Interface charge accumulation and decay of multi-layer oil-paper insulation under DC and polarity reversal voltages

2016 ◽  
Author(s):  
Jin Li ◽  
Boxue Du ◽  
Jiangong Zhang
Keyword(s):  
Polarity Reversal ◽  
Charge Accumulation ◽  
Interface Charge ◽  
Paper Insulation

scholarly journals Effect of Temperature on Space Charge Distribution of Oil–Paper Insulation under DC and Polarity Reversal Voltage

Energies ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 2271 ◽  
Author(s):  
Qingguo Chen ◽  
Jinfeng Zhang ◽  
Minghe Chi ◽  
Peng Tan ◽  
Wenxin Sun
Keyword(s):  
Electric Field ◽  
Space Charge ◽  
Electric Field Distribution ◽  
Operating Conditions ◽  
Polarity Reversal ◽  
Effect Of Temperature ◽  
Slow Decay ◽  
Voltage Polarity ◽  
Field Distortion ◽  
Paper Insulation

The electric field distortion caused by space charge is an important factor affecting the operation reliability of oil–paper insulation in a converter transformer. To study the accumulation and decay characteristics of the space charge within oil-impregnated pressboard under DC and polarity reversal voltage, and consider the possible operating conditions of the converter transformer, the space charge behavior of oil-impregnated pressboard was measured by the pulsed electro-acoustic (PEA) method in the temperature range from −20 °C to 60 °C. The effect of temperature on the accumulation and decay characteristics of space charge is also analyzed. The space charge accumulated within the pressboard at low temperature is mainly homocharge injected by the electrode, while heterocharge formed by ion dissociation counteracts some of the homocharge at high temperature. Thus, the space charge of pressboard first increases, then decreases, with an increase in temperature. However, slow decay of the space charge causes severe distortion of the electric field distribution in the pressboard during voltage polarity reversal.

Oil and Paper Insulation for DC Converter Transformer

2017 ◽  
pp. 194-231
Keyword(s):  
Surface Charge ◽  
Electric Fields ◽  
Power Flow ◽  
Heat Transfer Process ◽  
Transformer Oil ◽  
Polarity Reversal ◽  
Bulk Property ◽  
Hvdc System ◽  
Direct Fluorination ◽  
Paper Insulation

Transformer oil and oil-impregnated paper, serve as the essential parts of converter transformer, suffering various electric fields. The accumulation of surface charge on the paper would lead to flashover. When the power flow of the HVDC system is reversed, the charge field will easily lead to discharge. Direct-fluorination is a method which could affect the material property without alternating the bulk property. Besides, a new type of nano-modified transformer oil is a method to improve properties. This chapter presents a study of the effect of fluorination on surface charge behavior, the effect of polarity reversal voltages on interface charge behavior and the effect of Boron nitride (BN) nanoparticles on the high thermal conductivity of transformer oil. Results show that fluorination had an influence on the chemical property of the paper and BN nanoparticles has improvements in heat transfer process. In the polarity reversal test, the dissipation rate becomes smaller as the reversal time gets longer.

Energetics of AlN Epitaxial Wetting Layers on SiC (0001)

1996 ◽  
Vol 449 ◽  
Author(s):  
R. Di Felice ◽  
J. E. Northrup ◽  
J. Neugebauer
Keyword(s):  
First Principles ◽  
Three Dimensional ◽  
Layer Growth ◽  
Layer By Layer ◽  
Two Dimensional ◽  
Charge Accumulation ◽  
Wetting Layer ◽  
Interface Charge ◽  
Wetting Layers

ABSTRACTWe present a first-principles characterization of the initial stages of formation of AlN films on c-plane SiC substrates. Studying the competition between two-dimensional films and three-dimensional islands as a function of Al and N abundances, we find that a two-dimensional film can wet the surface in N-rich conditions. Ordered layer-by-layer growth can proceed to some extent on this wetting layer, and is improved by the formation of an atomically mixed interface which eliminates interface charge accumulation. Our results indicate that the stable AlN films grow in the (0001) orientation on the Si-terminated SiC(0001) substrate.

