1 Raising automation level at a Swiss HPP Rene Neubert, Sales Director Valmet, Automation business line Austria Abstract Energie Wasser Bern Felsenau hydroelectric power plant is situated on the Aare River in Bern, Switzerland. The electricity capacity of the Felsenau power plant is 11.3 MW. The annual production amounts to about 70,000 MWh. The plant was completely renewed in late 80 s to an automated bulb-turbine plant. Earlier control system faced problems, since several electronic components were no longer available. The power plant was forced to replace the control, protection and some other systems. It proved to be most cost effective to modernize the entire control system at the power plant and the Engehalde dam. Fortunately, this also became an opportunity to raise the automation level of the plant. In its new configuration the raised automation level includes, in addition to conventional functions, advanced functions for fault clearing, simulator for operator and maintenance crew training and advanced river/dam control. The new control system, while reaching a high level of integration, is still maintaining the similarity to previous operator interface, making the transfer from earlier to new system as smooth as possible.
2 Valmet solution for hydro power plant automation Valmet was chosen as an automation supplier for the Felsenau project. Valmet s proven DNA DCS (Distributed Control System) is the core of the solution. Valmet DNA Hardware delivery consisted process station cabinets for fully redundant control system, Io cabinets for approximately 1500 I/O s, fully redundant network and modern control room equipment including operator stations, large screens and information station for historian analyses. Figure 1. Valmet DNA automation system for hydro power. The system has been used both to small hydro power as well as controlling larger damns. Valmet has 90 years experience in power automation and was one of the first DCS suppliers in the market over 30 years ago.
3 Turbine controller, including hydraulic positioning is implemented in Valmet DNA. Modern DCS system has very short cycle times from measurement to control so for example hydraulic positioning can be done directly with the DCS process controller. As well condition monitoring system is implemented in Valmet DNA directly using same family IO cards and process stations as rest of the system. Thus there are minimum amount of unreliable links in the system. Figure 2. Turbine controller display showing critical machine condition information. All information is easily available and visible for the operators. According to customer this was one of the key benefits compared to old system.
4 More complicated controls or monitoring solutions are easy to implement in a DCS system engineered for advanced process control applications. Valmet DNA has been used as a platform for Model predictive control and Fuzzy logic for twenty years already in order to optimize paper machine and complicated boiler controls. Thus even complex and demanding water balance controls or penstock monitoring and leakage detection calculations are easy to implement. Plant information management tool stores all alarms, events and binary & analog data for years long. Different reports and analyses are created for plant standard reporting and disturbance handling. Figure 3. Valmet DNA automation solution covers all required functions of the modern hydro power plant. Solution can be tailored to meet requirements of small hydro power as well as larger damns or complicated river cascades.
5 River/dam control The river in question is forming a large bend in a densely populated area. The power plant is situated in a favorable place, shortcutting the river through a 100 m³/s tunnel, creating 10 14 m of head for the plant. Figure 4. Schematic drawing of the Felsenau power plant. The natural river bed must remain river-like, so the control system must give the river its minimum flow and prevent flooding. The natural bed water is run through a small tubular turbine and through four gates. The amount of minimum water is dependent on natural flow and of calendar, varying between 10 12 m³/s. The upper water level must be kept at a fixed level (± 5 cm) at the smallest possible fluctuations and discharged over the river bed or the turbine. The power plant has one 11,5MW Kaplan Bulb turbine and sufficient overflow to discharge 65 m³/s of water. The critical upper water level measurement is triplicate and using 2 out of 3 method. The control is duplicated so that losing one process station doesn t affect the control. Naturally also electricity supply is from two independent sources. The complete plant regulation is rather complex and delicate matter. The water levels and flows must be kept as static as possible and still be able to cope abrupt changes as emergency
