Research On Effect Of Stray Magnetic Field To Performance Of Heavy Current Transformer

The capacity of generating units is growing because of the developing power systems, resulting the bus current’s increases, which makes the current transformer, used in bus, suffers tens of thousands of amperes’ primary current, brings new challenges to the manufacture and design of the current transformer. Including effects of tens of thousands of external amperes of current to the current transformer and verification of transformer rated primary current up to tens of thousands of amperes.In response to these challenges, by theoretical analysis, numerical simulation, physical verification experiment and simulation comparison methods, the paper researches the influence of outside current to the current transformer, and the shielding methods to stray magnetic field, and the proper method used in this super heavy current transformer, the main work is as follows:1. Research in-depth of the reason how external magnetic field affects large current transformers, and established the theoretical derivation on two-dimensional plane, as well as the simulation model for three-dimensional electromagnetic field, to demonstrates the conclusions from theoretical derivation by physical experiments and finite-element simulation.2. Focus on the influence of stray magnetic fields to the transformer core, obtained transformer core flux under the outer conductor, as well as the impact of the outer conductor to the transformer depending on whether exit the outer conductor. Moreover, the paper determined the conversion formula about the disturbance of the current from the rest of the five-phase bus to the remaining one phase bus bar under three-phase six-wire power system, the paper also pointed out the errors of before researchers.3. Focuses on analysis of the "four 90" winds evenly balanced winding method in the electromagnetic shielding studies for large current transformer, and demonstrates the correctness of this approach by physical experiments and finite element simulation.4. Present three common test methods in the study of the error detection for large current transformer, and focuses on the "a bus mandrel Law", which is achieved by physical experiments in this paper.