Research On The Protection Principle And Simulation Of The Double Circuit Lines On The Same Tower

With the rapid development of the national economy, the shortage of transmissionchannel resources has become a global problem in the construction of global large-scalegrid. The most prominent advantage of double circuit lines on the same tower is the abilityto take advantage of the limited transmission corridors to improve the transmission capacityof the power system, save the investment and construction of capital. It has been widelyused since last80s. The difference between the double circuit lines on the same tower andthe single circuit transmission line is the increase of the line number. The distance betweenthe adjacent lines is so short that the mutual inductances between the six lines becomebigger, which leads to asymmetry of the line parameter and complexity of the analysis infault. Due to the diversion of its construction characteristic and fault type, experts andscholars at home and abroad has done a lot of research on the double circuit lines on thesame tower. Most the of research focus on the symmetry line and asymmetric lineprotection research still needs to be further studied. Funded by the National Natural ScienceFoundation of China, this paper have done some preliminary exploratory study on theprotection of the double circuit lines on the same tower.This paper proposes a protection program on the double circuit line on the same tower,which do not depend on the communication. The protection program is made up of faultphase selection，fault line selection and fault location. Besides, this paper have also donesome research on the static characteristics of the relay, which provides a research platformfor the validation criterion for the latter part of the distance protection.According to the characteristic of the double circuit line on the same tower and the PItype transmission lines in the Dynamic Simulation Laboratory, this paper establish thecircuit model of the double circuit line on the same tower with the help of PSCAD. Firstly,the paper gives a detailed analysis of phase selection in the single circuit line. The two samephases could be handled as a whole in the phase selection of the double circuit line. Thus,the theory of the phase selection in the single circuit could be used in the two circuit line,and the detail effects of such theory were analyzed. With reference to the theory of the transverse differential protection, the paper proposed the criterion of line selection on thebasis of two-phase current and the differential mode value of the phase current on the samephase. The measured impedance was disproportionate to the distance when the location ofthe line changed in the double circuit line on the same tower. In order to solve this problem,the paper proposed a method to locating the fault point. The method consists of two steps.The first step is the location of line segment in which there is fault point. The second step ifthe location of the fault point. Then, the paper gave a detail introduction of this method.The simulation program about the static characteristic of relay on the basis of Matlabwas also analyzed. The simulation model had two problems. One of the problems was thatthe model is not easy to change and expand. The other one is that the modeloverwhelmingly dependent on the component and calculation is based on the form of vector.Aimed to solving the two problems, the paper completed the analysis of the operationcharacteristic of the simulation model based on PSCAD.Lastly, the paper gave a summary and prospected for further work.