Study On Impact Of GIC On Converter Transformers

The converter transformer working at the rated state will partially be saturated, when GIC invades a power system via the grounded neutrals of transformer. And its magnetizing current will be distorted accompanying with various harmonic and reactive power loss, resulting in transformer damage or transformer life reduction, even system voltage fluctuations or the protective relay malfunctions. As the rapid development of China's High-voltage DC transmission (HVDC) system, high-voltage,long distance,high-capacity transmission had been widely used, these factors will suffer the converter transformer from the threat of GIC more and more serious. Therefore, the research on the influence of converter transformer due to GIC in power is causing scientists and engineers more and more attention.In this paper, the DC bias'mechanism of converter transformer under GIC is studied. Then based on the magnetization curve and UMEC theory, the converter transformer simulation model for analyzing the GIC problem was founded and great simulations were carried out in PSCAD/EMTDC using this model, including the converter transformer magnetizing current harmonic characteristics, network side and valve side harmonic characteristics, reactive characteristics and the converter bus-voltage distortion; at the same time DC current of DC converter station was simulated to analyze the impact on the DC side of HVDC under GIC.Finally, some measures restraining GIC such as putting a resistor in seires between transformer neutral, putting a capacitor in seires between transformer neutral, putting a capacitor in seires on AC transmission line, reverse DC current compensation and DC electric potential compensation were analyzed, in which some typical methods was simulated using the above model, then the good result achieved in suppressing GIC problems was fully validated, to provide good ideas for solving GIC problems that may arise in the future of China.