Very Fast Transient Overvoltage Measurement With Dielectric Window

The method of using the electrode inserted into gas-insulated switchgear (GIS) to form a capacitor sensor has the best bandwidth to measure the very fast transient overvoltage. However, the power in the GIS conductor has to be cut off during the repair and replacement of the sensor. In order to overcome the disadvantage, a dielectric window structure is proposed to be installed between the GIS tank and the sensor. The thickness of the dielectric slab is calculated to ensure safety under high SF6 pressure, and the electric characteristics of the dielectric window are carefully investigated to avoid limiting the sensor bandwidth. Moreover, the bandwidth of the measuring system is calibrated under different voltage and frequency. The experimental results demonstrate that the bandwidth of the measuring system with a dielectric window is 6.75 Hz-179.7 MHz, which satisfies the requirement of VFTO recording. Finally, voltage waveforms generated by 252-kV disconnector switch operation are recorded to verify the feasibility of the field application.