2009-01-28 - ABB’s long and distinguished heritage came into play recently when the Dinorwig hydroelectric substation in Snowdonia chose an ABB AK100 gas analyzer to replace a 30-year-old gas detection system originally supplied by Kent.
The technology at the heart of the new ABB katharometer is the same as that of the instrument it replaces, because the essential approach has never been bettered.
The system is designed to check for leaks of sulphur hexafluoride (SF6) from high-voltage contactors, where the gas is used as an insulator. Leaks could lead to both suffocation and dangerous arcing in the switchgear.
A katharometer detects the presence of a gas by comparing the thermal conductivity of a sample with that of a reference gas – in this case air. The katharometer comprises a Wheatstone bridge, each arm of which contains a fine, glass-coated, platinum wire. One pair of parallel arms is sealed in a reference gas of known thermal conductivity and the other pair is exposed to the sample gas. A constant current is passed through the bridge network. Any difference between the thermal conductivities of the reference and sample gases causes an imbalance of the bridge. This imbalance is a function of the difference in thermal conductivities of the two gases, with the resulting difference being used to express the measurement in terms of the percentage of one gas to another.
“The AK100 uses established technology which has been refined over a number of years,” says ABB Product Systems Manager, Andy Jones. “The peripheral things around it may have changed quite a bit but the basic technology is so simple and robust that no-one has ever come up with a better alternative.”
The Dinorwig system monitors six sample points using a common katharometer and a stream switching unit comprising a timer and valves. Construction was completed at ABB's Instrumentation factory at Stonehouse, UK.
Dinorwig substation is also known locally as Electric Mountain. Operational since 1984, it is a 1728MW pumped storage hydroelectric scheme in the Pass of Llanberis on the edge of the Snowdonia National Park in Gwynedd, North Wales,UK.
More commonly used to monitor hydrogen purity in hydrogen cooled generators, the AK100 is a complete gas analysis system comprised of five products. A display and control monitor indicates all measurement results with fail-safe reliability. Two thermal conductivity analyzers and two power supply units complete the system.