Modernizing power plant control systems presents several challenges. The first is efficiently verifying that the new controls operate as specified. Because system installation is performed during a set outage period, new controls need to be as accurate as possible to meet important deadlines for timely plant startup.
The second challenge is training the staff in the operation and maintenance of the new equipment to ensure a smooth technology transition without interrupting service or performance. The third challenge involves continuing education for existing employees and qualifying new employees for safe and efficient plant operation.
PacifiCorp is upgrading process control and information systems at several of its plants, including its four-unit coal-fired Jim Bridger plant. The first unit was commissioned in 1974 and the last unit in 1979. Bridger is moving from traditional analog controls to the Ovation expert control system from Emerson Process Management.
So far, Units 2, 3 and 4 have been converted, with Unit 1’s conversion scheduled for 2006. When completed, the new system will control boilers, burners, data acquisition, scrubbers, steam turbines, motor control, boiler feed pumps and turbine control for the plant’s four units. The system will also control common systems such as water treatment.
To address these challenges, PacifiCorp installed a high-fidelity simulator while the first Bridger unit (Unit 3) was being upgraded to Ovation. A high-fidelity simulator provides a first-principles replica of plant parameters during steady-state operation and periods of dynamic response to equipment operation, control actions and malfunctions. The high-fidelity simulator is typically a complete mathematical model of the plant and is sufficiently accurate that it can be used for testing plant tuning as well as changes in the plant control system.
The four units and their respective control systems are nearly identical. The simulator is therefore a hardware replica of each unit’s Ovation control system, consisting of nine controllers, seven operator workstations and one engineer workstation. For PacifiCorp, this similarity translates into increased efficiency on two fronts. First, control system validation was streamlined because operators only needed to go through the process on the first unit, eliminating the need to validate controls as each successive unit was modernized. Second, the similarity meant the Unit 3 simulator can be used to train operators for all four units prior to startup.
PacifiCorp selected a stimulated simulator configuration, which includes the use of actual control vendor hardware, control logic and operator consoles. The primary advantage of this type of simulator is that all programs are identical to the unit’s controls. Operators are therefore trained on the actual control system, producing a highly realistic training environment. Simulators can teach users to fully understand plant control by giving them a thorough understanding how their actions impact plant operations and overall plant efficiency.
For example, PacifiCorp is able to simulate stuck valves, burned-up motors, broken couplings, plugged mills and feed pump trips. The ability to simulate such malfunctions keeps operator skills sharp and prepares them to respond quickly to emergency plant conditions. PacifiCorp is also training laboratory technicians, and has plans to train control and electrical technicians. “We’re also considering leasing time on the simulator to operators from other utilities,” said Gerry Aust, DCS Project Engineer/Plant Engineer for PacifiCorp.
Beyond training, the stimulated configuration allows control changes to be easily transferred from the simulator to the control system, and vice versa. As an example, changes to the control system can first be explored on the simulator, then uploaded to the plant hardware, thereby minimizing risks to the plant.
Building a high-fidelity simulator is a dynamic process consisting of a series of well-defined, precise steps. Because no two units operate alike, the development process is interactive, and calls for regular, ongoing coordination between the customer and vendor. PacifiCorp worked with Emerson to develop the simulator far in advance of the installation and had a partially working model eight months prior to the system coming online.
Emerson and PacifiCorp have been working hand in hand to build the simulator in a collaborative, ongoing process. For example, early on Emerson shipped hardware with a copy of another PacifiCorp plant’s simulator to Jim Bridger for initial testing. Emerson maintained a separate set of hardware at its Pittsburgh site, where the models were developed in tandem with the control system. Once the Bridger controls and model were at a preliminary, but working level, Emerson sent regular updates to PacifiCorp to load on their machines. This enabled PacifiCorp to train and provide feedback on an ongoing basis.
“During the initial development process, simulators are tuned on specs. However, real-world experience proves that each plant is unique in how equipment responds. So while the simulator development process is very detailed, it is valuable in that it can unearth - then fix - problems with the control system logic,” says Gene Abruzere, manager, simulator products for Emerson’s Power & Water Solutions division. “This ability to validate the control system prior to actual installation paves the way for a much smoother plant startup.”
Brian Gallagher, supervisor, plant operations for PacifiCorp, cites an example. In the midst of starting up Unit 4, a problem with the fuel-oil ratio calculation was discovered. PacifiCorp technicians and the Emerson field engineer tested the logic with the simulator, then applied the revised logic to the unit control system, thereby preventing damage. This potential problem would not normally show up unless certain conditions were met. However, one of the simulator’s functional capabilities gives operators a snapshot at any point in a process. This function also allows users to move forward and backward in a process to scenarios that have been saved previously. “This capability made it possible to detect, then correct, the problem before it happened,” explains Gallagher.
As part of the retuning process, finalized controls for Unit 3 were downloaded to the simulator, and the appropriate adjustments were made to the models. This final version of the simulator is expected to be up and running this summer.
“Experience proves that a customized simulator is a valuable and flexible tool to improve plant operations through operator training and engineering analysis,” says Abruzere. And virtual controller technology is the latest advance in simulation. In a virtual architecture, the actual Ovation hardware is replaced with virtual controllers that reside on a Microsoft Windows-based PC, known as the virtual host. This differs from the traditional simulator configuration that offers a hardware replica of the plant’s control system. Up to five virtual Ovation controllers can reside in one PC.
“Despite their reduced footprint, virtual controllers provide one-to-one functionality that mirrors the Ovation controllers comprising the plant control system,” explains Emerson Project Engineer Erin Flannery. “In other words, virtual controllers are identical to Ovation controllers in every way, except for where they are housed.”
The virtual controllers offered by Emerson Process Management utilize the control system’s standard engineering tools and operator interfaces, and run the point scanning, alarming and complete algorithm set, including advanced control algorithms as they exist in the plant’s controllers. And because the control logic is identical between the simulator PC and the Ovation control system controllers, the user is able to quickly and easily make control changes, and efficiently transfer these changes from the simulator to the control system. p