A series arc fault can easily ignite surrounding flammable objects, leading to safety hazards. Therefore, accurately detecting the arc fault is essential. However, the fault characteristic information carried by the current when series arc faults occur is easily masked by the so-called screening load. As a result, series arc faults are not easily detected. To address this problem, this paper proposes an arc fault detection model based on L2/L1 norm and classification algorithm. L2/L1 norm is introduced to quantify the fluctuations in the current signal when an arc fault occurs, and then combined with some commonly used time domain indexes and frequency domain indexes to extract the features of the arc fault current. Next, the extracted features are filtered to create a high-quality data set. Subsequently, a random forest model is constructed and the data set is used to train and test the model. Finally, the parameters of the random forest model are optimized using the grid search method to obtain a highly accurate arc fault detection model. The effectiveness of the introduced feature is verified using the arc fault data under different loads. Meanwhile, the proposed method is tested and compared with seven commonly used machine learning methods, which reflects the superiority and accuracy of the proposed method.

The importance of high-power relays used to interrupt dc current has been significantly growing recently. In their arc chambers filled with nitrogen or its mixtures, bridge-type contacts with permanent magnets are major measures widely used for arc extinguish. Arc dwelling for a short duration after arc ignition, until its voltage increases rapidly, plays a crucial role in contact erosion. In this paper, arc dwelling time in a nitrogen environment during the entire bridge-type contacts interruption process of a resistive dc circuit is studied both experimentally and numerically. A multiphysics model coupled with the fluid flow, the temperature, the current density, as well as the E- and M-fields was built based on the magnetohydrodynamics theory for the arc chamber. The model was solved in COMSOL. The external resistive electric circuit was connected to the model, and the electric field in the arc was solved by adopting a floating potential. The detailed arc dwelling process is presented and preliminarily discussed according to the calculated temperature and current density distribution sequences. The calculated arc voltage shows good agreement with experimental results. Furthermore, the influence mechanism of breaking velocity on arc dwelling is analyzed by arc voltage. In this sense, the arc dwelling time could be shortened by increasing the breaking velocity within the reasonable extent.

In order to solve the problem of high voltage spikes on the secondary side of the high-frequency transformer when the three-phase high-frequency isolated matrix inverter (HFIMI) operates under the conventional modulation strategies, a new modulation strategy is proposed without introducing an auxiliary circuit. In the proposed scheme, the H-bridge inverter adopts phase-shift control. The matrix converter (MC) adopts the voltage-type de- and recoupling idea, and the decoupled positive and negative group inverters are, respectively, applied with a modified Space vector pulse width modulation (SVPWM) strategy to operate synchronously with the H-bridge inverter. When the H-bridge inverter is in dead-zone mode, the switching tubes of MC are all turned on to provide continuous flow paths for leakage inductance and output filter inductance current and suppress high voltage spikes. The operating mode of the three-phase HFIMI under the proposed modulation strategy is analyzed in detail, the realization conditions for soft switching are designed, and the soft-switching ranges are also discussed. The feasibility and validity of the voltage spike suppression strategy are verified by building a 3-kW principle prototype. The experimental results show that the voltage spikes are effectively suppressed, all switches achieve zero-voltage soft-switching, and the peak efficiency of the three-phase HFIMI can reach 95.2%.

Evaporation erosion of the contacts is one of the fundamental failure mechanisms for relays. In this paper, the evaporation erosion characteristics are investigated for the copper contact pair breaking a resistive direct current (dc) 30 V/10 A circuit in the air. Molten pool simulation of the contacts is coupled with the gas dynamics to calculate the evaporation rate. A simplified arc model is constructed to obtain the contact voltage and current variations with time for the prediction of the current density and the heat flux distributions flowing from the arc into the contacts. The evaporation rate and mass variations with time during the breaking process are presented. Experiments are carried out to verify the simulation results.

The micro-mechanism of molten pool and metal droplet sputtering are significant to the material erosion caused by breaking or making arcs especially for high-power switching devices. In this paper, based on Navier-Stokes equations for incompressible viscous fluid and potential equation for electric field, a 2D axially symmetric simplified hydrodynamic model was built to describe the formation of the molten metal droplet sputtering and molten pool under arc spot near electrode region. The melting process was considered by the relationship between melting metal volumetric percentage and temperature, a free surface of liquid metal deformation was solved by coupling moving mesh and the automatic re-meshing. The simulated metal droplet sputtering and molten pool behaviors are presented by the temperature and velocity distribution sequences. The influence mechanism of pressure distribution and heat flux on the formation of molten pool and metal droplet sputtering has been analyzed according to the temperature distribution and sputtering angles. Based on the simulation results, we can distinguish two different models of the molten metal droplet sputtering process: edge ejection and center ejection. Moreover, a new explanation is proposed based on calculated results with arc spot pressure distribution in the form of both unimodal and bimodal. It shows that the arc spot pressure distribution plays an important role in the metal droplet ejected from molten pool, the angle of the molten jet drop can be decreased along with the increment of the arc spot pressure.

An electrical connector is an important component for achieving the interconnection of electric equipment. However, the degradation of contacting parts within the electrical connector under repetitive mechanical insertion and extraction operations causes a decrease in the contact reliability level, resulting in considerable safety hazards. The coating quality, determining the degree of degradation of contact pairs, is considered a critical factor in fabricating more reliable and safer electrical connectors. In this paper, a gold and nickel coating is deposited onto the surface of a pin within an electrical connector using magnetron sputtering and is compared to an electroplated pin, and the effects of different processing techniques on the microstructure, mechanical properties, and wear behavior are systematically investigated. The measurement results indicate that the surface quality (uniformity and defect density) and mechanical properties (hardness and elastic modulus) of the gold/nickel coating based on magnetron sputtering are significantly better than those achieved using electroplating, showing excellent wear properties and electrical contact stability after repetitive insertion–extraction operations. This study is critical for the development of advanced coatings using a novel deposition technique.