Wen Xishan

Study on the fault diagnosis of transformer based on the grey relational analysis

Transformer incipient faults are often diagnosed with dissolved gas analysis (DGA) of transformer oil. Various methods have been developed to interpret DGA results such as IEC ratio code and the Rogers method. But, they sometimes fail to determine these faults. In this paper, the grey relational analysis method is applied to diagnose the fault pattern of power transformer. Based on the principles of grey relational analysis, a group of reference sequences are selected from fault data. Practical data are analyzed through the method and compared with other methods. The results of diagnosis have proved that grey relational analysis is a useful tool for evaluating the faults of power transformers. With the method introduced, the diagnosis will be more effective.

Research on characterization of RTV silicone rubber/LS (layered silicate) electrical insulation nanocomposites

Presently, the security of power system is seriously threatened by pollution flashover. Room temperature vulcanized (RTV) silicone rubber has been widely used into coat porcelain insulators to render water repellency to prevent the formation of water filming on the surface and thus to suppress the leakage current and consequently flashover, due to their hydrophobicity and migration of hydrophobicity. However, in order to obtain an increase of service life and better service effect, some properties of RTV silicone rubber (RTVSR) coatings still need to be improved, especially the abilities of mechanics performances. In this paper, nanotechnique is used for the reformation of RTVSR, by which RTVSR/layered silicate nanocomposite is synthesized by means of solution. The mechanical properties, such as tensile strength, elongation at break and adherence grade are theoretically and experimentally analyzed and compared with that of RTV silicone rubber without nano fillers with the help of SEM, FTIR and XRD. The test results prove that layered silicate can be dispersed in the silicone rubber matrix uniformly. Moreover tracking tests and hydrophobicity contact angle test are conducted, and the influences to the electrical parameters such as tan /spl delta/, and /spl rho//sub v/ are also found, considering that RTV silicone rubber is a kind of electrical insulation materials.

Study on RTV silicone rubber/SiO/sub 2/ electrical insulation nanocomposites

Surface contamination and leakage current have caused operating problems for utilities since electric power was its infancy. A flashover in a substation may result in the destruction of an insulator or many others electrical equipments. In order to reduce the incidence of insulator flashover and damage, the liquid silicone RTV (room temperature vulcanized) has been used for coating porcelain and glass insulators to provide water repellency (hydrophobicity) on the surface. Nano science and technology (nano-st) is a promising research field. In this paper, from previous research results in the other research fields, we decide to select nanoSiO/sub 2/ to try to reform RTVSR. First, different kinds of nano SiO/sub 2/ from different fabrication methods such as sol-gel and gas phase method etc are selected. Then dispersal situation of nano SiO/sub 2/ synthesized by different ways and disposed with or without coupling agents in RTV silicone rubber were studied and analyzed with SEM. Some basic properties of RTVSR/SiO/sub 2/ nanocomposites and pure RTVSR were compared and analyzed in detail. In addition, some electrical performances tests are also conducted, and the influences to the electrical parameters such as tan /spl delta/, and /spl rho//sub v/ were found as well, considering that RTV silicone rubber was a kind of electrical insulation materials. The resulting hybrid had more excellent mechanical, thermal stability than pure RTV silicone rubber.

Corona ageing tests of RTV and RTV nanocomposite materials

Silicone rubber insulating materials are superior to conventional porcelain materials, whose special water repellency and transfer of water repellency is favorable in power industry. However, two points are concerned in its application, and these are long-term reliability and lack of methods to assess their long-term performance. Corona and arc are important factors that induce degradation of RTV insulating materials during operation. Nanomaterials are used to modify the properties of RTV silicone rubber. Corona aging tests have been conducted, and the results of water repellency and IR analyses show that these nanomaterials can markedly improve its corona aging performance.

3D analysis and calculation of stator temperature field of hydrogenerator in the case of sudden short circuit

Sudden short circuit is a serious transient process though it is short in time. In this paper, 3D transient equations of heat conduction as well as its equivalent functional equation are presented. Short circuit current of stator is performed. Sudden short current and heat of the stator are analyzed and calculated. Base on the construction symmetry of ventilating system in hydro the solution region of stator temperature field is determined as the range of half tooth, half trough and half axial core section, and heat dissipation coefficients of each surface and equivalent heat conductivity coefficients of iron and stator winding considering the insulation layers. In addition, the heat sources are analyzed. Finite element method (FEM) software-ANSYS is applied to calculate the transient temperature field of a kind of 125 MW hydro-generator under sudden short circuit

Theory and practice of semiconductor lightning eliminator

The paper introduces the structure and function of the semiconductor lightning eliminator (SLE). It is pointed that the SLE can limit the main discharge current and reduce the rate of lightning current rise. Therefore SLE is very suitable for the lightning protection of microelectronic equipment and flammable and explosive facilities.

Research of 3D Temperature Field of Hydro-generator with Aging Insulation

Mathematic model and equivalent variation equation of temperature Held is inferred. Base on the construction symmetry of ventilating system in hydro-generator, the model of analyzing stator temperature field is determined as the range of half tooth, half slot and half axial height. The hypotheses and corresponding border conditions are provided for simplification. In addition, heat conductive coefficients of iron core and stator winding considering the insulation layer and heat dissipation coefficients of each surface are confirmed. Using the finite element method software ANSYS, the stator temperature field of the hydroelectric generator is analyzed and calculated, the corresponding temperature field pictures and the highest temperature points are given considering the aging insulation.

Research on electric potential distributions of composite insulators and glass insulators by numerical simulation

At present, glass insulators and composite insulators are widely used in high voltage line owing to their outstanding features. In this paper, finite element method (FEM) is introduced and simulation modeling is outlined, and FEM software-ANSYS is employed to calculate the electric potential distribution of composite insulators and glass insulators under different conditions. The aim of the computation is to analyze and compare these two kinds of insulators from the electrical angle. The suspension insulators using in 500 kV transmission lines are studied. The result can be served as a basic reference in the optimum design and proper use of line insulators in practice

Technical and Economic Performance Analysis on Vertical Grounding Electrodes of ±800KV UHVDC

According to alternative grounding place situation of plusmn800 KV DC project, this paper selects the theoretically suitable place to design several different arrangement scenarios of vertical grounding electrodes and then compares the technical and economic performance when the sub-electrode length remains invariable while other parameters are changed and when the sub-electrode quantity remains invariable while other parameters are changed. The results show that both step voltage and grounding resistance conform to the system requests in these scenarios, but soil temperature near ground rods can not satisfy the request. Simultaneously, a series of conclusions are reached by selecting a best one of these scenarios to compare with level two-rings grounding electrode.

Resistance to high and low temperature of RTV nanocomposite

Room temperature vulcanized silicone rubber (RTV-SR) is widely applied to outdoor insulation in power system. It is aged under the conditions of outdoor environment. Temperature is one of the ageing factors. So the resistance to high and low temperature of RTV is important to its ageing performance. In the paper, two kinds of RTV nanocomposite are achieved, and the resistance to high and low temperature is tested with the help of TG (thermogravimetry)/DTG (differential thermogravimetry) and DSC (differential scanning calorimeter). The decomposing temperature and glass transition temperature of RTV nanocomposite are obtained. The test results show that RTV nanocomposite has better resistance to both high and low temperature, which may lead to better ageing performance of RTV material. The mechanisms are also discussed.