Dear Slobodan

You are right. I have some priority in dealing with transients in motor drives.

In the first place it is induction motor, as the induction motor drives are of the highest power and the transients there do somtimes much damage. They cause for example torsional vibrations of shafts and are a cuse of shafts fatigue damages. Also the electrical transients have much influence on mechanical integrity of windings, especially the parts outside the the slots and the connections. They also have strong influence on power transformers supplying induction motors and sometimes they influence other motors supplied from the same transformer.

I am also interested in interaction between electrical and mechanical transients in motor drives, that could be named electromechanical transients; they are quite obvious in small power induction motor drives, which are more 'jumpy' - because they have much smaller electromechanical time constant.

The methods I use are mostly energy conversion methods, which are equally applicable to all electromechanical problems on the basis of the "least action principle'.

I do not work on problems of thermal transients, which are of quite different nature and are extremally important, but on very much longer time scale.

With kind regards - Piotr Wach, Opole, Poland.

In electric drives mechanical transients (speed and torque) are dominant and the most important for drive work. Certainly, there is connection between mechanical and electromagnetic values. Overloading (greater torque than nominal) causes over currents. The shorter overloading could be solve with forcing excitation (flux too). Problems are very complex. But take care that electrical time constant is in (ms) and mechanical time constant is in (s), i. e. there is difference 100-1000 aprox.

Agree in electric drives mechanical transients are very much related to torque that relates to currents in the machine systems, linked back to drives for transients and excessive current drawn would also lead to overloading, thermal impacts and no relation to electromagnetic values......

Generally the shaft fatigue damages are not very extensive in IM unless the system is not designed appropriate ..... the impact of the transients would not be high on medium and low power applications .....

The main question in drives is how to get needed speed in time. Selection of transient value depends on the problem you research. Modern mathematical methods (state space variables in matrix form) are necessary for solving transients.