What is it about?
Even if the electrical power industry is investigating and partially already using alternative insulation gases, SF6 is still a commonly used insulation gas in electrical switchgear (GIS gas insulated switchgear, circuit breakers , insulators and other electrical equipment in HV/MV transmission and distribution). Approximately 80 % of today’s manufactured SF6 gas is used in the electrical power industry.
SF6 has perfect insulation properties but on the other hand it is the most potent greenhouse gas. In accordance with the clear regulations (such as IEC 62271-1), the industry has committed itself to reducing SF6 emissions as far as possible. Besides the goal to avoid SF6 handling losses as far as possible it is important that the leak rates itself are kept at very low levels, typical state of the art criteria for the leak rate is 0.1 % or 0.5 % (loss of SF6 filling per year). Quantifying low leak rates in a reliable way needs sensitive and stable measurement technology.
What to measure?
The CIGRE SF6 Tightness Guide (430) describes different ways and technologies to quantify leak rates for SF6. Photo-acoustic spectroscopy is a proven technology that can be used for high voltage (HV) and for medium voltage (MV) equipment. Furthermore photo-acoustic technology is the most sensitive technology allowing to quantify lowest leak rates down to 0.2 mg/a in the best case. Commonly used method is to quantify the test units leak rate in an integral test (tight test chamber, tent, gas tight plastic sheet). Typical setup is shown in the following scheme:
SF6 from leaks is accumulating over time in the chamber, the SF6 concentration in the chamber is continuously measured and after a certain time (for example 15 or 30 minutes) the increase of SF6 concentration in a given time interval can be calculated / scaled to the yearly leak rate (in % of filling per year), respectively can be compared with the calculated PASS/FAIL criteria of the device for quality control / acceptance test purposes. Needed measurement time depends on the free internal volume in the chamber as well on the leak rate. If selected carefully, reliable leak rate quantification can be performed within a few minutes.
As described before it is important to allow sensitive measurements: GASERA’s unique Cantilever Enhanced Photoacoustic Spectroscopy offers a detection limit of ≤ 5 ppb for SF6
Besides the very good sensitivity it is also important that the measurements are stable without any drift over time to enable reliable tests even if increase in concentration is only a few ppb.
Measurement at zero ambient background level, with a standard deviation of ~ 2 ppb over eight hours measurement.
- GASERA ONE PULSE is easy to operate, allows to set individual user levels, low or nearly no risk of wrong operation
- Stable calibration, recommended recalibration interval 12 month, low cost of ownership
- GASERA ONE PULSE can take up to ten optical filters to measure additional / other gases. H2O measurement always included
- 12 channel MULTIPOINT SAMPLER is available as accessory to measure several chambers at the same time or to measure at different locations inside larger enclosures (tents)