Impact of Coupled Transmission-Distribution on Static Voltage Stability Assessment

With the rapid growth of distributed generators, the distribution static voltage stability assessment (D-VSA) becomes as important as the transmission voltage stability assessment (T-VSA). However, the T-VSA and D-VSA normally treat the transmission and distribution separately, neglecting the interactions between transmission and distribution (T-D). This letter studies the impact of coupled T-D on VSA via physical analysis and numerical simulation. We observe that without considering the T-D interaction, D-VSA may exaggerate the actual load margin significantly, and T-VSA may either exaggerate or underestimate the actual load margin, both of which are unreliable. Hence, the coupled T-D interactions must be considered in both T-VSA and D-VSA.