Research On Improving Measurement Accuracy And Ability To Endure Transition Resistance In Distance Protection

By using the variation characteristics of voltage and current at short circuit simultaneously,the protection range and sensitivity of distance protection are less affected by the change of system operation mode.Therefore,Distance protection is widely applied to high voltage and EHV transmission lines.However,when the actual power system faults,the electrical quantities which need to be measured often contain the aperiodic component,which leads to large errors in the extraction of fundamental wave.Meanwhile,the presence of transient resistance will add additional impedance to measurement impedance.Those above factors obviously affect the performance of distance protection.For the errors in the extraction of fundamental wave caused by aperiodic component,an error correction algorithm is proposed.Using the sampling value integral of two different power frequency cycle,this algorithm can obtain the decay time constant and initial value of the aperiodic component via expanding the logarithmic function into Taylor series.Thus,the calculation error caused by the aperiodic component can be computed,and the true fundamental wave can be obtain by eliminating this calculation error from the traditional Fourier algorithm results.Secondly,some corresponding optimization measures are proposed for improving the accuracy of calculating the parameters of the aperiodic component,which enhances the performance of this error correction algorithm.Furthermore,application conditions for error correction algorithm are set up to let this algorithm adjust its data window automatically according to the influence of the aperiodic component,which gives consideration to both speed and accuracy.The results of practical calculation example and RTDS dynamic simulation show that the error correction algorithm can reduce the influence of the aperiodic component and improve the accuracy of extracting the fundamental wave effectively,and the amplitude error of the fundamental wave are limited to ±3%.For the errors in measured impedance caused by transition resistance,this paper analyzed the limitation of traditional distance protection algorithm from the point of solving equations and improved the equations of traditional algorithm,then proposed an improved distance protection algorithm by replacing the phase of the current in the fault point with the phase of the negative sequence current in the node where distance protection is located.Furthermore,the rationality of the substitution of phases is discussed.The simulation results of 500kV actual system based on PSCAD show that the influence of transition resistance is reduced by the improved algorithm effectively.When grounding fault with large transition resistance,the improved algorithm can also obtain the fault distance precisely,which enhances the correct operation of distance protection...