At the recent In-Pit Crushing and Conveying (IPCC) 2014 conference held in Johannesburg and organised by IM Events, Siemens Senior Account Manager Christian Dirscherl updated delegates on the status of its gearless drives for conveyor offering. Siemens and ThyssenKrupp now have two gearless conveyor systems (Prosper Haniel inGermany and Antapaccay in Peru) in operation. Moreover, they currently have two projects in the commissioning phase in Chile and Peru and have recently received another order located in Peru.

For the gearless drives installed at Antapaccay, Siemens used cycloconverters rather than voltage source inverters. Cycloconverters have the highest reliability and efficiency (99.5%) as well as high overload capabilities which are
especially required for low speed operation. On the downside, cycloconverters have a low power factor and generate harmonics. Cycloconverters were selected for the Antapaccay gearless grinding mills as they were the only economical
solution for large gearless mill drives.

ThyssenKrupp and Siemens supplied the 6.5 km overland conveyor to transport the copper ore from the mine to the
processing plant. The conveyor has a 1,370 mm wide belt, travels at 6.2m/sec and has a design capacity of up to 5,260 t/h of ore. It features an innovative gearless drives system providing a power output of 3,800 kW for each of the two drive pulleys. Both drive systems are located at the same drive station. Antapaccay was initially designed with a
conventional drive system, variable frequency inverters with squirrel cage induction motors together with couplings and gearboxes.

The design comprised four motors with 1,900 kW each, however, the gearless drives system uses only two drive pulleys, each with a 3,800 kW rating. Hence only two cycloconverters and two medium voltage switchgears were needed as opposed to the original four VFDs and four medium voltage switchgears. By reducing the electrical equipment, the E-house footprint was half of the original size, and from the mechanical side, the gearless drives now only require the
maintenance attention of four pulley bearings instead of 48 bearings and 8 couplings. The gearless drive system for Antapaccay was realised with the same CAPEX as originally estimated for the conventional design. However, the OPEX is outstandingly reduced from a combination of approximately 3% to 4% lower power consumption and the requirement of fewer spare parts.

This innovative solution completely eliminates high cost spare parts, such as gearboxes, couplings and squirrel cage induction motors. The annual OPEX costs of the gearboxes are completely eliminated with the gearless drives solution. With the significant reduction in mechanical components of the gearless solution, there is a direct link to an increased reliability, thus preventing potential downtime. In mines of this magnitude, loss of production can easily cost
several thousand dollars per hour. The motors themselves are air-cooled, but an air-water exchanger is mounted on top of the stator. The heat exchanger cools the air drawn into the motors. For the Antapaccay facility, a closed-loop water circuit equipped with an external water-air heat exchanger is used to cool the cooling water. The external heat exchanger uses a redundant pumping station. Antapaccay has been commercially operating since November
2012, and reached an availability of 99.5% within the first 12 months.