The integral diagnostics factor used for the evaluation of turbine island condition is the turbine heat rate corrected to constant steam parameters and condenser pressure which is called “corrected turbine heat rate”. In case of excessive deviation of corrected heat rate from its normal value, it is necessary to implement a diagnostic subsystem for determining the source of the deviation. The following subsystems of the turbine island have to be taken into consideration: turbine steam path, turbine end seals, control valves, etc. For each subsystem it is necessary to select the calculated or measured parameter(s), which will be used as diagnostic factors for turbine condition evaluation purposes. For the turbine steam path subsystemthe internal efficiency of the high pressure turbine (HP) and intermediate turbine (IP) can be used. Selection of the internal efficiency as diagnostics factor is based on its high sensitivity to variations in steam path conditions (erosion, steam path fouling and so on), as well as to steam path diaphragm and radial sealing conditions. However, the basic internal efficiency calculation results of HP and IP turbines at different loads, using measured parameters, show very high sensitivity of the calculation results to random measurement errors, random components of the regulation process and variations in spatial and time distribution of the temperature and pressure fields. This high sensitivity causes the uncertainty of the calculation results to approach ± 1.5 % and means that the results can not be used for diagnostic purposes. To achieve acceptable results for uncertainty (± 0.3 %) special methods of mathematical analysis need to be applied, including robust estimation, precise multivariate approximation, filtration and others. Furthermore, the HP turbine internal efficiency depends on control valve position and thus can not be directly used as a diagnostic factor in an on-line turbine diagnostic system. To solve this problem, special methods were developed for correcting the real efficiency value to the valve wide open position. The developed method was verified by a set of specially designed tests and results have shown that this technique can be applied for on-line calculations. The described system for on-line turbine internal efficiency monitoring was developed in cooperation between IEC and Berman Engineering Ltd. The system was implemented on a 550 MW unit and has been in operation for two years. The results of operation show that the system yields the required expanded uncertainty in the range of ± 0.3 %. The system is characterized by high reliability and a friendly interface.
In this paper, a turbine on-line performance calculation system is presented. The system was implemented on a 575 MW unit of the Israel Electric Corporation and has been in operation for one year. The system was developed jointly by IEC and Berman Engineering Ltd. The main feature of the described system is the precision of the turbine heat rate calculation. This increased precision of the turbine heat rate calculation was accomplished by utilizing sophisticated statistical techniques, such as parametric and nonparametric regression, robust estimation, special filtration methods, autocorrelation methods, and uncertainty estimation methods. This high precision allows using the calculated heat rate as the main input to the turbine diagnostic system. The selection of turbine heat rate as the main diagnostic input is due to its high sensitivity to efficiency deviations of each turbine subsystem (turbine internal efficiency, condenser cleanliness, regenerative heaters’ cleanliness, etc.). However, despite this high sensitivity, the turbine heat rate cannot be used directly without implementing the sophisticated statistical techniques mentioned above because: • relatively small variation of the calculated heat rate over the entire turbine load range (only about 3%); • the presence of systematic and random measurement errors; • low signal/noise ratio as a result of the above items. In order to develop the techniques mentioned above, a detailed study of the error characteristics and error propagation was carried out. This study defined the problems which had to be solved in order to achieve an acceptably high precision of the calculation results. The current results allow using turbine heat rate as a tool for the following purposes: • turbine cycle efficiency estimation for all modes of operation and for turbine cycle scheme variations; • turbine internal condition estimation; • reliability control of measuring instrumentation which is used for turbine heat rate calculations; • determination of heat rate deviation which is above a preset acceptable value (heat rate “out of range”). The structure of the developed system is presented as well as examples of results which show the calculation precision. Also, examples are presented to illustrate how the heat rate can be using for identification of various abnormal situations which may impact the turbine cycle efficiency.
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