Research On Dielectric Surface Flashover System At Atmospheric Conditions

With the development of the national economy, more and more electricalenergy is demanded by the society. Because the development of productivity indifferent area is different, the power consumption mainly concentrated in the easterneconomic developed area. But the things such as coal, oil, water and other naturalresources which can be used for power generation are distributed in the western andNorthern regions. This kind of power demand and the unbalanced distribution ofresources prompted the State Grid to take the large capacity, long-distancetransmission pattern. In order to reduce the power loss in the transmission processand improve the line transmission capacity, we take ultra high voltage high voltagelevel even UHV conveying electric energy. Without doubt the increase of voltagelevel is a great challenge for insulation systems. This paper develops a set of systemwhich can be used for surface flashover experiment of insulating materials. So itprovides a good experimental platform for research on the performance of insulatingmaterial.In order to carry out the flashover experiment better, this paper introduces thedesign of impulse voltage generator and DC voltage source which are used toprovide the experimental power. And the Rogowski coil is used for measuring thesurface flashover current, meanwhile capacitor divider is used for measuring thesurface flashover voltage. The experimental system uses coaxial cable to transmitthe signal of voltage and current, and considers the wave process of surfaceflashover voltage and current. The impedance matching is designed at the junctionwhich is between the coaxial cable and a different device to prevent the voltage andcurrent signal reflection occurs in the transmission process, so the measurementresult is really produced by surface flashover process.Capacitor C1and C2is charged to get respectively+80kV and-80kV as DCvoltage source of the experimental system by the half wave rectifier. Compacted impulse voltage generator is designed and manufactured.6pulse capacitor ischarged parallely to about80kV and then discharged seriesly by the ignition ball gapand the middle ball gap to get the pulse voltage which amplitude is about460kV andrise time is about36ns as the pulse voltage source of the experimental system. Selfintegral Rogowski coil is used for measuring element of current signal and severalnon ideal working conditions of the Rogowski coil are analysed ang simulated. Itdoes not affect the measurement results when the measured current conductordeviates from the center position of the coil. The interference on measurementresults which by the vertical component of the surrounding magnetic field can beeliminated by increasing the "wrap around" when the parallel component has noeffect. The measurement result will be smaller when the measured current conductorand the plane of the Rogowski coil is not vertical. At last, the paper gives theexperiment and analysis for the homemade Rogowski coil. Distributed capacitorDivider is used for dividing the surface flashover voltage and combined with theoscilloscope can be used to measure the voltage signal. It can be found through theanalysis and simulation that high voltage lead will cause the divider outputwaveform oscillation and the oscillation can be eliminated by connecting a dampingresistor in the high voltage lead. The stray capacitance between the divider withground will cause the output voltage by the low arm smaller. The shielding case onthe high arm will make the output voltage by the low arm larger and can compensatethe error caused by the stray capacitance between the divider with ground. At last,the paper gives the analysis and experiment for the homemade capacitor divider.