INSTRUMENTATION & CONTROLS
Upgrading to digital--twice
The E.W. Brown Generating Station of Kentucky Utilities (KU) is located in the town of Burgin, about 30 miles southwest of Lexington. The plant's three generating units burn an average of 1.5 million tons of coal annually, delivering some 750 MW of power (Figure 1). By 2005, the control technology that had been installed 35 years prior was beginning to show its age and replacement parts were becoming harder to find. KU's management concluded that the long-term benefits of replacing E.W. Brown's aging control systems warranted the investment. The goal became keeping the cost as low as possible.
1. Time for a change. All three units of Kentucky Utilities' E.W. Brown Generating Station need to have their controls systems upgraded. Some systems are three decades old, and replacement parts have become scarce. Shown is Unit 7. Courtesy: Invensys Process Systems
"We figured we had five years to upgrade three systems," said Jeff Fraley, plant manager. "Because of budget constraints, evaluated cost was a major criterion in our vendor selection process. Another was the supplier's ability to evaluate our control strategy and help us achieve optimal performance in both the short and long terms."
Most of the controls were so old that they required total replacement, from field device wiring and terminations through the controls. However, the field wiring, terminations, and cabinets of the data acquisition controls serving one of the Brown plant's three units—Unit 7—were still intact (Figure 2).
2. Feeling its age. After 35 years of loyal service, the old control room was ready for a facelift. Courtesy: Invensys Process Systems
Of the controls vendors from which KU invited bids, only the Foxboro unit of Invensys Process Systems said it could deliver a modern digital control system that would preserve Unit 7's existing infrastructure. Doing so would not only save the considerable cost of rewiring, but it also would reduce costly downtime by enabling the change from old to new controls to happen in hours, instead of the weeks estimated by competitors.
"We were able to switch from our legacy 1,334-point Westinghouse WDPF distributed control system [DCS] to a new I/A Series system over a weekend," said Greg Wilson, KU Brown project manager. "What's more, the job was so easy that we did it ourselves."
Carpe diem
Because the I/A Series I/O modules plug easily into existing cabinets and racks, there was no need to move process wires or enlarge the system's footprint. All that had to be added at the Brown plant were controllers and workstations (Figure 3).
3. Fits like a glove. I/O module replacements fit into existing cabinets and racks, saving the existing wiring and installation time. Courtesy: Invensys Process Systems
To minimize service disruption during the switchover, the plan was for Foxboro engineers to assist with the installation during a scheduled shutdown. But when an unexpected tube leak forced an earlier shutdown of two days, KU engineers and technicians seized the opportunity and completed the entire installation over a weekend using their own maintenance technicians.
The techs handled the cutover flawlessly, plugging in the cards rack by rack and then testing all of the racks individually.
Having fully upgraded the data acquisition system (DAS) controls, the team then made good use of the later, scheduled outage. They reautomated Unit 7's boiler, feed pumps, motor controls, and balance of plant using I/A Series technology and even extended the system to the turbine to optimize its performance and that of the overall unit. That required the addition of new Foxboro Fieldbus I/O modules, controllers, and workstations, which were integrated seamlessly with the plug-in Foxboro replacement of the legacy Westinghouse WDPF system.
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