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.
"By migrating our design to PACSystems RX7i hot standby CPU redundancy, we achieved a tremendous improvement in system performance," says Stephen Altman, Alstom's control system product engineer. "The improved processing speed translates to tighter regulation of the turbine and greater efficiency. Synchronized data flows much faster, which reduces our cycle times. For the plant, this means a bumpless system, so operations will stay up and the turbine/generator won't trip."
Better Insight for Better Power
To secure consistent, quality electric service in smaller process applications, many users rely on uninterruptible power supplies (UPSs), which are also gaining new monitoring and alert/alarm capabilities via their HMIs or other interfaces.
For example, Captronic Systems Pvt., Ltd. (http://captronicsystems.com) in Bangalore, India, makes automation testing equipment, and it recently needed to build a reliable, flexible, remote-monitoring system to acquire UPSs' electrical power and environmental health monitoring data. Consequently, it implemented National Instruments' NI LabView software, NI PXI real-time platform to serve as a remote terminal unit (RTU), and NI-DAQmx driver software to create a data acquisition (DAQ) system that can continuously monitor and control a UPS station in real time.
"The UPS industry is dramatically changing. Power providers and users concerned about reliability are increasingly focusing on power quality and protection and on power station health. One way to ensure reliability is to remotely monitor UPS power system performance," says Himanshu Goyal of Captronic. "So, we decided to build a system that can address most of the limitations and drawbacks of currently available systems and applications. With our system, users can remotely view real-time data from UPS power station devices and sensors, identify the causes of power system disturbances, and address problems before they cause interruptions. Our system can also integrate with virtually any UPS power station, and remotely monitor and control all UPS power station electrical parameters, including voltage, current, power factor, frequency, and phase angle. We can also remotely control and monitor security devices and sensors, such as humidity and temperature sensors, door open/close contactors, wet floor sensors, smoke sensors, hydrogen cylinder status sensors, and IP surveillance cameras."
Similarly, Arizona Electric Power Cooperative (AEPCO) is a rural generation and transmission cooperative in southeastern Arizona that owns and operates the Apache Power Generating Station in Cochise, Ariz., which serves more than 115,000 homes and businesses. The station has 605 megawatts of combined gross generating capacity, two steam units that can burn coal or natural gas, one natural gas-fired boiler and four gas turbines.
To manage and optimize its power operations, AEPCO's Apache station employs GE Intelligent Platforms' Proficy iFix HMI/SCADA software. The plant has used and upgraded Proficy iFix over many years, and it presently manages coal handling, water treatment, remote wellsites, DCS interface for boiler/turbine control, remote gas turbine control for peaking units and even plant security.
However, when AEPCO evaluated its turbine controls, three of the Apache station's four gas turbines were being controlled with older technology with no or very limited communications. "We wanted remote start and control functions without the added costs of RTU interfaces and configurations," explains John Franklin, AEPCO's logic systems administrator.
As a result, AEPCO used iFix to write its own communication drivers, which allowed hooks to the turbine control systems. This gave AEPCO the remote start and control abilities it was seeking without extra RTU expenses. "If we'd taken the RTU approach, it would have been almost as costly as a $150,000 total system upgrade, and we still would have had to pay for an HMI package." Just right.