Current issues on high-power cycloconverter - fed gearless motor drives for grinding mills

Mining operations are facing the challenge of competitiveness because of low metal prices and operating costs. The only way to solve the problem is applying new design concepts in management, process operation, R&D and technologies, where industrial electronics and information technologies are taking a decisive role concerning process control, automation and personnel safety. The size reduction, crushing and grinding, is one of the main stages in mineral processing, because of energy, material and maintenance costs. Looking at economy of scale, new projects consider the use of big mill grinding circuits, where larger power gearless motor drives with cycloconverters in the range around 20 MW are being applied for semiautogenous (SAG) mills and recently, ball mills are also being considered. This work addresses some current issues involving design application of high-power drives employed in SAG grinding mills, highlighting industrial electronics aspects: complex nature of the process with large units; reliability and availability; operation within weak networks; power quality and harmonics control; process and knowledge-based instrumentation; mechanical and mechatronics aspects. Based on actual cases of application, the main constructive and operation aspects are described and the open problems for improving reliability and availability are discussed.