scholarly journals Aging Characteristics of Transformer Oil-Impregnated Insulation Paper Based on Trap Parameters

Polymers ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1364
Author(s):  
Yanhui Wei ◽  
Wang Han ◽  
Guochang Li ◽  
Xiaojian Liang ◽  
Zhenlu Gu ◽  
...  
Keyword(s):  
Thermal Stress ◽  
Energy Levels ◽  
Transformer Oil ◽  
Chemical Bonds ◽  
Defect Model ◽  
Trap Energy ◽  
Aging Mechanism ◽  
Space Charge Distribution ◽  
Simulation Results ◽  
Accelerated Thermal Aging

Oil-impregnated insulation paper is an important part of transformers; its performance seriously affects the life of power equipment. It is of significance to study the aging characteristics and mechanism of oil-impregnated insulation paper under thermal stress for transformer status detection and evaluation. In the work, the accelerated thermal aging was carried out at 120 °C, and DP1490, DP787, and DP311 samples were selected to represent the new, mid-aging, and late-aging status of the transformer, respectively. The space charge distribution within the specimens was measured by the pulsed electro-acoustic (PEA) method and the trap parameters were extracted based on the measurement curves. Further, the aging mechanism was studied by molecular simulation technology. A typical molecular chain defect model was constructed to study the motion of cellulose molecules under thermal stress. The experimental results show that the corresponding trap energy levels are 0.54 eV, 0.73 eV, and 0.92 eV for the new specimen, the mid-aging specimen, and the late aging specimen, respectively. The simulation results show that the trapped energy at the beginning of aging is mainly determined by the loss of H atoms. The changes in trap energy in the middle stage of aging are mainly caused by the absence of some C atoms, and the trap energy level at the end of aging is mainly caused by the breakage of chemical bonds. This study is of great significance to reveal the aging mechanism of oil-impregnated insulation paper and the modification of insulation paper.

scholarly journals Numerical Simulation Study on the Front Shape and Thermal Stresses in Growing Multicrystalline Silicon Ingot: Process and Structural Design

Crystals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1053
Author(s):  
Chengmin Chen ◽  
Guangxia Liu ◽  
Lei Zhang ◽  
Guodong Wang ◽  
Yanjin Hou ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Thermal Stress ◽  
Thermal Stresses ◽  
Simulation Method ◽  
Power Ratio ◽  
Radial Temperature ◽  
Front Shape ◽  
Simulation Results ◽  
Insulation Block ◽  
Transient Numerical Simulation

In this paper, a transient numerical simulation method is used to investigate the effects of the two furnace configurations on the thermal field: the shape of the melt–crystal (M/C) interface and the thermal stress in the growing multicrystalline ingot. First, four different power ratios (top power to side power) are investigated, and then three positions (i.e., the vertical, angled, and horizontal positions) of the insulation block are compared with the conventional setup. The power ratio simulation results show that with a descending power ratio, the M/C interface becomes flatter and the thermal stress in the solidified ingot is lower. In our cases, a power ratio of 1:3–1:4 is more feasible for high-quality ingot. The block’s position simulation results indicate that the horizontal block can more effectively reduce the radial temperature gradient, resulting in a flatter M/C interface and lower thermal stress.

scholarly journals First Principles Predictions of Intrinsic Defects in Aluminum Arsenide, AlAs

2011 ◽  
Vol 1370 ◽  
Author(s):  
Peter A. Schultz
Keyword(s):  
Point Defects ◽  
First Principles ◽  
Density Functional ◽  
Semiconductor Device ◽  
Energy Levels ◽  
Aluminum Arsenide ◽  
Functional Theory ◽  
Eigenvalue Gap ◽  
Rigorous Treatment ◽  
Simulation Results

ABSTRACTThe structures, energies, and energy levels of a comprehensive set of simple intrinsic point defects in aluminum arsenide are predicted using density functional theory (DFT). The calculations incorporate explicit and rigorous treatment of charged supercell boundary conditions. The predicted defect energy levels, computed as total energy differences, do not suffer from the DFT band gap problem, spanning the experimental gap despite the Kohn-Sham eigenvalue gap being much smaller than experiment. Defects in AlAs exhibit a surprising complexity—with a greater range of charge states, bistabilities, and multiple negative-U systems—that would be impossible to resolve with experiment alone. The simulation results can be used to populate defect physics models in III-V semiconductor device simulations with reliable quantities in those cases where experimental data is lacking, as in AlAs.

