Condition Monitoring and Fault Detection of Electric Drives

An electric drive consists of an electric machine, which converts electrical power to mechanical power, power electronics to operate the machine and a unit to control the motion of the drive. These are the components of the drive. Parts of each of these components could fail and give rise to specific failure scenarios. The drive types investigated in this chapter are limited to asynchronous induction machine and permanent magnet synchronous machines, since these are the most common machine types in modern electric drive applications. Faults of power electronics are not discussed since most failures lead to the outage of the drive as the power electronics usually show no symptoms before failure. The task of identifying and classifying drive failures from certain measured quantities is called fault detection. Under some conditions, fault detection may require certain safety protection actions. Example: A turn to turn short circuit in the stator winding of the machine is one example for a safety critical issue. If the short remains for a certain time, parts of the winding will be destroyed. This in turn could cause winding failures that lead to a larger short circuit current which may result in the failure and outage of the entire drive. In this sense, a safety critical issue is a time critical issue. If the failure cannot be detected within a certain time, the drive will be damaged and fails. It is thus highly demanded to accurately detect safety critical faults and to protect the drive (and the application) in this case.