Identification and location of long-term voltage instability based on branch equivalent

A new branch equivalent is proposed to identify and locate long-term voltage instability in both distribution and transmission network. In the proposed equivalent, not only the power flow and the sensitivity information remain consistent before and after the equivalence, but also the equivalent voltages and admittances are completely independent of loads, which ensure the equivalent accuracy in voltage stability analysis. Based on the proposed equivalent, an approach is presented to identify system voltage stability. The proposed approach also locates weak branches and buses, where an enhancement or operational measure can be used to improve system voltage stability. The effectiveness of the proposed equivalent and approach is demonstrated using two radial systems, five IEEE systems and four actual utility systems with a system size from 5-buses to 3120-buses.