The role of dynamic loads representation in dynamic analyses

Appropriate modelling of dynamic loads is of primary importance in voltage stability studies. The paper deals with the modelling of a load consisting of a static load plus an aggregate of induction motors. Three simplified models for such a load configuration are compared with a more complex one, considered as ‘reference’: i) a pair of static exponential models representing the static load and the induction motor respectively, ii) a static exponential load plus a dynamic Ist-order model for the induction motors, iii) a generic non-linear dynamic model of the 1st-order as proposed by Karlsson and Hill. The reference load model consists of one static exponential model for the static load plus one dynamic 3rd-order model for the induction motors. A power system with a longitudinal structure is chosen as case-study. It is shown that for specific cases only a dynamic model for the induction motors predicts the voltage collapse al the load bus. Discussion of the results is given.