SUBTRANSMISSION REDUCTION FOR VOLTAGE INSTABILITY ANALYSIS

In this paper, we present a new method for creating power flow subtran smission equivalents to be used in voltage instability analysis. We pr esent the motivating reasons for performing subtransmission reduction, and we show how the subtransmission reduction problem differs from mo re traditional reduction problems. Criteria for an acceptably reduced subtransmission system are stated, and Pacific Gas and Electric Compan y' s (PG&E's) reduction method is presented which utilizes the program LODRED (from the EPRI Dynamic Equivalencing Reduction Software) to pe rform load bus elimination and a new program called GALRED to perform generator bus aggregation. Unlike most reduction methods, this method produces equivalents that are independent of base case voltages and fl ows 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 bi pole outage of the Pacific DC Intertie.