Studies On Faulty Feeder Selection Scheme For Distribution Network With Inverter-interfaced Distributed Generators

The neutral point with non-effective grounding method are commonly used in traditional distribution systems,such as arc suppression coil.After a fault occurs,the arc suppression coil is automatically activated,whose inductive current is used to compensate the capacitor current at the fault point.Thus,the magnitude of fault current could be reduced to a lower value and has the advantages of extinguishing the arc and lower over-voltage.For such systems,single-phase-to-ground fault occurs frequently,and the grounding current more weaker during the compensation process that result in difficult detection with low fault discrimination features.In addition,the utilization of renewable energy such as solar,hydropower and wind,means the increasing number of distributed generators has been connected to systems.Under the high penetration levels,the traditional power flow change,multi-source network topology structure,but the fault process becomes more complex due to the random,intermittent current characteristic,which introduces lots of new challenge to the power relay protection with low fault features.Therefore,focus on the inverter-interfaced distributed generator(IIDG)that connect to systems by inverter,a non-setting fault feeder selection scheme based on Kaman filter algorithm,which combines the features of interphase current mutation to improve the accuracy of faulty feeder detection in active distribution networks.In this thesis,the faulty feeder detection scheme for distribution network with IIDG injection is studied as follows:Firstly,based on the generation mode and principle,the IIDG has been divided into voltage controlled current source and constant current source model,and the current output characteristic during the steady state and fault conditions are obtained as well.Different from traditional source has stable current,the current of IIDGs is randomness and intermittent and thus,the Gauss-seidel iterative method is introduced to pre-estimate their current according to the superiority in the field of optimal estimate,which provide data sources and theoretical support for the subsequent fault line selection scheme.Secondly,considering the impacts of fault current boosting and fault location under complex fault conditions for the distribution network with ⅡDG injection,based on a single fault feature may cause the misjudgment,the interphase current mutation after fault occurs and arc suppression coil adjusted are combined as fault feature.In addition,the current of IIDGs are added into the fault feature to pre-estimate fault feeder curve using Kalman filter algorithm,by computing the relative distance between fault characteristics of each feeders and pre-estimated faulty feeder curve to identify the faulty feeder.Finally,in order to verify the effectiveness of proposed faulty feeder selection scheme,fault case analysis was conducted to study the influence factors including fault occurs location,IIDG output power,fault resistance,fault initial angle,the range of compensation degree adjustment,IIDG penetration levels,etc.Simulation results shown that the space relative distance of each feeders has a good performance in fault feeder selection,which is conducive to solving the influence of high permeability of inverted-type distributed power into the distribution network.