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Meng X.-B.,Tsinghua University | Bian X.-M.,Tsinghua University | Zhao X.-S.,Beijing Extra High Voltage | Cao J.,State Grid Electric Power Research Institute of China | And 4 more authors.
Gaodianya Jishu/High Voltage Engineering | Year: 2010

The corona discharge effect is one of important problems in the design and operation of transmission lines. The transmission lines pass by the high altitude region with low air pressure, which brings many special problems to the design and operation of the transmission lines. Temperature and humidity also have obvious effects on the corona characteristics of the transmission lines. Consequently, it is significant to study the impact of air pressure, temperature and humidity on the corona characteristics and discharge mechanism of transmission lines. A computation model, which was established according to the gas discharge theory, was adopted to evaluate the corona inception voltage on conductors. The charge simulation method was introduced to the computation model to calculate the electric field intensity. Then the criterion of corona inception voltage, which considered whether the number of positive ions in the secondary avalanches was greater or equal to that in the primary avalanche, was used to calculate the corona inception voltage of conductors. The influences of air pressure, humidity and temperature on the corona inception voltage of conductors were analyzed systematically. The results show that, the corona inception voltage decreases as air pressure is lowered or temperature is raised. It is mainly due to the enlargement of ionization zone as a result of the increase of effective ionization coefficient. Simultaneously, the corona inception voltage decreases with humidity increasing for strengthening of collisional ionization intensity. Source

Bian X.,Tsinghua University | Yu D.,Tsinghua University | Chen L.,Tsinghua University | MacAlpine J.M.K.,Tsinghua University | And 3 more authors.
IEEE Transactions on Dielectrics and Electrical Insulation | Year: 2011

Relatively little investigation has previously been done on the effects of aging on conductor surface conditions, or on the ac corona discharges from these conductors. In the present work these were investigated by means of comparing corona on typical aged conductors with that on new ones. The aged conductors from the ac power transmission lines had been in service for 12, 15 and 20 years. Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis were employed to characterize the surface morphology and composition of the conductors; and a non-contact surface profiler was used to measure the surface roughness of the six samples. As a result of corrosion and the adherence of various substances to the conductors, their surfaces were far rougher than the new ones. The ac corona discharge characteristics of these conductors were studied in a small corona cage using an ultraviolet imaging detector. As a result of the rough surfaces, the corona discharge intensity for the aged conductors was found to be much stronger than that for the new ones; and the corona inception voltages for the aged conductors were 10 to 25% lower than the new ones. © 2006 IEEE. Source

Du B.X.,Tianjin University | Ma Z.L.,Tianjin University | Gao Y.,Tianjin University | Han T.,Tianjin University | Xia Y.S.,Beijing Extra High Voltage
Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, CEIDP | Year: 2011

Polymer nanocomposite has recently drawn considerable attention because nanocomposites or nanostructured polymers have the potential of improving the electrical, mechanical, and thermal properties as compared to the neat polymers [1]. In this paper, the polymer nanocomposite was made by the mixed addition of SiO 2 nanoparticle with the radio of 20 nm into room temperature vulcanized (RTV) silicone rubber (SiR), with the filler content from 0 to 5 wt% respectively. The typical needle-plate electrode was employed to investigate the relationship between electrical tree propagation characteristics and the content of nano filler with the ac voltage of 50 Hz. Both the structures and growth characteristics of electrical tree in SiR were observed by using a digital camera and a microscope system. Obtained results show that the distribution of tree structures is different between base SiR and its nanocomposites specimens. The growth speed varies a lot with the content of nano fillers, and there is an obvious improvement in tree initiation time as the increase of filler content. The possible reasons for the improvement in electrical tree growth and initiation time with the addition of nano fillers are discussed. © 2011 IEEE. Source

Yang J.,North China Grid Company | Sheng H.-H.,Beijing Electrical Power Corporation | Wei X.-W.,Beijing Extra High Voltage
Gaoya Dianqi/High Voltage Apparatus | Year: 2010

An accident of 500 kV transformer inner short circuit is explored by the change analysis of the oil chromatogram after accident, the local discharge online monitoring, and ultimate degradation analysis. It is found that this accident is caused by inner short circuit of high voltage winding. The insulation effect analysis of the phenomenon of Cu 2S in the accident is performed. The accident analysis also includes soldering quality, insulation quality, and working environment, etc. Preventing measure is hence suggested. Source

Bian X.,Tsinghua University | Yu D.,Tsinghua University | Meng X.,Tsinghua University | MacAlpine M.,Tsinghua University | And 4 more authors.
IEEE Transactions on Dielectrics and Electrical Insulation | Year: 2011

The effects of corona-generated space charge on the resultant electric field near a conductor were determined both for a simulated test line and a corona cage, since both are used in predicting the corona behavior of EHV and UHV transmission lines. Programs were developed for the calculation of the potential, the electric field and the space charge distributions for a simulated test line and a corona cage. Algorithms based on the charge simulation and the finite-element methods were used to solve Poisson¿s equation; and the method of characteristics to solve the current continuity equation. The resultant electric field on the ground plane of the two configurations was measured with a rotating field-mill, and the results fitted well with the calculated data. It was found the electric field at the surface of the conductor increased linearly, for both experimental configurations, before the voltage reached the corona inception value; but was reduced once corona-generated space charge was produced. The space charge and density distribution in the corona cage differed greatly from that around the test line: the electric field at the surface of the conductor in the test line decreased faster with voltage than that in the corona cage, the relative difference increasing as V/usb>app/Von was raised. The difference reached an asymptote of about 16% when the applied voltage was about 25% above the corona inception level. © 2011 IEEE. Source

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