6 shutdowns. All set point changes are to be done via adjustable ramps while reacting to set limits. Especially vulnerable is the plant intake tunnel. The plant can be driven on flow control or level control. After operator has set the wanted value, the system will do the rest automatically, keeping the river within permitted boundaries. In extreme cases, the system changes control mode to prevent unwanted situations. And of course when within permitted limits, the system maximizes the power production. Compared to the old system, the new raises the automation level of the plant by lessening the probability of operator fault and giving more accurate control of the river, thus contributing to whole community welfare. Fault clearing functions In most cases a fault at a hydro power plant is easily tracked. A preset value has triggered the machine; the cause is found and fixed. In some cases though, it can be very useful to find the root cause of things, what originally caused the problem. Was it operator actions, maybe outside circumstances? In the replaced system the fault clearing was conventional 80 s style, when common event and alarm lists replaced the indicator light panels. Instead of mere fault/position indication, it was now possible to gather history through a paper printer. For fault clearing this was definite improvement. In the new control system, however, there are still further improvements. Each digital alarm/event is time stamped at the I/O card with 1ms resolution and the protection relays are connected via IEC 61850, also giving time stamped information. Now the operator has a clear sequence of events, times are not depending on cycle times, bus load capacities, et c. Data is stored in the system, where it can be processed in multiple ways, giving much wider view of the power plant state and history. Sometimes for fault clearing, it becomes necessary to study in detail one or few value development history, the trend. In delivered system trending functions also include indication for subject alarms and events, controls and positions and diary notes. So now we have all relevant subject information in one view, thus again making decision making and fault clearing easier. The best new feature in the control system for fault clearing is the replay function, a sort of time machine, with which the operator can go back in time to really see what happened. The operator can move the control screen back and forth in time to establish a clear idea of what happened. Then he can file it and share it with experts to gain further knowledge or with colleagues to spread best practices.
7 Training simulator Energia Wassern Bern recognized need for operator training for the new system. They decided to include a training simulator for the delivery. In addition to operator training, main targets of the new simulator were sufficient process simulation and increase of the in-house knowledge of the new control system. Figure 5. Start display of the operator training simulator. The operator station has the same structure as the operating stations in the power plant with the same software. The visualization and operation are thus identical. Valmet DNA programming language is used for the process model programming. This has one critical advantage for the plant, process model life cycle is as long as automation system life cycle and models can be serviced by plant own automation engineers. Simulator covers all power plant sub-processes and reacts realistically to the inputs of the operator at the control station. The process simulator has also predefined scenarios with variants. The training simulator consists of the following subsystems: Operator Station Automation unit Process Simulator Storage space simulation Test Network The simulator was set up in the office separately from the actual control system. All relevant reactions of the process are simulated realistically. The automation unit is decentralized in the real plant, for the simulator all is included in one unit, still containing the same functions. The hardware is of the same product line as the automation units in the power plant.
8 The storage space simulation is a separate specialized software also installed in the Process simulator PC. The storage space simulation provides real-time water levels and flow rates. This allows dynamic processes (threshold operation, turbine quick-closing) simulation. The storage space and behavior is a function of inflow hydrographs simulated in the process simulator discharge data, taking into account the flow parameters. The simulator enables operator training in a safe environment. Skilled operators do correlate with more efficient production, better environmental aspect, less downtime and less equipment wear. Conclusions Due to strong increase of renewable sun and wind power, hydro power has important role being controllable, flexible and fast mean of controlling frequency. This increases demands for hydro power plant control systems. At the same time while electricity prices are falling, costs for operation and maintenance are under ever increasing focus. More must be achieved with fewer resources and many of the hydro power plants are operated remotely. In practice this leads to centralizing resources and, in some cases, outsourcing. Inevitable consequence in the long run is less time and understanding per power plant for both the operator and support staff. In this case EWB Energie has taken important steps to utilize modern control system and its functions in a way that enables operators increase safety and productiveness of the Felsenau Power Plant. Valmet DNA automation system has required functions for both small and simple power plants to more complicated large damns or river cascade systems.