Just as humans need quality coffee and carbohydrates served just the way they like them, process plants and applications need quality power served just right too.
And whether this electricity comes in big chunks from utilities via increasingly smart grids, or when it's sliced and diced into just the right profiles to help variable-speed/frequency drives run their motors with the most efficiency and least wear, the overall mission all along the circuit is still the same—consistency.
Luckily, most power monitoring and management tools are gaining intelligence from the same revolution in data processing that's been smartening up all process control and supporting devices. Their more capable microprocessors and software are giving users better, faster diagnostics and enabling them to control and optimize their power at all levels from generation to consumption.
For instance, Holcim El Salvador's cement, concrete and aggregates plant in La Libertad recently implemented ETAP's Real-Time intelligent, load-shedding (ILS) software to improve its performance and reliability (Figure 1). The cement plant's substation is connected to its local grid via a 20-kilometer transmission line, which is subjected to heavy rains and lightning strikes from May through October and averages 20 circuit-breaker/transmission-line trips per month during this period. The plant strives to maintain 18 megawatts of process load running 24/7 and also provides 10 megawatts back to the grid to offset peak loads, but it experienced 20 power outages in the year before adopting ILS.
Because its old load-shedding system was too slow and unable to respond to these diverse conditions, Holcim El Salvador implemented, commissioned and tuned ILS over two years and only had one power event during that time.
"ILS gathers system parameters throughout our electrical network, including generation and loading status, to adjust its ever-changing, load-shedding scenarios. By the time an event occurs, the substation's local controls have already been instructed by ILS to switch loads to properly load the generators and keep the plant running," says Douglas Aviles, Holcim El Salvador's power plant manager. "ILS remains several steps ahead of event conditions by constantly monitoring and modeling the entire electrical system, taking into account maintenance cycles, operational changes or any last-minute changes in process control. The system automatically senses changing conditions and responds with new instructions on a continuous basis, allowing the system overall to react to an event within 100 milliseconds. Our risk from unscheduled power outages has almost disappeared."
Software Revives Mill Turbine
Likewise, Alstom Power's Controls and Commissioning department in Midlothian, Va., recently overhauled an aging turbine/generator powering a major paper manufacturer's mill. The turbine/generator is a single-casing, three-pressure section machine, capable of running at full load with steam inlet conditions of 1,800 psi at 1,000 ºF and 800 million pounds per hour (MPPH) of steam-mass flow. Its two-part turbine control system (TCS) includes a closed-loop turbine controller and open-loop turbine safety system and auxiliary controllers. The safety system provides a second line of protection against potentially dangerous conditions, such as over-speed, loss of vacuum and bearing oil supply failure.
However, obsolete spare parts and maintenance issues were increasing unplanned downtime on the early-1980s generator, so the mill asked Alstom to help replace its outdated electronic and hydraulic systems. This TCS upgrade included redundant turbine, auxiliary and protection controllers, an automatic voltage regulator (AVR) and a new HMI. These controls are part of Alstom's P400 turbine/generator control system, which also uses GE PACSystems RX7i programmable automation controllers (PACs) with hot standby CPU redundancy from GE Intelligent Platforms
PACSystems RX7i optimized the mill's turbine start-up and performance, constantly monitors and adjusts for thermal design constraints, reduced maintenance and spare parts costs, improved diagnostics to reduce downtime, improved regulatory reporting, and gave the mill nearly 100% uptime power. Also, Alstom was able to migrate existing code from its previous TCS designs to the PACSystems RX7i and PACSystems Control Memory Xchange (CMX), which reduced execution time from 40 milliseconds to 14 to 16 milliseconds.