The concept of DG clusters is introduced with highly penetrated integration of distributed generation (DG) into active distribution networks (ADNs). DG clusters are referred to as parts of an ADN

including DGs

distribution lines and loads. The formation of DG clusters helps to optimally dispatch DG outputs within ADNs. In this regard

an integrated planning strategy of ADNs and DGs in cluster (IPNDGC) is proposed. In order to guarantee that the planning strategy meets the reliability requirements

a reliability assessment is considered in the proposed model. However

reliability assessment is generally accomplished according to a fixed network topology and known DG allocation

which makes it difficult to integrate reliability into planning models. To deal with this difficulty

a novel formulation method for reliability assessment is proposed considering the network topology uncertainties and isolated operating probabilities of DG clusters. The reliability index (RI) represented by expected customer interruption cost (ECOST) is employed in the proposed planning model. The planning model is formulated as a mixed integer second order conic programming planning model. An actual distribution system is employed to illustrate the accuracy and efficiency of the proposed planning model.