An offline three-level protection coordination scheme for distribution systems considering transient stability of synchronous distributed generation

Abstract

The growing penetration of synchronous distributed generation (SDG) affects the protection and stability of power distribution systems. The connection of SDG to distribution network may lead to change in the amplitude and direction of the current of feeders during the fault conditions and thus disturb the coordination of protection devices (PDs). On the other hand, the transient stability of SDGs as low-inertia machines after fault occurrence strictly depends on the fault clearing time which relies on the performance of the protection system. Therefore, an effective protection scheme should simultaneously consider both aspects of protection coordination of PDs and transient stability of SDGs. In this paper, an efficient and comprehensive offline three-level protection scheme is proposed to consider both protection coordination and transient stability indices. In the first level, the transient stability of SDGs is assessed in terms of critical clearing time (CCT) using offline simulations. In the second level, PDs are coordinated considering clearing time interval (CTI) of the main and backup PDs and CCT of SDGs. Finally, in the third level, the characteristic curves of PDs are modified if required by the transient stability of SDGs. The effectivity of the proposed method is demonstrated using the simulations on an active IEEE 33-bus distribution network in the ETAP software.