63. Best Practice

Modern MV switchgear fails very rarely, but with SF₆ gas, when it does occur the consequences can be serious. Author examines the latest requirements for safe management and operation. The inert, non-toxic gas sulphur bexafluoride (SF₆) has excellent physical properties and dielectric capabilities. It features very good cooling, insulating, and arc quenching capabilities in critical applications such as circuit breakers. Therefore, it is the gas of choice for electrical utilities worldwide. It is, for example, used extensively for MV and HV switchgear, compact gas insulated substations, and gas insulated transmission lines and transformers. Although SF₆ has been in use for about 45 years, it was only recently discovered that it is a powerful greenhouse gas, one of only six listed in the Kyoto Protocol. Its contribution to global warming is probably small, even though it has a global warming potential around 25,000 times greater than CO₂, and it probably accounts for only about 0.1 per cent of mankind's contribution to the greenhouse effect. Moreover, it does not contain chlorine, so has no effect on ozone depletion. Even so, it is essential that SF – which is highly persistent – is handled with great care so as to minimise emission to atmosphere.