This paper presents economic planning of synchronous distributed generations (SDGs) constrained to protection and operation indices in the distribution network. The proposed scheme has a two-stage formulation. In the first stage, optimal protection coordination (OPC) is modelled in the first phase in a network without SDGs. This phase considers the total operating time of all overvoltage relays in primary and backup protective modes for different fault locations constrained to the coordination interval and setting parameters of the relays. Then, candidate buses and maximum installable size of SDGs are extracted in the second phase in proportion to preserving the OPC based on calculating the protection coordination index (PCI). In the second stage, bi-objective planning of SDGs is modelled based on the results extracted in the first stage. In this stage, minimization of the weighted sum of planning cost of SDGs is presented by taking into account optimal AC power flow constraints and operation-planning model of SDGs. By implementing the scheme on standard distribution networks, numerical results verify the validity of the suggested scheme in maintaining the protection coordination when placing SDGs in distribution network and enhancing economic and operation indices in comparison to power flow studies.
