Effects of active and reactive power modelling in optimal load flow studies

Optimal load flow normally considers active and reactive power loads as independent of the voltage level. In the paper the exponential form of a static load model relating the active and reactive power components to the busbar voltage, is considered and the effects of incorporating this load model in the optimal load flow solution of several test systems are studied. The effects of modelling active and reactive powers are considered separately as well as when taken together. The results are compared with the respective standard optimal load flow solutions for a number of standard test systems.The differences in fuel cost, total power loss and voltage values when compared with the standard optimal load flow solution are significant for some systems. The fuel cost and power generation differences are the highest when only the active power variation with the voltage is modelled. The heavier the system loading, the lower the fuel cost difference between conventional OPF, and the OPF incorporating power variations with voltages. The differences in power loss are more pronounced when both active and reactive powers are modelled. The higher the loading, the less pronounced the difference in power loss. More significant deviations in voltage take place when both active and reactive powers are modelled. The modelling of reactive power is more influential on the voltages than is the modelling of active power on the voltage deviations. The contrary is true for the differences in phase angle and incremental cost of power delivered, wherein the main factor is active power modelling. There are no differences in iteration numbers for small-size systems. The larger and more heavily loaded systems exhibit a difference in the required number iterations.