Research On Distribution Line Protection With Distributed DFIG

After the distributed doble-fed induction generator(DFIG)connected into the distribution network with high permcability,the power distribution structure of the distribution network was changed from a single-power radial network to a double-end power supply structure.In order o make up for the problem that the truditional current protection will low selective,according to the technical regulations of the State Grid Corporation,the scheme of pilot protection and the addition of directional components to the current protection can be used.However,due to the influence of low voltage ride-through control,the fault current transient characteristics of the DFIC are different from those of traditional power supplies.As a result,the traditional pilot protrction und directional components constructed based on the system power supply transient characteristics will act incorrectly.Therefore,it is necessary to propose a pilot protection scheme snd directional components suitable for the distribution line with DFIG.First of all,this paper analyzes the transient characteristics of DFlG current of symmetric and symmetric fault under the input of Crowbar cireuit.There is a power freuence component related to the control mode and control parameters in the DFIG short circuit current under uninterrupted excitaton control,resulting in the short circuit current no longer being a stable power frequency compunent.After the fault occurs,the current randomly fluetuates,which is obviously different from the traditional power supply.The analysis results were verified by the recorded data of the low voltage ride through field test.Further,by analyzing the influence of the traditional differential prutection under the frequency deviation characteristic of DFIG,the operation value is unstable.Therefore,form the perspective of the time domain,the current waveform mismatch degree on both sides of the protected line is obtained through the Hausdorff distance algorithm,and a longitudinal protection scheme based on the waveform mismatch is constructed,and a sliding data window is added to increase the speed of the protection scheme.At the same time,improving the anti-interference ability of the Hausdorff algorithm.It can also operate quickty and reliably in theSNR5.On the basis of a lower sampling rate,except for the single-phase grounding,the sensitivity drops significantly.Other failure conditions can meet the basic requirements of the protection of the four characteristics,and the quick action is significantly improved than the traditional protection.Finally,referring to the construction ideas of traditional directional components,the difference between the forward and reverse fault current time-domain waveforms is analyzed.The current waveform before the fault 20ms is used as a reference component to compare the difference between the positive and reverse fault current and the reference current.The cosine similarity algorithm reflects the difference in angles and constructs directional elements.Finally,through the power system electromagnetic transient analysis software PSCAD/EMTDC,using the first domestic decentralized wind farm demonstration project as a model,a large number of simulations have verified that the proposed directional component can be reliable,sensitive and rapid under various fault conditions action.