A capacitive sensor based on the theory of electric field measurements using floating electrodes has been developed for the measurement of VFTO and the same has been fitted to the metallic enclosure of a 145kV gas insulated substation (GIS) experimental test setup available in the laboratory. The sensor has been calibrated in situ with sinusoidal, impulse and step voltage excitations of the HV bus of the 145kV GIS and the results are presented. The sensor was then used to measure the $50 H_z$ restrike pattern as well as the VFTO waveforms during a simulated disconnector switching operation in the 145 kV GIS test setup. It has been demonstrated that the same sensor is able to faithfully measure both the $50 H_z$ restrike pattern as well as the ns duration VFTO waveforms successfully.
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