ABSTRACT
In the traditional method, for the single-circuit transmission lines, when a sequence symmetrical current flows through the three phase circuit, only produce its sequence voltage without coupling with other sequences under the assumption that the parameters of transmission lines are symmetrical. For the parallel double-circuit, assumed that the geometry mean distance is far less than the distance between double circuits with electromagnetic coupling, the mutual inductances of the double circuits are equal. In fact, for the single-circuit transmission lines, especially the not transposed one, the space between the lines are asymmetrical; for the multi-circuit transmission lines, the distance between one phase of the circuit and the three phases of the other circuit are not equal, thus lead to the asymmetry of the parameters of three phases and the coupling between the each sequence. The positive sequence impedances, zero sequence
1 INTRODUCTION
The parameters of transmission lines, as the basic parameters of power system, have an important role in the calculation, analysis and protection of power system. Due to the variability and complexity of the lines construction field and the geographical environment, it is almost impossible to calculate transmission lines’ parameters precisely. therefore, the domestic regulations required that positive and zero sequence impedances of transmission lines must be measured actually.
