Voltage stability analysis: V-Q power flow simulation versus dynamic simulation

Several analysis methods are available for long-term voltage stability. The V-Q curve power flow method is widely used by Western Systems Coordinating Council utilities, and has some advantages. Long-term dynamic simulation with proper modeling, however, is clearly the most accurate simulation method. The authors compare the two methods for wintertime voltage stability problems in the Portland, Oregon, USA, load area. Results from the V-Q method can be misleading. The same is true of other power flow program based analysis employing conventional modeling. Results from these power flow methods may be pessimistic, causing overdesign or overly conservative operation.