Reliability of Adjustable Speed Drives

The reliability of ASDs has improved very much. The resulting MTBF from realistic estimation (which is 44 years) shows an MTBF for standard LV drives that will be acceptable for most applications in the chemical industry where programs such as "Improve Equipment Reliability," "Equipment Justification and Minimization," and "Risk-Based Engineering" are common. The highest effect in improving the MTBF lays in optimizing the engineering and failure response with respect to thermal overload trips. There is still one more remark to make on reliability. The problem with frequency converters, in situations where production losses and repair costs are very high, such as fans for a furnace, is the inability to monitor the electronics and smoothly shut down the plant before trip occurs. Mechanical equipment, such as a gearbox with all available vibration monitoring techniques, should still have an advantage in these cases.