Abstract
Assessment of very fast transient overvoltage (VFTO) requires good knowledge of the behavior of gas-insulated substation when subjected to very high frequencies. The international standards and guidelines generically present only recommendations regarding the VFTO suppression without a technical and mathematical background. Therefore, to provide an accurate image regarding the critical locations across a gas-insulated substation (GIS) from a transient response point of view, a suitable modeling technique has to be identified and developed for the substation. The paper aimed to provide an accurate assessment of the GIS holistic transient response through an electromagnetic field theory (EMF) approach. This modeling technique has always been a difficult task when it came to gas-insulated substations. However, recent studies have shown that through suitable Computer-aided design models, representing the GIS metallic ensemble, accurate results can be obtained. The paper investigated several simplifications of the computational domain considering different gas-insulated substation configurations in order to identify a suitable modeling approach without any unnecessary computational effort. The analysis was performed by adopting the partial equivalent element circuit (PEEC) approach embedded into XGSLab software package. Obtained results could provide useful hints for grounding grid designers regarding the proper development and implementation of transient ground potential rise (TGPR) mitigation techniques across a gas-insulated substation.
Highlights
The gas-insulated substation (GIS) requires 10–25% of the area allocated to a conventional air-insulated substation due to its superior dielectric characteristics of the insulation material, sulphur hexafluoride (SF6), compared to air
As a result of the relatively low speed of the disconnector switch contacts’ movement during switching events, 0.6 cm/s [3], there is dielectric breakdown phenomena occurrence followed by the appearance of electric arc in the contact cavity causing the generation of transient overvoltage characterized by very-high-frequency
The amplitude and waveform of the very fast transient overvoltage (VFTO) depends on the configuration of the GIS substation, the trapped charge stored by the GIS equipment [5], the resistance of the electric arc formed between contacts [6], the capacity at the transformer terminals [7], and the gas pressure [7]
Summary
The gas-insulated substation (GIS) requires 10–25% of the area allocated to a conventional air-insulated substation due to its superior dielectric characteristics of the insulation material, sulphur hexafluoride (SF6), compared to air. As a result of the relatively low speed of the disconnector switch contacts’ movement during switching events, 0.6 cm/s [3], there is dielectric breakdown phenomena occurrence followed by the appearance of electric arc in the contact cavity causing the generation of transient overvoltage characterized by very-high-frequency The amplitude and waveform of the very fast transient overvoltage (VFTO) depends on the configuration of the GIS substation, the trapped charge stored by the GIS equipment [5], the resistance of the electric arc formed between contacts [6], the capacity at the transformer terminals [7], and the gas pressure [7]. When the voltage increases over the breakdown voltage of the insulating arrangement, an arc discharge takes place [13] This is characterized by a heavy flow of current through the gas between the electrodes and the high dissipation of energy in the form of heat
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