The primary winding of the transformer will generate large inrush current due to the saturation of iron core when an unloaded transformer is switched-on. The inrush current not only causes mechanical interaction force...The primary winding of the transformer will generate large inrush current due to the saturation of iron core when an unloaded transformer is switched-on. The inrush current not only causes mechanical interaction force due to which the windings are damaged, but also induces the differential protection relays to operate incorrectly. In this paper, the mathematical model of unloaded single phase transformer in switch-on is analyzed; the computation formulas of the inrush current and its interruption angle are presented. The experiment investigation of single phase transformers with different capacities shows that the inrush current measurement result is consistent with theoretical analysis. The inrush current waveform is typically a steeple top waveform with high order harmonics and damping in one direction. In the same condition, large inrush current amplitude will be induced with smaller switching angle, larger residual flux and smaller saturation flux.展开更多
SnO2-based varistor samples doped with Co2O3,Nb2O5 and Cr2O3 were prepared by ball-mixed oxide method.The microstructure,nonlinear I-V characteristic and surge current performances of these samples were investigated.T...SnO2-based varistor samples doped with Co2O3,Nb2O5 and Cr2O3 were prepared by ball-mixed oxide method.The microstructure,nonlinear I-V characteristic and surge current performances of these samples were investigated.This paper mainly focused on the dependence of the residual voltage ratio behavior of SnO2-based varistors on Nb2O5 addition,different factors influencing the residual voltage ratio in different concentration of Nb2O5 were analyzed.The Nb2O5 addition influences its residual voltage ratio by changing the grain size,forming defects(especially the free electrons) and cumulative effect.The measured results indicated that the optimally obtained sample with 0.07mol% Nb2O5 possesses the lowest residual voltage ratio of 1.86,the corresponding nonlinear coefficient and the threshold electric field are 42.6 and 364.6 V/mm,respectively.展开更多
文摘The primary winding of the transformer will generate large inrush current due to the saturation of iron core when an unloaded transformer is switched-on. The inrush current not only causes mechanical interaction force due to which the windings are damaged, but also induces the differential protection relays to operate incorrectly. In this paper, the mathematical model of unloaded single phase transformer in switch-on is analyzed; the computation formulas of the inrush current and its interruption angle are presented. The experiment investigation of single phase transformers with different capacities shows that the inrush current measurement result is consistent with theoretical analysis. The inrush current waveform is typically a steeple top waveform with high order harmonics and damping in one direction. In the same condition, large inrush current amplitude will be induced with smaller switching angle, larger residual flux and smaller saturation flux.
基金supported by the National Natural Science Foundations of China (Grants Nos 50425721 and 50737001)
文摘SnO2-based varistor samples doped with Co2O3,Nb2O5 and Cr2O3 were prepared by ball-mixed oxide method.The microstructure,nonlinear I-V characteristic and surge current performances of these samples were investigated.This paper mainly focused on the dependence of the residual voltage ratio behavior of SnO2-based varistors on Nb2O5 addition,different factors influencing the residual voltage ratio in different concentration of Nb2O5 were analyzed.The Nb2O5 addition influences its residual voltage ratio by changing the grain size,forming defects(especially the free electrons) and cumulative effect.The measured results indicated that the optimally obtained sample with 0.07mol% Nb2O5 possesses the lowest residual voltage ratio of 1.86,the corresponding nonlinear coefficient and the threshold electric field are 42.6 and 364.6 V/mm,respectively.
