Research On A New Stray Loss Tester With Mirrorr Method And Shielding In Power Transformers

Magnetic shielding and electromagnetic shielding are widely used on tank, clamping et al. in large power transformer. They have many types and combination. After mainly transformer manufacturers in our country have developed1000-1500MVA/1000kV UHV transformer with super capacity, they demanded to further study of shielding, especially considering the cost of materials. Different types laminations, and combination with magnetic steel and non-magnetic steel, have different performance. The loss and flux distribution are paid more attention to when engineer designing transformer. A test device would be design and manufactured to further study shielding and give a quantized conclusion, not qualitative. The results of research can give to designer to reference and optimization, and used on large capacity widely.Air-core coil is generally used to generate leakage flux for the research of shielding in the laboratory. However, due to its reluctance is air mainly, the maximum leakage flux density air-core coil produced only is6mT. It is very littl e than large capacity transformer producted (100mT). It is difficult to reach the product-level. If did experiment and simulation directly in the actual transformer products, it would encountered high voltage, insulation, whole oil closed and many other problems. Through theoretical study and numerical simulation derivation, this paper provides a dual-core Stray Loss Tester with Mirror Method in order to solve the above problems. Magnetic shielding surface on the coil side can be approximated as a field normal boundary (the flux on the surface perpendicular to the magnetic shielding), which is equivalent to the surface plane as symmetry plane, has two equally iron-core coils on each side. Using this mirror principle, a iron-core coil with the same parameter was placed in the symmetry location of the exciting iron-core coil, in order to ensure the loss of the excitation component is essentially unchanged. Then obtained the loss and separated the loss of the specimen.After detailed comparison of the data of2D,3D numerical simulation (considering isotropic and anisotropic homogenization equivalent of laminations group), the magnetic field distribution under no-load (dual-core, no specimen) and load (with specimen) conditions is almost the same, no-load condition can simulate the loss of core and other exciting component under load condition, the dual-core mirror method is feasible and effective.After design optimization and manufactured, system test, measurement show that the dual-core Stray Loss Tester with Mirror Method can obtain equivalent strong leakage magnetic field(>100mT) within large capacity, exceptionally large capacity power transformers, reactors and other electromagnetic products in the laboratory. It gives a effective solution for product-level engineering problems. The measurement results of the loss and flux distribution are in good agreement with the simulation. The results of experiment and simulation confirm each other, and the anisotropic homogenization method of laminations group is correctly and effectively. The experiments also showed that magnetic field in no-load condition was in good agreement with load one, the leakage magnetic field essentially unchanged, dual-core mirror method can separate the loss of specimen correctly. The effectiveness of dual-core mirror method has been proved.