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In another eco-friendly effort, Lockheed Martin is using Schneider Electric’s Telemecanique 5-hp to 250-hp VFDs tied to Rockwell’s Allen-Bradley CompactLogix PLCs to run two 600-hp, 300-psi biomass-fueled steam boilers in its helicopter and flight control plant in Oswego, N.Y. The boilers will burn waste wood and supplement the plant’s oil and gas boilers, which supply the plant’s HVAC and controlled-environment facilities, including temperature and humidity controls, liquid nitrogen pressure in its test chambers and several product inspection sites.
“A lumber mill down the street processes 200 tons of logs per day, and since 48% of each log is still scrapped, we’ll get about 95 tons per day of chips and sawdust,” says Michael Magill, Lockheed’s site energy program manager. “Because waste wood is one-half to one-third the cost of oil or gas, we’ll be able to cut that portion of our energy bill in half and save $125,000 to $150,000 per month.”
Rick Kirkpatrick, Baldor Electric’s variable-speed drives product manager, adds, “VFDs have always been able to take on varied roles, but recently they’ve become dependable and reliable enough—and energy costs have gone up enough—for them to be used in even more process applications, and because VFDs allow you to vary the speed of an AC motor using PLCs, many added benefits have emerged as motors have become efficient. For example, in pumps or fans bearing quadratic or centrifugal loads, using a VFD means you don’t need to deliver full power to the motor to save a lot in energy costs. Now, as the motor slows, we even have automatic energy optimization routines in the drives, and these can automatically adjust power and voltage to reach an optimal point.”
Mark Kenyon, marketing manager for ABB’s low-voltage AC drives, adds that coordinating multi-drives fed from a DC source can help save power because using 100-hp motoring and 100-hp braking won’t use up power losses in the form of heat, as happened in the past. Instead, multi-drives allow feed power back into their application and so recover 95% of the power cut into transmission.
“We’ve been using inverse-gate, bipolar transistors for very fast, 16,000-Hz on/offs, and I think we’re now up to about 30-hp drives on a DIN rail,” says Kenyon. “HMI and SCADA software and other interfaces to drives have taken the user experience from using screw-drives to change switches to programming drives like a cell phone or iPod. Network capabilities have gone from discrete inputs and pulling six power leads and 12 controls leads at $150 each to two-wire fieldbuses, and now to Ethernet and to wireless in the future. Finally, PLC functions in eight I/O blocks have been added to many drives, so users can just program a drive instead of a PLC.”
Users are implementing smart drives and motor controls in a wide variety of process-related and environmentally friendly applications. Here are some of the most interesting:
Centrifugal loads, such as those on pumps and fans, offer the greatest potential for energy savings when operating at less than 100% of required flow or pressure conditions, says Dale Basso, of Baldor-Dodge-Reliance in Greenville, S.C., in his presentation “Energy Team Meeting: Energy Savings with AC Motors.”
For example, a 100-hp induction motor running at 100% speed and 100% load will cost $27,139 per year to run, according to the following formula: (100 hp) x (1/95% eff.) x (.746 kw/hp) x (.08 $/kWh) x (12 h/day) x (360 day/year) = $27,139.
However, the same 100-hp induction motor running at 60% speed and 22% hp will cost $5,970 per year to run, according to the same parameters: (100 hp) x (0.22) x (1/95% eff.) x (.746 kw/hp) x (.08 $/kWh) x (12 h/day) x (360 day/year) = $5,970.
Consequently, the resulting savings of $21,169 per year occur because affinity laws for motors reduce the horsepower required to run a motor by the cube of its speed. In this case, 0.60 x 0.60 x 0.60 = 0.216.
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