TRANSIENT ELECTRIC FIELD IN GAS INSULATED SUBSTATIONS AND COUPLING WITH SECONDARY CABLES

In the last years gas insulated substations (GIS) have found a broad range of applications in various countries, in particular inside densely populated cities. Switching operations in GIS are generating very fast travelling waves having 5 - 10 ns rise times which propagate outside the GIS enclosure. The coupling between the radiated electric field and low-voltage cables induces currents in cable sheaths.To improve the electromagnetic compatibility of electronic devices by proper shielding and correct cable routing, the estimation of the amplitude of these currents can be very useful. Modelling of GIS, calculation of the electric field radiated by the GIS enclosure and the coupling between this field and secondary cables are the main subject of this paper. The models have been created using three computer codes. First two codes are well known namely the Electromagnetic Transients Program (EMTP) and the Numerical Electromagnetic Code (NEC). The third code is a coupling code developed in our laboratory. The equivalent models of the GIS should be suitable for a wide frequency spectrum (from hundreds of kilohertz up to hundreds of megahertz). Measurements of different phenomena were performed in a 125 kV GIS of the Electrical Utilities of Lausanne. Verifications of simulation results with measurements are presented.