NEW MODEL FOR SINGLE-UNIT REPRESENTATION OF INDUCTION-MOTOR LOADS, INCLUDING SKIN EFFECT, FOR POWER-SYSTEM TRANSIENT STABILITY STUDIES

The paper investigates the dynamic representation of a group of induction motors by one or more equivalent motors for power system transient stability studies. Considering the fact that large induction motors constitute a large proportion of the total system load, and that the skin-effect has a very strong effect on the performance of these machines, this effect is therefore included in the model. To enable the skin effect (deep bar effect) to be included, the stator and the rotor windings leakage reactances are separated and the core losses are ignored; and the equivalent machine is represented by seven electrical parameters instead of the conventional five parameters. A clear procedure is described on how to obtain the unknown electrical and the mechanical parameters of the equivalent machine. An efficient grouping (homogeneity) criteria is proposed to obtain subgroups in the case of a diversified group of induction machines connected to the same bus and a power system subjected to disturbances of various types. The accuracy of the equivalent model is verified by simulating its response to different types of disturbances and comparing the results with the sum of the responses of the individual machines. Excellent agreement is obtained between the response of the model and the sum of the responses of the individual machines.