Broadband VFTO Measurement Method Based on Modified UHF Sensors

The very fast transient overvoltage (VFTO) generated by the operation of disconnectors in gas-insulated switchgears (GIS) features a wide frequency band and a steep rising edge, posing a severe threat to the safe and stable operation of power grids. Accurate measurement of VFTO is a core prerequisite for the insulation protection design of power equipment. Aimed at solving the problem that ultra-high frequency (UHF) sensors widely installed in existing GIS are limited by—the built-in inductance and inability to fully reconstruct the VFTO waveform—this paper proposes a broadband VFTO measurement method based on modified UHF sensors. The VFTO measuring system based on UHF sensors was constructed and tested by modifying the structure of UHF sensors and a broadband pulse source capable of outputting equivalent frequencies from 1 kHz to 10 MHz. The results showed that the measuring system exhibited excellent high-frequency (100 kHz~1 MHz) response performance but poor low-frequency (~1 kHz) response. By introducing a voltage-follower impedance transformation module based on a high-speed operational amplifier, the UHF measuring system could accurately reconstruct the VFTO waveform during the opening and closing of the 750 kV GIS disconnector. This non-contact measurement scheme provided a highly promising and reliable technical path for on-site VFTO detection for in-service equipment without altering the existing structure of GIS.