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PAPER MILL PIONEERS POWER
PROTECTION Competing in one of industry's most asset-intensive sectors, paper manufacturers must not only achieve efficient productivity but also maintain consistent throughput from their mega-million dollar mills in order to meet market demand. When a blackout hits a paper mill, the results can be disastrous: paper jams, fire, machinery damage, costly downtime, and sometimes miles of errant paper. One brief power failure can cost tens of thousands of dollars in production delays and repairs. Abitibi-Consolidated's Iroquois Falls, Ontario mill needed to upgrade to more reliable protection for one of its power generation stations, which feeds power directly to the paper mill via two 12 kV transmission lines - without power transformation. Abitibi-Consolidated is a global leader in newsprint and uncoated groundwood papers, with ownership interests in 27 paper mills in Canada, the U.S., the U.K., and Asia. The Iroquois Falls mill annually produces approximately 246,000 metric tons on newsprint and 46,000 metric tons of "specialty papers", including coloured newsprint, construction paper, and non-printing grades. Don Elliott (P.Eng.), Senior Power System Engineer chose to install a new type of protective relay from Schweitzer Engineering Laboratories, the SEL-311 Line Current Differential System, using their installed fiber-optic cable from plant to generating station. "We had a unique situation," explains Elliott, "We had power going from our two transmission lines (five generators) at one end...to the 12 kV bus, and our process loads at the other end. Because there were no transformers involved, the mill process was exposed to whatever problems nature gave us, such as transients and faults that occurred on our transmission lines. So, transient survival is paramount." Our paper machine rolls along at 1,200 meters per minute through a long winding process," says Elliott. "The slightest little bump or change in some component along the way can cause the papermaking process to be disrupted. There are electrical control systems involving voltage- and frequency-sensitive components that will drop out, or stop working if the normal 60 Hz signal isn't present." "Also, there are a lot of motor contactors in our process system, and if they de-energize due to a transient, they'll stay dropped out until there is intervention to bring them back on line. So, we really need to clear faults quickly. If we don't, we may have a mild ground fault that may not seem like a big deal, but within 2 or 3 seconds it becomes a 12 kV phase-to-phase fault not far from our bus, which is likely to cause a lot of equipment damage," adds Elliott. In the past, a transmission line fault would cause a trip, and the generation - and the paper machines would shut down. "This is a troublesome situation," Elliott says, "because transients endangered all mill processes, including dozens of pumps synchronized with massive rotating equipment." The power system at the Iroquois Falls mills was vulnerable because its "resistance grounded" 12 kV transmission lines lacked sufficient protection. "If we have a ground fault on a transmission line, the older protection was not sensitive enough to detect the fault. The fault would then remain, as an undetected ground fault, and ultimately propagate into a nasty phase-to-phase fault. Generally, then it would knock out the paper machines, which are synchronized with dozens of pumps operating with substantial inertia. If there was an insulation failure with any equipment, the resulting damage could be extensive, and it could include production losses as well as substantial repair costs." A Fiber-Based Solution Approximately two years ago, the Iroquois Falls mill replaced its 12 kV copper transmission lines with a new double-circuit ACSR (Aluminum Conductor, Steel Reinforced) cable. When the new line was constructed, we included optical ground wire (OPGW) containing 12, single-mode fibers into the circuit," Elliott explains. This enabled the use of fiber communications for protection. Protection of the new lines and cables was provided by Schweitzer's SEL-311L Current Differential System. "The SEL-311L was a good choice for line protection and automation," says Elliott. "This relay allows us to use our fiber-optic capabilities to implement efficient line current differential protection. We have to sense ground faults and clear them instantly." The negative-sequence sensing elements in the SEL-311L protection introduces a new level of fault sensing and high-speed tripping capability not available a few years ago. With easy to apply SEL-311L relays, users can protect lines and cables by applying three-pole subcycle current differential protection or optional single-pole differential elements for high-speed fault cleaning and improved system capability. This relay offers complete main and backup transmission line protection using line current differential, and a combination of four stepped-distance zones of phase and ground-distance elements in communications assisted schemes, with directional overcurrent element backup protection. Users can reduce their protection system costs by using the built-in distance and/or overcurrent backup functions. "We're also using the SEL-311L as a backup," Elliott says. SEL-311L standard features include programmable four-shot breaker autoreclose with synchronism and voltage check logic for optimal system restoration. Elliott says the relay's voltage check logic function is especially helpful in situations when the mill is separated from the grid. "We have a complicated system with large loads tied to our internal generators. If we get separated from the supplier transmission grid and completely blacked out, we have the ability to black start from our generating station. We will energize our transmission system and