Effects of Trap Energy Levels on Reverse Recovery Surge of Silicon Power Diode

2012 ◽  
Author(s):  
S. Machida ◽  
Y. Yamashita ◽  
T. Misumi ◽  
T. Sugimaya
Keyword(s):  
Energy Levels ◽  
Trap Energy ◽  
Power Diode

Density of States in a-Si:H from SCLC and Its Application in Modeling a Vertical TFT

2001 ◽  
Vol 664 ◽  
Author(s):  
Naser Sedghi ◽  
Bill Eccleston
Keyword(s):  
Space Charge ◽  
Density Of States ◽  
Energy Levels ◽  
Thin Film Transistor ◽  
Device Simulation ◽  
Space Charge Limited Current ◽  
Trap Energy ◽  
Limited Current ◽  
Hydrogenated Amorphous ◽  
Space Charge Limited

ABSTRACTSteady-state space-charge limited current (SCLC) measurements are used to investigate the density of states (DOS) in the mobility gap of hydrogenated amorphous silicon (a-Si:H). The density of states is calculated by different methods based on both continuous DOS and discrete traps assumptions. The density of states found by the SCLC measurements is used to set the trap densities and trap energy levels to model a vertical a-Si:H thin-film transistor (TFT) using the Medici device simulation package. The effect of different sets of traps in the bulk of a-Si:H and variation of the physical dimensions of the device on the characteristics of the vertical TFT is studied. The simulation on the space-charge limited current is performed to verify the validity and accuracy of the SCLC method.

Determination of trap energy levels in AlGaN/GaN HEMT

2013 ◽  
Author(s):  
Jie Yang ◽  
Sharon Cui ◽  
T. P. Ma ◽  
Ting-Hsiang Hung ◽  
Digbijoy Nath ◽  
...  
Keyword(s):  
Energy Levels ◽  
Trap Energy ◽  
Gan Hemt

scholarly journals Analyzing the effects of thermal stress on insulator papers by solid-state 13C NMR spectroscopy

Cellulose ◽  
2021 ◽  
Author(s):  
Paul Jusner ◽  
Markus Bacher ◽  
Jonas Simon ◽  
Florian Bausch ◽  
Hajar Khaliliyan ◽  
...  
Keyword(s):  
Thermal Stress ◽  
Nmr Spectroscopy ◽  
Structural Changes ◽  
Electrical Power ◽  
13C Nmr Spectroscopy ◽  
Mas Nmr ◽  
Transformer Oil ◽  
Thermally Induced ◽  
Cellulosic Paper ◽  
Cp Mas Nmr

AbstractMillion tons of cellulosic paper have been used for insulating coils in oil-filled electrical power transformers, thereby assuring the electricity supply for our societies. The high working temperatures in transformers constantly degrade paper insulators throughout their service life of up to 40 years. We approached the structural changes in oil-immersed cellulosic paper samples upon thermal stress in a study that compared unbleached softwood Kraft paper used as insulator paper with pure cotton cellulose paper. The model experiments used a thermal treatment in transformer oil at 170 °C for up to 14 days. The samples were characterized by means of 13C CP/MAS NMR spectroscopy, mainly based on deconvolution of the C4 resonance. An automated, fast, and reproducible C4 resonance deconvolution employing the “Peak Analyzer” tool of OriginPro 2020 (OriginLab Corporation, USA) was developed and used to exploit 13C CP/MAS NMR spectroscopy for the characterization of thermally stressed paper samples. Our results show that thermally induced structural changes depend heavily on the composition of paper, that hornification and coalescence of fibrils take place, and that the allomorph composition of cellulose crystallites is altered under the given conditions. Graphical abstract

Application of Finite Element Method of Composite Wall Insulation System

2012 ◽  
Vol 594-597 ◽  
pp. 2158-2161 ◽  
Author(s):  
Tao Cheng ◽  
Ke Qin Yan
Keyword(s):  
Thermal Stress ◽  
Three Dimensional ◽  
Stress Fields ◽  
Insulation System ◽  
Wall Model ◽  
Polystyrene Plate ◽  
Composite Wall ◽  
Simulation Results ◽  
Stress And Deformation ◽  
Dimensional Element

In this paper, the thermal stress characteristics of polystyrene plate - thin plaster wall are present. A three-dimensional element is selected to mesh the wall model, which can simulate the coupling effects of thermal stress and structural stress field. Thermal stress and deformation distribution are proposed after comparing and analyzing the two simulation results. Numerical simulation results indicate that: (1) Polystyrene plates thin plaster wall insulation system has very good thermal insulation properties；(2) Different stress fields concentrate significantly around windows and in the middle of wall especially around the windows. (3) The deformation of the polystyrene plate - thin plaster wall insulation system reach the maximum at the edge of the wall while the minimum in central.

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