Modern Mining May 2015

COVER STORY

 the overall height of the unit on a standard trailer would have resulted in an unaccept- ably high centre of gravity, increasing the risk of a rollover on a banked gradient. With these issues in mind, it was decided to design a step deck with a lower centre of gravity and the generator mounted to it. The electrical equipment enclosure with the fuel tank is mounted separately on the gooseneck. This proved to be the most successful arrange- ment as it brought the centre of gravity down by nearly 2 m and reduced the overall length by 4 m, resulting in a unit that is stable and relatively easy to manoeuvre. The trailer has to be towed by a suitably sized horse with a special low range gear- box to successfully cope with the low speeds needed to walk the rope shovel and negotiate the gradients of an opencast mine. Owing to the identical design of the trailers, two identi- cal horses were needed. A comprehensive fire detection and sup- pression system was installed in the engine compartment and a full detection system in the electrical compartment. The compact medium voltage switchgear is also state-of-the-art, with IP 67 encapsu- lated ingress protection of the environmentally friendly vacuum switching contacts and the MV conductors. This characteristic enables the switchgear to be submerged in water for three days without any negative effects on the main conductors. The durability of this section of the switchgear was one of the main reasons for its selection as it is highly suitable for a dusty desert environment. The very low voltage control circuitry eliminates potential hazards associated with dust or mois- ture contamination. These design measures do not mean the equipment is maintenance free and a strict maintenance schedule is in place. 

extensive design and planning collaboration between the teams to ensure that redesign dur- ing manufacture and assembly was limited to the bare minimum, thus avoiding time delays. Barloworld Power committed to delivering the first motivator to site a full two months ahead of schedule so that it could be used to move the first assembled rope shovel off the assembly pad on the mine. This meant that the unit had to be on site before the road embargo on abnormal goods in Namibia, which was effected on 3 December 2013. As the unit took four days to get to site, the delivery schedule was extremely tight. Barloworld Power’s Customised Solution Centre, together with the installation team, pulled out all the stops to ensure that this hap- pened and the unit was delivered to the Walvis Bay branch of Barloworld Namibia on Friday 29 November 2013. The second motivator was handed over on schedule by 31 January 2014. Optimum design The initial design of the unit incorporated all the equipment and the engine in a single enclo- sure, but during the detailed design phase this proved to be impractical for several reasons:  the trailer became too cumbersome and costly to manufacture;  the risk of fire damaging the electrical equip- ment if it all shared a common enclosure was deemed to be too great;  the risk of dust contamination on the electri- cal equipment was too great;  the size of the generator meant that if this solution was pursued, an 18 m long trailer would be needed. This would have made transport and movement of the unit on the mine prohibitively difficult as well as being very costly to build and maintain in the long term;

A motivator moves a Cat 7495 electric rope shovel.

Barloworld Power committed to delivering the first motivator to site a full two months ahead of schedule so that it could be used to move the first assembled rope shovel off the assembly pad on the mine.

May 2015  MODERN MINING  23