| Abstract |
This paper presents an overview of applications and a distribution of variable frequency drives (VFDs) on different load types in industrial and other processes. A survey of the reliability of VFDs has been performed, as well as a closer analysis of registered faults for different industrial applications, environment and converter design. Faults in the VFDs are compared with previous surveys for conventional AC drives. The present survey has been performed on inverters of more generations, and the results will have importance for the choice of system solutions and planning of monitoring and maintenance. The survey is based on collected data from service experience with 666 inverter units within varies types of industrial plants. 522 failures on these have been registered and analyzed. In addition some few motor failures have been registered. The results show that more than 50 % of all failures are in the control circuits, 7.7 % in the cooling fans and 37.9 % in the power circuits. For units below 50 kW the failure rate is about the same for VFDs as for conventional drives, but the failures are now registered for the converter rather than for the motor. For units above 50 kW the failure rate for VFDs are considerably higher than for that of the conventional drives, with a distinct maximum in the power range of 51-100 kW. The survey also shows that for higher power rates the failure rate for VFDs will decrease down to that of the conventional drives. The survey also indicates that the introduction of VFD has decreased the failure rate for the motor. |
