Considering Double Primary Relay Strategy

This chapter helps the industry professionals to model main‐1 and main‐2 relays in optimal relay coordination (ORC) problems. It discusses the selectivity criteria when both local and remote backup relays are involved and examines the coordination problem for the extreme case where the number of main‐2 relays equals the number of main‐1 relays. The chapter considers only electromechanical, only static, or a mixture of them for main‐2 relays and aims to explain incorporate both directional and non‐directionals inverse‐time overcurrent relays (ITOCRs). It provides one unified time‐current characteristic curves (TCCC) for all ITOCRs. The highly complicated scenarios, which are based on multiple TCCCs and relays with different technologies. The chapter formulates a full mathematical optimization model. However, this special ORC problem could also be solved analytically if all main‐2 relays are considered as local backup relays with dropping remote backup relays.