Performance Improvement of the Ceramic Outdoor Insulators has one method that insulators are coated silicone rubber coatings. Doing some experiments and this article introduces experimental result.
A. Analysis of Leakage Current Magnitude and THD
1) Leakage current for samples at clean fog condition (test 1-4):
Figure 2. LC magnitude as function of applied voltage for insulator polluted with various kaolin-salt pollution under clean fog leakage current (mA)
Figure 2 shows the dependencies of leakage current for clean sample and kaolin-salt polluted samples on the applied voltage for both RTV Silicone Rubber coated and non-coated insulator. It is clearly seen that LC magnitude increase almost linearly with the applied voltage.
Figure 2 also shows that the LC magnitude greatly affected by the different pollution levels applied on the samples. On applied voltage 10 kV, it can be seen that the LC magnitude almost the same for clean sample and kaolin-salt samples. Along with the increasing of applied voltage, the LC magnitude of kaolin sample is higher than the clean sample. The amounts of salt applied also affected the LC. The greater amount of kaolin-salt pollution caused higher LC magnitude. At 60 kV, the highest LC magnitude flowed on insulator polluted with kaolin-salt pollution at 3.6 mS and the lowest LC magnitude flowed on clean sample. The greater amounts of kaolin-salt pollution increase the surface conductivity. Conductive surface caused the LC flowed on insulator surface increased. It can also be concluded from Figure 2 that LC magnitude of insulator with greater amount of pollution has greater gradient as a function of applied voltage. We can also see form Figure 2 that LC magnitude of non-coated ceramic insulator much higher than LC of RTV Silicone Rubber in the same experimental condition (kaolin-salt 3.6 mS). It means that the RTV Silicone Rubber coated suppressed the magnitude of leakage current flowed. It also means that RTV Silicone Rubber coated can maintain surface resistance since the LC magnitude for various polluted conditions almost the same. This phenomenon does not happen for the non-coated ceramic insulators which cannot maintain its surface resistance under polluted conditions.
Figure 3 shows the dependencies of total harmonic distortion (THD) of LC waveform on the applied voltage and the amounts of kaolin-salt pollution. It is clearly seen that THD increase with the applied voltage. However, Figure 6 also indicates that THD value for kaolinsalt polluted insulator under clean fog was decreased together with the increasing amounts of pollution applied. This is due to the increase of surface conductivity and reduction of electric field. This phenomenon also applied for the non-coated ceramic insulators.
There was not any flashover or spark observed from clean and kaolin-salt polluted insulator with RTV silicone rubber coated. Whereas it was reported [4] that spark observed at 40-60 kV for ceramic outdoor insulator under similar experiment.
Figure 3. THD as function of applied voltage for insulator polluted with various kaolin-salt pollution under clean fog
These results indicate that RTV silicone rubber coating improves the performance of ceramic outdoor insulator. RTV silicone rubber coating suppressed the magnitude of leakage current, the harmonic content of leakage current and increased the flashover voltage. The low LC corresponds with high surface resistance which indicates high quality of insulator.
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