January-February 2019 NPJ

40 NuclearPlantJournal.com Nuclear Plant Journal, January-February 2019 Path to Digital... ( Continued from page 39) The power cabinet monitors and analyzes the electrical current flow to the control rod drive mechanism coils to confirm that the control rod drive mechanism grippers operate during rod motion. In essence, it confirms that one control rod drive mechanism gripper, whether movable or stationary, latches onto the rod before the other gripper unlatches from the rod during rod motion, preventing rods from dropping due to sluggish operation of the control rod drive mechanism. Additionally, since the existing single set of phase transformers is replaced with two redundant, simplified phase transformers, another single fault is eliminated. This is because the movable gripper can retain phase crossing and perform subsequent holding of the control rod in the event of the complete or partial failure of the stationary gripper power. This complete redundancy also allows maintenance to be performed on half the system. CE Plant Application For CE plant applications, replacement of the power electronics is recommended due to age, obsolescence and operating experience. As such, the ARCH control cards are incorporated into a new drawer assembly that will replace all the existing CPP power electronics or the CEDMCS power switch assembly and subgroup logic. The assembly is intended to mount into existing cabinet structures with minimal modifications. Coil Power Management Drawer This drawer is capable of driving four independent bridges that provide power to four rod drive coils. The drawers are segregated by coil type, which allows for holding to be maintained on an alternate gripper while the main holding gripper is de-energized and removed, eliminating the need for a hold bus. In addition to replacing the power electronics, the standard Ovation logic cabinet replaces the common logic electronics and portions of the power switch assembly subgroup logic previously in the CEDS cabinet or the CEDMCS cabinets. Field cabling is re- used as much as possible to minimize installation time. System Enhancements ARCH is a closed-loop system that actively monitors the current through the coils via shunt resistors and requires no calibration. Current Combustion Engineering systems are vulnerable to voltage drooping and dropping due to fixed-control points; ARCH is capable of adjusting the voltage output as necessary to maintain the required current levels. Engagement detection and all other functions of the previously provided `Advance Control Element Drive Mechanism Timing Module upgrade are built into the ARCH microcontroller. Hall Effect sensors are no longer needed, as current is directly monitored from the shunt resistors. Modification of power distribution to each drawer will remove single point vulnerabilities associated with bus duct circuit breakers, fuses and individual rod circuit breakers on the power switch assemblies. The upper gripper and lower grippers are powered separately so that a common fault cannot disable both grippers. In the event of an upper gripper fault, the lower gripper will engage to prevent a rod drop or slip. Coil Health Monitoring is also an option for Combustion Engineering plants; a separate printed circuit card can be added to each coil power management drawer. Coil Health Monitoring doesn’t impact system control but provides advanced coil health feedback such as the effective energized inductance as an indication of overall coil health. All Applications Ease of Surveillances, Diagnostics and Troubleshooting With the capability of a localized microcontroller, cabinet parameters are continuously monitored and displayed at an Ovation workstation where operators can view detailed alarm information, coil current and voltage, cabinet temperature and calculated holding CE Drawer.