User Guide for Non-SF6 Gases and Gas Mixtures in Substations

The brochure covers 

• two gas mixtures containing fluorinated compounds (F-gases) for use for insulation and interruption in gas circuit-breakers and 
• natural-origin gas mixtures (NOGs) for use with gas interrupters and vacuum interrupters. 

It provides a practical guide for users of non-SF₆ gases and gas mixtures as well as practical information in addition to the procedures given in IEC 62271-4. Moreover, this brochure describes “best practices” for non-SF₆ gases and gas mixtures regarding 

• gas handling procedures 
• gas handling equipment
• gas measurements
• tightness requirements and tests
• environmental, health and safety requirements
• end-of-life treatment and recycling requirements

For the topics listed above, special reference is made to the state-of-the-art knowledge of SF₆ applications, i.e. CIGRE Technical Brochures 234 (SF₆ recycling guide), 276 (SF₆ handling guide) 430 (SF₆ tightness guide) and 723 (SF₆ measurement guide). If applicable, differences between non-SF₆ applications and SF₆ applications are explained in this userguide. 

Gas handling

Today, all necessary handling equipment to handle the gases and gas mixtures covered in this brochure is available on the market. When handling non-SF₆ gases and gas mixtures in high-voltage switchgear, filling on site can be done either with bottles of pre-mixed components (in a gaseous or partly liquid state) or with individual bottles of pure components and a gas-processing cart. Gas-handling equipment is available for filling, top-up and recovery, for leak detection and leak location as well as for gas quality checks. 

Although some devices can be used for multiple gases, users should ensure that equipment dedicated for the specific non-SF₆ gas or gas mixtures is applied. To distinguish between different gases, the use of different connections and colours on the valves and handling equipment is recommended and some examples are given in this brochure. The same commissioning methods used for SF₆ apply for alternative mixtures. Top-up methods are described in IEC 62271-4, like adding one component of a mixture or adding a technical grade mixture. It is for the user to decide on the amount of gas and handling equipment to be stored.

Gas measurements

Unlike SF₆, non-SF₆ gas mixtures consist of several gases. typically at higher pressure to keep the same dielectric performance and with lower mass density, because natural-origin gases like CO₂, O₂ or N₂ often form the main part of the mixture. The use of gas mixtures introduces the need for gas concentration measurements to verify that technical requirements defined by the original equipment manufacturer and by IEC standards are fulfilled. 

Due to real-gas effects in such mixtures, e.g. at low temperatures, it is recommended that concentration measurements are performed using the unit mol% instead of vol% to guarantee comparability among measured values. Regarding humidity, the IEC requirement for a frost-point below -5 °C is also applicable to non-SF₆ gas mixtures. Practices for pressure or density monitoring are unchanged. Mobile analysers are available on...