The Analysis And Reduction Of Taishan Power Plant Transformer Inrush Current

The electric power transformer no-load merging into power system will cause inrushcurrent, because one winding of transformer’s voltage changes suddenly based onconstant-linkage theorem, and superimposition of residual magnetism and bias magnet mayleading to saturation flux density. Inrush current would reach six to eight times oftransformer’s rated current highest, and contains large of second harmonic, which not onlywill cause unwanted operation of relay, but also will bring serious influence by voltage’sdecrease, interference of harmonic, sympathetic rush, and so on. There are three500kVstep-up transformers in Taishan electric power plant, that suffer from unwanted operation,even contiguous generator’s load fluctuation by sympathetic rush, because of no-load merginginto power system. It seriously affected the safety and credibility of generator, and brought thecompany much bad influence, so we need to seek for an effective and suitable method torestrain rush current imminently.This paper starts with research and analysis of the origin and main influencing factor, toanalyses the correlativity among the residual magnetism, bias magnet, magnetic flow, rushcurrent, electric source. The article grasps the main point that as long as control the phaseangle of transformer switch off or switch on, then can control the numerical value anddirection effectively. Making a point that if the residual magnetism and bias magnet is theopposite polarity, equal and contrary reaction when transformer no-load merging into powersystem, then the magnetic flow must be few to avoid core stataration, restrain rush current.Simultaneously according to situation of Taishan electric power plant, by control one phase ofthree-phase transformer’s angle equal to90°when switch off or on，the other two phase eventhough do not operate on peak of voltage, but at least ensure do not overlying, at last avoid alarge of rush current. This theory is applied to the technology modification works to restrainour unit’s500kV step-up transformer’s rush current, research existing equipment and system,and confirm implementation plans. Pointing at the characteristic of restraining rush current inthis article, author launch many test and design several test program, and revise data byanalysis. It proves that this plans could really reduce rush current finally, which could controlrush current is not much than the rated current. The effect of the rush current technology modification of Taishan step-up transformers is excellent, the rush current no longer cause thedifferential protection malfunction or sympathetic rush, that achieve its goal.