| With the vigorous development of the 750 k V transmission project in Northwest China,the safe and stable operation of composite insulators,as an important external insulation device in transmission projects,directly affects the quality of clean energy outgoing from Northwest China.In recent years,there had been many cases of abnormal temperature rise of composite insulators in Longnan area of Northwest China.After investigation,the abnormal temperature rise of local composite insulators is related to its external humid climate conditions,and the composite insulators are subjected to high voltage level frequency voltage for a long time,when the moisture is infiltrated into the composite insulators,the polarization loss generated by internal defects may lead to the local temperature rise of insulators.Infrared temperature measurement technology,as a common means of power equipment fault detection,plays an important role in the energized detection of composite insulators,however,the surface temperature of composite insulators can be affected by external factors such as solar radiation,which brings certain interference to infrared temperature measurement and fault diagnosis.Therefore,the study of the temperature rise law of composite insulators,which are heated by moisture immersion,when they are affected by external solar radiation,is an important guideline for the fault detection of composite insulators,thus ensuring the safe and stable operation of 750 k V transmission and substation systems.Firstly,to investigate the effect of solar radiation on the surface temperature rise of intact composite insulators,the thesis used outdoor infrared temperature measurement tests to carry out temperature rise tests on clear sky days and cloudy days for intact composite insulators exposed to the external environment.The results show that the temperature difference of each temperature measurement area on the surface of the composite insulator has a more obvious value under a clear sky day in the same month,while the maximum average temperature difference of each temperature measurement area is only 0.3℃ during a cloudy day.Based on the above results,the temperature measurement tests on clear sky days in March,June,and September were continued.From the test results,it can be seen that the solar radiation intensity and the maximum average temperature of composite insulators increase and then decrease with the solar altitude angle as the seasons change.Finally,the validity of the numerical simulation model was verified by establishing a numerical simulation model with the external heat source as solar radiation and comparing the simulation results with the above experimental results.Secondly,moisture infiltration inside the high voltage end sheath is a more common form of fault causing abnormal temperature rise of composite insulators.Therefore,in the thesis,a simulation model of composite insulator with complete and presence of internal defects of moisture infiltration is established using COMSOL,and the distribution patterns of electric and temperature fields are obtained.The calculation results show that the intact composite insulator runs well after pressurization,and the axial electric field intensity distribution shows an oscillating asymmetric "U" curve and no abnormal temperature rise;however,for the composite insulator containing moisture infiltration internal defects,the electric field intensity distortion value is the largest at the junction of the two ends of the defects,and as the degree of moisture in the sheath increases,it can be found that the peak electric field intensity at the intersection of the sheath and core rod is approximately proportional to the degree of moisture in the sheath,and the temperature peaks at the intersection of the sheath and core rod and the surface of the sheath also increase respectively.Finally,based on the above solar radiation simulation model and the coupled electric field-temperature field calculation simulation model for the presence of moisture infiltration internal defects,the effects of different solar radiation intensities and different orientations on the temperature rise of intact and composite insulators with moisture infiltration internal defects are studied and analyzed.The results show that the magnitude of solar radiation intensity and the temperature rise value on the surface of the composite insulator is approximately linearly increasing.With the same solar radiation intensity,the composite insulator’s orientation varies as a result of the solar radiation,which also affects the temperature rise distribution of the sheath towards the high voltage end.Due to the change of the orientation of the composite insulator,the peak temperature of the sheath surface decreases sequentially between the insulator considering only the solar radiation and the insulator considering both the solar radiation and the moisture infiltration.The findings of this thesis have a significant bearing on composite insulator maintenance and can help people in charge of the electric operation and inspection increase the effectiveness of composite insulators. |
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