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Lianwei Bao,Jian Li,Jing Zhang,Xudong Li 대한전기학회 2016 Journal of Electrical Engineering & Technology Vol.11 No.6
Insulation of valve-side windings in converter transformer withstands pulsating voltages, which will produce more serious insulation problems. In this paper, the electric breakdown experiments of oil-paper insulation specimens were executed at pulsating voltages and different temperatures. Experiment and analysis results showed that the breakdown voltage decreased with increasing temperature under pulsating voltage. The influence of temperature proves to be more significant once the temperature exceeds a limitation threshold. A fitting formula between breakdown voltage and the temperature was reported. Finally, in order to clearly understand the breakdown properties under pulsating voltage, the electric field distribution and space charge behavior under pulsating voltage at different temperature were discussed.
Partial Discharge Process and Characteristics of Oil-Paper Insulation under Pulsating DC Voltage
Bao, Lianwei,Li, Jian,Zhang, Jing,Jiang, Tianyan,Li, Xudong The Korean Institute of Electrical Engineers 2016 Journal of Electrical Engineering & Technology Vol.11 No.2
Oil-paper insulation of valve-side windings in converter transformers withstand electrical stresses combining with AC, DC and strong harmonic components. This paper presents the physical mechanisms and experimental researches on partial discharge (PD) of oil-paper insulation at pulsating DC voltage. Theoretical analysis showed that the phase-resolved distributions of PDs generated from different insulated models varied as the increase of the applied voltages following a certain rule. Four artificial insulation defect models were designed to generate PD signals at pulsating DC voltages. Theoretical statements and experimental results show that the PD pulses first appear at the maximum value of the applied pulsating DC voltage, and the resolved PD phase distribution became wider as the applied voltage increased. The PD phase-resolved distributions generated from the different discharge models are also different in the phase-resolved distributions and development progress. It implies that the theoretical analysis is suitable for interpretation of PD at pulsating DC voltage.
Bao, Lianwei,Li, Jian,Zhang, Jing,Li, Xudong The Korean Institute of Electrical Engineers 2016 Journal of Electrical Engineering & Technology Vol.11 No.6
Insulation of valve-side windings in converter transformer withstands pulsating voltages, which will produce more serious insulation problems. In this paper, the electric breakdown experiments of oil-paper insulation specimens were executed at pulsating voltages and different temperatures. Experiment and analysis results showed that the breakdown voltage decreased with increasing temperature under pulsating voltage. The influence of temperature proves to be more significant once the temperature exceeds a limitation threshold. A fitting formula between breakdown voltage and the temperature was reported. Finally, in order to clearly understand the breakdown properties under pulsating voltage, the electric field distribution and space charge behavior under pulsating voltage at different temperature were discussed.
Partial Discharge Process and Characteristics of Oil-Paper Insulation under Pulsating DC Voltage
Lianwei Bao,Jian Li,Jing Zhang,Tianyan Jiang 대한전기학회 2016 Journal of Electrical Engineering & Technology Vol.11 No.2
Oil-paper insulation of valve-side windings in converter transformers withstand electrical stresses combining with AC, DC and strong harmonic components. This paper presents the physical mechanisms and experimental researches on partial discharge (PD) of oil-paper insulation at pulsating DC voltage. Theoretical analysis showed that the phase-resolved distributions of PDs generated from different insulated models varied as the increase of the applied voltages following a certain rule. Four artificial insulation defect models were designed to generate PD signals at pulsating DC voltages. Theoretical statements and experimental results show that the PD pulses first appear at the maximum value of the applied pulsating DC voltage, and the resolved PD phase distribution became wider as the applied voltage increased. The PD phase-resolved distributions generated from the different discharge models are also different in the phase-resolved distributions and development progress. It implies that the theoretical analysis is suitable for interpretation of PD at pulsating DC voltage.