Schottky Barrier Lowering in 4H-SiC Schottky UV Detector

2008 ◽  
Vol 600-603 ◽  
pp. 1215-1218
Author(s):  
Antonella Sciuto ◽  
Fabrizio Roccaforte ◽  
Salvatore di Franco ◽  
Vito Raineri
Keyword(s):  
Schottky Barrier ◽  
Thermally Grown Oxide ◽  
Time Parameter ◽  
Charge Accumulation ◽  
Oxide Interface ◽  
Uv Detector ◽  
Thermally Stimulated Current ◽  
Interface Charge ◽  
Schottky Type ◽  
Photo Current

The Schottky barrier lowering in 4H-SiC interdigit Schottky-type UV photodiode is investigated in the presence of a thermally grown oxide layer on the exposed active area. Gain photocurrent is observed and correlated with the presence of the oxide and with the charge traps at the semiconductor/oxide interface. Photo-thermally stimulated current measurements evidenced that interface charge accumulation is optically promoted. Rise and fall photo-current measurements provided the time parameter of the trapping phenomenon.

scholarly journals Beitrag zum dielektrischen Verhalten des Öl-Papier-Isoliersystems unter Gleich- und Mischspannungsbelastung

2021 ◽  
Author(s):  
◽  
Tobias Gabler
Keyword(s):  
Charge Carrier ◽  
Dielectric Behavior ◽  
Charge Carriers ◽  
Polarity Reversal ◽  
Insulation System ◽  
Dc Voltage ◽  
Voltage Stress ◽  
Paper Insulation ◽  
Ohmic Conductivity ◽  
Calculation Models

Converter transformers of HVDC transmission systems connect HVDC and HVAC systems. To ensure a reliable operation during the entire lifetime, their oil-paper-insulation system must be designed appropriately. An optimized dielectric design demands a fundamental understanding of the dielectric stresses as well as a reliable modeling of the insulation system both under operating voltages and under superimposed, transient overvoltages. Hence, in this work the dielectric behavior of the oil-paper-insulation system is investigated. Based on dielectric tests the investigations are performed under DC voltage stress and a composite voltage stress of a DC voltage in stationary conditions superimposed by a lightning impulse voltage. The comparison of numerical calculations using a charge-carrier-based approach according to Poisson-Nernst-Planck (PNP) with breakdown experiments clarifies the dielectric stress of the oil-paper-insulation system. Furthermore, the comparison with results determined by the established, resistive-capacitive calculation models shows that it is mandatory to take the influence of the charge carrier accumulation into account. The presented results, which were obtained at oil-paper-insulated arrangements which represent the dielectic stress of real arrangements, show the influence of the charge carriers accumulating at interfaces or in the paper insulationon on the dielectric stress. The results confirm the calculations and the assumptions according to the charge-carrier-based model as well. Due to the charge carrier accumulation, the highest dielectric stress occurs in the mineral oil and not in the paper insulation. In contrast, the findings obtained assuming an ohmic conductivity would results in a higher dielectric stress of the oil-paperinsulated arrangements. Furthermore, polarity effects in homogeneous but asymmetrical, paper-insulated electrode arrangements or the influence of the surrounding oil in the test vessel demonstrate the effects of the charge carriers. Under composite voltage stresses it is also shown, that the applied superimposed voltage as well as the fast polarity reversal does not lead to a higher dielectric stress of the arrangements compared to the pure DC voltage stress. Commonly used calculation models would determine higher stresses due to the fast polarity reversal instead. Consequently, the applicability of the charge-carrier-based PNP calculation model is verified qualitatively in the presented investigations. Furthermore, it is demonstrated that the simplified assumptions of the commonly used calculation models cannot simulate the dielectric stresses under DC voltage stress and under the investigated superimposed voltage stresses. Hence, the determination of the dielectric stresses of oil-paper-insulation systems under DC voltage stress according to the commonly used calculation models assuming an ohmic conductivity does not correspond to the current state of research.

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