Study On Protection Schemes For Collector Lines In The Wind Farm And Its Teed Line

With the rapid development of wind power generation technology,the consumptive ability of power grid has significantly increased.In accordance with the principle of proximity,the electric energy from wind turbines in the wind farm is collected by the corresponding teed lines.If the protection setting and coordination of the collector lines is inappropriate,the scope of removing fault will be expanded.In serious cases,this will affect a number of wind farms around and cause large scale cascading trip-off of wind turbines.After the wind farm is connected to grid as a teed line,the correct operation of teed lines protection is very important to ensure the power supply reliability and operation stability of the three side system.Therefore,it is of great theoretical significance and application value to carry out the research on the relay protection of collector lines in the wind farm and its teed lines.Based on typical unit capacity,operation parameters,low voltage ride through strategy and wiring form in the wind farm,a detailed electromagnetic transient simulation model of wind turbine and wind farm,which is connected to grid as a teed line,is built in DIgSILENT/PowerFactory.On the basis of the above simulation model,the research work on the existing protection adaptability analysis and new protection scheme is carried out.For collection lines,the adaptability of the existing two stage overcurrent protection is analyzed.It is pointed out that the overcurrent zone-? and the fuse protection have improper coordination.The sensitivity of overcurrent zone-? of the collection line is too high,and its selectivity is not enough.The overcurrent zone-? is not fit with the LVRT characteristics of wind turbines,which results in its failure to distinguish between the internal fault and external fault.In order to solve the above problems,a new three section current protection scheme for collection lines is proposed based on protective characteristic of fuses and LVRT characteristic of wind turbines.Theoretical analysis and model simulation show that the proposed protection scheme has good performance.For teed lines,the adaptability of current comparison pilot protection and distance protection is analyzed.It is pointed out that the current supplied by the wind farm which is connected to grid with a teed line may lead to the misoperation of current comparison pilot protection.A mathematical model for measuring impedance is built.It shows that measuring impedance is not linear with the short-circuit distance due to the influence of the transient impedance and the equivalent sequence impedance of the wind farm.Therefore,a new comprehensive pilot protection scheme is proposed for teed lines with wind farms.From the point of view of teed lines topology,using the relationship between the positive-sequence voltage and positive-sequence current at the three sides,the main criterion based on comprehensive voltage amplitude difference is proposed.Based on the measuring impedance characteristic,an adaptive distance auxiliary criterion is proposed to eliminate the dead zone of the main criterion.The proposed protection scheme can realize whole line high speed performance.Theoretical analysis and model simulation show that the proposed protection has the advantages of strong resistance to the fault resistance,low requirement for data synchronization and little influence from wind power fault characteristics.