start building up our internal network from that point. The SEL-311L is the component that will basically supervise the closing of the line breaker and energize the line from the generating station," says Elliott. The Iroquois Falls mill also has an SEL-2030 Communications Processor installed, using Ethernet to interrogate the system for records and data from the SEL relays' Sequential Events Recorder (SER), directly from Elliott's office, rather than having to visit the remote equipment. The relays are connected to the SEL-2030, and the SEL-2030 communicates to the Ethernet system LAN. "We also have an "Arbiter 1093B" satellite clock input to the SEL-2030, so that all relay records and all the relay time bases are time-stamped to one millisecond accuracy. When we have an event, we'll reconstruct it and analyze exact information from all sources, correctly time-stamped to the same standard GPS-synchronized time," Elliott says. The current protection scheme at Abitibi-Consolidated's Iroquois Falls mill includes two SEL-2PG10 Phase Distance Ground Overcurrent Relays, five SEL-321 Phase and Ground Distance relays, one SEL-311C Distance Relay, four SEL-311L Relays, 12 SEL-300G Generator Protection Relays for added primary and backup generator protection, five SEL-351A Distribution Protection Systems, two SEL-501 Dual Universal Overcurrent Relays, and two SEL-547 Distributed Generation Interconnection Relays used for islanding detection. The SEL-2030 can accept IED information on any of its 16 ports, so the relays can be easily accessible to Abitibi's engineering staff for analysis of events and feature enhancement. Schweitzer Engineering Laboratories
ARTIFACT PROBING Accepting parts off the machine tool is a rapidly growing trend in manufacturing as companies strive to make 100% good parts in the lowest possible cycle time. For the machining center to serve as an inspection instrument, it must first be process capable - able to achieve accuracies that meet the design specification for the part to be produced. Most machining center users are familiar with laser calibration and CNC error compensation for systemic errors in linear and rotary axis motion. However, relatively few realize that the spindle-mounted probe can also serve as an error-compensation tool, says Dave Bozich, product manager-Machine Tool Probes for Renishaw, the inventor of contact probing and metrology technology leader. A probing technique called artifact or reference comparison lets machining centers test their positioning accuracy against dimensional masters to determine corrective compensations. It is especially effective for angular and transient thermal errors -- "two types of error that laser compensation cannot address," says Bozich. "Artifact comparison can be used to enable almost any machining center to hold tolerances near its repeatability specification, as well as compensate for thermal effects," he says. This basic metrology technique uses a pre-measured artifact as the reference master, he explains. To qualify as a master, the artifact's actual dimensions are measured on a CMM that is calibrated to a traceable standard. The artifact is then located in the machining envelope, typically as part of the setup or fixture. It should be made of the same material as the parts being machined to ensure it responds identically to thermal changes, advises Bozich. By probing the artifact before a critical machining pass, the CNC can check its own positioning against the known dimensions and program an offset to compensate for any discrepancy. "Artifact probing makes on-machine inspection seamless and ultra-accurate, and greatly increases the level of confidence in measurements," he says. This technique is used by Renishaw in its own manufacturing to hold tight tolerances on small, precision components in an automated machining system, points out Bozich. An artifact is indexed into the machining envelope as part of every batch of parts. At various points in the machining cycle, a spindle mounted probe measures the size of a feature on the artifact for geometry and thermal errors, enabling Renishaw's machining systems to run unmanned for 140 hours per week with full assurance that conforming parts are being produced. At the opposite extreme in part size, he says, Pratt & Whitney's commercial jet engine manufacturing operation uses artifact comparison to maintain accuracy to +/-0.010" on 118-inch dia. fan containment cases. In this application, features on the part fixture itself serve as the artifact master. After measurement on a traceable CMM, the artifact dimensions are stamped on the fixture for reference in determining offsets. The following techniques will optimize the accuracy gains from artifact probing, according to Bozich: * The reference surface must be located as close as practical to the feature machined and share two of the feature's three coordinates wherever possible. * Reference measurements should be taken in the same plane and directions as the machining operation to minimize dynamic errors. * The critical machining pass should immediately follow the reference comparison. * Tool length should approximate the length of the probe. All these conditions limit the opportunities for angular and thermal errors to affect the process and minimize accumulated error in the move from the master to the part," stresses Bozich. "Every machine has its own set of numerous small errors in its motions and structure," he says. "As a result, there is always a slight discrepancy between a CNC's programmed position and the true position of the tool tip - even after laser compensation has brought the two into closer agreement. Programmable artifact probing provides a way to further compensate for remaining machine errors. It gives process control feedback to enable positioning accuracies that can approach the machine's repeatability spec." Renishaw Inc.
