Essentials of SF6 monitoring

01/01/2012

Because SF6 has a global warming potential that is almost 24,000 times greater than CO2, it gets a lot of attention. And since the electric power industry is responsible for nearly 80% of the world’s usage, our industry has taken significant steps to reduce or eliminate the emissions from gas insulated switchgear.

 

It would be foolish and factually incorrect for anybody to claim that SF6 Gas Insulated Switchgear (GIS) does not leak. All GIS leaks! That is why Transmission Network Operators in today’s environment have to deal with the design, installation and operation of new GIS, as well as the integrity of older installations. Both instances require up-to-date SF6 inventory control and a modern SF6 gas monitoring system to ensure compliance and reduce cost. With a current average price of $9.00 per pound, leak reductions could not only save the environment, but could also save a significant amount of money.  Utilities that participated in the EPA’s voluntary reduction program, were able to save $2.5M from 1999-2002.

 

According to the EPA1, the most promising and cost effective options to reduce SF6 emissions are:

  • Leak Detection and Repair

The EPA estimates that if consistently and aggressively implemented in the U.S., SF6 emissions could be reduced by 20%.

 

  • Use of Recycling Equipment

The EPA estimates that SF6 recycling could eliminate 10% of total related emissions from the U.S. electric industry.

 

  • Employee Education/Training

Making employees aware of the environmental impact of these emissions and establishing a corporate policy for managing SF6 is critical. You cannot manage what you don’t measure!

 

Modern SF6 Monitoring techniques should be seen as essential companions to the design, manufacturing and installation of GIS and not as a mechanism to discredit or prove unreliability, albeit rare, in modern switchgear. Here are a few points to consider:

  • With conventional methods of SF6monitoring using mechanical gauges and fixed contacts for alarming, you can expect an accuracy of >5% SF6 loss per annum. By installing and proactively using a continuous, intelligent trend analysis solution it is possible to limit SF6losses to within 0.5% per annum, which has the ability to potentially decrease the loss 10 times. Equally important, it will provide early awareness of losses.

  • By providing real time data on SF6 gas inventory combined with long term predictions on SF6 losses, a user is able to accurately report and provide an auditable trail of their SF6.

  • Trending SF6 gas loss, sampling at a rate of 10 measurements per second continuously using highly accurate SF6 density measuring devices enables the production of accurate and reliable long term predictions. Such information equips a user with the ability to plan maintenance activities proactively and based on asset condition as opposed to following unnecessary scheduled or reactive maintenance techniques.