Puffer-type load break switch for medium voltage gas insulated switchgear filled with dry air

Gas-insulated switchgear (GIS) are key components in medium voltage (MV) distribution networks. Sulphur hexafluoride (SF6) gas has excellent dielectric, thermal and arc quenching properties and has been the preferred insulation medium for GIS. For several years, significant efforts have been made to develop SF6-free switchgear to reduce the use of greenhouse gases in the electrical industry. In 2019 ABB presented a puffer-type load break switch (LBS) for MV applications in switchgear filled with the AirPlusTM gas mixture. However, due to recent changes in European regulations this gas mixture must also be replaced after 1st Jan. 2026. For this purpose, natural origin gases are proposed as insulating medium by most market players. When a gas with lower dielectric properties than SF6 and AirPlus is used for voltages above 12 kV, maintaining similar physical dimensions as for SF6 and AirPlus filled equipment can be achieved by increasing the gas pressure in the GIS. This paper shows that the puffer principle also works well for load current switching in natural origin gases at filling pressure greater than 1.4 barabs. Current interruption with the LBS works in dry air 12 kV and 24 kV applications. This is proven by simulations and full-scale interruption experiments according to the “active load” test duty of IEC standard IEC 62271-103 [1]. Concerns about the effect of current interruption on the quality and safety of the insulating gas have been addressed by collecting and analyzing gas samples after 100 successful current interruptions in a full-scale switchgear. The gas samples showed only trace amounts of decomposed gas, and no toxic by-products were present. This switch offers a cost-effective, user-friendly and safe solution for load current switching in natural origin gas based insulating gases. The new LBS panel matches the technical specifications of the equivalent SF6 product while maintaining the same physical dimensions.