A Hybrid Method Based on The Simultaneous Use of Nanocrystalline Rings and XLPE Cables to Reduce Very Fast Transient Overvoltages in High Voltage Gas Insulation Substations

Use of Gas Insulated Substations (GISs) at high voltage power systems is expanding due to their advantages such as: less required space, resistance to environmental pollutions, high reliability and no need for continuous maintenance. One of the phenomena that threatens the insulation distances inside the closed enclosure in these substations is the occurrence of Very Fast Transient Overvoltages2 (VFTOs). These overvoltages that are resulted from switching3 operation in the GIS are dangerous for the equipment connected to or inside the GIS and can damage the internal insulation of the equipment. Moreover, these transient overvoltages can cause serious damage to the expensive substation equipment in special cases such as extremely high voltages. In this paper, while reviewing the existing methods to limit VFTO in different sensitive points of the GIS, a new hybrid method is proposed based on the simultaneous use of Nanocrystalline rings in busbars and parallel XLPE4 cable path to connect power transformer to the GIS. The simulation results for Shiraz University 230 kV GIS show that in the case of switching operation, the proposed method has the lowest amplitude of overvoltages compared to other methods at different places in this substation. Using the proposed hybrid method, the amplitude of VFTO in the terminal of power transformer of the under-study network is reduced by 59.7% and this reduction can be seen in other points of the substation, as well.