Patent Number: 050230450
Section: summary

BACKGROUND OF THE INVENTION This invention relates to a plant malfunction diagnostic method for sensing a malfunction and identifying the cause thereof in a plant such as a nuclear power station or thermal power plant in which there are a large number of parameters to be monitored and the parameters are interrelated in a complicated manner. Plants such as nuclear power stations or thermal power plants generally use a large number of announciators adapted to issue an alarm to inform the operators of the occurrence of a malfunction if a level of plant state variable exceeds a predetermined limit value. For example, in a nuclear power plant or the like, the number of announciators can be as many as several thousand, and a large number of lamps can flash in the occurrence even of a minor accident. Hence, it is difficult for an operator to be supplied solely with the information necessary. Consequently, various countries are developing systems for diagnosing malfunctions by utilizing computers. Typical systems are the nuclear power generating support system of Japan, the Gesellschaft fur Reaktorischerheit (GRS) of West Germany, the STAR being developed by the Halden project of Norway, and the DAS being developed by commission of the EPRI (the Electric Power Research Institute of the United States). A malfunction diagnostic method referred to as cause consequence Tree (CCT) is employed in these systems. For example, in accordance with CCT, the relationship between the causes of malfunctions and their consequences is represented in the form of a tree. When a malfunction occurs, the state of its consequence is observed and the branches of the tree are traversed in the reverse direction to arrive at the cause. Ordinarily, retrieval by CCT starts at the beginning of operation of an announciator set to a level which is .+-.10-20% of a plant state variable under power operation. Therefore, after the occurrence of a malfunction which propagates rapidly in tens of seconds, the possibility arises that the operator may not be able to perform the proper recovery operation. SUMMARY OF THE INVENTION An object of the present invention is to identify the cause of a malfunction by detecting the malfunction at a level which is .+-.3-7% of the peak of a plant state variable during nomal operation before the announciator is actuated, and to improve availability factor and safety of a plant by allowing the operator to perform the appropriate recovery operation with a sufficient time margin. According to the present invention, the foregoing object is attained by providing a plant malfunction diagnostic method comprising a step of determining by simulation a change in a plant state variables at the time of a malfunction and forming a pattern of changes in plant state variables obtained by autoregressive analysis of the change in plant state variable, a step of inserting the formed pattern among the plant state variables in a neural network comprising an input layer, a middle layer and an output layer, and performing learning within a preset precision, and a step of identifying the cause of the malfunction by inputting the pattern of plant state variables formed from the plant state variable, after detection of an actual plant malfunction with respect to a neural network having connection weight between processing elements (neurons) in the input layer and the middle layer and between the middle layer and the output layer. Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings.