| Very fast transient overvoltage (VFTO) generated by disconnector operation in gas insulated switchgear (GIS) is very important to insulation coordination in EHV and UHV power system. Due to lack of research in the physical characteristics of arc caused by breakthrough of the contact gap, precise model for VFTO simulation could not be achieved.In this paper,252kV GIS experimental platform was established to measure the waveforms of VFTO and VFTC simultaneously by electronic measuring system. Experiment results were used to compare with the simulation results. Fast speed cameras were used to capture the images of high frequency arcs, followed by digital processing and dimension research by MATLAB. Results showed that intensity of light decayed and arc tunnel increased from 0.75mm to 2.25mm with the development of the arc. Insulation recovered after 3150ns when the arc tunnel break off. Spectrum information was obtained by the plasma diagnostic system formed by fast speed camera and spectrograph. Based on the method of double line spectral thermometry, plasma information of the arc were measured. Constant arc temperature is about 14000K, electron density is about 2.23×1023m-3 and arc conductivity is about 6078S. Arc constant resistance is about 3.7Ω. In the arc physical characteristics experiments, high frequency arc resistance increased with the increase of SF6 pressure and length of contact gap and decrease of the amplitude of VFTC. Modified disconnector high frequency arc model based on the physical characteristics were simulated under the SF6 pressure of 0.5MPa with 7mm and 12mm contact gap length respectively. Simulation results agree with the experimental results. |
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