Effect of surface contamination on sensor flashover voltage under lightning impulse

Author： GOZ Electric Time：2024-09-19 09:49:42 Read：12

[Purpose] In order to give full play to the function of micro-sensors as important monitoring equipment in distribution networks, it is necessary to analyze the flashover characteristics of micro-sensors under polluted conditions.

[Method] Taking the epoxy resin of the micro-sensor insulation part as the research object, the solid layer method was used to simulate different degrees of pollution, an impact generator was used to generate lightning waves, and more than 500 lightning impact tests were conducted.

[Results] The relationship between different salt density (ρESDD), gray density (ρNSDD) and lightning impulse flashover voltage was obtained. The results show that both ρESDD and ρNSDD will have an impact on the lightning impulse voltage, that is, the lightning impulse flashover voltage will change with the two. decreases with increase.

[Conclusion] The flashover voltage distribution of gray density is basically consistent with the dispersion under clean conditions, while the flashover voltage dispersion of salt density increases significantly. The influence characteristic index of salt density and gray density are 0.17 and 0.12 respectively, that is, the influence characteristic index of salt density is greater than that of gray density.

Keywords: micro sensor; dirty conditions; insulation characteristics; lightning impulse voltage generator

In recent years, as the coverage of power transmission and distribution networks has become wider and wider, the requirements for grid security have become higher and higher. The establishment of a panoramic intelligently aware power distribution network has become an inevitable requirement for the development of digital grids. The important monitoring objects in the transmission and distribution network are voltage and current. However, the traditional voltage transformer (PT) and current transformer (CT) have shortcomings such as large size, high cost, and narrow frequency band. There is an urgent need to find alternatives. Currently, the development of embedded devices with voltage/current sensing units is one of the important ways to replace traditional PT and CT, and micro-sensors achieve sensing by integrating intelligent sensing units and power grid equipment. Cai Wei et al. implanted fiber grating sensors inside composite insulators to monitor the internal stress and temperature of composite insulators. At present, when focusing on the monitoring performance of voltage and current, the insulation performance of newly-distributed micro-sensors is often ignored, and the application of micro-sensors must consider their safety in harsh environments.

Domestic and foreign scholars have studied the flashover mechanism of equipment under polluted conditions and believe that the flashover process can be divided into charge accumulation, resistance heating, surface wetting, local corona, etc., and have summarized the flashover theory. Shen Hao et al. believe that both salt density and gray density will have an impact on flashover characteristics, that is, both salt density and gray density will reduce the flashover voltage. Zhang Zhijin et al. verified the relationship between AC flashover voltage and salt density through experiments. That is, as the salt density increases, the pollution lightning voltage of 27.5kV and 110kV composite insulators decreases. Cheng Xian et al. studied the creepage flashover of solid insulators under polluted conditions and found that the flashover voltages of salt density and gray density both conform to the power exponential law. However, they did not analyze the different effects of salt density and gray density.

Epoxy resin-poured micro-sensors can adapt to various complex environments and have a long service life and good insulation. However, there are relatively few domestic studies in this area. This study uses the research method of the influence of power frequency voltage and lightning voltage on the flashover characteristics of insulators to study the lightning flashover characteristics of epoxy resin insulation parts under different salt densities and gray densities.

in conclusion

This study uses epoxy resin samples as the research object to explore the insulation properties of lightning impact of micro-sensors under harsh conditions. As an insulating material for solid micro-sensors, epoxy resin insulating parts have good hydrophobicity and strong stain resistance. Through the analysis of test data and test phenomena, the following three conclusions are drawn.

①The lightning flashover voltage of epoxy resin insulators is significantly affected by salt density and gray density. At the same gray density, as the salt density increases, the lightning flashover voltage of epoxy resin insulation parts decreases significantly. The influence of gray density on flashover voltage is similar to the law of salt density, that is, an increase in gray density will lead to a decrease in lightning flashover voltage, and as the gray density increases, the decrease in flashover voltage tends to be gentle.

② When the gray density increases, the flashover voltage decreases with the increase of gray density, but the dispersion of breakdown voltage is similar. The dispersion of flashover voltage increases significantly with salt density. This shows that under salt density, the flashover voltage The formation of network paths is more random, and the discharge mechanisms of gray dense and salt dense are different.

③ By fitting the test data with the least squares method, it can be obtained that the flashover voltage U = 0.29ρ -0.17/ESDD ρ -0.12/NSDD, and the characteristic indexes of the influence are 0.17 and 0.12 respectively, that is, the lightning strike of epoxy resin insulation parts For the network, the impact of salt density is greater than that of gray density.