Limerick Cuts Costs With PCR System
By Ann Chambers,
PECO NUCLEAR has instituted a drive to reduce total operating costs at Limerick Generating Station in Montgomery, Pa. One problem area for Limerick was the 28 maintenance-intensive, large-case, multi-point chart recorders associated with its generators. PECO determined that replacing the old chart recorders with two high integrity PC-based paperless chart recorders (PCR) would help decrease plant costs and boost availability. Limerick is one of the nation`s largest nuclear-powered stations, generating 2.1 GW from two 1.163 MW boiling water reactors as a cost of $14.52 per MWh.
Each PCR comprises a pair of networked workstations using Solartron`s isolated measurement cards (IMC) for data acquisition from the balance-of-plant inputs on each generator unit. This technology is fully proven, according to Solarton. There are more than 25,000 of these systems in use globally, providing distributed measurement of plant parameters such as temperature, strain and vibration in a variety of applications. The units offer high-precision measurements, digital status monitoring, and analog and digital control.
At Limerick, 18 rack-mounted IMCs provide the 256 channels needed for the temperature, conductivity, vibration, eccentricity and expansion measurements on key items of the generator auxiliary plant, including the feedwater, reactor recirculation, circulating water, main turbine and main steam systems. The IMCs are daisy-chained together via high-speed bus and interfaced into the PC workstations. The PC interfaces operate in either master or standby mode: installing two interfaces allows dual-redundant networks in distributed monitoring systems to be implemented for a modest investment.
In the Limerick installation, one workstation serves as the primary data acquisition host while the other functions as a backup. During normal operation, the PCR acts as the dedicated host and scans the network of IMCs every few seconds, furnishing data to the backup PCR via an Ethernet link. In the event that a fault occurs which prevents the primary workstation from being able to poll the I/O network, the system is configured with an automated switch-over enabling the backup PCR to assume acquisition with no data loss.
Computer-based data acquisition offers the opportunity to provide a broader range of functions than those available from paper-based chart recorders. Limerick`s main control room is fitted with two 21-inch, wall-mounted touch screen display units for each generating unit. The independent, high-resolution displays present all acquired data and calculated values in the traditional strip chart format. The touch-screen interface provides quick access to all recorder functions and allows operators to select various displays, including animated process graphics, scaleable XY trend graphs, bar charts and alarm summaries.
Each PCR provides four-level alarm detection on individual channels and on user-selectable channel groups, and allows the operator to validate whether data points have exceeded a predetermined upper or lower limit. Graphical displays highlight alarm conditions and invalid points, and activate external annunciators inside the unit control rooms.
Limerick Generating Station