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Modelling for very fast transients (VFTs) requires good knowledge of the behaviour of gas insulated substation (GIS) components when subjected to high frequencies. Modelling usually takes the form of circuit-based insulation coordination type studies, in an effort to determine the maximum overvoltages and waveshapes present around the system. At very high frequencies, standard transmission line modelling assumptions may not be valid. Therefore, the approach to modelling of these transients must be re-evaluated. In this work, the high frequency finite element analysis (FEA) was used to enhance circuit-based models, allowing direct computation of parameters from geometric and material characteristics. Equivalent models that replicate a finite element model’s frequency response for bus-spacer and 90° elbow components were incorporated in alternative transients program-electromagnetic transients program (ATP-EMTP) using a pole-residue equivalent circuit derived following rational fitting using the well-established and robust method of vector fitting (VF). A large model order is often required to represent this frequency dependent behaviour through admittance matrices, leading to increased computational burden. Moreover, while highly accurate models can be derived, the data extracted from finite element solutions can be non-passive, leading to instability when included in time domain simulations. A simple method of improved stability for FEA derived responses along with a method for identification of a minimum required model order for stability of transient simulations is proposed.

This chapter includes subjects that are related to Gas Insulated Substations (GIS). Environmental Life Cycle Assessment is increasingly important in view of total life cycle assessment and the environmental impact assessment of the product during its entire life cycle, the commissioning and decommissioning processes and with consultations with authorities. Life cycle cost analysis is of relevance to initial purchasing when searching for the best and most economical solution. The chapter discusses the effects and influences of insulation coordination, and explains the impact of overvoltages and the grounding system. It examines the very fast transient (VFT) voltages and transient enclosure voltages (TEVs) for GIS, and details the planning issues for the project scope development. The chapter also explains the health and safety impact of GIS. The electric field in operation and during short circuit of GIS is also described.