Dynamic behavior of a doubly-fed motor-generator during and after the fault

This paper presents the dynamic behaviour of a large doubly-fed motor-generator during and after the fault. Such machines will be included in pumping-storage plants in Slovenia and they will become an important part of Slovenian electric-power system, so it is important to know the behaviour of these machines. During the fault-where doubly-fed motor-generator operates as an asynchronous machine-the machine meets the saturation and in combination with the network-voltage reduction this largely affect the electrical torque of the machine. The difference between static and dynamic power-to-speed characteristic is presented with the application of trajectories of rotor speeds. Besides various resistances of crow-bar protection were considered. Results of simulations show that during a fault a crow-bar resistance has an important role-in order to increase the transient stability of doubly-fed motor-generator, proper value of crow-bar resistance should be applied.