Reliability of megawatt drive concepts

In the process industries, reliability of production machines has a strong influence on the profitability of a plant. Examples for such machines are mills, extruders, compressors, pumps, fans and others. Increasingly, such machines are equipped with megawatt rated electric variable speed drive systems (VSDS). The requirements for the reliability of VSDS in such applications are extraordinarily high. In this paper, a comparison of the potential reliability for a number of different high-power medium-voltage drive concepts is made, like load commutated inverters, voltage source inverters, and cellular converters based on building blocks. Redundancy is introduced as a means of increasing reliability, and different approaches to redundancy in a VSDS are discussed. Besides component reliability and redundancy, also the maintenance strategy has an impact on the reliability of a VSDS. As a result, recommendations for the choice of a drive concept and maintenance strategy are given.