Research On Pilot Protection Of New Energy Power Generation Grid-Connected Tie-Line

New energy power generation such as wind and photovoltaic has recently developed rapidly,especially in centralized grid-connected.Compared with the traditional power plant connection type,the centralized grid-connected new energy station connection type is complex and diverse,and its impact on the grid-connected tie-line protection needs to be analyzed and studied.At the same time,due to the influence of the inverter control strategy,the sensitivity of the pilot protection of the new energy grid-connected tie-line is reduced.Therefore,it is urgent to carry out research on new protection principles or schemes suitable for the new energy grid-connected tie-line.This paper has completed the following research work:(1)The fault characteristics of the new energy grid-connected tie-line are analyzed,mainly manifested as limited fault current amplitude,unequal positive and negative-sequence impedance,and controlled phase angle.By analyzing the adaptability of traditional pilot protection,it is found that the sensitivity of pilot protection decreases or even refuses to operate.The adaptability of the sequence component direction element of the new energy grid-connected tie-line is analyzed.The results show that the positive and negative-sequence direction elements will be affected by the inverter control strategy,resulting in the positive and negative-sequence direction elements not operating,while the zero-sequence direction element can operate correctly.(2)A pilot protection method of negative-sequence current amplitude ratio on both sides of the line is proposed.According to the control strategy of the inverter to suppress the negative-sequence current,the expression of the negative-sequence current amplitude ratio between the system side and the station side is derived when the internal and external faults of the grid-connected tie-line occur.The analysis shows that the negative-sequence current amplitude ratio is much larger than 1 when the fault occurs in the grid-connected tie-line.When the photovoltaic power station side reverse direction fault occurs,the negative-sequence current amplitude ratio is about 1.The amplitude of the negative-sequence current on both sides of the grid-connected tie-line is small when the fault occurs outside the system side.Based on this,the protection criterion is proposed.Furthermore,the criterion and method of negative-sequence current amplitude ratio protection for the photovoltaic grid-connected teed transmission line is given.(3)A new energy grid-connected tie-line zero-sequence directional pilot protection setting method is proposed.Considering various connection groups of main transformers in the new energy stations,including YNd,YNdd,and YNynd connection type,the expressions of zero-sequence measured impedance on both sides of the line are derived when ground faults occur inside and outside the grid-connected tie-line.The results show that the zero-sequence measurement impedance of the new energy station side of the main transformer with YNd,YNdd connection type is related to the main transformer connection group when the grounding fault occurs in the grid-connected tie-line area.And the YNynd connection type is related to the main transformer connection group and the system operation mode.Based on the results,the setting method of the maximum sensitive angle and action zone of the zero-sequence positive and negative directional elements of the new energy grid-connected tie-line is given.A new energy station and its grid-connected system are established by PSCAD/EMTDC,and a large number of fault simulations and analyses are carried out.Considering different fault locations,transition resistance,new energy output,and other factors.The simulation results are consistent with the analysis conclusions.The proposed protection principle and method can correctly identify faults and have certain sensitivity.