Research On External Insulation Performance And Structure Optimization Of EMU High Voltage Equipment

High-speed railway has entered the era of exponential growth pattern since Beijing-Tianjin high-speed railway was put into operation on August lth,2008. By the end of 2015, the total operating mileage of high railway has reached up to 19,000 kilometers, which accounting for 60% of the total high-speed railway mileage and ranking first in the world. High-speed railway will continue to maintain a rapid development trend during the "13th Five-Year Plan" period, which clearly states that high-speed railway will cover more than 80% of the cities within five years. The complex and changeable weather conditions bring new challenges to the operation reliablility of high voltage apparatus for electric multiple units (EMU). In order to reduce the flashover frequency of EMU roof insulator and evaluate the influences of environmental factors such as high speed airflow, moisture, run-time, sand, high altitude on insulator performance, it is of great significance to carry out the research on external insulation performance and structure optimization strategy for EMU high voltage equipment.Taking EMU high voltage apparatus as object and experiment as an important means, pollution distribution law, flashover performance of insulators, influences of environmental factors such as water, sandstorm and run-time on insulator performance lever were systematically studied and an optimization strategy for external insulation structure optimization of EMU high voltage equipment was proposed. The research in this paper can provide a reference for China’s EMU high voltage equipment external insulation structure design, manufacture and operation. The main contents of this paper are as follows:Impacts of insulator materials and wind speed on the contamination distribution rules were analyzed by the results of contamination tests carried out in a closed wind tunnel. By collecting the field insulator daily pollution solution in fog and haze weather, comparatively analyzing the differences of pollution distribution between wind tunnel test results and field data, the results provides a basis for the following artificial pollution flashover experiment.1:1 full scale test platform and artificial climate chamber were built in order to carry out the pollution flashover experiments of EMU external insulation equipment. Flashover performances of epoxy resin and silicone rubber composite insulators were studied based on the pollution test results under the condition that pollution layer distribution with different patterns. And then a full-scale external insulation test of EMU roof high voltage equipment was carried out. Basing on the analysis of date trend and discharge process, flashover performance and insulation structure weaknesses in EMU roof high voltage system were discovered.Comparing variation regularities of temperature rise caused by moisture intrusion and surface wetted pollution based on infrared thermal image, the two different heating mechanisms were analyzed and a preventative maintenance strategy was suggested by using infrared imaging technology in the insulation performance on-line monitoring for EMU roof high-voltage equipments. The contamination and erosion experiments of epoxy resin post insulator for EMU roof high voltage system were carried out in the wind tunnel with sand particles. The influences of sand particle sizes and test duration on pollution distribution, erosion and flashover performances were obtained. Based on hydrophobic test and pollution flashover experiment, insulating property variation rule was studied.As for EMU external insulation weaknesses of roof insulator and existing high voltage box cannot meet the assessment requirement (OV4,170 kV) for Lanzhou-Xinjiang high-speed railway which crosses high altitude area. Structure optimization strategies for isolation switching electrode and high voltage box insulation structure were introduced. Both simulation and experimental results showed that optimized electrode structure could uniform the electric field distribution and avoid accelerating the aging processing of shed. By adding a kind of insulation sheath with reasonable structure to the high voltage fittings, the lightning impulse withstand voltage of optimized high voltage box can meet the requirement for using in areas where altitude is 3500 meters and below.