4. Conclusion
The feasibility study of the 420 kV gas insulated transmission line with an insulating gas mixture of N2/SF6 has been proven as an ecological and economical alternative to overhead lines in areas where they cannot be built and to synthetic cables, where high power ratings and/or long distances are needed. The electrical testing of the dielectric behaviour of the gas mixture showed, that even with the low content of SF6, a reliable electrical system can be built. The laying methods, developed to meet the requirements to travel across the country, are giving the high productivity needed to build long lines at acceptable costs.