For economy of scale, new projects consider grinding circuits with SAG and ball mills with 36' or larger mill diameters with cycloconverter-fed drives with powers in the range near 20 MW. For the huge volume of slurry flows, big pumps with low-speed gearless drives fed by medium voltage converters in the range of 1-2 MW are being considered. Due to the high mechanical torque involved and process control, variable-speed is a must. Variable speed gearless drives consume variable reactive power and inject harmonic and variable-frequency interharmonic currents into the electrical network causing voltage distortions. For a good performance and reliability of the electrical system regarding efficiency, power factor, power quality and avoidance of dangerous resonances, the proper design, for compatibility and operation of harmonic filters and electrical equipments, emerges as a very important issue. This work presents a concept design and an application case for dealing with the new scenario where low-damping factors and high-non-linear character of converter loads state a challenge to be faced for the design and reliable operation of the electrical equipment. (C) 2004 Elsevier Ltd. All rights reserved.