Loop type DC micro-grid protection

The aim of this thesis is to propose a protection scheme for low voltage loop type DC micro grids. This type of micro grids is a perfect solution for the problem of power distribution in the rural areas and far areas where the utility transmission lines is difficult and very expensive to be extended there. The increasing needs to electricity and the need to sustainable sources, is the basic motive to many new innovative solutions. One of these methods is using the renewable energy sources in distribution level and construct a micro grids to provide customers with electricity. In the second chapter in this thesis we get through the definition for micro grids, the structure of micro grids in both their type AC and DC, their different components are defined. A comparison is held between AC micro grid and DC micro grid in many different aspects to identify which micro grid type is more feasible. Both operation modes (on and off grid) and different operation strategies which includes economic, environment friendly and technical aspects are all explained. In the third chapter micro grid protection issues is defined for micro grids. Method to calculate the current contributions in both micro grid modes is presented. AC micro grid protection using overcurrent technique and providing time-current tripping curve is detailed. In addition, the disadvantages of this method of protection is pointed. Secure communication using Ethernet – based system is the proposed communication technique for AC micro grid feeder protection. After that, line current differential protection (LCDP) system and its communication system is explained and protection method used for feeder protection of AC micro grid is explained too. The next section contains detailed explanation of the DC micro grid requirements for protection system and possible faults type in DC systems, in addition, the components of protection system is mentioned. In chapter four a method for the protection of low voltage loop DC type micro grid is proposed with its flow chart. A percentage directional line current protection scheme is used and a reliable and high speed digital communication channel is proposed.in chapter five a simulation for the DC micro grid is done using matlab /Simulink. The simulation include the normal operation of the micro grid in addition to the faulty condition by creating short circuit on the transmission lines of the DC micro grid. And the simulation for clearing the faults by using percentage directional line current protection technique. Conclusions are drawn in sixth chapter. The main purpose of this thesis is achieved and the proposed protection scheme is worked successfully.