Rewind and play again

Process deviations leading to power plant trips tend to occur suddenly and the plant operator does not have enough time to take action or make decisions. In most cases the plant ends up in a shutdown. Frequently, a subsequent thorough analysis determines that a simple action, taken in good time by the operator, would probably have avoided the turbine shutdown, or at least have prevented it in part. It is easy to draw these kinds of conclusions and make operational recommendations once the event has already occurred and one is under no time pressure. But even then, although these conclusions and recommendations may reach all the operational staff, some problems still remain unresolved:

• How to make sure that in a future similar event the plant operator is able to come to the right decision in due time, ie make a decision previously analysed under no pressure.

• How to make sure that the rest of the shift teams that have not personally experienced the emergency really understand the way the associated events have occurred and triggered the plant shutdown, ie, how to make sure that other shift teams are well informed in dealing with shutdowns.

With the purpose of finding answers to these questions, Genelba CCGT plant has developed an application that allows operators to virtually “rewind” DCS historical files and replay them as and when they want to and in an environment very similar to real plant operational conditions. Then each operation shift team has the opportunity to experience the failure and perform the corresponding emergency operations. This tool is much more effective than a traditional simulator and the cost of the development is considerably lower.

The Genelba plant

Central Termoeléctrica Genelba is a CCGT power plant based on Siemens V94.3A gas turbines in a 2+1 arrangement. The plant is located in Marcos Paz, 50 km away from Buenos Aires, Argentina. In 1999 it started its commercial operation as a merchant power plant in the deregulated and competitive Argentine market.

In 2000 Genelba certified its Quality Management System in accordance with ISO 9000:2000. The plant also has ISO 14001 for its environmental management system, OSHAS 18001 for its safety and occupational health system and SA8000 for its social accountability.

The gas turbines at Genelba run only on natural gas, and as Petrobras has its own gas production and transportation facilities, the fuel is always available, and the plant has low production costs, allowing the generators to be permanently in operation, most of the time in base load. Genelba also has an excellent availability record, one of the highest in the Siemens fleet, over 95% in the last few years.

These two characteristic features of the plant endow it with excellent performance values. Although from an operational view point they are very positive, their disadvantage is that operational staff rarely experience and handle machine start-ups or shutdowns, which are almost exclusively carried out only as scheduled procedures for minor GT inspections every 4000 equivalent operating hours. New staff are of course even less well acquainted with unscheduled outages.

Owing to the need to keep operational staff at a high level of training, and to maintain the high levels of plant performance, the idea arose of incorporating a tool which could reproduce real operations.

SIMULGEN

Starting with the premise that this tool should reflect real operation values and conditions and also be an exact replica of Genelba’s facilities we devised software that we call SIMULGEN.

SIMULGEN exactly reproduces past plant operations and displays them on the Siemens Teleperm XP screens, allowing the operator to experience past events occurring during a plant start-up or shutdown – and also the sequence of events immediately prior to a trip, or important deviations from the normal operational parameters. Thus, all the staff are able to practise on past events, and those who were not present when the real event occurred can see it as if they had been there at that very moment. In addition, it is a very useful tool for studying the causes of a plant trip, or part of it, and to experience it without depending on a list of events that do not dynamically represent the sequence of events.

SIMULBUILDER

SIMULGEN is entirely developed in Visual Basic and requires another tool (developed in the same software) that we call SIMULBUILDER. The latter is in charge of collecting all data from the Siemens Telepern XP operating system with the text file extension .TXT. It analyses it and after complex internal processing inputs the data to a Microsoft Access database (this is a temporal, in this case time stamped, database). Moreover, SIMULBUILDER has a pre-arranged database which can be modified by the system manager if it is necessary to incorporate new signals. This database includes all the operational screen TAGs (KKS) and their corresponding status signals.

When the SIMULBUILDER data collecting process starts, it browses each database KKS and looks for it in the temporal database taken from Teleperm. When the system finds any KKS matching between the two databases, it places the value found in the final database and in the right position in each screen. This same process is applied to analog and binary data. In the case of the latter, two different files must be checked since it first sees the file with the initial status and then decides if there has been any change of status during the sequence of events. If there were no events at all, the KKS status will appear as in the initial status. Otherwise, the new status will be shown. As in the case of analog data, once all the data has been checked, it is input in the final database.

How SIMULGEN works

SIMULGEN reproduces in the replicated screens of the Teleperm system all the data processed by the SIMULBUILDER and browses cell by cell the entire database. Each column in this database is connected to a window or object in the operation screens, indicating the analog values of the different screen windows and the status changes in the objects, depending on the binary value that it receives from the Access database. The objects will be related to pieces of equipment such as: pumps, fans, gas line heaters, air driers, switchers, electrical ignition valves, pneumatic valve controllers, among others, and also to elements like Sub Group Control, Sub Loop Control, Group Control, leds, etc.

All the screens developed by SIMULGEN look exactly the same as the screens the operator has in the plant control system. The effect of that is extreme familiarity – the operator feels during training that he is working with the same elements he usually works with.

