Accurate modelling of very fast transient overvoltages in a 245kV GIS and research on protection measures

Based on 245kV GIS substation, very fast transient over voltages caused by disconnecting switch operation of GIS is simulated and calculated in this paper with B2SPICE program. The different protection measures are compared and analyzed, such as adding ferrite rings, adding opening and closing resistor, metal oxide arrester and R-C absorber. A low voltage experiment was conducted to estimate transient overvoltage's during switching operation. These transient voltages are recorded by using surge sensor and digital storage oscilloscope with sample rate 1GS/s and 500MHz frequency range. Suppression techniques are employed practically to verify the validation of simulation results. The simulation results are closely matched with the experimental results in the case of ferrite rings application in reduction of maximum peak of VFTO generated during switching operation.

1. Introduction

Gas Insulated Substations have found a broad range of applications in power systems because of their high reliability, easy maintenance, small ground space requirements etc. In a Gas insulated substations very fast transient over voltages (VFTO) are generated during the switching of disconnectors in 245kV and above voltage level's GIS. VFTO generated in a GIS should be considered as an important factor in the insulation design. For designing a substation it is essential to know the maximum value of VFTO. Fast operating disconnector switches are usually used to reduce time of the breakdown, however, it can not eliminate the harm of the VFTO. Several inhibition methods are simulated in this article, which can provide the reference the for protection of VFTO.