Today`s simulation systems go beyond “try before you buy”
By S. S. Godbole, Framatome Technologies
Modern technology brings simulation benefits to a power plant from plant design to long-term maintenance and training
The fast-paced advances in affordable personal computer (PC) hardware and software have revolutionized simulation technology. Powerful simulation tools have emerged because of the ever-increasing speed, memory, and storage capacity of PCs and the availability of user-friendly, high-level and often graphic-based software. With the advent of Internet communication, using these tools in a team environment has never been easier or more effective. The PCs, software simulation tools and interactive environment have affected the life cycle of existing, retrofit and new power plants in many positive ways and will continue to do so in the future1.
A typical simulation development system2 and its resulting simulations are usually PC based, and much of the development process is automated. Users configure models graphically by selecting icons that represent plant components (also called modules) from a point-and-click menu, placing them at desired locations on the screen and interconnecting them to represent the plant arrangement. They can then customize selected icons by entering operating and physical data and tunable parameters for the components in associated data forms (Figure 1).
The completed model can be executed on a single PC, a multiprocessor PC or a network of PCs in an interactive environment that allows simulation control, online parameter change, response monitoring and analysis. For example, users can stop or resume the simulation, open or close valves, start motors, change plant load and introduce failures (Figure 2). Most systems allow users to monitor the response to such changes graphically (Figure 3) or on simulated dials and gauges. Users can also perform analyses such as performance statistics, time constants, stability and linear analysis. In applications such as training, the model responds in real time, at the same rate as the actual plant. Simulation developers or users can integrate the distributed control system (DCS) and man-machine interface (MMI) emulation software with the plant model to enhance the effectiveness and appeal of the simulation.
Plant design application
For new plants, retrofits and repowering applications, progressive plant owners, project managers and architect engineers have begun to include simulation in the project scope. During the initial stages of power plant design and engineering, project engineers can use simulation to verify the interfaces between equipment supplied by different vendors and existing and new equipment. Simulation also allows them to verify and optimize performance during transients (e.g., the ability to ride through load changes, equipment lineup changes, malfunctions, upsets, etc. without tripping and without challenging safety systems). A fair amount of detail, such as control and safety system logic, interlocks, permissives, overrides, and logic for equipment lockout and auto-backup (standby) can also be developed using simulation before the DCS vendor configures the control system. Using simulation at such an early stage in the power plant life cycle brings to the surface sensitive areas of plant operation or shortcomings of the design and equipment specification, and allows time to fine tune the design or to prepare backup plans. These early warnings minimize subsequent surprises, potential cost escalation and schedule delays. In rare cases, simulation may indicate everything is satisfactory; even then, this finding gives added assurance and peace of mind about the adequacy of the plant design.
By developing a simulation at this early stage, the project team can incrementally upgrade it for use during other stages in the plant life cycle. For example, during the initial stage, the model need not respond in real time. However, during later stages (during DCS development, for example), the simulation must be a real-time model.
Engineers also use power plant simulation in real-time mode to develop the DCS for new plants and for changeout of existing analog control systems. At an early stage, the developers emulate much of the DCS functionality, including the MMI, to debug the control logic and MMI configurations. Then by loading the debugged configurations into a mini-DCS (a small, but adequate, subset of the final DCS hardware), and connecting the configurations with the plant simulation, they can further verify the efficacy of configured control logic and MMI.3 Such a system is called a stimulated system. This ap proach makes the development, installation and startup of the DCS a smooth process, minimizing the possibility of cost overrun and schedule delay. It`s possible this ap proach could significantly shorten the on-site plant startup time.
A DCS vendor can also use this approach to develop a DCS application. Because the DCS vendor has full access to his proprietary library of control and MMI function blocks and protocols, he can take advantage of both emulation and stimulation to significantly shorten the DCS delivery time by doing control logic configuration and hardware assembly in parallel.
