|Extreme winter and springtime weather conditions at Agnico Eagle’s Kittila mine in Finland caused ongoing interruptions due to condensation on PLCs used to control the concentrator’s sedimentation process. The standard-grade PLCs were replaced with ABB’s XC PLC units, which have circuit boards that are conformably coated to protect against moisture ingress. The units are also resistant to vibration and shock damage.|
Underground mining, depending on location, depth and many other factors, can pose problems for electronic equipment caused by excessive heat, cold, humidity, corrosion, vibration, or the general wear and tear that accompanies routine mine operations, to name just a few. And conditions on the surface may not be that much better, particularly in concentrators and ancillary facilities that experience temperature extremes, airborne contaminants, and constant shock and vibration. Here are two control- and communications-related solutions from vendors that offer avenues for higher reliability and performance under these conditions.
Automation and power technology solutions provider ABB reported that it is currently upgrading the automation system at Agnico Eagle’s Kittila underground gold mine in Finland’s Lapland, installing eight ruggedized PLCs to replace the standard original units that control the sedimentation process at Kittila’s concentrator.
ABB won the original contract for the main automation system at Kittila, and configured and installed electrical automation there based on its 800xA Extended Automation system and industrial IT architecture. The project required a large number of ABB automation components including ABB’s 800 series operator interface panels and AC500 PLCs for control of pump, air conditioning and crusher motors underground.
However, a number of items of plant equipment came with automation from other vendors, including PLCs that were supplied with the sedimentation facility that forms part of the mine’s concentration process. The PLCs were standard industrial-grade types, housed in freeze-protected cabinets located outdoors. However, from installation on, this facility experienced multiple process stoppages annually due to power outages, extreme cold, or the presence of water droplets that form on the PLC modules when the protective cabinets were opened. If a stoppage happens during winter the impact can be severe, as the weather can quickly add to the problem by freezing and blocking pipelines. During the winter months, condensation affecting the PLCs could occur almost instantly when the cabinet doors were opened and the benefits of the cabinet's ingress protection were lost. The same problem can also happen in springtime, when temperatures can change from -25°C at night to 15°C during the day, also resulting in heavy condensation.
The mine decided to upgrade this part of the control system to improve reliability and uptime. They had been pleased with the performance of the PLCs that provided control in the hot and humid underground environment and turned to ABB, the supplier of those units, who proposed a solution based on their XC PLC. The XC version, an “extreme conditions” variant of the AC500 PLC line that had been installed underground, has built-in protection against a wide variety of harsh environmental and operating conditions including high and low temperatures, high humidity, low air pressure, salt mist and hazardous gases, vibration, and shock. The new ABB XC PLCs are being installed at the mine's above-ground processing center, with some I/O modules located at a remote water pumping site and connected using ProfiNET.
|ABB’s XC PLC, shown here, is made to withstand extreme environmental conditions.|
According to ABB, mining is a key target application for this device, and the harsh environment at Kittila should pose no problem for XC PLCs that can function in temperatures down to -30°C and ensure reliable system startups in temperatures as low as -40°C—easily accommodating the extreme range of temperatures encountered at the site. The XC PLC’s circuit boards are conformably coated to protect against moisture ingress and the unit is protected against vibration and shock, tolerating mechanical stress such as accelerations up to 4 g from random vibrations up to 500 Hz, or 2 g from sinusoidal vibration. This built-in protection allows the PLCs to be installed in standard uninsulated stainless steel cabinets and without need of freeze-protection heaters.
“Ruggedized PLC technology opens up new design possibilities, allowing automation to be sited right where the control I/O is needed, in many cases without high-specification environmental protection—as at this mine, deep inside the Arctic circle,” said Risto Haavisto of ABB Finland.
Kittila is considered Europe’s largest gold mine, located 150 km above the Arctic Circle. Its reserves are reported to be almost 33 million tons and mine life is predicted to extend to 2037. The mine employs more than 600 staff and contractors, most of whom are local residents. Although ore was originally mined from the surface starting in 2008, mining has taken place underground since 2010. Currently about 3,000 metric tons per day (mt/d) of ore are transported to the crushing facility on the surface by underground haul trucks via a 3-km-long ramp access system.
