Improved SF6 gas testing key to switchgear condition management

By Trevor Lord, LORD Power Equipment

Whilst SF6 switchgear has traditionally been marketed along the lines of a ‘fit and forget’ asset, the reality is far from this stance.

The SF6 breaker population is now nearing and end-of-life scenario in many Australian installations. Coupled with a rapid uptake in recent times of GIS installations (many of unproven quality), the industry has become increasingly motivated and focused to introduce appropriate techniques for improved asset stewardship and condition assurances. Indeed, Australia is leading international trends in the extent of such efforts.

It has become abundantly clear that the longevity and integrity of the SF6 gas itself, as well as the physical internal condition and performance of the breaker, is directly correlated to the management of moisture levels in SF6. Once moisture levels rise in GIS units, where arcing is a normal phenomenon, moisture is directly responsible for the formation of corrosive gas decomposition products during arcing and for subsequent internal damage to the breaker. Clearly, SF6 moisture management is the key to routine GIS stewardship.

In parallel with condition-driven GIS management, there is presently strong interest internationally in improved practices with regard to routine SF6 testing. Taking this message further, Cigre are to release an extremely-relevant SF6 Gas Tightness Guide in late 2010 that will contain all the SF6 best practice ‘handling’ practices, a reinforcement to containment of gas during testing, as well as very practical guidance on means to repair or contain leaks. ‘Handling’ encompasses the entire spectrum of the management of SF6 gas, including containment of lost gas from leakage, lost gas during maintenance and testing, and reclamation.

In regard to routine testing of gas condition, the need for regular assessment of moisture and purity of SF6 in switchgear is widely accepted. There has been a similarly-motivated upgrading of older equipment which was not only hard and time consuming to use, but also wasted gas to atmosphere during the testing process.

New testing technologies are becoming increasingly taken up across Australia. In general, these new testers are able to offer simplified testing and exceptional environmental compliance. Advancements now allow for an in-built gas retention and pump back facility, the provision of the pressure-independent ‘ppmv and ppmm’ moisture measurements, fully automated operation, long-term calibration stability, and lab-quality performance in a rugged field enclosure.