Training simulator applications
Using a plant simulator to train plant operators and instrumentation and control maintenance staff prior to starting up a new plant or system shortens the startup phase and reduces the likelihood of human error. For training application, the real-time simulation is cast in a compact simulator configuration consisting of several PCs interconnected through a local area network to simulate continuous and analog processes, to emulate sampled-data processes and to provide an instructor interface. For stimulated simulators, the actual DCS and MMI take the place of the emulated ones.
After plant startup, plant managers can use the training simulator to train new operators and recertify existing operators. They can also use the training simulator model and the models used during the design phase for studying and debugging better ways of operating, monitoring and controlling the plant; for analyzing unusual behavior observed during plant operation; and for verifying plant equipment upgrades. Even for existing plants that are further along in their life cycles, it is not too late to benefit from simulation.
Where to get it
Project managers can procure PC-based simulators either directly from a simulator vendor or from a DCS vendor as a part of the DCS order. In a plant-design-stage simulation, the DCS vendor may not yet be selected or the project team may prefer to keep the DCS options open until later. In that case, they must procure the simulation from a simulation vendor or develop it in house using simulation tools provided by simulation vendors. DCS vendors tend to offer stimulated systems, whereas simulation vendors tend to offer either emulated systems or partially stimulated systems. Key factors influencing the choice include plant simulation and simulator expertise, platforms supported, simulation features, third-party (independent) review of control logic and MMI configurations, saving of capital resources by emulation, single-point responsibility, and for a stimulated simulator, the availability of software for interfacing simulator equipment with DCS.
As PC and simulator technologies advance, expect features like artificial intelligence, virtual reality and multimedia to be incorporated into simulations. For example, simulation tools may include a typical physical and operating database for common equipment such as boilers, turbines and pumps, eliminating the need to wait until all specific data are available. A user may start with a simulation having a combination of specific and typical data and progressively substitute specific data as they become available. Reference models may be available online from which he can copy, paste and edit to accelerate the model development process. Further, the user may integrate the simulation environment with expert system applications to optimize plant performance and provide online operating guidance to prevent catastrophic errors or efficiency loss. With virtual reality and multimedia, simulation developers will be able to effectively take into account site- and plant-specific aspects to produce a realistic simulation that has many actual plant cues.
Spinoffs of modern simulator technology will find their way into plant operations and maintenance. For example, the DCS database can be put into a user-friendly graphical database for quick online queries, searches, editing and drawings. Remote monitoring tools may also be available to provide inexpensive remote monitoring capability for the plant.4
State-of-the-art simulation technology has given power plant designers and operators the powerful, low-cost option of “try before buy.” This option is indispensable in producing optimized plants at lowest cost in the current environment of open architecture and global participation. More and more plant owners, project managers and architect engineers will include simulation in the scope of new, repowering, or retrofit power plant projects, making it an integral part of the power plant life cycle. z
Sadashiva S. Godbole is an advisory engineer and expert in Framatome Technologies` simulation services unit. He holds a doctorate in electrical engineering and a master`s in engineering administration. Godbole has formerly held positions with Bharat Heavy Electricals (India) Ltd. and has been involved in simulation and control systems for the last 26 years. He also consults internationally with customers on power plant simulation and control applications, and conducts training in this field. Mr. Godbole can be reached at (804) 832-2696, [email protected]
.com, [email protected] or at Mail Code OF52, Framatome Technologies, Lynchburg, VA 24506-0935.
1. NEED AUTHOR NAME, “Plant design: meeting the challenge,” Chemical Engineering, March 1996, p. 5.
2. McKim, FIRST NAME and M.T. Matthews, “Modular Modeling System Model Builder,” presented at the 31st Intersociety Energy Conversion Engineering Conference, Aug. 11-16, 1996, Washington, DC. (pp. 2,039-2,044 of Proceedings).
3. Rostron, Bill and Phillip Liddle, “Oconee Nuclear Station Control System Upgrade,” Nuclear Plant Journal, July-August 1996, pp. 40-42.
4. Sneed, FIRST NAME and G.F. Malan, “Remote MMIs –DCS MMIs Displayed on Remote PCs,” 1996 International Fossil Simulation and Training Meeting, April 8-12, 1996, New Orleans, La.
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