With the rapid development of DC power systems and the increasing demand for DC circuit breakers, electromagnetic repulsive drives-based Thomson coil actuators (TCA) are widely investigated to provide the high-speed actuating required for ultra-fast mechanical switches, especially those used in hybrid DC circuit breakers. The actuating mechanism is required to be fast, reliable, and economic. This article summarizes the development of Thomson coil actuators in circuit breakers in recent years, further illustrating the basic principles and the actuator topology. In addition, it discusses the various structural components of TCA and describes the utilized modeling and simulation methods. The main objective was to provide a comprehensive overview of the TCA field.

Fast mechanical switches play a significant role in the control and protection of DC power systems. The need for fast response, rapid actuating, and compact size actuators is the key enabler for the development of future DC grids. Regardless of their stroke limitation, piezoelectric actuators are fast, very controllable, and highly reliable. They can fit in fast mechanical switches or disconnectors designed for hybrid circuit breakers. In this study, a fast-mechanical switch driven by an amplified piezoelectric actuator is proposed, analyzed, fabricated, and tested. The coupling dynamics of the piezo based switch are formulated based on the electrodynamic model. The influence of key structural parameters on the switch characteristics was calculated, and the static and dynamic performances were obtained. According to the calculation, a prototype was constructed, and the travel of the proposed switch was experimentally validated. Furthermore, operational factors that influence the switch were investigated. Finally, the switch was insulated in a vacuum chamber and integrated as a fast-mechanical switch in a constructed hybrid circuit breaker platform. The proposed switch achieved an accumulated gap of 0.95mm in 1ms and interrupted a DC power of 220V/100A and 500V/20A within 1.2±0.2ms.

Amplified piezoelectric actuators have gained considerable attention due to their inherent advantages, including rapid response, reliability, and efficiency, making them promising candidates for Direct Current (DC) switching applications. They can operate in two distinct operational modes: Block–Free (B–F) and Free–Free (F–F) configurations. These two modes offer diverse mechanical constraints and are chosen based on the application’s specific requirements. This study aims to present a comparative assessment between the two modes to evaluate each configuration’s applicability in DC fast switching. Accordingly, the principle behind each actuation scheme was illustrated, and both designs were modeled and analyzed by the finite element method. Subsequently, two prototypes were assembled, each resembling a different operational mode. The established prototypes were then subjected to actuation and interruption tests to investigate their travel and switching performances. Comparative results revealed that while block–free could deliver a higher apparent stroke, the accumulated gap for each configuration is almost the same. Both actuators demonstrated high capability when utilized as actuation units for fast vacuum mechanical switches integrated into a hybrid circuit breaker for DC interruption. However, the free–free operation excelled in terms of fast response, as it managed to clear the mimicked fault current faster than the block–free configuration.

Piezoelectric actuators provide several advantages, including rapid response time, travel control, high resolution and actuation efficiency. They are a good candidate for actuating mechanical switches designed for electrical circuit breakers. This study investigates the utilisation of an Amplified Piezoelectric Actuator (APA) in Block-Free (B-F) operational mode as an actuation unit for a Fast-Mechanical Switch (FMS) and an Ultra-Fast Disconnector (UFD) to be utilised in a DC Hybrid Circuit Breaker (HCB). Initially, the principle and construction of the piezoelectric actuator actuating scheme were described and illustrated. A Finite Element Analysis (FEA) model was built to simulate and analyse the presented switch/disconnector static and dynamic behaviours. A prototype was constructed based on calculations, and the travel characteristics were experimentally validated. Subsequently, the proposed switch/disconnector was insulated once in a vacuum and later in a nitrogen gas interruption chamber. Both arrangements were integrated into a DC Hybrid Circuit Breaker test platform to investigate their interruption features. Results show that the presented switch/disconnector achieved a total gap of approximately 1 mm in 1.4 ms and interrupted a DC power of 0.6 kV/60 A within 0.85–1.5 ms in vacuum and 0.98–1.45 ms in nitrogen gas.

In most industrial applications, plasma has an important feature that the erosion products produced by plasma will undergo a phase transition and affect the properties of plasma mixtures. Calculating the transport coefficients of the plasma mixtures, usually, gas–metal mixtures, is an important approach to study this feature. However, most transport coefficient calculation methods have some difficulties in dealing with the solid and liquid components of gas–metal plasma mixtures. In this study, a modified method for calculating transport coefficients of gas–metal plasma mixtures containing solid and liquid status is proposed, considering that the liquid and solid components are usually in the form of clusters. Based on this modified method, the influence of the metal phase transition on the transport coefficients of gas–metal plasma mixture is explored with the example of H2–Cu plasma mixture. The findings revealed in this study are as follows: (1) The modified calculation method is applicable for not only gas–metal plasma mixtures but also other plasma mixtures containing solid and liquid status. (2) Ignoring the metal phase transition in the calculation of transport coefficients of gas–metal plasma mixtures will inevitably produce considerable variances. (3) The variances, caused by ignoring the metal phase transition, are tightly associated with the pressure, the proportion of metal, and the unbalanced degree of gas–metal plasma mixtures. In summary, the variances caused by ignoring the metal phase transition might be ignorable only when the pressure, proportion of metal, and unbalanced degree of gas–metal plasma mixture are all in extremely small values.

Accurate prediction of plasma composition during the phase transitions of ablation products remains challenging under thermodynamic nonequilibrium conditions. To address this issue, a plasma composition calculation method based on an electron–heavy-particle–cluster three-temperature assumption is proposed in this work. In the proposed method, condensed-phase clusters formed through the aggregation of gaseous atoms and molecules are treated as independent species, while individual temperatures are assigned to electrons, heavy particles, and clusters to investigate the effects of thermal nonequilibrium on plasma composition. A total Gibbs energy function is then formulated for the three-temperature plasma system and transformed into an objective function compatible with metaheuristic optimization. The proposed method is assessed through comparisons with previously reported gas-phase composition and equilibrium phase-transition results and subsequently applied to investigate the phase transition of Cu-containing ablation species in an air–Cu plasma system. The results reveal that thermodynamic nonequilibrium between heavy particles and clusters can lead to a pronounced difference between the deposition and melting temperatures of ablation products, which significantly modifies the plasma composition across phase transitions. These findings highlight the importance of accounting for heavy-particle–cluster nonequilibrium in plasma composition calculations involving ablation products. Further independent validation of the proposed method under three-temperature nonequilibrium conditions is still required.