HVDC System Grounding Electrode Line Protection Research

The grounding electrode as an important part of HVDC system, reliable protection is essential to achieve.Grounding electrode is mainly composed of earth electrode line,earth electrode body and related control equipment.The earth electrode line is usually double parallel lines,and for dozens of kilometers long,The protection configuration is usually include the differential current protection, time-domain pulse protection and impedance protection.Grounding electrode fault most of the short circuit fault and disconnection fault,restricted by factors such as fault characteristic is not obvious,the protection of the existing methods are unable to realize fault types, lead to HVDC system blocking accidents often occur,seriously affected the stability of the dc transmission.Therefore, this paper studies the adaptive imbalance protection action selection criterion and put forward the longitudinal differential protection method of grounding electrode.Firstly, the paper introduce the HVDC system grounding electrode protection methods,and comparing the characteristics of existing DC system grounding electrode protection methods and scope of application.Defects of existing protection methods, use of the characteristics of unbalance current, study a imbalance protection adaptive action selection criterion method, reduce the probability of protection malfunction and refused, to ensures the accuracy of the action criterion.Combining the operating characteristics of the grounding line and their own parameters,creatively put forward the longitudinal differential protection principle on the grounding line protection.In order to solve the unbalance protection method can’t distinguish between fault types,paper analyzes the change of the characteristic in different fault types,in combination with characteristics of transverse differential protection and longitudinal differential protection action for accurate identification of the fault type.In determining the fault types of premise, the protection of DC operation mode under different actions to improve,enhance efficiency of the protection strategy.Paper using MATLAB software to set up a HVDC system model.Combined with the theoretical analysis, verify the effectiveness of the protection methods.Theoretical analysis and simulation data show that,this paper puts forward that the imbalance of adaptive protection action criterion compared to the traditional action criterion, the threshold value according to the grounding current to setting,to improve the protection action of sensitivity.Based on the principle of longitudinal differential protection grounding protection method is put forward,and combined with the feature of traditional imbalance protection action,under the premise of ensuring rapid action to achieve an accurate identification of the type of fault.In addition, the optimized strategy of protection operation, improve the effectiveness of the protection action and reduce the probability of HVDC system Lockout.