The large leakage current of the roof arrester caused by the high-frequency resonant overvoltage on the high-speed train occurs intermittently, which will cause the arrester to overheat locally. In this work, the overheating issue of the arrester under Ultra Harmonics Overvoltage is studied. Then, the relationship between the active power and the voltage (including amplitude and frequency) of the arrester is investigated, and the impact mechanism of the harmonic voltage on the overheating fault of the arrester is analysed based on experiments in this work. It is found that the total leakage current of the arrester is proportional to the amplitude and frequency of the applied voltage. The internal resistance of the arrester is independent of the amplitude of the voltage, but it will decrease with the increase of the frequency. The main reason that leads to thermal breakdown of the arrester valve under high-frequency harmonic voltage is the heating power elevation of the arrester valve. The research study can provide theoretical basis and data support for the design, type selection and monitoring of the high-speed train roof arrester.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
A conductive metallic particle in a gas-insulated metal-enclosed system can charge through conduction or induction and move between electrodes or on insulating surfaces, which may lead to breakdown and flashover. The charge on the metallic particle and the charging time vary depending on the spatial electric field intensity, the particle shape, and the electrode surface coating. The charged metallic particle can move between the electrodes under the influence of the spatial electric field, and it can discharge and become electrically conductive when colliding with the electrodes, thus changing its charge. This process and its factors are mainly affected by the coating condition of the colliding electrode. In addition, the interface characteristics affect the particle when it is near the insulator. The charge transition process also changes due to the electric field strength and the particle charging state. This paper explores the impact of the coating material on particle charging characteristics, movement, and discharge. Particle charging, movement, and charge transfer in DC, AC, and superimposed electric fields are summarized. Furthermore, the effects of conductive particles on discharge characteristics are compared between coated and bare electrodes. The reviewed studies demonstrate that the coating can effectively reduce particle charge and thus the probability of discharge. The presented research results can provide theoretical support and data for studying charge transfer theory and design optimization in a gas-insulated system.
In flowering plants, sperm cell development involves a special postmeiotic process. During the process, each microspore generated by pollen mother-cell meiosis undergoes unsymmetrical mitosis to result in a large vegetative cell and a small generative cell enclosed in the vegetative cell. The vegetative cell exits the cell cycle, and the generative cell undergoes further mitosis to generate 2 sperm cells. Functional genomics studies of generative and sperm cells are essential for understanding the molecular control of fate determination and the function of sperm cells and cell-cell recognition during double fertilization. These studies require isolated and purified generative and sperm cells. Here, we summarize the main methods used to isolate and purify generative and sperm cells from pollen grains and tubes of diverse plant species since the 1970s, discuss the advantages and disadvantages of each method, and analyze factors affecting output, purity, longevity and viability of purified generative and sperm cells.
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