EMT Simulation of Very-Fast Transients in Gas-Insulated Substations Using Modified Carson's Formula

This article proposes modified formulas of Carson's and approximate earth-return impedances for overhead lines which can deal with high-frequency displacement currents. The calculated results by the proposed methodology are compared with those calculated by accurate formulas, and a satisfactory accuracy of the proposed methodology is confirmed. The proposed formulas are applied to very-fast transients (VFTs) in a gas-insulated substation, and it is made clear that the proposed formulas with the earth-return admittance cause no numerical instability of electro-magnetic transient (EMT) program simulation, while the original Carson's formula and its approximate one implemented in existing EMT-type programs result in the numerical instability. EMT simulation of VFTs can be easily performed using the proposed simple formulas with the earth-return admittance.