Dissolution behavior of Al_(2)O_(3)inclusions into CaO-MgO-SiO_(2)-Al_(2)O_(3)-TiO_(2)system ladle slags

To investigate the dissolution behaviors of Al_(2)O_(3)inclusions in CaO-5wt%MgO-SiO_(2)-30wt%Al_(2)O_(3)-TiO_(2)system ladle slags,confocal scanning laser microscopy was conducted on the slags with different TiO_(2)contents(0-10wt%),and scanning electron microscopy was performed to study the interfacial reaction between Al_(2)O_(3)and this slag system.The results disclose that the dissolution of Al_(2)O_(3)inclusions does not result in the formation of new phases at the boundary between the slag and the inclusions.In TiO_(2)-bearing and TiO_(2)-free ladle slags,there is no difference in the dissolution mechanism of Al_(2)O_(3)inclusions at steelmaking temperatures.Boundary layer diffusion is found as the controlling step of the dissolution of Al_(2)O_(3),and the diffusion coefficient is in the range of 4.18×10^(-10)to 2.18×10^(-9)m^(2)/s at 1450-1500℃.Compared with the solubility of Al_(2)O_(3)in the slags,slag viscosity and temperature play a more profound role in the dissolution of Al_(2)O_(3)inclusions.A lower viscosity and a lower melting point of the slags are beneficial for the dissolution.Suitable addition of TiO_(2)(e.g.,5wt%)in ladle slags can enhance the dissolution of Al_(2)O_(3)inclusions because of the low viscosity and melting point of the slags,while excessive addition of TiO_(2)(e.g.,10wt%)shows the opposite trend.

Calculation of Eddy Current Loss and Short-circuit Force in SSZ11-50000/110 Power Transformer

The ?method is used in this paper to calculate the leakage magnetic field of SSZ11-50000/110 Power transformer, and by which the structures’ influences to the main leakage flux are analyzed. Through the combination of the product and TEAM Problem 21B, the surface impedance method shows its great advantage in the calculation of eddy current loss.

Microcosmic mechanism and correction of moisture effect on furfural diffusion and equilibrium in oil‐paper insulation

Furfural content in oil is considered as an effective parameter to evaluate the ageing state of oil-immersed transformers.In previous thermal ageing experiments at 130℃,we found that moisture increment in oil-paper system makes more furfural distribute in oil.However,the microcosmic mechanism of moisture effect on furfural diffusion from paper to oil is still unknown,and the furfural equilibrium law at transformers'typical operating temperatures is also unclear,resulting in the unreliability of the existed furfural evaluation model.To elucidate the above problems,molecular dynamics simulation and furfural equilibrium experiments at 60℃ were carried out at different moisture contents.The results show that high moisture content makes part of furfural diffuse from paper to oil indeed.Supposing moisture content increases from 1% to 2%,mass fraction of furfural in oil may increase from 32.98% to 49.83%,leading to furfural content in oil increases from 0.76 mg/L to 1.06 mg/L when the degree of polymerisation of insulation paper is about 524,which increased by 39.5%.The increase in moisture content makes cellulose form hydrogen bonds with H_(2)O preferentially,decreasing the hydrogen bonds interaction between cellulose and furfural.Thus,partial furfural falls off cellulose and diffuses into oil,leading to an increase in furfural content in oil.To eliminate the moisture interference,a corrected furfural assessment model based on the moisture equilibrium curve has been constructed,which can accurately evaluate the ageing state of insulation paper regardless of the moisture influence.