The role of load models and reactive power support during large frequency transients

The goal of this work is to study the different dynamic behavior of the Italian electric power system, when subject to large disturbances, in relation to adopted load model and reactive power compensation devices considered for the network. Effectiveness of Defence Plans has already been proved by system Operators, but little attention is paid sometimes to the influence of used models. The adoption of a realistic load model implies a better representation of the system: in particular, the conclusions are that if the load is modeled as dynamic and voltage and frequency dependent, frequency perturbations resulting from the simulated contingencies are less dangerous as compared to more simplified models. Furthermore, the possibility to support voltages at particular buses damps voltage transient consequent to large perturbations and avoids further disconnection of loads, keeping the same security level. The conclusions are supported by tests carried out both on a relatively small portion of the Italian system (Sicily) and on a larger area (central and southern part).