Foxboro I/A Series DCS Control Systems

THE COMPETITIVE ADVANTAGE Invensys Operations Management offers premiere feedwater control systems using the Foxboro® I/A Series® Distributed Control System (DCS). Recent implementations have offered operation philosophy enhancements, improved startup and runtime performance and significant reduction of unplanned unit trip outages. 

These advanced control techniques allow for less operator required interaction, more time of automatic control - including during start-up and shut-down when most unit trips are caused - making the entire control system more capable of handling process upset conditions along with normal operation. 

BEFORE I/A SERIES AT THE OMAHA PUBLIC POWER DISTRICT Before the I/A Series DCS was installed on the feedwater controls at the Omaha Public Power District at Fort Calhoun Station, there were many operational

challenges. The controls were poorly tuned. Level perturbations were not uncommon during changes in power, with poor low level control. 

John Steinke, Senior Nuclear Design Engineer at the facility states that “Having splitrange 3-Element control on the bypass feed water valve as well as the main valve allowed for automated controls to handle the switchover from the bypass to the main valve. This reduced operator direct manual interaction, and thereby reduced operator challenges. We also rotate our Steam Generator Feedwater Pumps. The split range 3-element controls greatly reduce the perturbations associated with rotating those pumps. More precise tuning and control have maximized our unit’s capability factor (ability to produce electricity) while removing undue burden from the Licensed Operators who are operating the system. To date, we have not tripped based on the DCS or garnered extra down time.” 

There was a plant transient soon after the controls were installed in which the Hotwell Makeup Valve failed to open. The operators, by that time, overcame their instinct to place the feedwater system in manual, and instead let the controls take action. The feedwater DCS response was called “outstanding.” It would have been a much more stressful event for operations using the pre-DCS controls. There have been multiple similar incidents after which Operations commented that the unit would have tripped if the steam generator level control was not on the DCS.

Mr. Steinke also stated how the use of the DCS provided much more system and process information. They are able to use this type of data to ascertain process characteristics (valve and pump nonlinearities). The system then had the tools to compensate for these characteristics and provide a better response to control actions.