Assessment of voltage stability limits calculated using component-based load models in the KwaZulu-Natal transmission network

The operation of power systems has become very difficult due the fact that they are operated very close to their operating limits. In order to accurately take into account this uncertainty related to power system operation, component based load model parameters will be utilized to objectively conduct voltage stability studies. Eskom usually utilizes constant power models when conducting power system analysis, for both steady state and stability studies. The steady state results obtained in this situation represent a conservative picture (i.e., for loadflows and voltage stability). In the case of stability studies, the results obtained may not be reflective of the actual system being studied. The basis of the approach is that the correct modelling of power system loads will result in the computation of representative voltage stability margins for the system. In this paper, work is presented on how more representative load models yield the correct approximation of the voltage stability margin. The transfer capability of the system for constant power, constant impedance, and constant current are compared to those of component based models under normal operating condition and when subjected to n-1 contingencies.