Optimal application of reclosers and sectionalisers to reduce non-distributed energy in distribution networks

This paper presents a method for optimal placement of reclosers and sectionalisers in overhead distribution networks to reduce Non-Distributed Energy (NDE) caused by permanent faults. The proposed algorithm uses an effective numbering method to determine the distribution network topology. This numbering method is very useful in the optimisation procedure and determination of savings achieved by reducing the non-distributed energy. Then a method is described for optimal placement of a recloser and sectionalisers in the network. Both voltage type and current type sectionalisers are considered at this stage. In the next stage, the optimal number of sectionaliser s is determined based on economic considerations. Lastly, the validity of the presented method is evaluated by applying the algorithm on a typical Iranian 20 kV distribution feeder and the results are presented. INTERDUCTION Statistics show that over 70% of faults on the overhead distribution networks have transient nature, which can be cleared successfully by the reclosing operation. On the other hand, the permanent faults percentage is low, but their duration is high, compared to the transient faults. The affected region due to these faults can also be reduced by applying sectionalisers, since they split the network to some sections. Here a large portion of network is saved from energy cut-off, except the faulted section. As a result, electricity authorities consider seriously about the application of reclosers and sectionalisers in their network. In recent years, more attention has been given to the application of these devices to reduce NDE caused by permanent faults. In the first step, the network topology should be defined properly for the optimisation procedure. Unlike the transmission systems, in distribution systems numbering the network branches and nodes is very important. This paper presents a numbering method for the distribution systems. It has been a common practice to install reclosers in the subtransmission substations. In this case, the feeder circuitbreaker can be controlled by a recloser relay. In the recent years, recloser packages are largely introduced into distribution networks. These are composed of a circuitbreaker and a recloser relay and can be installed anywhere on the distribution feeder. Optimal number and placement of the sectionalisers can be determined regarding the saving obtained by installation of sectionalisers. Since sectionalisers can not break the fault current, their installation point greatly depends on the location of the recloser. This saving also depends on economic and technical factors. Technical factors are the network dimensions, the number of annual permanent fault occurrence on the network, the energy demand of the network, and the required maintenance time. Economic factors consist of period of study, load growth, interest and inflation rates, costs of NDE, and cost of reclosers and sectionalisers and their installation. The installation point of the recloser affects the procedure of finding optimal number and locations of the sectionalisers. The presented method in this paper firstly determines the optimal position for a sectionaliser. The gained saving is determined with respect to the installation and maintenance costs of the sectionaliser. If the saving is positive, installation of the sectionaliser is economically feasible. Then the saving obtained by using two sectionalisers is calculated. In the installation of two sectionalisers, their type is important, in their placement. The gained saving is compared with the saving of one sectionaliser. If the saving of one sectionaliser is more, the optimal number of sectionaliser s is one. Otherwise, installation of more sectionalisers on the distribution feeder should be considered. This process continues until the saving obtained by installation of k sectionalisers becomes less than the saving of k-1 sectionalisers. The optimal number of the sectionalisers would be equal to k-1.