Research On Feeder Protection And Fault Self-healing Technology Of Active Distribution Network

The integration of distributed generators(DG)with feeder improve the reliability of distribution networks and increase the consumption of renewable energy,but also change the network structure of traditional distribution networks,making them from the single-ended power supply radial power supply network to multi-power multi-ended power supply active network.In active distribution network,the operation mode,power flow distribution and short-circuit current characteristics have changed,and the conventional three-stage overcurrent protection will no longer apply.In addition,according to the grid connection method,DG can be divided into motor type distributed generators(MTDG)and inverter-interfaced distributed generators(IIDG).The fault response and short-circuit current characteristics of the two are quite different further increasing the difficulty of feeder protection for active distribution networks.In this regard,this paper focuses on the feeder protection and fault self-healing of active distribution network with multiple types of DG.The main contents and research results of the paper are as follows:(1)The influence of the integration of DG on feeder protection was analyzed.The applicability of the positive sequence fault component(PSFC)current in feeder protection for active distribution network was discussed.And the fault characteristics of MTDG and IIDG are analyzed,which lays a theoretical foundation for the research of feeder protection for active distribution network with multiple types of DG.(2)A pilot protection scheme for active distribution network based on PSFC current is proposed.This scheme uses the amplitude ratio of PSFC current at the two ends of the feeder as the action parameter,and uses the phase difference of PSFC current to construct an adaptive braking threshold.This scheme has high sensitivity and ability to withstand transition resistance.It is applicable to distribution networks with different types of DG.This scheme only needs current information and has a good application prospect in feeders without voltage information.(3)Based on the proposed active distribution network pilot protection scheme,a distributed topology identification and fault self-healing scheme for the distribution network was developed.And a prototype of the distribution network smart terminal unit with a modular structure was developed to realize active distribution network distributed fault location,isolation and self-healing.(4)Using the power system dynamic model simulation laboratory,an active distribution network model containing MTDG was built,and the developed smart terminal prototype was connected to the model.The fault location and isolation function in the case of DG grid connection and exit are tested.Using the RTDS system,an active distribution network closed-loop test platform containing an IIDG was constructed,and the fault location and fault self-healing function of the smart terminal prototype in different fault scenarios were tested.The results of above tests show that the developed smart terminal prototype can correctly judge the faulty section under various fault conditions,and isolate the faulty section in a short time,has good reliability and speed,and a certain ability to withstand transition resistance;at the same time,the power recovery time of the non-fault section is much shorter than the fault self-healing method of centralized distribution automation.