To ensure the reliability of power supply, a dual power supply structure appears in the power distribution system. Power supply switching is a complex physical process. This paper presents a novel model of electromechanical contactors. This model can simulate the multi-physics process of power switching. This article completes the simulation framework for power switching through contactors for the first time. Among them, the structural topology for contactors is also proposed. On the basis of the novel structure topology, an equivalent magnetic circuit model is established to calculate the relationship between driving force, flux linkage, current, and displacement. Then, a co-simulation model is established between the above equations and Adams to obtain the speed characteristics and flight time of the contactor. Subsequently, through the use of Fluent and its secondary development, a magnetohydrodynamic model is established, and the above-mentioned velocity characteristics are imported into it to analyze the arcing characteristics of the contacts under the conditions of the transverse magnetic field and the insulating grid. The effectiveness of power switching is judged by comparing the flight time of the electromechanical model and the arcing time of the magnetohydrodynamic model. The prototype is manufactured and tested on the basis of simulation. Through experimental waveforms and high-speed photography, the accuracy of the simulation model and the practicability of the contactor are verified.

A plasma jet-triggered gas switch (PJT-GS) has been developed as an important piece of equipment to operate in an $\pm$800 kV ultra-high voltage direct current transmission system (UHV DC) to achieve grid system protection and control. The crucial factors that would affect its operational performance, such as the current level the PJT-GS could withstand and the gas gap distance between the two rotating electrodes, are comparatively studied in the present work by analysing the arc dynamic characteristics. The rotating electrode used in the PJT-GS is designed with a helical-slotted structure, and the arc can be rotated circularly driven by the produced transverse magnetic field (TMF) along the electrode edge. The objective of such research is to provide a thorough study of the arc dynamic behaviour during the current flowing process of the PJT-GS and also to characterise the physical mechanism that affects the arc rotation and the PJT-GS operation performance. The magnetohydrodynamic-based (MHD) approach is applied by establishing a 3D arc model. Following such a study, the variation of arc characteristics under different operation conditions could be thoroughly determined and it also could provide the guidance for the PJT-GS optimum design reasonably to support its corresponding engineering applications.

The asynchrony of the multi-break dc relay has an important influence on its arcing characteristics. Through the experimental test platform, the arc characteristics of the single bridge-type contact and the double bridge-type contacts are compared. Arc images are acquired through high-speed photography. On the basis of asynchronous action, the influence of action speed and overtravel difference on arcing characteristics is analyzed. A multi-breakpoint asynchronous arc model is established to study the nonlinear relationship between overtravel difference and arc duration. The distribution characteristics of the double-bridge arc are analyzed. Experiments and simulations show that the double bridge-type contacts have better arc-extinguishing characteristics. Increasing breaking speed is conducive to reducing arc energy difference between fractures. When the overtravel difference is small, the bridge $B$ (bridge with larger overtravel) arc can enter the diffusion state, and the arc voltage of bridge $B$ is higher. Reducing the overtravel difference can effectively reduce the arc duration.

The on-load tap changing transformer can maintain voltages at desired levels by changing the tapping in primary winding of the transformer according to the load. It plays an important role in smart distribution grid. The key part of on-load tap changing transformers is on-load tap changer (OLTC), which is a complex mechanical device. The diverter switch of OLTC is traditionally accomplished in the oil. The Oil will be stained by arcing during operation and must be consequently purified by an oil filter. In order to reduce the disadvantages of conventional oil switching OLTC, OLTC applied with vacuum switch is presented in this paper. This vacuum OLTC is driven by permanent magnetic actuator. The capacity and the switching reliability of the vacuum OLTC are remarkably enhanced. The electrical life as well as the maintenance interval of the OLTC has been extended. In consideration of the electromagnetic field on site, Programmable Logic Controller (PLC) is applied to the intelligent controller of OLTC. The action sequence of the vacuum diverter switch is programmed based on the structure of vacuum OLTC. The controller using PLC can greatly decrease the complexity of the OLTC control system and effectively improve the reliability and stability of the vacuum OLTC.

In this paper, NdFeB is used to design a new type of magnetic force actuator (MFA) with simple structure and high reliability. The permanent magnets are fixed on the static iron-core to generate a magnetic field, while the movable part locates within the magnetic field. It can drive the arc extinguishing unit powered by the Lorentz force, and this can be applied to the operation of the long-stroke high voltage circuit breaker (HVCB). At the open and closed position, the PMs generate holding force for the moving iron-core to keep the static state. Then, the finite element method(FEM) and prototype test are adopted to study the properties of PM and characteristics of the actuator. The simulation concludes that the material type and structure size of PM, end cap material and processing deviation of the actuator will impact the static characteristic of the actuator. The results of the test on prototype show that MFA using NdFeB can achieve the high power output, which is conductive for electronic control as well as the displacement tracking. Due to its stable performance, NdFeB is reliable in the running of the magnetic force actuator.