Research On Effect Of Distributed Generation On Protection Of Distribution System

With the increasing depletion of traditional fossil energy sources and the continuous improvement of power supply reliability demanded by power users, distributed generators(DG), especially renewable energy, such as wind, solar and other small generators, with its unique green energy, efficiency, flexibility and other advantages, have been developing rapidly.However, distributed generators access to the traditional radial distribution network from a single source network into a multiple power supply system, which will change the fault current level and direction,and thus brings the traditional distribution network protection nuisance tripping, misopreation, desensitization, reclosing failure and other problems, so the former overcurrent protection cannot hold any longer.In order to solve these problems and to eleminate those disadvantages of DG, this paper has done some research on the types of DG, the connection stadard, control strategy and performances during and after faults, and then on the basis of these, a reasonable equavalence model has been built, and has been tested on PSCAD. At last, new improved protection schemes have been presented:1) For the upstream relays of DG, protective devices should be installed, and the direction elements are added on both sides. The pilot protection is adopted as the main protection, while the overcurrent protection as the backup protection.2) For the downstream relays of DG, in order to solve the desensitivity problem, a new adaptive protection scheme has been presented. The setting of relays will change with the fault current level by itself. The protection principle is tested on a real 10kV distribution system, the results have proved its effectiveness.