Gas turbines are high value, capital equipment around which plant or vehicle uptime is highly dependent. These turbines continually run at their optimum rotational speed, so relatively small performance changes can result in significant cost or even failure. General wear-and-tear, erosion and combustion damage eventually degrades the engine performance and an overhaul is deemed necessary. The engine is de-commissioned and installed in a secure test stand for testing and measurement. Testing is expensive, so ensuring good quality, valid data – every time – is essential.
The Measurement Challenge:
Accurate and effective pressure measurement within each stage of the turbine is necessary to optimise performance and ensure efficiency. Efficiency is usually determined by measuring combustion pressure during the development phase, during production build and during overhaul. Test pressures need to be measured at many annular tappings in the wall of the turbine, along its full length, between each compressor stage, from atmospheric pressure, at the inlet, to as high as 850 psi or more at the tail. The turbine is rotated under steady state conditions and readings are taken from each tapping for comparative purposes to determine overall efficiency data. Often the tappings will feed a manifold to determine an average pressure per annulus, but any leakage becomes hard to detect, so individual readings are more effective. High speed, synchronous data collection is necessary from the huge array of pressure tappings to ensure integrity of the collected data. Often multiple scanners (as 3000 channels of data per turbine is not uncommon) of different ranges will be used axially, as well along the length of the turbine, positioned to measure the pressures radially around the walls for pressure distribution measurements to be made. Commonly, the pressure sensors will be regularly checked, calibrated and zeroed to ensure accuracy and repeatability of the scanned pressure data in-situ between test points and data frames.
So how do you become operationally efficient? Download the full application note here:
