Research On The GIC Harmonic Response Characteristics Of The Current Transformer

The Current transformer (CT) an important electrical secondary equipment which is now widely used in power system, its ability of transferring the primary current correctly is crucial to electrical measurements and protective relaying. Geomagnetic induced current (GIC) and the High Voltage Direct Current (HVDC) systems under mono-polar operation may lead to DC bias of current transformers(CT), core saturation, distortion of the exciting current and generating harmonics, which will have an effect on transferring characteristics of CT and result in the electrical measurement error and transformer differential protection. Currently, research on DC bias of the transformers induced by GIC has been carried out, however, DC bias of CT and its harmonic analysis is rather limited. Therefore, this paper will conduct a study on the harmonics response characteristics of the CT, which will have a important significance for the secure and stable operation of power system.Firstly, this paper analyzes the generation mechanism of DC bias of CT caused by GIC, and further investigates the equivalent circuit and Core magnetizating model for GIC bias, and the CT model based on Jiles-Atherton theory is adopted. Secondly, this article establish an equivalent analysis model of CT under the A.C. systems with GIC, and large work of simulation experiments is carried on in PSCAD/EMTDC. This paper also study the distortion of the exciting current and the harmonic distribution level by means of changing the magnitude and frequency of GIC, the winding ratios, etc.Finally, how the GIC bias of CT affect the electrical measurement error and relaying protection is discussed and put forward some method to reduce the harmonic content of CT.