چكيده به لاتين
The appropriate performance of protection relays plays an essential role in sustaining the reliability and stability of the network. On the other hand, changing the structure and power supply of system loads is inevitable due to various factors such as the combined use of overhead and cable lines in densely populated areas or with high environmental constraints and the presence of distributed generation units. The protection of distribution networks is usually designed so that the network is fed from one side entirely. Connecting distributed generation sources to distribution networks changes the range and direction of short-circuit currents seen by protection equipment. These changes cause the protection relays to malfunction. As a result, network reliability is reduced. Due to the fact that the main protection of distribution lines is provided by overcurrent relays and fuses, so after connecting the distributed generation, it is necessary to reconfigure these relays with regards to the direction and current level of the short circuit in the network and system protection returns to normal; However, it will be very challenging to reconfigure these relays In conditions of increasing the distributed generation potential and complicating the network. In this thesis, different methods for protection of mixed overhead-underground lines are examined with the presence of distributed generation resources and a new method based on the use of distance protection is presented an alternative to conventional overcurrent protection schemes. The efficiency of the distance protection method in both radial and loop modes for distribution feeders has been investigated. Furthermore, distributed generation units of different types are connected to feeders to test its effect on the efficiency of the protection scheme. Also in this thesis, the induction current and voltage of the cable sheath in different methods of grounding the cable sheath are evaluated by analyzing the simulation results under normal conditions and during the fault and the best method for grounding the cable sheath is selected.
