The Research On The Magnetic Properties Of Silicon Steel Sheet And The Iron Losses Of Magnetic Shielding Model Of Transformer

In large power transformers the stray loss of structural parts is mainly determinedby the leakage magnetic field and its distribution. The leakage magnetic field incentralized distribution causes localized overheating resulting in thermal aging issuesof insulation materials, thereby affecting the reliability and lifetime of the transformeroperation. To reduce the losses and the temperature rise caused by leakage flux, themagnetic and electromagnetic shielding is widely distributed in the transformer tank,core tie-plate and other metal parts. The generally applied magnetic and hybridshield are made of high magnetic permeability oriented silicon steel stacked together,therefore the research in electromagnetic properties of silicon sheet material isparticularly important.Firstly, this paper studies the magnetic shielding material, namely the magneticproperties of magnetic silicon steel. It investigates the related influence factors(frequency, strip angle, ambient temperature) on the mean path length of the Epsteinframe by Epstein frame magnetic measuring experiment carried out for silicon steelsamples. According to the3D simulation calculation, the condition of two Epsteinframe approach is proved out. Considering the influence of its different zones on themean path length, it proposes triple Epstein frame first level weighted processingmethod and two-level weighted processing approach to determine the actual effectivepath length of standard25cm Epstein frame. Design the experimental measurement ofexcitation power by combining power analyzer WT3000with Epstein frame. Andmeasure the specific total loss of different average flux density, sampling angles,frequencies, ambient temperatures and exciting power. It reflects its superiority bycomparing with double Epstein frame method. The available experimental results andthe analysis conclusions have industrial application value to the further magneticproperties study of large power transformer’s core and magnetic shielding.Secondly, do researches for the application of silicon steel materials, namelymagnetic shielding. However, the loss of shielding is difficult to measure directly. It isneeded to be separated from the total loss measured. This paper introduces mirrormeasuring method, which is able to complement leakage flux for effectivelyseparating shield loss from the measuring total load loss. The mirror model istwo-dimensional modeling, simulation analysis to verify the reasonableness of themirror measuring method. According to the improved experimental platform from R&D Center, Tianwei Group Co, LTD measuring shielding losses and flux density,experiments are carried out for the five shielding models (the magnetic shield, thehybrid shield, the magnetic shield and magnetic plate, the hybrid shield and magneticplate, the electromagnetic shield and magnetic plate).Finally, the five shielding models are made three-dimensional modeling andsimulation with electromagnetic field analysis software MagNet V7.2. The excitingwindings are homogenization processed and considered nonlinear and anisotropiccharacteristics of silicon sheet in the models. On different excitation conditions, theflux density and loss of the models are detailed comparative analyzed and effectiveexperimental verification providing reference value for the actual product application.