Representation of damper bars in computer models of synchronous motors supplied from variable frequency inverters

The authors investigate the modelling of damper windings to predict damper currents in variable speed drives. In this type of drive two simple thyristor line-commutated bridges supply a synchronous machine. The machine is over-excited to produce a leading input power factor, and in this condition the terminal voltage of the machine is capable of providing natural commutation of the output thyristor bridge. The lack of forced commutation results in a relatively simple variable-speed drive using industrial grade thyristors. The action of the damper bars is critical to the performance of the drive and a computer programme is described which is capable of predicting the induced damper bar currents under saturated conditions