribution was acquired. Some nonuniform coefficients of contact pressure distribution were proposed and analyzed to evaluate the contact performances between the armature and rails. A series of simulations was conducted at different magnitudes of magnetic pressure, and with different armature structure parameters. The characteristics of the nonuniform coefficients were investigated and discussed. The dependences of the nonuniform coefficients on the equivalent uniform load and armature structure parameters were obtained.

Investigation of positive streamer-leader propagation under slow front impulse voltages can play an important role in the quantitative research of positive upward lightning. In this work, we performed a large-scale investigation into leader development in a 10-m rod–plane gap under a long front positive impulse. To describe the leader propagation under slow front impulse voltages, we recorded the leader propagation with a high-speed charge coupled device (CCD) camera. It is important to figure out this phenomenon to deepen our understanding of leader discharge. The observation results showed that the leader mechanism is a very complex physical phenomenon; it could be categorized into two types of leader process, namely, continuous and the discontinuous leader streamer-leader propagation. Furthermore, we studied the continuous leader development parameters, including two-dimensional (2-D) leader length, injected charge, and final jump stage, as well as leader velocity for rod–plane configuration. We observed that the discontinuous leader makes an important contribution to the appearance of channel re-illuminations of the positive leader. To clarify the above doubts under long front cases, we carried out extensive experiments in this study. The comparative study shows better results in terms of standard switch impulse and long front positive impulse. Finally, the results are presented with a view toward improving our understanding of propagation mechanisms related to restrike phenomena, which are rarely reported.

In this paper, taking the minimum metal conductor usage of an air core reactor as optimization goal, the influence of air ducts width and encapsulation number on thermal efficiency and electromagnetic efficiency are analyzed. Combined with the equation constraint conditions for maximum temperature rise conservation, inductance conservation and structure function of reactor considering the change of air ducts width and encapsulation number, the thermal and electromagnetic combined optimization curves are formed, and design results are achieved based on the initial design parameters. Meanwhile, the temperature field simulation model of the reactor is established and the results verify the correctness of the optimization method. According to the design results, the proportionality factor of metal conductor usage is only 0.61 compared with the initial design parameters of the reactor, which shows that the proposed comprehensive optimization method can significantly reduce conductor usage, improving the metal conductor utilization ratio.

In this paper, the breaking process of the vacuum circuit breakers is briefly described, and the main factors that influence the post-arc process are analyzed. Based on the detachable vacuum interrupter, the experimental platform of AC breaking is built, and the experiments of the post-arc current measurement and cathode spot observation are completed. The voltage and current during the period of current zero are measured, and the images of cathode spots during the arcing process are obtained. The experimental results show that at the same frequency, the post-arc current I_pac and the post-arc charge Q_pac increase with the increase in ${\frac{\mathrm{d}i}{\mathrm{d}t}}_{\text{cz}}$ ($\frac{\mathrm{d}i}{\mathrm{d}t}$ at current zero). Under the same conditions of ${\frac{\mathrm{d}i}{\mathrm{d}t}}_{\text{cz}}$ , I_pac and Q_pac decrease with the increase in frequency, but both are unchanged with frequency when the frequency is high enough. With the increase in current frequency, the distribution diameter of cathode spots decreases under the condition of the same ${\frac{\mathrm{d}i}{\mathrm{d}t}}_{\text{cz}}$ value. According to the characteristics of cathode spot distribution, the metal vapor density under different conditions is calculated. Comparing the calculation results of metal vapor with the experimental results of post-arc current, the concept of metal vapor ionization is put forward. An ionization process of metal vapor after the current zero crossing occurs. The ionization of metal vapor will cause an increase in the number of electrons after the current zero crossing, which affects I_pac, Q_pac, and sheath growth.