Research On Relay Protection Strategy Of Distribution Network Containing Distributed Generation

As the development of distributed generation technology, an increasing amount of distributed generators intergrated into distribution networks.The intergrating of DG impact the operating characteristic of distribution networks, especially the conventional current protection strategy. In this thesis, we proposed a protection strategy for distribution networks with DG intergrated.Firstly, the state-of-art of distribution networks protection and the technical requirment for DG intergration is analyzed.The theory, methods and auto-reclosure of conventional current protection strategy were reviewed. On this basis, the analytic expression of the impact of DG to current protection was proposed and then tested by simulation.Secondly, protection scheme one put the low voltage protection integrated into the current protection, through the cooperation to protect the distribution network including DG In the case of distributed generation connected to the feeder line, the scheme of restricting the penetration level is proposed, with the calculation method of the maximum penetration level and the cooperation program of the line protection and the DG protection presented afterwards. For the situation of a single invert-interfaced generation connected to bus, an improved overcurrent protection is proposed, with the added low-voltage reverse direction protection and the improved setting calculation method considering the invert-interfaced generation.Finally, the second protection scheme discussed the feasibility of distance protection for containing DG distribution network, and pointed out the primary problem is that the short circuit point of transition resistance can affect the impedance measurement precision. To solve this problem, an algorithm that not affected by transition resistance was proposed, the proposed method was verified by the MATLAB simulation experiment. The simulation results show that the proposed method has the characteristics of small error and high precision.The two novel protection schemes this paper proposed are simple, practical and reliable with less local information, which meet the present requirements of the protection of the distribution network containing DG.