Engineering & Mining Journal

JUL 2019

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ELECTRICAL POWER SYSTEMS JULY 2019 • E&MJ 39 www.e-mj.com improving the safety and satisfaction of the staff at the mine. "The staff are really proud of their work and we are honored to have helped them achieve this. We did this by design- ing, supplying and training the staff on a modern electrical control and monitoring system, which manages their electrical substations. It shows the grid status and automatically dispatches staff for fault rectification or maintenance." Safety First Safety is a major area where digitalization and automation can make a difference. As the energy intensity and com- plexity of mining processes increases, interest is naturally growing in upgrades for legacy systems and the associated safety improvements they can deliver: less complexity and more transparency in electrical systems equal a safer work- place for everyone. Mark Pollock, global product manager for the Industrial Business Unit at Littel- fuse, said, "Safety is the top trend [in this space]. More customers are looking to re- duce hazards and create a safer working environment than ever before. "Protection against catastrophic elec- trical faults that would damage or destroy equipment and other capital assets has been commonly used in mining. Now, the development of engineering controls to reduce or eliminate the risk of electrical shock and arc flash are being welcomed and widely adopted. A greater focus has been put on personnel safety." Littelfuse recently launched a signifi- cant update to the industry-standard SE- 330 Neutral-Grounding Resistor (NGR) Monitor. While prior versions of this re- lay have been extensively used in mining to prove proper grounding by detecting failed open NGRs on distribution trans- formers, the newest version adds the abil- ity to detect a short across the NGR. A reduction in resistance or a short across an NGR leads to an increase in potential ground-fault current, and as such, the de- tection of a shorted NGR has been added to the latest 2018 version of the Canadi- an Electrical Code. As mines become larger and more energy intensive, reducing the hazard associated with using larger and high- er-powered equipment also becomes challenging. When considering the elec- trical distribution system, larger trans- formers, higher-powered equipment, and longer trailing cables all result in larger values of charging current, which can represent a hazard. Grounding systems and the related protective relays must be carefully chosen to allow operation of the equipment, yet maintain the safest power distribution system possible. Pollock said one of Littelfuse's most widely used products in mining is the ground-fault ground-check monitoring re- lay. These are used to monitor the portable trailing cables that supply power to move- able or mobile electrical equipment, such as scoops, draglines, pumps and fans. "As the frame of the portable equip- ment is bonded to ground using the ground conductor in the portable trailing cables, and considering the harsh envi- ronment and rugged conditions these cables are exposed to, it is extremely im- portant to continually monitor the ground connection from source to load to prove the equipment remains properly ground- ed," he explained. Electrical systems applied in surface versus underground mines differ in sever- al areas, and methods for system ground - ing and protection of trailing cables also differ between the two. An underground mine is typically small- er in size, meaning distances between the power distribution transformers and the mobile or moveable electrical equip- ment tends to be relatively small. Shorter lengths of trailing cables are used, lower powered equipment (compared to surface mines) and lower voltages are possible. Ground-fault ground-check relays used in underground applications need to be rugged in nature, able to monitor cables up to and including 4,160 volts (V), and able to drive a monitoring signal through cables no more than 500 m in length. In a surface mine, however, the dis- tances between the source and the load can be substantially greater, and in cer- tain cases well over 1,000 m in length. Due to the longer cable lengths and higher power equipment used in surface mining, higher voltages are required. The ground-fault ground-check relays for sur- face mining still need to be rugged, but also need to operate over a wider tem- perature range as they may be exposed to extreme temperature fluctuations. They must be able to monitor trailing cables at voltages up to 25 kV, and drive a monitor- ing signal for well over 1,000 m. "Our NGR monitors, ground-fault ground-check monitors, earth-leakage monitors, arc-flash relays, and motor- and feeder-protection relays are used exten- sively in mines around the world and are being provided in OEM equipment on an ongoing basis," Pollock said. "An interesting recent project was the use of more than a dozen SB6100 Industrial Shock-Block products on a shaft-sinking project at a Canadian Electrical systems must be able to withstand the harsh conditions of underground mines. (Photo: Littelfuse)

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