Reliability, availability and maintainability (RAM) of high power variable speed drive systems (VSDS)

This is an overview of various aspects of reliability, availability and maintainability of large AC drives (medium voltage and >5 MW). The focus is on the definition and practical use of the relevant and most frequently used terms in this field, with the purpose to provide a base for common understanding between customers and suppliers. It is also mentioned how reliability evaluation procedures have been applied in a few cases. Reference is made to typical misinterpretations. The overview is limited to electric drives and does not include comparisons with other drive systems like gas- and steam turbines.