Research On Applied Technology Of High-performance Grain-Oriented Silicon Steel In Power Equipment

High-performance grain-oriented(GO)silicon steels are the key materials for the manufacture of ultra-high voltage(UHV)alternating current(AC)/direct current(DC)transformer,distribution transformer with high efficiency and energy saving,saturation reactor of DC converter valve.Improving the quality of domestic GO steel and solving the problem of core material being stuck by foreign countries are of great significance for independently guarantee the safety and project progress of UHV transformer and saturation reactor.In this paper,the application techniques of0.23-0.30 mm high magnetic induction GO steel,0.18 mm ultra-low core loss GO steel,heatproof domain-refined GO steel,and ultra-thin thickness(below 0.1 mm)GO steel during the localization process were researched.The electromagnetic characteristics of high magnetic induction GO steel under complex working conditions,the selection method of AC/DC transformer core material,and the evaluation method of service state and service life of GO steel were studied.For samples with the same core loss under normal condition,the thick silicon steel with low magnetic induction shows lower power loss and excitation current under DC bias condition,while the thin silicon steel presents lower core loss under harmonic condition.The mechanism behind this phenomenon was analyzed.The selection proposals of GO steels with different core loss,thickness,magnetic induction,and tensile stress for 3 types of power transformers(AC transformer affected by neutral current in HVDC ground-return system,converter transformer with DC bias and harmonics condition,and lager AC transformer with harmonic condition)were put forward respectively.Besides,the equivalent relation between the accelerated deterioration test condition of the insulation coating and the coating state after the actual operation for several decades in transformer was established.The electromagnetic characteristics and service reliability of 0.18 mm ultra-low core loss GO steel were studied.The simulation analysis and experimental verification of the S15 transformer core were carried out based on the Mag Net finite element analysis software.When the magnetic flux density was 1.35 T,the loss of18QH065 GO steel was as low as 0.349 W/kg,which was close to the level of amorphous alloy,and the magnetic induction(B₈₀₀)was 0.32-0.40 T higher than that of amorphous strip.After holding at 130?for 1200 h,the growth rate of core loss of0.18 mm GO steel was less than 2%.The harmonic loss of 0.18 mm silicon steel was obvious lower than that of the conventional thickness silicon steel.The influence of DC bias on core loss was mainly showed in the low magnetic density region,and the loss was almost the same after magnetic flux saturation(B_m?1.9 T).Finally,the no-load loss of designed 10 k V/630 k VA transformer is 417 W(26.7%lower than that of transformer with first-grade energy efficiency in standard of GB 20052-2013),and the load loss was reduced by 12.8%,which means obvious advantage of energy conservation.The microstructure,grain orientation,and magnetic performance of heatproof silicon steel during stress-relief annealing were investigated.Based on heatproof GO steel,the Epstein-SST(single sheet tester)conversion factor and equivalent magnetic path length were calculated,and then an ultra-high energy efficiency transformer was developed.Results show that,the average size of micrograins in notched region increased from 42.3?m to 68.2?m after annealing at 850?for 0-8 h.The orientations of micrograins grown on large-size Goss grain included not only the non-<001>orientations,such as{210}<-241>,{215}<1-20>,and{110}<1-12},which were harmful to the magnetic properties,but also the favorable{100}<001>and Goss.Correspondingly,the core loss of the Epstein specimens first decreased then increased slowly(the growth rates below 1.2%)during annealing.The Epstein-SST conversion factor?P for 23ZDMH80 heatproof steel was 8.6%(higher than 5.0%the value recommended by IEC standard),and the equivalent magnetic path length was0.489 m.Finally,the developed 10 k V/400 k VA transformer with TDWC presented ultra low no-load loss of 289 W,load loss of 3072 W,and noise of 35.4 d B,it shows significant advantage of energy conservation and environmental protection.An inorganic insulating coating on the surface of ultra-thin GO steel was prepared by using aluminium phosphate,nano-aluminium silicate and chromic anhydride as the main raw materials.The effects of coating on magnetic properties and service safety were studied,and the electromagnetic and noise characteristics of ultra-thin GO steel were evaluated.Results show that,under the optimum sintering and solidification process at 700?/20 s,the adhesion of the coating is grade A and the insulation resistance coefficient reaches 22.5?·cm².The mathematical equation between reduction rate of core loss?P and coating thickness?is established.In addition,The voltage breakdown strength test device of ultra-thin GO steel coating was designed and built,and the comparison test of the U-I curve between self-developed coating and imported coating was completed.The variation rules of core loss of thin strip at frequencies of 50 Hz-10 k Hz,5 times,7 times,9 times,11times harmonics and phase difference of 0°,90°and 180°were obtained.When the applied tensile stress increases from 0 MPa to 20 MPa,the magnetostrictive coefficient and noise decrease first and then rise,the?_p-pand L_{v A}reach the lowest point under 4-5 MPa tensile stress.The ultra-thin GO steel with coating has been used to manufacture the saturation reactor of converter valve in±800k V UHVDC engineering,and the results promoted the localization of high-quality ultra-thin GO steel strip.