Abitibi mill plugs in power protection.

Abitibi-Consolidated is working toward the complete automation of its electric power system at its Iroquois Falls, Ontario, Canada mill. The system now includes SEL protective relays and communications processors as part of an upgraded power scheme designed to improve uptime, efficiency, and safety. Several years ago, the mill decided 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 has annual production of 246,000 metric tons of newsprint and 46,000 metric tons of specialty papers, including colored newsprint, construction paper, and non-printing grades.

According to Don Elliott (P.Eng.), senior power system engineer, the mill chose to install a new type of protective relay from Schweitzer Engineering Laboratories (SEL), the SEL-311L Line Current Differential System, using their installed fiber-optic cable from plant to generating station. "We had a unique situation," explained 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 on our transmission lines. So, transient survival was paramount."

"Our paper machine rolls along at 1200 meters/min through a long winding process," Elliott continued. "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 nominal 60 Hz signal isn't present.

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"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," he continued. "So, we need to clear faults quickly. If not, 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 can cause equipment damage."

In the past, a transmission line fault would cause a trip, and the paper machines would shut down. Said Elliott, "This was a troublesome situation because transients endangered all mill processes, including dozens of pumps synchronized with massive rotating equipment."

The power system at the Iroquois Falls mill was vulnerable because its "resistance grounded" 12 kV transmission lines lacked sufficient protection. "If we had a ground fault on a transmission line, the older protection was not sensitive to detect the fault," said Elliott. "The fault would then remain, as an undetected ground fault, and ultimately propagate into a nasty phase-to-phase fault. Generally, it would then knock out the paper machines, which are synchronized with dozens of pumps operating with dozens of pumps operating with substantial inertia. If there was an insulation failure with any equipment, the resulting damage could include production losses and repair costs."

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 explained. 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. 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 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 clearing and improved system stability.

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 said.

SEL-311L standard features include programmable four-shot breaker autoreclose with synchronism and voltage check logic for optimal system restoration. According to Elliott, the relay's voltage check logic function is especially helpful in situations when the mill is separated from the grid.

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"We have a complicated system with large loads tied to our internal generators. If we get separated from the supplier transmission grid and are blacked out, we can 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," said 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 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," said Elliott.

The mill's current protection scheme 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 Over-current Relays; and two SEL-547 Distributed Generation Interconnection Relays.

Elliott's team has standardized on SEL products. One reason is Schweitzer's service, according to Elliott. "I have a long and stable relationship with Schweitzer," he said. "They have great product coverage and a high level of service, including field technical support. During our upgrade, I got fast and reliable answers to technical questions about configuration choices."

ABOUT SEL:

Schweitzer Engineering Laboratories (SEL), Pullman, Washington, USA. SEL designs, manufactures, supplies, and supports products and services for power system protection, control, and monitoring. SEL System and Services Division (SSD) assists in the application and use of products as well as providing complete systems customized for the specific application. For more information, contact SEL by phone [phone]; fax[phone], or on the Web at www.selinc.com.

IN THIS ARTICLE YOU WILL LEARN:

* How Abitibi-Consolidated's Iroquois Falls mill is working toward automation of its electric power system.

* Why the mill chose to install a protective relay system.

* How the new system helps prevent shutdowns.

ADDITIONAL RESOURCES:

* Abitibi-Consolidated Web site: www.abitibiconsolidated.com

* Schweitzer Engineering Laboratories Web site: www.selinc.com