An Estimation Method of Zero-sequence Circulating Currents using Single Phase Formation

Abstract

In this paper, a method of estimating the zero-sequence circulating current ZC in the steady state and the grounded faulted state of the power system is proposed, when three-phase constant data is given in part of transmission line data of the power system. The proposed method can efficiently estimate the ZC of each grid point for any grid configuration. The methods of estimating ZC for pre-determined specific systems configurations have been used in Japan for many years, but lack generality to complex system configuration. On the other hand, three-phase calculation, which is a direct means of calculating ZC, has advantages in accuracy and the applicability to any system configuration, but is difficult to apply to large-scale systems. In this paper, a new ZC estimation method is proposed by taking the transformation of the a-b-c variable in the phase coordinate system into the 1-2-0 coordinate variable in the symmetric coordinate system. (1) Arbitrary system configuration and system scale are allowed to estimate. (2) Based on symmetric coordinate method single-phase data, only three-phase data is needed for a target of ZC estimation. (3) ZC of each part of the system can be efficiently estimated, not only in steady state but also in any grounded fault condition. The usefulness of the proposed method was verified by demonstrative application for the test system.