Studies On The Degradation Depth Of Silicon Rubber Insulator In Service

Composite insulator,due to its advantages like light weight,great mechanical property and excellent hydrophobicity,is widely applied to overhead transmission lines of different voltage levels.As its external insulating material,silicone rubber,is exposed to the environment,and with its aging,the insulation of composite insulator to the moisture becomes less and less effective during its long-time running,and in severe case,it may even cause its breakdown and fracture,which brings great hidden danger to the safe running of power grid.Therefore,it is rather important to study the microstructural changes of silicone rubber composite insulator when its shed is aging and to quantitative analyze its aging condition.This dissertation firstly,based on infrared micro-spectroscopy,develops a method to measure the degradation depth of silicone rubber,and explores the steps of testing,experiment parameter as well as data processing method.Then,infrared micro-spectroscopy,thermo gravimetric analysis(TGA)and gas chromatography techniques are applied to the measure and analysis of corresponding degradation depth,surface organic silicon component and small molecule content of 500 kV,220 kV and 110kV running silicon rubber insulator sheds,so as to quantitative analyze their degradation depth of sheds.Main conclusions are as follows:(1)Using infrared micro-spectroscopy technique to measure changing situations of peak area of methyl groups(2960 cm-1)from the surface to the center can calculate the degradation depth of silicon rubber shed.The depth of silicon rubber sample section is 15 ?m,light spot reaches the biggest and the size of diaphragm is 50?m ×50 ?m.Transmission method is applied to the experiment.When the depth of line scanning is 150 ?m,with the step of 5 ?m,the degradation depth could be obtained by striving for the second derivative to fitting function.When the area scanning depth is 200 ?m with the lateral movement of 150 ?m and the step of 10 ?m,the degradation depth could be obtained by contour line.(2)In this paper,the sheds at different positions of two running silicone rubber composite insulators were selected to study corresponding degradation depth and surface organic component consumption,using infrared micro-spectroscopy and thermo gravimetric analysis(TGA)techniques.Data obtained from infrared micro-spectroscopy suggest that the average degradation depth of a shed vary with its position,showing a reversed hump-shape line from the high-potential end to low potential end for these composite insulators studied.The average degradation depth of shed at low-potential end is only second to that of shed at high-potential end,and the middle part is the smallest.For the shed at high-potential end,its standard deviation of degradation depth is high,indicative of non-uniform surface aging condition.The depth of deepest place reaches to 126 ?m,while the lowest place only 29 ?m.It is postulated that the major aging factor of an in-service composite insulator is different intensities of corona discharges induced by the wide distribution of the surrounded electric field density in the transmission line,and the environmental factors,such as ultraviolet radiation etc.,are in the second place.The TGA results show that the shed containing of organic composition in a depth of 60 ?m from surface is the lowest at high-potential end,suggesting the faster consumption compared with other positions.Meanwhile,the surface organic composition consumption of sheds at different positions show a same trend as that of reversed hump-shape line obtained by infrared micro-spectroscopy.While the result of gas chromatography experiment indicates that,comparing with insulators off the line,the content of short chain molecule of those running ones' shed drops sharply,which demonstrates the large amount of consumption of short chain molecule during running process.On the other hand,comparing with other positions,the content of short chain molecule of shed at high-potential end is relatively lower,indicating serious aging problem,while the content of those at low-potential end and at the middle part is comparatively higher,indicating lighter aging then those at high-potential end.(3)The degradation depth of shed of 220 kV running insulator at high-potential end is the biggest,while that of shed at low-potential end is only second to that of shed at high-potential end,and the middle part is the smallest.The thermal analysis result finds that the consumption of PDMS content of 220KV surface shed at the high-potential end is the highest,and those at the low-potential end and the middle part are close to each other.The result of module test shows that the remaining module content at three positions are similar to each other,and those at high-potential end is the smallest,with those at the middle part being the biggest.The degradation depth of shed of 110 kV running insulator at low-potential end is the biggest,while that of shed at high-potential end is only second to that of shed at low-potential end,and the middle part is the smallest.The thermal analysis result finds that the consumption of PDMS content of surface shed at the low-potential end is comparatively the lowest,and the result of module test shows that the remaining module content at low-potential end is also the smallest,which demonstrates the aging problem of 110 running insulator shed at low-potential end is the most severe.The contrast of degradation depth of shed at different positions under different voltages finds out that with the reduction of voltage,the degradation of shed at high-potential end goes an apparent decline,while that of shed at middle part slightly rises.The change of degradation of shed at low-potential end with the drop of voltage is relatively not evident.