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Industrial Processes

Health check for gas turbines

   
 
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The integration of several monitoring techniques has resulted in a system that can produce an almost instant indication of the health of an industrial gas turbine and of faults that are developing within the engine.
The computer based analysis system allows a turbine operator to detect the onset of faults that could lead to expensive down-time and repairs. The failure of a blade in a gas turbine, for example, could destroy much of the engine within seconds unless the turbine is switched off quickly.
The three collaborators in the project, known as GASTEM, have for the first time analysed, almost in real time, acoustic and thermal signals from a turbine along with readings of the aerothermodynamic conditions in the engine, using expert system computer techniques.

Conditioning monitoring techniques based on the measurement of characteristics such as bearing vibrations are well established throughout industry, and alert the user to changes in a machine that could indicate developing faults. The techniques are, however, often difficult to apply in the harsh environment within industrial gas turbines, which are used widely for power generation, pumping, compression or other applications. Yet faults can develop very quickly in turbines and the failure of one of the many blades in a machine can have a devastating effect. Even small faults can require costly repair work, and expensive downtime. Other faults can reduce global thermodynamic efficiency and degrade the economical justification of operating such an industrial powerplant.
GASTEM has tackled the problem of how to monitor the health and effectiveness of gas turbines by developing computer models that can analyse in an integrated manner both the noises produced by a turbine and the thermodynamic measurements from the operating engine. The expert system software combines the different forms of signals to diagnose faults, such as a blade being twisted out of its normal position, within about 10 seconds. This allows rapid action by the operator to prevent further damage to the turbine. The partners are the acoustics and noise specialists Metravib RDS of France, the gas turbine manufacturer European Gas Turbines (EGT) of the UK, and the National Technical University of Athens (NTUA) which is expert in turbomachinery.

Widespread applications

The partners believe there is a huge potential market for the portable computer system they have developed to monitor the health of turbines. They estimate that in the European Union there are 1,800 industrial gas turbines, 850 of them smaller than 10 MW. World-wide there are believed to be 12,000 industrial turbines, including 4,500 smaller than 10 MW.
A typical severe fault that requires modification of an engine before a later scheduled service could easily cost 40,000 ECUs say the partners. A correct diagnosis of a major fault could avoid a cost of about 100,000, ECUs or potentially much more if the cost of lost production is taken into consideration.

Taking engine soundings

One of the important features of GASTEM has been the ability to use different forms of data collected from a turbine. The innovative aspect of this development was to combine an acoustic approach with thermodynamic techniques. Data fusion of the readings from different measurement techniques is difficult to achieve, but allows faults to be pinpointed through, in effect, a mutual learning process. GASTEM cost 1.5 million ECUs and a follow-on VA-GASTEM project, under the Value programme, to develop a practical version of the monitoring system, cost 266,000 ECUs. The European Commission contributed 930,000 ECUs of the GASTEM cost, and 130,000 ECUs to the VA-GASTEM project. GASTEM followed an earlier three-year project by the partners to explore advanced experimental techniques, particularly a holographic technique known as acoustic phased imaging. This involves using an array of microphones to pick up the sounds from an engine, with the array processed to achieve a significant acoustic directivity, somewhat comparable to an 'acoustic binocular'. This also allows the array to be some distance from the hot and dirty atmosphere around the turbine, therefore reducing the background noise and producing a high signal-to-noise ratio for easier analysis.
Acoustic signals are collected using a low-frequency array of microphones for sound in the 100 Hz-3.5 kHz range and a high- frequency array for signals in the 3.5 kHz-17 kHz range. This improves directivity, as the acoustic focus is different at different frequencies. Microphones would not need to be placed more accurately than a few tenths of a centimetre away.
GASTEM also uses pressure sensors, thermocouples and other sensors to produce more conventional monitoring signals. The computer software assesses the signals, with different types of signal being evaluated together to provide confirmation of the conditions inside the turbine.

Data reduction methods

The system must carry out signal processing to reduce the huge flow of acoustic and accelerometer data, which is typically 2 M bits/second, to produce indicators of the mechanical and thermodynamic conditions within the turbine. This processing involves fast Fourier transform analysis of the spectra by techniques such as filtering and detection of signal peaks, and the formation of 'spectra of spectra'. In the latter case, acoustic tones are selected from the different spectra of tones to form the so-called 'cepstrum' of the signal. The software also reduces the aerothermodynamic and general operating signals to a small number of indices that define the condition of the gas turbine. The result is a set of 40 parameters that are integrated and subjected to an expert system analysis to diagnose faults. This has required the partners to develop a library of faults against which signals from a turbine under investigation can be compared.
The expert system is known as CLIPS and is derived from computer language originating from the NASA space agency. Military missile designers have also integrated different types of monitoring signals to provide rapid alarms of faults that might require destruction of the missiles. The CLIPS software identifies the faulty component on a turbine, such as the compressor, and the faulty part, such as a burner. The results are displayed on a computer screen, with fault indication and alarms, depending on the level of fault.

Portable monitoring unit

VA-GASTEM turned the project results into a practical demonstrator unit. It involved work on a Tornado gas turbine from EGT that generates power at the beer and lemonade factory of the Bavaria BV company in Holland. The aims were to reduce the cost of the system, make it more user friendly and more suitable for industrial conditions.
The resulting system costs about 25,000 ECUs, compared with the 200,000-ECUs cost of the GASTEM version. The system now weighs about 75 kg, rather than the original 300 kg, making it practical for use in the field. The information displayed on the personal computer screen of the system has also been reduced to simplify use. Particularly important is the ability of the system to deliver results within 10 seconds, thus providing an almost real-time health survey. This speed is needed to detect vibration of a turbine blade, for example. Also the system can learn the parameters of the engine that it might be used for in less than 15 minutes, compared with the one hour needed on the GASTEM version.
The health monitoring system is now ready for the commercial market. An estimated 40,000 ECUs would be needed to extend its use on turbines other than the Tornado, and a further 20,000 ECUs for the equipment needed, such as acoustic arrays. The partners say that the potential savings from better maintenance could far outweigh the costs incurred to bring it to market. GASTEM could be a stand-alone system for use on different engines, or integrated with the turbine's management control system. The expected development of computer technology offers the potential for GASTEM's health monitoring software to be available as a marginal extension of the control system computing power, says one of the partners.

 

 

Project Title:  
Gas turbine health monitoring demonstrator.

Programmes:
Industrial and Materials Technologies (BRITE-EURAM/CRAFT/SMT)

Contract Reference: BE-4192

Cordis DatabaseFor more information on this project,
go to the CORDIS Database Record

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