Every GIS substation faces the same question: is the SF6 gas staying where it belongs? Gas compartments are sealed, but seals age, joints move with thermal cycling, and a slow leak can go unnoticed until the gas pressure falls below the operating minimum. Finding leaks quantitatively is the job of the portable leak detector, and the technology behind the detector determines how reliable the survey is. This article explains non-dispersive infrared (NDIR) measurement and the HUWOR SF6 infrared quantitative leak detector (model HMJ-9051-S).
The NDIR measurement principle
The HMJ-9051-S is based on dual-beam, dual-wavelength non-dispersive infrared absorption spectroscopy. In an NDIR sensor, infrared light passes through a sample cell containing the gas drawn from the leak point. SF6 absorbs infrared at specific wavelengths. The instrument measures the light at the absorption wavelength and at a reference wavelength, and the ratio between the two gives the gas concentration.
The dual-beam, dual-wavelength design has two practical advantages. First, the reference beam cancels the effects of cell contamination, lamp ageing and temperature drift, so the measurement stays stable in the field. Second, the measurement is a direct physical one – no chemical reaction and no consumable sensing element that needs periodic replacement. The instrument is equipped with a high-speed embedded microcontroller that processes the signal and presents a quantitative reading to the operator.
What the detector is used for
The HMJ-9051-S is designed for quantitative detection and localisation of SF6 leakage. Typical work:
- Routine leak surveys of GIS compartments, bushings, pipework and valve blocks
- Circuit breaker checks during maintenance windows
- Pre-commissioning tightness verification of new or repaired compartments
- Environmental reporting, where the leak rate of each compartment must be quantified
The operator moves the probe along the seals and joints; the fast response of the infrared cell shows the concentration rising at the leak and the reading quantifies it for the report.
Infrared versus other SF6 detection methods
SF6 leak detectors use several technologies, and each has a role:
- Negative ion capture (electron capture) detectors are highly sensitive and well suited to finding very small leaks, but their response can be influenced by interfering gases.
- Infrared (NDIR) detectors are selective to SF6, stable over long surveys and free of consumables, which makes them a good choice for quantitative routine surveys.
- Halogen/heated-diode detectors are simple and cheap but less selective and less suitable for quantification.
For a utility running regular quantitative surveys, an infrared instrument such as the HMJ-9051-S offers the stability and selectivity that keep the readings comparable from one survey to the next.
Building a leak-management programme
A complete SF6 management programme combines three layers:
- Continuous gas pressure and density monitoring on the compartments, which flags a falling trend.
- Periodic quantitative surveys with a portable detector such as the HMJ-9051-S, which find and measure the leaks.
- Repair and refill records, which close the loop and quantify the annual SF6 consumption.
The portable detector is the layer that turns a flagged compartment into an actionable repair order with a measured leak rate.
Summary
Dual-beam, dual-wavelength NDIR measurement gives the SF6 survey team a stable, selective and consumable-free way to quantify leaks. The HMJ-9051-S applies this technology in a portable instrument with a high-speed microcontroller, ready for routine GIS and circuit breaker surveys. HUWOR supplies the detector with OEM/ODM support. Contact the HUWOR sales team for specifications and a survey procedure.