Sulphur hexafluoride (SF6) is the insulating and arc-quenching gas used in high-voltage circuit breakers, GIS and other switchgear. It is an excellent gas for the application and a potent greenhouse gas when released. Every compartment develops small leaks over time, and a leak that is not found means gas refills, falling pressure, and ultimately a risk to the dielectric strength of the equipment. Quantitative leak detection – finding the leak and measuring its rate – is therefore a standard maintenance task in every GIS substation. This article explains the HUWOR SF6 gas quantitative leak detector (model HMJ-9051-SJ).
The negative ion capture principle
The HMJ-9051-SJ adopts the negative ion capture principle. When SF6 is present in the sample gas drawn from a suspected leak point, the detector’s sensor captures the characteristic ions produced by the gas and converts the concentration into a quantitative reading. The technique is chosen for field use because of its combination of properties: high sensitivity to SF6, good stability over time, a fast response as the probe moves along a flange or a valve, and simple operation that a patrol engineer can use after a short briefing.
What the detector provides
The instrument performs two tasks in one scan:
- Detection – finding the leak point by moving the probe along the joints, flanges, valves and gauge connections of the equipment while watching the response.
- Quantification – measuring the concentration at the leak point so the severity can be judged and the repair prioritised.
According to the published specification, the detection range of the HMJ-9051-SJ is 0-2000 ppm, measured under the reference conditions stated in the product datasheet. This range covers the practical concentrations found at SF6 leak points during routine surveys.
Where it is used
The detector is deployed wherever SF6 equipment is installed and maintained:
- GIS substations, where the compartments, bushings and connecting pipes have many sealed joints
- SF6 circuit breakers, both outdoor and indoor, including the valve block and the pressure gauge
- Instrument transformers and other SF6-filled apparatus
- Manufacturing and testing workshops where new SF6 equipment is quality-checked before despatch
In each case the work follows the same pattern: the pressure is checked first, then the probe is passed slowly over every joint and seal, and the readings are logged. A leak that shows a rising concentration is marked for repair; a compartment that shows no response is confirmed tight.
Why quantitative matters
Two leaks are not equal. A small weep on a gauge connection can wait for the next scheduled outage; a large leak on a bushing flange may require prompt action because the gas pressure will fall below the minimum operating level. A quantitative reading separates these cases and lets the maintenance planner schedule the work by severity instead of by coincidence of discovery. It also supports the environmental reporting that many utilities are now required to provide for SF6 usage.
Combining survey and online monitoring
Periodic leak surveys with a portable detector are complemented by gas pressure and density monitoring on the compartments themselves. The online monitoring system tracks the gas trend and flags a compartment whose pressure is falling; the portable detector is then used to find and measure the leak point. This is the same combination of trend and localisation that drives good practice in partial discharge monitoring.
Summary
SF6 leak testing needs sensitivity, speed and a quantitative result. The HMJ-9051-SJ uses the negative ion capture principle to detect and measure SF6 leaks over a 0-2000 ppm range on circuit breakers, GIS and other SF6-filled equipment, with the fast response and stable operation that field surveys require. HUWOR supplies the detector with OEM/ODM support. Contact the HUWOR sales team for specifications or a leak-survey procedure template.