The Research Of Improving The Ability To Withstand Fault Resistance In Distance Protection Based On Double Terminals

Distance protection is one of important means for fault handing on transmission line. But fault resistance is an important factor to influence the distance protection performance. The opposite terminal is easy to obtain in smart grid. Based on the original input on distance protection, using the opposite terminal can improve the ability to withstand fault resistance in distance protection. This paper firstly summaries the research of the current situation on transmission line protection, then proposes a new principle to improve the ability to withstand in distance protection which based on double terminal’s electrical information, aiming to solve the problems of the traditional distance protection caused by the exist of the change of transition resistance.The paper is based on 1 mode equivalent circuit of transmission line, derive a ranging equation for protection in a particular frequency according to the characteristic of equal voltage of the point of failure.Then expands the functions of hyperbolic sine and cosine into the Taylor series in equation of distance protection. Then Ignore polynomial of high order to approximate in three methods, we can get three kinds of ranging equations for protection,using least square optimization algorithm to obtain the fault distance. Finally, the most suitable algorithm can be determined by comparing estimation accuracy of the fault distance under the three algorithms and considering the amount of computation algorithms. The Taylor series expansion and simplified calculation is the innovation of this paper.In order to actualize the improvement of protection performance using the principle which is proposed, we need to filtered the information of the specific frequency component in transient according to a Band pass filter. So in this paper a FIR digital band pass filter which meets this algorithm is studied and designed in this paper.Lastly, a double ended power supply system in which transmission line length is 300 km and voltage level is 500 kV is chosen and simulated in EMTP. Then the new principle of improving the ability to withstand fault resistance in distance protection which is actualized inMATLAB. The simulation results have verified the accuracy of the distance protection principle which is presented. The protection method is not only affected by the change of transition resistance or system operation, but also can directly reflect the fault location.