KALTECH MANUFACTURING With the assistance of the A4 Groove and Turn System and other tools from Kennametal, Kaltech Manufacturing of Delta, BC has become a dominant metalworking shop in an area typically known for its sawmill, pulp and paper industry. Established in 1999 by Josef and Susan Kaltenegger, their two sons Hans and Jeff, and son-in-law Nico Morowat, Kaltech Manufacturing specializes in white-iron machining and many job shop contracts requiring versatility, specialization, and quick turnaround. One of Kaltech's primary customers makes massive steel components used in anchoring large cables on hydroelectric dams to secure them against earthquake damage. Kaltech's job is to supply the bolts needed to assemble them. The A4 Groove and Turn System used for primary roughing greatly reduces the time Kaltech needs to finish a large-diameter thread by removing the bulk of the material before finish passes are made with the Threading insert. Although A4 was engineered for turn, face, profile, OD and ID groove, bore, and cutoff applications, it is used in 95% of Kaltech's threading functions where large OD Square Threads are required. "The A4 tooling enables our machinists to precut the course thread on very large bolts," says Hans Kaltenegger, operations manager. Kaltech is also known for machining tough and very abrasive materials such as high-chrome steel products, which can be difficult to handle. Here, A4 is used to groove the white iron while withstanding the extremely high temperatures these workpieces generate. For the cable-tightening bolts, Kaltech's machinery has to remove a lot of material -- the thread on this extremely large steel bolt is a 460-mm x 14-mm trapezoidal thread. The shop needed a dependable tool that could handle roughing out the entire piece, then flawlessly finish the bottom or root. Kennametal Metalcutting Systems Engineer Ron Christiaens recommended the A4 because of its rigidity and depth-cut capability. At the time, we were ordering an insert from Sweden, and it just wasn't convenient or cost-effective," Kaltenegger recalls. "We didn't think there were any other inserts in North America," he continues. "After talking with Ron, we put A4 to work and it performed above and beyond our expectations." Kaltech was able to push the tool beyond its average range to accommodate their thread feed of 50 inches per minute, or 88 rpm. Machinists are now threading eight pieces per A4 edge, helping to significantly reduce production time by 70%. "There was no failure with the A4 because of its rigidity," Christiaens notes. "You need a tool with a lot of rigidity and strong cutting edges when dealing with a heavy-duty thread." "The bolts are manufactured from large amounts of material, so we often have a lot of overhang, which usually causes chatter," Kaltenegger adds. "A4 significantly minimizes the chatter and leaves a terrific finish." A4 is especially valuable in Kaltech's operations because it was designed for high productivity on machines with limited tool positions. Kaltech machines a lot of material on Cincinnati CNC lathes, so it's inconvenient and time-consuming for a machinist to stop production and change the insert. The double-ended A4 effectively has four cutting edges so the workload can be divided using just one tool. The versatility of A4 enables Kaltech to incorporate it into their operation as a job shop, including the machining of white iron. Kaltech machinists often receive overnight requests with little time for production planning. "Most of our jobs are one-day turnarounds, and we're able to meet our goals through the availability and durability of Kennametal tools, especially A4," says Kaltenegger. With immediate customer demands, Kaltech can't afford to stock specialized tools and does not have time to wait for them to be ordered and delivered. A4 is so versatile; one tool performs several functions, allowing exceptionally fast cycle times and no turret indexes. A4 completes most of Kaltech's grooving applications, so it eliminates the need to purchase extra tools that only perform specific operations. This lowers inventory and costs. "We run with two shifts, so the A4 tool is often left out on the shop floor," Kaltenegger says. "It moves around quite a bit, and if there's an application where it can be used, the guys use it." A4 is an extremely cost-effective tool to have around the shop. When used in machining a total of 50 cable-tightening bolts, A4 saved Kaltech roughly 25% in costs. Kaltech saved approximately 20% per part in labour costs and approximately $300 per part in insert costs. Hans Kaltenegger estimates a competitor's tool would have taken five inserts per part to complete the job. "It's amazing," says Christiaens. "A4 is saving Kaltech thousands of dollars in parts and production costs and enabling them to get quality jobs done on time." Kennametal Inc.
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Canadian Industrial Equipment News October 2005 |
May 16, 2008
Practicing
what it preaches, Renishaw mounts a reference artifact (lower foreground)
in the same fixture as workpieces, enabling dimensional checks for
possible compensation before machining of critical features. Renishaw's
NC1 laser toolsetter (bracketing the workpieces) verifies tool diameter
for comp adjustment. Renishaw created the horizontal rotary fixtures,
which allow three part faces (top and two sides) to be machined by
indexing 90° left or right from vertical. Besides milling and drilling,
Renishaw also uses vertical machining centers (VMCs) for turning and
boring by fixturing workpieces in special toolshanks that are mounted in
the spindle and rotated against fixed tool blocks. Automated load/unload
enables Renishaw to achieve 140 hrs/week of largely unattended processing
per machine tool.
A4
continuously threads the OD of large cable-tightening bolts. The tool
completes the entire threading operation, as well as finishes the root of
the thread. Since incorporating the four cutting edges of A4 into the
machining process, Kaltech is able to thread eight pieces per edge.
Ron
Christiaens, Kennmetal Metalcutting Systems Engineer (center) explains to
Josef (left) and Hans Kaltenegger (right) the threading capabilities of
A4. The Kennametal team assured the Kalteneggers the versatility and
rigidity of A4 make it the right tool for their job shop.
Josef
Kaltenegger (left) reviews a blueprint for a product with Christiaens
(right). As a job shop, Kaltech often receives last-minute orders, so it
relies on the versatility of A4 to complete a number of different jobs.
Kaltech
manufactures large bolts used to secure cables for hydroelectric dams. A4
has enabled the shop to save 25% in bolt production costs and has reduced
production time 70%