Quickly Deployable Fiber Optics for Mining Environments
Access to communication networks is critical for transporting data, voice, and video, and other supporting applications that are essential for efficient and safe underground mining operations. Whether accessing ERP or Maintenance Management Systems, conducting fleet management, video surveillance, or access control, or tracking miners with wireless locator systems, these networks serve as a literal lifeline between underground workers and surface operations.
Optical Cable Corp. (OCC), which manufactures fiber optic cabling, connectors and assemblies for harsh environments, contends that mines need more than permanently installed network cabling to maintain this lifeline—they also require unique deployable systems designed for quick installation, extension, and even relocation as active mining areas shift or when equipment is moved in and out.
Given the increasing bandwidth requirements and concerns about electromagnetic interference (EMI), the company claims that fiber optic cable is quickly replacing copper cable, the traditional choice—pointing out that ruggedized fiber optic cabling can withstand adverse physical and environmental factors.
|OCC’s MSHA-rated breakout cable protects the optical fiber strands with sub-cable coatings.|
Fiber optic cable, however, is only one component of a complete, deployable system, explained Rick Hobbs, director of business development at OCC. According to Hobbs, other key elements include hardened cable jacketing; genderless connectors that enable quick cable deployment without regard for male or female ends; and hybrid options that include copper and fiber elements.
For locations that require compliance with U.S. Mine Safety and Health Administration (MSHA) Part 7, Subpart K of Title 30 of the Code of Federal Regulations for signal cables in mining applications, OCC typically recommends its MSHA-rated B-Series breakout cable, noting that these cables are designed to withstand the rigors of difficult pulls, high tensile loading and severe crush occurrences and can repeatedly endure the abuse associated with the extreme conditions in surface and underground mining.
Each individual, color-coded sub-cable is individually coated to protect the fiber. In addition, the cables have a tightly bound, extruded outer jacket. This combination of a helically stranded core and extruded outer jacket offers crush and impact protection and increased tensile strength, according to OCC.
“The breakout cable is essentially a double-jacketed construction,” said Hobbs. “Instead of 900 micron buffers and an outer jacket, each of the 900 micron buffers has a 2.5-millimeter sub-cable protecting it.”
However, if cost is an issue and conditions warrant, MSHA-rated distribution style cabling may be an alternative, according to the company. This cable also features a helically stranded core and extruded outer jacket, but not the additional 2.5-mm sub-cable for each fiber.
According to Hobbs, other MSHA-rated cable designs are also available, offering escalating degrees of cable protection to meet the specific needs of an application. These include alternative jacket materials, such as PVC and polyurethane, which are specifically tailored to meet the mechanical and environmental needs of the application. Additional options within each cable type include jacket materials for applications requiring lower coefficient of friction, chemical resistance, and temperature flexibility for both low and high extremes. Water-tolerant options are also available that take advantage of the qualities of tight buffered cable and super absorbent polymer aramid yarn.
For applications that can benefit from both fiber optic and copper elements, hybrid cables offer both within the same cabling sheath, providing the convenience of a bundle that includes the high performance of fiber along with the copper power or control line in one cable. This reduces the number of cables that must be designed, purchased and deployed into a system.
Hybrid cabling also facilitates installation of wireless access points underground. Unlike traditional wireless networking devices that require 110-vac power for each device, with a hybrid system 12-vdc or 48-vdc, power can be supplied in the same cable to power wireless routers, as well as other electronic devices. As a result, certified devices such as VoIP communicators or IP cameras can communicate throughout the network.
With genderless connectors, multiple identical cable assemblies can be daisy-chained together over a distance of up to several kilometers while maintaining polarity. Polarity can be an issue when connecting an odd number of traditional male to female gender connectors. In such cases, additional connectors, which add signal loss, are required to correct polarity. Genderless connectors, designed for quick deployment, allow cables to be quickly connected with one another without regard for male or female ends. OCC and other suppliers have further simplified the genderless design with user-friendly mating interfaces (such as OCC’s EZ-Mate family). The connector system is designed to resist extreme harsh mechanical and environmental conditions including high vibration, mechanical and thermal shock, and fluid immersion.
Spare cable assemblies, fitted with genderless connectors, can be stored near areas where the risk of damage to installed cabling is elevated to allow for fast and easy replacement with minimal interruption to operations.
According to Hobbs, “When system engineers realize the increased bandwidth opportunities afforded by installing a fiber network, they usually expand their requirements, and identify creative new ways to utilize the technology to provide innovative solutions for their applications.”