In recent years, appearance of Distributed Generation (DGs) in power systems networks has provided important implications. Important advantages of DGs include increased reliability, loss reduction and improving voltage profile. In case of failure in the network, DGs can provide islands (isolated networks) resulting in continuation of supply loads and may reduce the number and/or duration of interruptions for customer residing within their protection zones. In this article, using a combination of Ant Colony system (ACS) algorithm, Analysis Hierarchical Process (AHP) and sensitivity analysis, optimal placement of RECLOSERS and DGs are carried out based on economic and power quality considerations. The cost function include improving reliability, voltage profile and network losses. The method was implemented on a modified 34-feeder IEEE distribution network. Simulation results validated the effectiveness of the proposed method.

In addition to the many advantages of Distributed Generation (DG) for the distribution networks, they change the direction and increase the level of fault current. These changes may cause the loss of protection coordination of RECLOSERS and fuses in distribution networks. Usually, the operation time of RECLOSERS is determined by two main settings, TDS and IP, but two other parameters (A and B), which are defined by the standards of traditional RECLOSERS, are also influential on the operation time of RECLOSERS. These two parameters can be modified in digital RECLOSERS. In this article, these two characteristics are optimized with TDS and IP to restore protection coordination. For this purpose, first, the location and the size of the DGs are specified, after that to alleviate the effects of the DGs, the location and the impedance of FCLs are optimized by a multi-objective optimization function to reduce the loss, improve voltage profile, and reduce the effects of changes in the feeders’ fault current while DGs are connected to the distribution network. Then, to restore the protection coordination, and to reduce the operating time of the protection equipment, fuse, and recloser, the parameters A, B, TDS, and IP are optimized using a multi-function optimization. To validate the proposed approach, the IEEE 33-bus network in the presence of synchronous DGs and resistive SFCL has been simulated in DIgSILENT software.

In this paper, a multi-stage protective scheme is proposed to maintain the fuse and RECLOSERS coordination. The proposed method operates online and proportional to the photovoltaic sources penetration rate. In the first step, a non-standard Current-Time-Voltage curve is used for fuse saving. If the new calculated TDS from the first stage is not implementable to the RECLOSERS, the second stage of the protection scheme will be activated, and the fault current contribution of photovoltaic sources decrease proportional to inverter PCC voltage. It should be noted that the proposed method is a combitionary method that in the first step, the effect of RECLOSERS sensitivity in modifying the RECLOSERS fast characteristics is taken into account in compared to other schemes presented in this regard, and in the second step, there is less limitation on the output power of PV sources under fault conditions than other inverter current control presented equations. It It is noteworthy that in order to implement the proposed protection method, there is no need to telecommunication infrastructure. The ETAP software simulation results validates the proposed scheme effectively.

This paper describes an algorithm that determines the optimal application and coordination of over current protective devices such as fuses, rec1osers, and sectionalisers in distribution networks. The priority is given to providing all main feeders and the laterals with rec10ser protection, while considering security and selectivity of the protection system. In order to achieve these, first the rec10sers are located, then for protection of the laterals suitable fuses are selected based on coordination with the back-up rec1osers. At this stage also the time settings of RECLOSERS are chosen. If, for a lateral, it is not possible to find a suitable fuse from the available fuse range, then a sectionaliser would be required instead. Based on the proposed algorithm, a software program with graphic interface and user friendly features has been developed to assist coordination of over current protection devices in a distribution network. The software has been tested on an Iranian 20kV network and the results presented show the effectiveness of the algorithm.

In this paper, the different protection challenges of active distribution networks are reviewed and the conventional and non-conventional schemes are examined. In active distribution networks, due to the presence of distributed generations at different levels of distribution network, the functionality of the conventional protection strategies are partially or totally are affected. Therefore, the protection strategies should be updated, and the conventional protective schemes and characteristics should be changed. In this paper, first, the potential protection issues raised of active distribution networks are reviewed. Among the challenges, the bidirectional flow of the fault current, the increased amplitude of fault current, the dependency of the fault current on the operating point, the reduction of reach of the relays, the blinding of the protective relay, unwanted islanding, and etc. are reviewed. Then, the performance of the conventional protections including fuses, overcurrent relays, RECLOSERS under such conditions has been investigated. Furthermore, the existing modified protection methods in the literature are examined, which are classified into two general categories of (i) protective relays with unconventional characteristics, and (ii) adaptive protective relays. Finally, the studied different methods are compared with each other, and their performance characteristics are evaluated.