Identification of Critical Protection Functions for Transient Stability Studies

Historical information and ex-post analysis of blackouts reaffirm the critical role of protective devices in cascading events, thereby confirming the necessity to represent protective functions in transient stability studies. The representation of protection functions greatly enhances the accuracy of the transient stability study and leads to a better understanding of power system states during emergency conditions. Although modeling all of the protective relays within transient stability studies may result in a better estimation of system behavior, representing, updating, and maintaining the protection system data becomes an insurmountable task. Inappropriate or outdated representation of the relays may result in incorrect assessment of the system behavior. This paper presents a systematic method to determine essential relays to be modeled in transient stability studies. The desired approach should identify protective relays that are critical for various operating conditions and contingencies. The proposed strategy is verified as a viable technique based on results obtained from the WECC 179-bus and the IEEE 145-bus test cases, while considering various operating states and contingencies. The results of the transient stability studies confirm that modeling only the identified critical protective relays is sufficient to capture system behavior and precludes the need to model all of the protective relays.