Subtransmission reduction for voltage instability analysis

A new method for creating power flow subtransmission equivalents to be used in voltage instability analysis is presented. The reasons for performing subtransmission reduction are given. How the subtransmission reduction problems differs from more traditional reduction problems is shown. Criteria for an acceptably reduced subtransmission system are stated, and Pacific Gas and Electric Company´s (PG&E´s) reduction method, which utilizes the program LODRED (from the EPRI Dynamic Equivalencing Reduction Software) to perform load bus elimination and a new program called GALRED to perform generator bus aggregation is presented. Unlike most reduction methods, this method produces equivalents that are independent of base case voltages and flows and consequently highly accurate for voltage instability analysis. Validation of the new method is performed using a 71% reduced model (29% of its original size) of PG&E´s transmission system to simulate bipole outage of the Pacific DC Intertie