Repair Solutions for
28 March, 2008 – OVERVIEW OF APPLICATION COMPLETED IN 1993
Sulphur Hexafluoride, or SF6, is an inorganic compound used widely as a gaseous insulator in high voltage breakers, busses and other equipment – referred to as gas insulated switch gear, or GIS. SF6 gas is colorless odorless, non-toxic and non- flammable, but is considered to be 25,000 times more effective as greenhouse gas as CO2 and is therefore considered an environmental hazard and is rigidly controlled. It is also quite expensive with a cost exceeding $ 2500.00 per 100lb bottle.
The GIS Technology was first used in North America at BC Hydro’s MICA Generating Station, a large power dam on the Columbia River in central British Columbia, completed in 1973 and brought on line over the next few years. It formed the Kin Basket Reservoir and was the highest earth filled dam in the world at that time.
Gas insulated switchgear manufactured by ITE, considered state of the art at that time, was imported from Europe and installed. The GIS installed at Mica GS use SF6 pressured to about 45psi as an insulator. Pressure is monitored and fresh SF6 is added if any loss is detected. Unfortunately Mica GS immediately began to loose significant amounts of SF6 gas. Newer installations using GIS did not experience similar losses due to advances in design, manufacturing and installation. Various efforts were made to seal the buss work but leaks persisted.
Meanwhile during the early 1990’s Belzona Elastomers were being used to seal oil filled transformers for BC Hydro and one of the senior technologists believed that these materials might work to seal GIS leaks at Mica GS.
Over the course of 2 maintenance outages in 1993 the identified problem areas were sealed with Belzona 2211 and 2221 MP Elastomers and in some cases Belzona 1321 Ceramic S Metal. The two types of leaks addressed were flanged joints – by far the most common and also the most difficult to seal – and pin holes in welds.
SF6 leaks can only be located by electronic “sniffers” and since it is heavier than air it tends to flow along the switchgear and drip from any low point so pinpointing the actual leak is difficult. Since the gas can flow beneath a suspect spot the entire joint should be encapsulated.
The Belzona materials applied in 1993 have proven completely effective for more than a decade now. SF6 consumption had dropped from more than 50 bottles per year to a mere 2-3 – a savings of more than $1 million over 10 years. More important SF6 gas was kept out of the atmosphere.
The switchgear at Mica GS is currently being replaced with more up to date equipment as spare parts are no longer available. However, should leaks develop in the new equipment Belzona Elastomers will be the product of choice, based on its past history and performance.