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As the main material of the converter transformer dry-type bushing, the dielectric properties of epoxy/crepe paper at different temperatures and frequencies are related to the electric field and thermal field distribution of the bushing, which directly affects the safe and stable operation of the bushing. Here we report the dielectric response of samples of dry-type bushing insulation measured at a range of temperatures appropriate to operation and down to frequencies below those usually used. A significant loss peak observed below power frequency is interpreted as originating from the charging of internal epoxy resin interfaces by the transport of charge carriers on structured paths in the epoxy-impregnated crepe paper layers. A simulation model is proposed that allows estimation of the space charge and field distribution at any given frequency. [ABSTRACT FROM AUTHOR]

The converter transformer epoxy impregnated paper bushing is a multi-media electrical equipment, and the main materials include the internal conductor, the external conductor, transformer oil, SF6 gas, the air inside internal conductor, the main insulation material epoxy impregnated paper, sheath, and fittings. In actual operating, the converter transformer bushing is undertaken by the harmonic current with large number of high harmonics and the temperature distribution of the epoxy impregnated paper converter transformer bushings under actual current waveform needs to be researched. What's more, the temperature distribution of the epoxy impregnated paper converter transformer bushings is affected by several factors and to provide basis for the optimization of bushings it's necessary to research about the impact of these factors on the temperature distribution of the epoxy impregnated paper converter transformer bushings. In this paper, on the basis of our previous paper [8], the 3-D temperature distribution of the 400 kV epoxy impregnated paper converter transformer bushing under actual current waveform with large number of harmonics has been simulated by using the computational fluid dynamics (CFD) and finite element method (FEM) analysis. The temperature distribution regularity of the 400 kV converter transformer bushing under different influencing factors has been computed and analyzed. The dissipation structure of the bushing has been optimized and the DC steady-state electric field distribution of the 400 kV converter transformer bushing has been obtained considering the temperature gradient in epoxy impregnated paper. [ABSTRACT FROM PUBLISHER]

With the increase of transmission power in China, the heating problem of converter transformer resin impregnated paper (RIP) bushings is increasingly serious. In this paper, applying the computational fluid dynamics (CFD), using a 3D electromagnetic-fluid-thermal analysis method, and considering the heat conduction, convection, and radiation effects, the temperature field distribution of the converter transformer RIP bushing has been simulated; according to the simulation results, the max-imum temperature of epoxy impregnated paper is above the heat distortion temperature 120 °C. Then, to verify the accuracy of the simulation method, temperature rising experiment has been car-ried out. Through the comparison, the temperature difference percentage between the simulation results and the experimental results is within 9 % proving the rationality of the simulation method. Finally eight optimization schemes for the 400 kV con-verter transformer RIP bushing were proposed which include the heat conductors with different diameters and numbers and the thermal conductive oil inside the inner conductor. Through the simulation of the eight optimization schemes, it can be proven that the heat conductors and the thermal conductive oil inside the inner conductor can effectively decrease the temperature distri-bution of converter transformer RIP bushings and improve the stable operation of transmission line. [ABSTRACT FROM PUBLISHER]

The temperature distribution is vital to the lifetime and reliability of converter transformer bushings. However, the temperature distribution of epoxy impregnated paper converter bushings under a certain current has usually been calculated through the two dimensional model, without considering the heat convection and radiation effects. In this paper, using the computational fluid dynamics (CFD) and finite element method (FEM) analysis, a 3-D electromagnetic-fluid-thermal analysis method has been proposed. With the considering of heat conduction, heat convection and radiation, the temperature distribution of the converter transformer bushing has been simulated according to the actual operating environment. The temperature and velocity distribution of the converter transformer bushing has been obtained. Moreover, the simulation results have been compared with the experimental results to verify the accuracy of the simulation method. The simulation results, especially for the inner conductor, external conductor and the epoxy impregnated paper, are very close to the experimental results and the maximum temperature difference percentage is within 10 %, which indicates the accuracy and effectiveness of the electromagnetic-fluid-thermal analysis method proposed. [ABSTRACT FROM AUTHOR]

The transient electric field distribution under lightning impulse voltage (LIV) is vital to the reliability of 750 kV composite cross-arm. However, the transient electric field of electrical equipment under impulse voltage has usually been substituted by the equivalent sinusoidal voltage, without considering the variation of permittivity with frequency. Using the frequency decomposition computation method (FDCM) based on finite element method (FEM), this paper presents the study of transient electric field under LIV for a 750 kV composite cross-arm. The LIV waveform has been decomposed via Fourier transformation. The complex dielectric functions of the insulation materials used in composite cross-arm have been investigated, and the computation parameters for the dc and each harmonic component of LIV have been obtained. Then, the transient electric field distribution can be computed through the superposition of responses from dc and each harmonic component. Moreover, the computation results have been compared with that using traditional method. The comparison indicates that the potential distribution of composite cross-arm is similar. The maximum percentages of electric field strength difference on fittings and silicone rubber sheath are 2.9 %, 14 %, respectively. [ABSTRACT FROM AUTHOR]

As composite cross-arm will be used in domestic 750 kV AC transmission line for the first time, careful and meticulous preparatory work is highly needed. Using a threedimension (3-D) finite-element method (FEM) software, this paper presents computation results of the potential and electric field distribution for composite crossarms in the process of structure optimization. Several optimization programs for composite cross-arm have been studied and the final design is made to omit the suspension insulator string, to increase the length of post insulators and to configure suitable grading and shielding rings based on preliminary design. A set of grading and shielding rings configuration program has been proposed. The comparison between optimized composite cross-arms and 750 kV line composite insulators indicates that composite cross-arms have better potential distribution. The electric tests demonstrate that optimized composite cross-arms have good electrical performance and can meet operation requirements. [ABSTRACT FROM AUTHOR]