Two Factors Failure Model of Oil-Paper Insulation Aging under Electrical and Thermal Multistress
Li, Jian,Wang, Yan,Bao, Lianwei The Korean Institute of Electrical Engineers 2014 Journal of Electrical Engineering & Technology Vol.9 No.3
Converter transformers play important roles in high-voltage direct current transmission systems. This paper presents experimental and analysis results of the combined electrical and thermal aging of oil-impregnated paper at pulsating DC voltages. Breakdown voltages and time-to-breakdown of oil-paper specimens were measured by using short-time and constant-stress tests. The breakdown characteristics of combined electrical and thermal aging on insulation system were discussed. According to the relationship between failure time and aging temperature, the two-parameter Weibull model was improved. On the basis of the competing risk algorithm and the improved Weibull model, the two factors failure model was calculated. And the influence of temperature in the insulation system has been analyzed. This model performs better than the two-parameter Weibull model when both time and temperature are considered as variables in estimating the lifetime of oil-paper insulation.
Space Charge Behavior of Oil-Impregnated Paper Insulation Aging at AC-DC Combined Voltages
Li, Jian,Wang, Yan,Bao, Lianwei The Korean Institute of Electrical Engineers 2014 Journal of Electrical Engineering & Technology Vol.9 No.2
The space charge behaviors of oil-paper insulation affect the stability and security of oil-filled converter transformers of traditional and new energies. This paper presents the results of the electrical aging of oil-impregnated paper under AC-DC combined voltages by the pulsed electro-acoustic technique. Data mining and feature extractions were performed on the influence of electrical aging on charge dynamics based on the experiment results in the first stage. Characteristic parameters such as total charge injection and apparent charge mobility were calculated. The influences of electrical aging on the trap energy distribution of an oil-paper insulation system were analyzed and discussed. Longer electrical aging time would increase the depth and energy density of charge trap, which decelerates the apparent charge mobility and increases the probability of hot electron formation. This mechanism would accelerate damage to the cellulose and the formation of discharge channels, enhance the acceleration of the electric field distortion, and shorten insulation lifetime under AC-DC combined voltages.
Two Factors Failure Model of Oil-Paper Insulation Aging under Electrical and Thermal Multistress
Jian Li,Yan Wang,Lianwei Bao 대한전기학회 2014 Journal of Electrical Engineering & Technology Vol.9 No.3
Converter transformers play important roles in high-voltage direct current transmission systems. This paper presents experimental and analysis results of the combined electrical and thermal aging of oil-impregnated paper at pulsating DC voltages. Breakdown voltages and time-tobreakdown of oil-paper specimens were measured by using short-time and constant-stress tests. The breakdown characteristics of combined electrical and thermal aging on insulation system were discussed. According to the relationship between failure time and aging temperature, the twoparameter Weibull model was improved. On the basis of the competing risk algorithm and the improved Weibull model, the two factors failure model was calculated. And the influence of temperature in the insulation system has been analyzed. This model performs better than the twoparameter Weibull model when both time and temperature are considered as variables in estimating the lifetime of oil-paper insulation.
Lingyu Li,Haomeng Yang,Weibo Ren,Bei Liu,Dongmei Cheng,Xinhong Wu,Jirui Gong,Lianwei Peng,Fang Huang 한국식물학회 2016 Journal of Plant Biology Vol.59 No.4
Sheepgrass [Leymus chinensis (Trin.) Tzvel] is a valuble forage plant highly significant to regional grassland productivity of Euro-Asia steppes. Although effects of environmental stress including drought have been studied, impact of nutrient deficiency in particular phosphate (Pi), one of the essential macronutrient, is not reported. Here, we investigated low-Pi effect on its photosynthetic apparatus via physiological and biochemical analysis. We show that PSII activity was significantly reduced based on chlorophyll fluorescence measurements. We observed decreased amount of core proteins of PSII by immunoblot analysis. Further analysis of thylakoid membranes using 2D-BN/SDS-PAGE and immunoblot detection demonstrated that the amount of PSII complexes was closely correlated with the Pi levels within the range. Together with reduced number of thylakoid grana stackings observed, we suggest that the maintenance of PSII is impaired under Pi-limited condition. Moreover, enzyme activity assays revealed that the activity of several ROS scavenger enzymes was stimulated by low-Pi treatment. Based on these experimental results we conclude that PSII is the component of photosynthetic apparatus most sensitive to Pi supply and the enhanced anti-ROS activity is mainly subjective to protection of PSII against low Pi-induced photo-oxidative stress in the organism.