420 kV SF6-free Live Tank Circuit Breakers and Gas-Insulated Switchgear for 80 kA Applications

Such grid expansion leads to a higher magnitude of short-circuit currents due to increased meshing, reduced damping and additional sources of short-circuit current. Studies (e.g. [1]) conducted on Germany’s transmission grid show that the maximum short-circuit current will be in the future often higher than 63 kA and can attain a magnitude up to 80 kA. Therefore, the equipment needs to be ready to handle the stress of the increased short-circuit currents and a circuit breaker having adequate making, breaking and withstand capabilities is needed. Other solutions which try to avoid the increase of the short circuit current have other disadvantages, like e.g. the negative influence on system stability due to preventive decoupling of busbars and circuit breakers sequential tripping (see [1]).

Live tank circuit breakers (LTBs) and gas-insulated metal-enclosed switchgear (GIS) capable to handle a short circuit current of 80 kA therefore represent a crucial part of this transmission infrastructure. Until today, these pieces of equipment have been made available for 80 kA only in SF6 technology due to the excellent insulating and arc-quenching properties of this gas.

However, SF6 is the world’s most potent greenhouse gas and its use must be avoided wherever possible. This paper outlines how the existing SF6-free gas technology has been used to respond to the demands for 420 kV switchgear capable to handle short-circuit currents up to 80 kA. The impact of the differences between 63 kA and 80 kA application requirements on the product development process are described. The product design changes implemented to enhance to 80 kA the making, breaking and withstand capabilities of the existing 420 kV SF6-free LTB and

GIS already type tested and released for 63 kA are also covered. The associated test programme successfully adopted to validate such changes and the verification of the suitability of the switchgear for 80 kA application are addressed as well.

The deployment of switchgear which responds to the demand for a protection equipment able to cope with 80 kA requirements also proves the scalability of the environmentally friendly gas technology further supporting expansion and operation of grid infrastructure with compact solutions.