To improve the performance of fault isolation and restoration in distribution grids, the feasibility of relay protection based on time-delay coordination in distribution systems is investigated. The adaptive ranges of time-delay coordination in case of instantaneous over-current relay protection installed are analyzed. Design considerations of hybrid fault isolation and restoration combined by time-delay based relay protection and distribution automation system (DAS) are given. The influences on the fault treatment process in case of distribution generation (DG) implanted and without time-delay coordination are discussed. It is concluded that the time-delay coordination is feasible with which the outage of a branch can be avoided when a fault occurs in a custom and the outage of a trunk can be avoided when a fault occurs on one of its branches. Even in the case of instantaneous over-current relay protection installed, the corresponding feeder has some capacities of time-delay coordination. The performance of fault isolation and restoration can be remarkably improved by the combination of relay protection and distribution automation system.