Increased Distributed Generation (DG) presence on radial distribution feeders is becoming a common trend. The existing Overcurrent Protection (OCP) scheme on such feeders consists mainly of overcurrent protection devices (OCPDs) such as fuses and reclosers. When DG is placed on the remote end of a 3-phase lateral, the radial configuration of the feeder is lost. As a result, OCP issues may arise which lead to permanent outages even when the fault is temporary. This thesis presents a new approach that revises the existing OCP scheme of a radial feeder to address the presence of DG. The fuses on the laterals with DGs are removed and multifunction recloser/relays (MFRs) are added to address three specific OCP issues; fuse fatigue, nuisance fuse blowing, and fuse misoperation. The new approach requires no communication medium, provides backup protection for the DG unit, and allows the remaining laterals to retain their existing protective devices. The results are reported using the IEEE 34 node radial test feeder to validate the new approach and the IEEE 123 node radial test feeder to generalize the approach. The new approach completely mitigated the fuse misoperation and nuisance fuse blowing issues and most of the fuse fatigue issues that were present on the radial test feeders. Specifically, the approach demonstrates that coordination between the existing protection devices on radial distribution feeders is maintained in the presence of DG.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2009 / Recently, due to concerns about the liberalization of electricity supply, deregulation and global impact on the environment, securing a reliable power supply has become an important social need worldwide To ensure this need is fulfilled, detailed investigations and developments are In progress on power distribution systems protection and the monitoring of apparatus which Is part of the thesis. The main objective of a protection schemes is mainly to keep the power system stable by isolating only the affected components or the section of the electricity network in which the fault has developed while allowing the rest of the network to continue operating. It is important to note that the protection equipment does not prevent faults from occurring, but it limits the damaging effect of the fault and protects other healthy equipment. This is only achieved if the protection system of the electrical network involved complies with the requirements and purpose of the electrical protection standards. These requirements include the Operational speed, Reliability, Security and Sensitivity. In conventional substations that are still existing Within the utilities networks, a number of long cables are then used to complete the links between substation equipment in order for them to communicate (hardwired). This method is uneconomical and is being phased out completely in the near future. Over the last few years a new standard for substation automation communication has been developed Within the International Electrotechnical Commission (IEC), the IEC 61850. This standard defines the integration requirements of multi-vendor compliant relays and other lED's for multiple protection schemes as well as control and automation techniques. In this particular thesis, Distribution protection is the area of interest, particularly the application of Time and Overcurrent protection schemes. A look into different protection alternatives and the application of new technologies for Electrical Power Distribution Systems that unify protection and control units so that they can be incorporated into Intelligent Substation as opposed to the most existing (conventional substation) is analyzed. The proposed algorithm has been verified through simulations of the CPUT and Eureka three phase power distribution systems. A testing Lab is also part of this thesis and Is meant for experiments as well as simulation performance in order to gain knowledge and skills for designing and engineer substations with lEG 61850 standards equiprnents. The results indicate that the reduction of copper wiring cable has increased and the communication speed has improved and simplified.

Ce travail est lié au système de protection des réseaux de distribution. Les réseaux radiaux dedistribution peuvent être protégés simplement par une protection placée en tête du départ. Maisl'exploitation future des réseaux de distribution, qui se transforment en réseaux intelligents,flexibles et adaptatifs, va sûrement nécessiter une protégeabilité plus complexe. Parconséquent, un nouveau plan de protection pourrait être nécessaire afin d’augmenter la fiabilitédu réseau de distribution et le taux de productions décentralisées. Il pourrait inclure plusieursprotections déployées sur un départ. Le but principal de ce travail est d'étudier comment lesprotections pourraient agir (sur quel genre de grandeurs les protections reposeront, quellecoordination faut-il choisir) et d'analyser les limites de ces nouvelles protections. En déployantplusieurs protections qui divisent le départ en des zones plus petites, le plan de protectionproposé, reposant sur une formulation modifié et optimisée, proche de celle des protections dedistance classiques, déconnectera ainsi moins de consommateurs et de producteurs lors del’apparition de défauts. Cela devrait réduire le temps de coupures brèves et de diminuerl'énergie non fournie. Ce manuscrit présente une solution pour les réseaux HTA radiaux faceaux défauts monophasés. / This work is related to the protection system of distribution networks. Radial MV distributiongrids can be protected by a single protection relay located at the beginning of the feeder. Butthe future operation mode of distribution grids turning into Smart Grids should impose morecomplex operations. Therefore a more advanced protection scheme could be needed, in orderto improve the reliability of the distribution network and to enhance the DG interconnection. Itcould include several protection relays in series on a same MV feeder. The main purpose of thiswork is to investigate how the protection relays could work (on which measurements should theprotection decisions be based, how to coordinate the relays without communication) andanalyze the limits of such new protection schemes. Since the goal is to insert severalprotections that divide the grid into smaller sections, the proposed protection system, based onan adapted and optimized formula, inspired by distance relays algorithm, would thereforedisconnect fewer loads and producers when faults occur in the MV network. This should reducethe clearing operation time and Energy Not Supplied criteria. This paper presents a solution fora radial MV grid facing single-phased faults.

Current trends in electric power consumption indicate an increasing use of dc in end-user equipment, such as computers and other electronic appliances used in households and offices. With a dc power system, ac/dc conversion within these loads can be avoided, and losses reduced. AC/DC conversion is instead centralized, and by using efficient, fully controllable power-electronic interfaces, high power quality for both ac and dc systems during steady state and ac grid disturbances can be obtained. Connection of back-up energy storage and small-size generation is also easier to realize in a dc power system. To facilitate practical application, it is important that the shift from ac to dc can be implemented with minimal changes. Results from measurements carried out on common household appliances show that most loads are able to operate with dc supply without any modifications. Furthermore, simple, and yet sufficiently accurate, load models have been derived using the measurement results. The models have been used for further analysis of the dc system, both in steady state and during transients. AC microgrids have gained research interest during the last years. A microgrid is a part of power systems which can operate both connected to the ac grid, and autonomously in island mode when the loads are supplied from locally distributed resources. A low-voltage dc microgrid can be used to supply sensitive electronic loads, since it combines the advantages of using a dc supply for electronic loads, and using local generation to supply sensitive loads. An example of a commercial power system which can benefit from using a dc microgrid is data center. The lower losses due to fewer power conversion steps results in less heat which need to be cooled, and therefore the operation costs are lowered. To ensure reliable operation of a low-voltage dc microgrid, well-designed control and protection systems are needed. An adaptive controller is required to coordinate the different resources based on the load-generation balance in the microgrid, and status of the ac grid. The performance of the developed controller has been studied and evaluated through simulations. The results show that it is possible to extend use of the data center dc microgrid to also support a limited amount of ac loads close to the data center, for example an office building. A protection-system design for low-voltage dc microgrids has been proposed, and different protection devices and grounding methods have been presented. Moreover, different fault types and their impact on the system have been analyzed. The type of protection that can be used depends on the sensitivity of the components in the microgrid. Detection methods for different components have been suggested in order to achieve a fast and accurate fault clearing. An experimental small-scale dc power system has been used to supply different loads, both during normal and fault conditions. A three-phase two-level voltage source converter in series with a Buck converter was used to interconnect the ac and the dc power systems. Together the converters have large controllability, high power quality performance, and allow bi-directional power flow. This topology can preferably be used together with energy storage. The tests confirm the feasibility of using a dc power system to supply sensitive electronic loads. / QC 20100908