| With the interconnection of distributed generation (DG), the fault characteristics arechanged and the protection of distribution network is unavoidably affected. For solving theseproblems, great many scholars have done much work. However, in the study on faultcharacteristics of DG, the control scheme of DG was not considered. DG was considered assame as traditional resources and the fault analysis of distribution network with DG is basedon the voltage resource equivalent model for DG. Obviously, this is inconsistent with the fact.Aiming to solve these problems on fault analysis and protection, this paper studies the controlscheme and output characteristics of DG with inverter interface. Then a fault analysis methodby considering the control scheme of DG is advanced. At the same time, an adaptive distanceprotection and a novel pilot protection based on calculation voltage difference of point ofcommon coupling (PCC) are put forward by considering these DGs interconnected withfeeder.For these DGs with electronic interface, the fault current is determined by its faultride-through control scheme. By studying the control scheme and output characteristics, thispaper proposes a PCC voltage controlled current resource equivalent model for DG undersymmetrical fault and a PCC positive voltage controlled current resource equivalent model forDG under unsymmetrical fault. By studying the control scheme and output characteristics ofdoubly fed induction wind generator under uninterrupted excition for fault ride-through, avoltage equivalent model is advanced for calculating the fault current. Under unsymmetricalfault, a superposition method is proposed for calculating the positive and negative sequencecurrent of DFIG by analyzing its output characteristics. The simulation result verifies thecalculation method.Aiming at single DG’s access, this paper put forward a fault analysis method forsymmetrical and unsymmetrical fault. Under symmetrical fault, the equations between thenode voltage and feeder current are built. Based on this, the solving equations between faultcurrent of DG and PCC are deduced. Thus, the precise method for fault analysis is obtained.Under unsymmetrical fault, the equations between the positive, negative sequence voltages ofPCC and DGs’ currents are built. The solving equations for the positive voltage of PCC arededuced. Thus, the precise method for fault analysis under phase-to-phase short-circuit faultsis obtained. A10kV distribution network case is built in DIgSILENT and the proposedmethod is verified.Aiming at multiple DGs’ access, this paper studies the interrelationship between DG and node voltage. Based on this, the node equation is built by considering the control scheme ofDG. In order to resolve the non-line relation between voltage of PCC and DG fault current, amutual iterative calculations method between voltage of PCC and DG fault current isadvanced for fault analysis.. The simulation result verifies the method.This paper firstly analyzed the effect of DG on distance protection, which PCC is in thefeeder. Based on this, in order to cope with the requirement of feeder protection, an adaptivedistance protection is proposed. Additionally, the relation between the setting of adaptivedistance protection and DG fault current is analyzed. By considering control scheme, equationfor calculating the reactive current of DG is built. Under this fact that the reactance is muchbigger than resistance in distribution network and reactive current of DG fault current is underpriority control during ride-through, a method that substituting reactive current for DG faultcurrent on adaptive setting calculation was advanced. Thus, the adaptive setting is obtained.At last, a case is built in DIgSILENT and the proposed method was verified.Aiming at this DG which PCC locates at feeder, this paper builds the voltage calculationequations of PCC from both sides and analyzes the relation between the voltage differencevalue and fault point. Then the pilot protection based on difference value judgment isadvanced. And the equation between the setting of voltage difference value and equivalentimpedance of the maximum load is deduced. In order to resolve the low sensitivity of pilotprotection, a direction protection is put forward. Thus, all the line is included in the protectionscheme. At last, a case is built in DIgSILENT and the proposed method is verified. |
