A Reliable Wide-Bandwidth VFTO Sensor Based on Surface-Mounted Devices

A capacitor sensor with a high-voltage electrode inside the GIS tank has the best bandwidth among the sensors developed to measure the very fast transient overvoltage (VFTO). However, the low-voltage arm of the current measurement system is usually a handmade film capacitor which has disadvantages of unassigned capacitance value, temperature effect, and short lifespan. With a novel lower voltage arm based on surface-mounted devices, a wide-bandwidth, stable, and easy maintenance measuring system is proposed in this paper. It is found that the slight inherent inductance in the ground trace of the printed-circuit board can induce unexpected oscillations, which are demonstrated with theoretical analysis and experimental study. With the reforming of the printed-circuit board layout, the oscillation is reduced and 200-MHz high-frequency cutoff frequency is achieved. The environment experiment shows that the temperature effect on the developed sensor is much smaller than that on the conventional sensor. The VFTO generated by disconnector operation in 1100-kV GIS is measured by the developed system and a conventional broadband capacitor sensor. The contrastive results prove that the characteristic of the measuring system can meet the requirement of VFTO measurements. Thousands of measurements on ultra-high voltage GIS indicate that the developed measuring system is stable, and characteristics of the VFTO are gained.