It is a myth that your SF6 analyser shouldn’t be used if the gas is too heavily arced. The reality is that you are most likely going to see arced gas and you need to know how bad it is:
Most SF6 analysers perform the SO2/HF test (acidity) first before moving on to the other gases, this is in some part the reason for such long test times (>5mins).
Typically where SO2 readings are above 15ppm, analysers will automatically shut down and require purging. This is in contrast to their advertised measuring range of 0-150ppm or 0-500ppm!
In addition HF sensors in analysers only have a range of 0-10ppm.
The IEC limit for total acidity is 25ppm, so analysers are shutting down, giving “bad” gas indications even if the gas is still below the IEC limits.
The analyser will not give results for the SF6 or H2O levels.
The reason for this is to ensure the levels are not too high and damage the instrument or sensors. Most manufacturers do not maintain their warranty guarantee if the analyser has seen high acid levels.
The EMT Way:
AT EMT we have designed our analyers to meet the demand of the application.
We measure the SO2 and HF at the same time as all the other gases, reducing measurement time to 2mins and ensuring you always get a result.
Our SO2 and HF sensors have suitable measurement ranges; 0-150/500ppm SO2 and 0-200ppm HF. Ensuring we will always get a reading and to the right IEC limits; no more false positives.
We have designed the analyser for this application and as such our sensors have lifetime warranties (IR) and SO2 sensors a 5 year warranty. This warranty is still valid even if heavily arced gas has been seen.