Figure 1 shows the screen where the database is created from the SIMULBUILDER. It includes the following information: failure or event name, description, observations and the name of the person who created the database. On the left side of the screen, the following data are added: failure date, start time, end time, failure time interval (it can last from 1 second to hours) and the number of records. These data are taken from the database created with the text file manager.

Once the database is created, analog data on failure is processed together with alarm messages. Alarms are in a different file set aside for alarm text messages.

In the analog data processing screen (Figure 2) both the database where the event information will be saved and the source files are selected. These source files are downloaded from the Siemens Teleperm and are given the same name with a ‘.TXT’ extension. At this time the user can decide if some or all the screens are to be processed. Once the parameters are set, the analog data processing starts. If a signal problem occurs during the data processing, it will appear at the bottom of the screen and once the process has finished, a text file with a description of all the errors will be created.

When the analog data processing has finished, the binary data processing starts. For this purpose, we go to the digital data processing screen (Figure 3) and proceed as in the previous case. As in the case of analog data, if a signal problem occurs during the data processing, it will appear at the bottom of the screen and once the process has finished, a text file with a description of all the errors will be created.

After going through the stages mentioned above, the databases are transferred to SIMULGEN.

Using SIMULGEN

SIMULGEN (Figure 4) shows all the data processed by the SIMULBUILDER in the operation screens, replicated from the Siemens Teleperm XP.

In this screen, you can select the desired failure or simulation and by pressing the “Loading Simulator” button cause all the data to be loaded into the programme. After that, you can start the programme and see the parameter variations in all the screens.

To run the application, the following controls are used (Figure 5):

• TOP: Goes to the start of the event

• >: Moves backwards incrementally within the event interval

• STOP: Stops the event run

• START: Starts the event run

• >: Moves forward incrementally within the event interval

• END: Goes to the end of the event

• Interval: modifies the data scanning speed, allowing a change in the exercise duration. This enables long-duration failures or events to be examined in less time than the real ones, or, conversely, allows more time to be devoted to looking at that part of the simulation that is of particular interest.

Furthermore, this control allows you to highlight any stage during the failure or simulation run, in order to reproduce only some parts of the event and repeat them as many times as you want. This is useful when you want to analyse a particular section, without having to repeat the whole failure, reducing the dead time and focusing on a specific area of interest. It is also very important for practising and to repeat the simulated failure or event which you want the staff under training to ‘focus’.

SIMULGEN runs on two PCs which are synchronised with each other. The purpose is to have more than one screen available and thus follow the failure or event at different stages in the process. In addition, it is possible to show the alarm screen in one monitor and the process screens in the other (Figures 6 and 7).

Although this tool lets you visualise the whole event, you are unable to change or modify operating conditions. Although it may seem to be a disadvantage compared with other simulators on the market, during a real plant start-up or shutdown the operator is in any case a mere spectator.

It is worth mentioning that the tool designed by Genelba is a “Full scope replica” that allows the operator to use exactly the same screens as in a real operation and any upgrade of the same. They can be easily modified by the programme manager.

Lessons learned

Advantages

• The program developed at Genelba allows the plant owner to keep people interested who would otherwise in all likelihood not be in position to experience real events.

• Operator training is based on real plant events; allowing operators to identify early symptoms of a repeated event.

• During the practice assessment, it is possible to pinpoint training needs on weak areas.

• Screens are always updated with different plant upgrades.

• The cost of the programme is far less than any other comparable simulator on the market.

• The tool allows you to analyse failures during a shutdown or trip and experience the event without absolutely depending on a static list of events. It is possible to recreate the failure and analyse each aspect, repeating the same part as many times as necessary.

Disadvantages

• The system does not allow the operator to change operating parameters.

• It has limited scope for failures and events (ie it only records what has happened in the plant).

• It is difficult to incorporate new, ie invented failures because it is not a mathematical model.

Benefits of revision

When learning a foreign language, in order to acquire a structure or pronunciation you need to ‘rewind’ and listen to a sentence several times. Likewise for the operator to acquire familiarity with the sequence of events during a plant start-up or shutdown or a turbine trip, he needs to recreate the situation several times to see what happened, depending on the event. Then the operator can immediately identify the first signs of a failure by comparing the real operation with what he has learned during the practice.

Practice sessions may be attended by people who have already been in a real failure situation, but experiencing it for a second time through the SIMULGEN helps them to identify situations and variations that were unseen at the time of the real event.

As for new operators, who have not experienced many plant start-ups, shutdowns or trips, practicing with SIMULGEN enables them to visualise all the steps to follow and to analyse what occurred without the pressure of a real event.

In addition, these practices help to pinpoint weaknesses in the knowlege of operational staff and consequently improve training on the required areas. And that works both ways – some operators participated in the development of this training tool by providing their knowledge on installation and processing

But all in all, to sum up, if you want to learn from the past, then – rewind and play.