Influence of Gap Distance on Vacuum Arc Characteristics of Cup Type AMF Electrode in Vacuum Interrupters

The greenhouse effect of SFe is a great concern today. The development of high voltage vacuum circuit breakers becomes more important. The vacuum circuit breaker has minimum pollution to the environment. The vacuum interrupter is the key part of a vacuum circuit breaker. The interrupting characteristics in vacuum and arc-controlling techniue are the main problems to be solved for a longer gap distance in developing high voltage vacuum interrupters. To understand the vacuum arc characteristics and provide effective technique to control vacuum arc in a long gap distance, the arc mode transition of a cup-type axial magnetic field electrode is observed by a high-speed charge coupled device （CGD） video camera under different gap distances while the arc voltage and arc current are recorded. The controlling ability of the axial magnetic field on vacuum arc obviously decreases when the gap distance is longer than 40 ram. The noise components and mean value of the arc voltage significantly increase. The effective method for controlling the vacuum arc characteristics is provided by long gap distances based on the test results. The test results can be used as a reference to develop high voltage and large capacity vacuum interrupters.

The Discharge Development and Arc Modes in Vacuum at A Long Gap Distance in Vacuum Interrupters

The influence of an arc current on the discharge development and the arc modes of a single coil type axial magnetic field （AMF） electrode were investigated by a high-speed charge couple device （CCD） video camera in a long gap distance of 40 mm. The distribution of the axial magnetic field of the single coil type AMF electrode was computed. By computational results, the single coil type AMF electrode could generate higher axial magnetic flux density than the slot type AMF electrode. It was found that the single coil type AMF electrode could perform better than the slot type AMF electrode with the same designing parameters. And the development of the arc modes experienced diffuse mode, constricted but unstable mode, and constricted and stable mode with the amplitude of the arc current increasing. The correlation between the vacuum arc and the noise components of arc voltage was investigated too. The interruption capability could be known in a practical commercial vacuum interrupter by the test results in a demountable vacuum interrupter （DVC） with a electrode diameter of 50 mm and a gap distance of 40 mm.The test results could provide reference to design the high voltage vacuum interrupter adopting the single coil type AMF electrode.

Examining the characteristics between time and distance gaps of secondary crashes

Understanding the characteristics of time and distance gaps between the primary(PC)and secondary crashes(SC)is crucial for preventing SC ccurrences and improving road safety.Although previous studies have tried to analyse the variation of gaps,there is limited evidence in quantifying the relationships between different gaps and various influential factors.This study proposed a two-layer stacking framework to discuss the time and distance gaps.Specifically,the framework took random forests(RF),gradient boosting decision tree(GBDT)and eXtreme gradient boosting as the base classifiers in the first layer and applied logistic regression(LR)as a combiner in the second layer.On this basis,the local interpretable model-agnostic explanations(LIME)technology was used to interpret the output of the stacking model from both local and global perspectives.Through SC dentification and feature selection,346 SCs and 22 crash-related factors were collected from California interstate freeways.The results showed that the stacking model outperformed base models evaluated by accuracy,precision,and recall indicators.The explanations based on LIME suggest that collision type,distance,speed and volume are the critical features that affect the time and distance gaps.Higher volume can prolong queue length and increase the distance gap from the SCs to PCs.And collision types,peak periods,workday,truck involved and tow away likely induce a long-distance gap.Conversely,there is a shorter distance gap when secondary roads run in the same direction and are close to the primary roads.Lower speed is a significant factor resulting in a long-time gap,while the higher speed is correlated with a short-time gap.These results are expected to provide insights into how contributory features affect the time and distance gaps and help decision-makers develop accurate decisions to prevent SCs.