Distribution Network Protection Considering The Characteristics Of New Energy Fault Current Limiting

Encouraged by boosting advancements and wider applications of power electronic techniques,the new energy power generations have been extensively employed.An increasing number of distributed generations are integrated into distribution networks,but also bring about some problems.When Inverter Interface Distribution Generator(IIDG)is connected to the distribution network,the distribution network changes from a single power supply radial structure into a multi-supply network structure,"which changes the characteristics of original fault current in the distribution network.The traditional protection configuration may no longer be valid.In this dissertation,based on the limited current of distributed power supply,a delay-based distance protection method is proposed distribution networks with distributed generations.Firstly,according to the requirements of low voltage ride through(LVRT)in photovoltaic grid-connected power system,it is found that the fault current characteristics of IIDG in LVRT duration are affected by the corresponding control strategy.Therefore,it is necessary to establish a proper LVRT control strategy for IIDG to satisfy the related grid code,then a theoretical model can be derived to analyze IIDG fault current and further figure out the time domain expression of the fault current.In the case of balanced and unbalanced faults,through examining the IIDG fault currents,IIDG can be regulated to output only positive sequence current,and the fault current would not exceed 1.2 times of the rated current.Furthermore,a protection configuration method for distribution network based on delay enabled distance protection is proposed.As the photovoltaic capacity is much smaller than the system capacity,and the photovoltaic fault current does not exceed 1.2 times the rated current,the activation of protection can be postponed,which subsequently isolates the faults.By setting different types of faults at different points outside or inside the area,the correctness of the delay distance protection configuration is verified.The influences of the transition resistance and white noise on the distance protection are studied.The influences of additional load branch on the delay protection is also analysed,thus consolidating the effectiveness of the delay based distance protection.Finally,the fault section identification method of distribution network based on transient current is proposed.When the internal distribution network with distributed power supply fails,the distribution network faults and the closed static switch will cause two obvious changes in the current of the faulty line.The value of the transient current is far greater than the non-fault line current transient quantity.In this regard,the fault section identification method of distribution network based on transient current is proposed.When the detected two changes in the current transient magnitude are greater than the set value,it is identified that the fault occurred in the protected area.The effectiveness of the method is verified by simulation.