چكيده به لاتين
Use of distributed generation (DG), sustainable energy resources and resiliency of the supply system are the main features of modern distribution networks (DNs). Protection is one of the most challenging issues in DNs in the presence of DG units. Factors such as uncertain renewable DG output, DG size, DG location and type, and grid-connected and islanded DN modes of operation complicate the protection coordination problem in modern DNs. This thesis discusses the importance of a stand-alone protection strategy and presents some preliminary ideas and simulation results to address the issues. The study can initiate a great deal of research into the development of new communication-independent methods which may even be incorporated into standards.
The main part of the thesis is to identify the behavior of measurable electrical parameters such as voltage, current and frequency, or any combination of these such as impedance during fault condition in DNs. It is known there are systematic changes to these parameters depending on pre-fault operation status and fault condition. There are some systematic changes in the DN electrical parameters during fault. For example, any system fault is associated with a voltage dip at the DN buses where a bus closer to the fault location has a higher voltage dip irrespective of the DN operating mode, as well as DG type, size and location. These fault-induced changes can be investigated and then expressed in a mathematical formula as a relay characteristic to respond appropriately to any fault condition in the network.
The fuse saving scheme is an issue since the presence of DG may lead to the lack of coordination. Some new recloser characteristics for recloser-fuse coordination in DN with high penetration of DG are presented. In a DN that its DG units are out of service the proposed methods operate quite the same as using standard characteristics, whereas the protection coordination can still be maintained in the presence of high DG penetration in the DN by the new proposed methods.
For relay-relay coordination in DNs with high penetration of DG, some non-communication protection methods are presented. The proposed methods are based on relay characteristics which have an effective performance in both grid-connected and islanded modes of operation, hence no adaptive method is required for resetting the relays for the appropriate mode of operation. Therefore, the same setting is used for both modes of operation, independent of the DG type, size and location.
The proposed protection methods are validated by simulation study on a modified practical DN under different fault conditions, and different DG size and location. The study shows that by identifying the overall voltage/current/impedance changes in DNs with DG units, protection methods can be developed without the need for a communication system. The proposed methods can provide fast and reliable protection in both DN operating modes. The research work is based on the fact that some of the electrical parameters change during a fault and follow a certain pattern which is independent of the DN operating mode.
