Effect Of The Distributed Generation To The Distribution Network Protection And Automatic Devices And Its Countermeasures

With the depletion of fossil fuels, the deterioration of the environment and the dependence on energy dependence of human society, governments have begun to focus on clean new energy. In recent years, the clean energy(DG) has been widely applied in the distribution network.The application of DG in the distribution network makes the operation structure, control mode and operation mode become more complexed, which brings about profound changes to the distribution network. One important aspect is the impac t of DG access on the protection of distribution network.The operation mode and the control method of the traditional distribution network are simple, and the operation generally is the radiation network. When the distributed power supply is connected to the distribution network, the distribution network will become a network active power distribution network with a bidirectional power flow. The topology, operation and fault characteristics of the distribution network have been changed, the size and the direction of the original fault current are also changed.If we continue to use the traditional 3-sectional current protection, the protection device will appear to reduce the sensitivity of the device, to resist the action, the error and the failure of the recloser.In order to eliminate the impact of DG on protection, this paper analyzes the classification of DG, power generation principle, control strategy and fault characteristics. Based on this model, the equivalent model of DG is established. In this paper, the effect on the 3-sectional current protection and the recloser when DG access to the network are studied, and it is verified by PSCAD simulation software.In this paper, the improvement scheme is proposed for the three-phase current protection: 1) For DG upstream line, on both sides of the line loaded with a protection device of the directional element. The system side installed a no-voltage recloser and the grid side installed synchronous recloser.2) For DG downstream line, the protection of the downstream protection is set up according to the new fault current, and the speed of the line is accelerated at the beginning of the line.Aiming at the problem that the time limit of the anti- time overcurrent protection for DG output is random, the improvement scheme of the inverse time overcurrent protection based on user defined characteristic is proposed.The improved scheme has been verified by simulation. The results show that the scheme can meet the requirements of network protection.