Protection Scheme For Active Distribution Netwoks

The increas of the intensity to develop and utilize new energy has greatly promoted the rapid development of distributed generation technology. But the capacity of traditional passive distribution network to absorb the promising distributed generation is limited. Active distribution network has been the future development direction of distribution network in order to improve the utilization rate of power equipment and the penetration of new energy. The improvement of penetration of distributed generation and the complexity of the control mode may cause protection maloperation, misoperation or reclosing failure problems. So adequate attention should be paid to the protection of active distribution network. This paper is aiming at the problems of active distribution network protection..Firstiy, this paper starts with the energy development situation, drawing the conclusion that it is urgent to develop active distribution network. Due to the high penetration, bi-directional power flow and the flexibility of management mode, it is difficult to configure protection scheme for active distribution network. Existing research achievements of the active distribution network protection are summarized from six aspects. As an important part of active distribution network,the principle of distributed generation is introduced, several demonstration project of active distribution network is also briefly introduced, the forecast future of active distribution network is prospected.Secondly, this paper analyzes the influencing factor which may influence the protection of active distribution network, including distributed generation and energy storage equipment, isolation strategy of distributed generation when fault occurs, control mode and active management. More attention has been paid to the impact on active distribution network caused by distributed generation. From the point of view of mathematics, the influence caused by the changes of fault point and the capacity of distributed generation on active distribution network protection is analysed.Finally, considering the practical fact that existing directional protection should use voltage signal, while distribution network can not provide a large of voltage signals. A novel protection scheme adjusts to active distribution networks is proposed in this paper. By designing the fault direction criterion based on phase comparison of positive-sequence fault current, the scheme can quickly and accurately find the fault line and cut it off. To the definite fault, protection installed in the upstream and downstream would operate correctly through the protection coordination. The robustness of the criterion has been improved due to the set of generalization angle because of the consideration of the errors involved in measuring process, which makes the selectivity and sensitivity of the direction criterion higher. This scheme uses only postfault current information instead of voltage information to avoid the installation of voltage transformers. As protection coordination is only needed to transmit the determination result signals namely blocking signal and trip signal, this reduces the demand to communication channel. Finally, O n active distribution network model established by MATLAB/Simulink, the effectiveness of the proposed scheme.is verified for different fault types and fault resistance, penetration of distributed generation sources.