Large cycloconverter drives in mining applications

The trend towards increased throughput on modern mining projects is driving grinding mill sizes to greater levels than ever before. The drives needed to power these mills exceed the power capable of being delivered through ring-geared systems. An alternate solution has been the application of wrap around (gearless) drives fed from cycloconverter adjustable speed systems. However, the harmonics generated from the cycloconverters offer unique problems, especially if not properly filtered. This paper takes a look at the special nature of cycloconverter drives and their application on large copper concentrators. It also considers the special requirements of harmonic filtering that these drives introduce and the problems associated with unfiltered correction to neighboring facilities. A typical industrial system is analyzed and the impact of harmonic filtering is considered. This paper discusses the lack of IEEE Standard 519[1] to adequately address the issue of interharmonics and the need for appropriate guidelines.