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Title: Impact of high penetration of renewable energy sources on the relay coordination of distribution system
Authors: Olatoke, Abraham Oladele
Advisors: Darwish, M
Keywords: Coca-cola network 33kv circuit;Leaf-node algorithm;Bidirectional dc-ac-dc converters;Plug setting and time setting multipliers;Etap12.6 software
Issue Date: 2016
Publisher: Brunel University London
Abstract: The rate at which the integration of distributed generation (DG) penetrates the public power supply has started to put various demands on the distribution system, since they are directly connected to the network. Distribution level protection is based on a time-overcurrent design. The design is to clear faults with as little impact and minimum time on the equipment and the customer. The increasing demands placed by grid services on the DGs, especially the PV types have a serious impact on the distribution system. For example, special protective devices are required to prevent the risk of danger in the event of mains interference. In this thesis, the main focus was on the contribution of fault currents to the distribution networks, and how the high penetration of DGs especially the renewable energy resources (R.E.S.) types affect the coordination of overcurrent (O.C.) protection. In view of the changes in the international regulations, the DGs are expected to stay connected and perform grid-related control functions, instead of shutting down at the first sign of a fault. This problem becomes more acute when the DGs stay connected during faults, known as voltage ride through (VRT). This thesis presented its findings on the impact of the DGs of various types of DGs (synchronous generator, asynchronous and power electronic) on the protection coordination by the high increase of fault currents, and the mitigation techniques of the impact of the inverter interfaced DGs (whose fault current contribution was not so high) on the overcurrent protection. The impact on system’s over-current protection coordination in such hybrid AC and DC microgrid, how the fault current changes by the high penetration of DGs in the hybrid microgrid and their effects on the protection over-current coordination were presented, as the name microgrid was adopted for networks having a point of common connection (PCC). The inverter interfaced-equipment were never in the conventional systems, the few that were there were all on the load side of the distribution system. The inverter interfacing DGs (PVs) and the synchronous types are the types of DGs that affect over-current protection of the distribution system and these were mitigated accordingly, considering the first few cycles of the fault events of the ride through capabilities. The analysis of the different penetration levels of the DGs in an existing 33kV in the Nigerian distribution network, (CocaCola-Challenge Industrial feeder) was thoroughly analysed, for less than 20%, more than 60% and 100% of the feeder load. Most of the DGs, presently existing in that network are the synchronous types, but they are only used as standby sources of power, and the renewables (RES) like the photovoltaics (PV), run of flow (RoF) Hydo and the wind turbine generators (WTG) are proposed additions. The objective of this thesis was to explain the fundamentals of distribution generation (DG) and especially the RES, in relation to distribution protection relay coordination to see why there should be urgency in carrying out the study especially in a developing environment where the grid is unstable, the load is rapidly expanding and RES is intermittent. The radial distribution system (DS) with high penetration of DG was introduced. The motive was to critically investigate protection coordination problems and the solutions to the problems. The main objective was to optimally recommend the type, size and location of the DG for an actual distribution feeder in an unstable environment where the grid supply is not steady. The effect of 100% and above of feeder load penetration on such feeders formed the objective of this research. The literature review which was for investigating in greater details the technical aspects of the operation and control of the high penetration of RES in the distribution system were thoroughly analysed. The review of the existing radial distribution protection system and the effects of high penetration of DG on the protective relaying were thoroughly investigated. The issues of power electronic based inverters and the protection coordination problems, were investigated. The protection coordination as regards to fault level changes and grounding, intentional and un-intentional islanding were major important aspects which were treated in the technical review.
Description: This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University London.
Appears in Collections:Electronic and Computer Engineering
Dept of Electronic and Electrical Engineering Theses

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