Study On Adaptive Protection Strategy For Collector Line In Wind Farm Considering Power Uncertainty

In recent years,off-grid accidents of large-scale wind power generator keep occurring,which challenges the existing protection scheme in wind farm.By taking the protection of the collector line in a wind farm with DFIG as the research object,this paper proposed an adaptive protection scheme of the collector line considering the power uncertainty.Based on the analysis of DFIG fault characteristics and power uncertainty,the problems of the existing protection are analyzed.Firstly,,the delayed action of zone I protection may cause off-grid accident of largescale non-fault line.Secondly,the zone II protection is not sensitive to the failure at the end of transformer and there is an incorrect tripping risk in the reverse direction fault.The analysis indicates that the fundamental problem of the existing current protection is that the protection setting value cannot be adjusted properly according to the operation mode,low voltage ride through mode and fault types.Aiming at the above problems,this paper proposed an adaptive protection scheme of collector line,which can adapt to the output uncertainty,the change of fault types and the LVRT mode of non-fault lines.The adaptive setting value method is put forward.With the use of communication and the introduction of the voltage,the protection setting value will be adjusted so that the protection can adapt to the change of the operation mode and the low voltage through mode of the wind farm.The protection selectivity can also be improved effectively while the protection acts correctly in the guarantee area at the same time.This paper put forward the tripping logic of zone I protection based on the off-grid risk factors.Each wind generator calculates a risk factor of off–grid according to its relay operation margins,the higher the risk is,the faster the protective action is.The result shows the risk factor can be effectively reacted to the dangerous situation of the off grid accident,and the action logic can guarantee against the large-scale off-grid accident and meet the selectivity of transformer fuse at the same time.This paper puts forward an improved method on zone II protection based on the weak-infeed property of the collector line.The improvement can use the difference of impedance amplitude in the network of fault component between forward and reverse direction fault to judge the fault direction.Compared with the original zone II protection,the proposed zone II protection is more sensitive and have directionality,which overcomes the shortcomings of the original II segment protection with lack of sensitivity and the possibility of misoperation.Finally yet importantly,this paper built a simulation model of wind farm collection line on Matlab/Simulink and proved that the proposed adaptive protection scheme of wind farm collector line is effective by simulation and comparative analysis.