Comparison between suppressing approaches of very fast transient over voltages in gas insulated substation

Abstract

Very Fast Transient Over-Voltage (VFTO), which is a unique electromagnetic transient phenomenon generated by SF6 gas discharge in disconnector gap in Gas Insulated-Substation (GIS), could bring damage to power devices, especially to power transformers. The peak magnitude and high-frequency oscillations of VFTO cause reduction of dielectric of gas insulation, high inter-turn voltages and internal resonance in the transformer windings. Due to all of these disadvantages related to VFTO, VFTO becomes a criterion to determine the insulation level of the GIS, and VFTO damping is rising as an essential issue to be solved. However, the researchers concern on finding the optimum technique for suppressing VFTO, this paper aims to discuss the most feasible methods for mitigation of the overvoltage magnitude of VFTO and determine the most efficient approach for VFTOs attenuation by presenting the advantages and disadvantages of each approach. In this review paper, some suppression methods of very fast transients in GIS are presented, including adopting a resistor-fitted disconnector, ferrite rings, surge arresters, and high-frequency resonator. The results show that the peak value of VFTOs can be decreased to a great level by employing the proposed damping methods. Finally, the best approach for the suppression of VFTOs is chosen based on deep discussion for each method with its features.