Research On High Sensitivity Traveling Wave Protection Technology For HVDC Transmission Lines

Due to its large transmission capacity and long transmission distance,HVDC transmission has developed rapidly in recent years and has become an important part of China’s power system.Its main transmission conductor is an overhead line,the line distance is long,the corridor environment is complex,and it is easily affected by the weather.It is the component with the highest failure rate of the DC transmission system.Traveling wave protection is the main protection of existing DC transmission lines.Although the action speed of traveling wave protection is fast,the sensitivity is low and the ability to withstand the transition resistance is poor.Improving the sensitivity of traveling wave protection of HVDC transmission lines is of great significance for the safe operation of HVDC transmission systems.Therefore,this paper has conducted in-depth research on this problem.Firstly,based on the PSCAD/EMTDC off-line electromagnetic transient simulation platform,a double-ended HVDC transmission system simulation model was established,and multiple sets of ground fault simulations were carried out.The traditional pole wave rate protection effect was systematically analyzed.Secondly,for the traveling wave protection setting of DC transmission line,the fluctuation of fault index values caused by different sampling points is analyzed systematically,and the wavelet transform protection algorithm is taken as an example for system analysis.For the same continuous fault traveling wave,there are countless different discrete sampling sequences.The study found that the fluctuation range of the fault index value can reach several times in different sampling sequences.Therefore,it is necessary to avoid the fluctuation of the fault index caused by the sampling sequence selection in the protection setting stage.The paper proposes that through the small step size simulation,the multi-sampling method can be used to accurately estimate the fluctuation range of the fault index value,which has certain reference significance for the protection and setting work of the actual project.Finally,the sensitivity of the traditional polar wave rate of change method is low,and the wavelet transform method is complicated.The paper proposes a new type of traveling wave protection method.In the mathematical principle,the new method extends the traditional polar wave rate of change method,which is called the generalized polar wave rate of change method.The simulation example shows that the sensitivity of the generalized polar wave rate of change method is much higher than the traditional polar wave rate of change method.When there is a transition resistance,its sensitivity is also slightly higher than the wavelet transform method.When the new method is run online,the calculation amount is only more than several times multi-multiplication and addition operation of the traditional polar wave rate of change method.The calculation cost increases little,which is much smaller than thewavelet transform method.The new method has important reference value for the protection and setting of actual DC transmission engineering.