Main Generator Voltage Regulator
The main generator voltage regulator controls operation of the generator based upon load demand. In the past, the analog main generator voltage regulator routinely experienced equipment reliability issues, which resulted in the units being operated in a manual mode for extended time periods. The digital voltage regulator upgrade included an automatic digital system from ABB. This included redundancy to prevent plant trips and transients. As one example of the benefits of this upgrade, a developing issue on the measuring unit board was detected and the associated inputs were disabled in order to prevent a plant trip.
The main generator voltage regulator digital upgrade was completed in 2008.
Main Feedwater Pump Control System
Oconee uses two steam-driven variable-speed main feedwater pumps to provide water to steam generators for primary system heat removal. The main feedwater pump control system controls the speed of the main feedwater pumps using an input demand signal from the ICS. The digital upgrade of the main feedwater pump control system is the last upgrade that was recommended by the plant trip and transient review report.
Currently, design activities for this upgrade are in progress; implementation is scheduled to start on Unit 3 in 2010. The planned design incorporates redundancy in the control system to address equipment failure single-point vulnerabilities.
Process Control System
To upgrade numerous pneumatic controllers and instrumentation, the digital modernization project used a process control system based on a foundation fieldbus infrastructure. The pneumatic instrument loops are on the secondary side of the ONS units and impact the efficiency of the station’s performance. The conversion of each pneumatic instrument loop to an electrical instrument loop was not the preferred option due to limited space for installation of the cabling needed for the loops. Thus, the infrastructure was installed in the plant with remote access points that have trunk connections to the process control system. This infrastructure was installed with the conversion of approximately 50 instruments on each unit to foundation fieldbus technology.
The process control system used equipment from Smar Technology to set up plant infrastructure (Figures 6 and 7). This infrastructure addresses pneumatic equipment obsolescence and provides a means to continue with the upgrade of hundreds of additional pneumatic instruments over the next decade. The performance of the fieldbus controllers has demonstrated improvements over the pneumatic equipment with respect to equipment reliability. As additional loops are converted to foundation fieldbus on the process control system, improved plant efficiency is expected from better equipment performance and tolerances on the digital devices.
6. Hardware holders. Each Oconee Nuclear Station unit has four process control system field hardware cabinets. These cabinets contain all power supplies and linking devices to support up to 16 segments of H1 hardware. Courtesy: Duke Energy Corp.
7. Continuous connection. Each unit at the plant has a network/power cabinet that provides uninterruptible power and network connection between field cabinets and system servers for the process control system. Courtesy: Duke Energy Corp.
Completed in 2008, the installation of the process control system is a nuclear industry first for large-scale utilization of foundation fieldbus.
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