2015 CCJ Best Practices Awards: Best of the Best
When Dogwood Energy Facility placed an order for a new vented lead/acid battery system management decided to investigate the benefits of supporting that purchase with a continuous monitoring system. O&M personnel typically agree that battery systems are among the most labor-intensive devices in the plant concerning monitoring and testing. This is ironic given their static nature and infrequent use. But because of the importance of batteries during emergencies, and the amount of monitoring and testing required by regulatory authorities, they are heavily scrutinized during NERC audits and are an easy target for violations.
Solution. Dogwood Energy, a 660-MW 2 ×1 combined cycle in Pleasant Hill, Mo, managed by Steve Hilger, looked into the benefits of installing full-time monitoring. Most obvious was the convenience of collecting bank voltage, cell voltage, float amps, and cell temperature at one location; however, staff wanted to justify monitoring based on more than just convenience. Plant personnel learned that continuous monitoring offered significant safety benefits as well.
Like many powerplants, Dogwood has a battery arrangement where the upper row of cells is set above and stepped back from the lower row. The person taking readings often requires a ladder to reach the upper row and then has to lean across the lower row of cells. This must be done for each of 30 individual cells. Any time you are dealing with individual cells there is the risk of shorting one or more cells by contact with the posts of the batteries.
Maintenance of vented lead/acid batteries includes taking specific-gravity readings frequently. This means dealing with the electrolyte, an acid. Protective gear is required to protect against chemical burns and other injuries. So how does having a monitoring system address taking samples for specific gravity and dealing with the electrolyte? IEEE 450-2010 states that “For technologies other than lead antimony, if battery float charging current is not used to monitor state of charge, specific gravity must be checked (number of cells depends on the periodicity of the test being performed).”
Dogwood wanted its diagnostic system to monitor the float current of the plant’s lead/calcium batteries. This would eliminate the need for personnel to perform regular testing of the electrolyte—thereby eliminating the chemical hazard as well as the chance of inducing a short in the battery system by reaching over cells. Another benefit is the increased efficiency of data collection attributed to pure convenience. The system would allow personnel to download data for regular trending and reporting over long periods. The monitor also can be programmed to alarm at a specific value of a specific variable.
Results. Dogwood decided to install two monitors on its new lead/acid batteries for the steam turbine system, based on the decisions mentioned above. Plans are in place to extend the monitoring capabilities to the control room this year. Also, monitors for the gas-turbine battery systems will be installed in 2015, concurrent with battery replacements on those units. Even though readings will be made remote from the location of the actual batteries, it is Dogwood’s philosophy that battery monitoring does not replace the need to conduct regular local visual inspections; however, the personnel risks associated with regular visual checks have been eliminated or greatly minimized.
