Naiyi Li

Potential distribution computation and structure optimization for composite cross-arms in 750 kV AC transmission line

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 three-dimension (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.

Measurement of Electric Fields Around a 1000-kV UHV Substation

This paper investigates the power frequency electric fields around a 1000-kV ultra-high voltage (UHV) substation which is located in Jingmen, China. Detailed field measurements around this substation as well as numerical results in a 1000-kV area are provided. Most values observed are below the reference level indicated in the relevant national design guideline. Therefore, we can conclude that the power frequency electric fields around this UHV substation are safer for working personnel.

Electric field calculation and grading ring optimization for 1000 kV AC post porcelain insulator

Grading ring design is an important step in the post porcelain insulator design process, appropriate grading ring configuration can improve the electric field distribution of post insulators and extend the service life. In this paper, a static 3-D model of 1000 kV AC post porcelain insulator was established by using a finite element method (FEM) analysis software ANSYS. The calculation results of electric field distribution along the insulator were presented. The effect of grading ring structure to the electric field distribution of the post porcelain insulator was analyzed and a use of double ring configuration at the conductor side of the insulator is beneficial. Therefore, Artificial Fish Swarm Algorithm (AFSA) was applied to optimize the dimensions and location of grading rings, then the maximum electric field magnitudes on the surfaces of grading rings, flange and insulator sheds were compared and appropriate parameters of grading rings were recommended finally. The achievements of this paper have been successfully applied on the 1000 kV ultra-high voltage (UHV) pilot project in China and it was proved very effective by field observations with an ultraviolet camera.

Design and dielectric characteristics of the ±1100 kV UHVDC wall bushing in china

The ±1100 kV UHVDC wall bushing is the important power equipment in the ±1100 kV DC power transmission project of China. However, the reported literatures rarely mention its design method and the optimization of its insulation structure. In this paper, two specific designing schemes including the resin impregnated paper (RIP) condenser and the metal-shielded core have been both adopted in the design of the wall bushing. Moreover, the actual operating environment and the rated parameters of the ±1100 kV UHVDC wall bushing have been analyzed in detail. Then, the nonlinear finite element method (FEM) analysis has been applied in the three-dimensional electric stress simulation of the UHVDC wall bushing. The electric field and temperature dependencies of the composite insulation used in the wall bushing have been taken into account. The E-field simulation results indicate that with the RIP condenser, the potential and electric field distribution can be much more uniform along the composite insulator of the bushing. Therefore, the compact design of the wall bushing can be obtained by this designing scheme. On the other hand, with the type of the metal-shielded core, the high E-field strength areas are mainly concentrated on the metal shield and the outer grading ring of the wall bushing. Therefore, the nonlinear FEM was applied in the structure optimization of the internal metal-shielded system used in the wall bushing. Finally, the maximum E-field strength of the wall bushing can meet the control requirement. Based on the simulation results and the optimization structure, the ±660 kV scaled prototype of the UHVDC wall bushing has been produced and passed through all the type tests according to the IEC 62199. The feasibility of the design of the ±1100 kV UHVDC wall bushing has been verified. This paper can provide the theoretical guidelines for the design, manufacture and operation of the UHVDC wall bushing.

The DC electric field analysis of valve side outlet device in converter transformer considering nonlinear and anisotropic characteristics

Valve side outlet device, which consists of bushing terminal and surrounding barrier system, is the insulation structure located in the connection part between valve winding lead and bushing. The insulation structure of outlet device is made up of oil and paperboard. It is the most complicated and the most important insulation part in converter transformer, and it not only withstands AC voltage, but also withstands DC voltage in operation stage. The electric field distribution is determined by the resistivity of each material under DC steady state voltage. Resistivity of oil and pressboard are affected by the electric field strength applied to them, so the resistivity of both insulation materials is nonlinear. Moreover, the resistivity of pressboard is anisotropic. There is a great difference value between the direction of through and along the paper layer. In this paper, the nonlinear and anisotropic DC electric field distribution of valve outlet device was calculated, and the result was compared with the results which not considering anisotropism or nonlinearity of material. The comparison revealed that anisotropic and nonlinear characteristics must be taken into account in the research and design process.

Transient electric field calculation of UHV GIS spacer under lightning impulse

Transient process takes place when a rapidly changing excitation is imposed on a insulation system, like lightening impulse voltage, polarity reversal voltage, et al. In previous studies transient electric field is calculated considering the relative permittivity as a constant. However, a fast changing excitation contains many high frequency harmonic components under which the permittivity may become quite different. In this paper, a frequency division calculation (FDC) method for transient electric field is proposed. For a fast changing excitation applied to a system, its waveform in frequency domain contains many different frequency harmonic components and its response is the sum of the response of each harmonic component. Different frequency component is calculated with corresponding permittivity, therefore the variation of permittivity with frequency is taken into consideration. FDC method is applied to compute the transient electric field (TEF) distribution of a whole ultra-high voltage (UHV) 1100kV GIS spacer under lightning impulse voltage with finite element software ANSYS. Material parameters for calculation are acquired from experiments. Influences of the frequency properties of dielectric medium on FDC method results are also investigated.

Effect of dynamic glass transition on space charge behavior in epoxy resin

The mechanical and dielectric properties change significantly when the temperature is close to the glass transition temperature (Tg) for epoxy resin, which is a dry-type insulation materials used in the high voltage direct current (HVDC) power transmission system. In order to study the effect of dynamic glass transition on space charge behavior in epoxy resin, samples with Tg as approximately 82 °C were prepared and space charge distribution was measured with an improved pulsed electro-acoustic (PEA) set-up at temperatures far below (40 °C) and close to Tg (75 °C) respectively. When the temperature is far below Tg, both homocharge (close to cathode) and heterocharge (close to both electrodes) accumulation can be found with poling time at different poling fields (10 kV/mm, 30 kV/mm). It implies that charge injection and ionization of the organic species have taken place in epoxy resin. However, when the temperature is close to Tg, only heterocharge (close to both electrodes) distribution can be observed in the epoxy resin samples for different poling fields. The injected negative homocharge might be neutralized by the large amount of positive heterocharge arising from the ionization of the organic species in epoxy resin. And this is thought to be related to temperature enhanced dissociation of the organic species and charge mobility in epoxy resin when the temperature is increased to Tg.

Corona test of grading ring for UHV insulators using gradient equivalent method

Corona test is necessary for verifying the validity of grading ring design for insulators on ac transmission lines. But there seems a lack of standards about simulation test method for ultra-high voltage (UHV) power fittings, such as grading ring for insulators. This paper describes a test approach that specifically applies to grading ring for UHV insulators. First, based on finite-element (FE) calculation, a gradient equivalent coefficient which reflects difference of electric stresses acting on surface of grading rings mounted on different sites is determined. Next, refer to IEC and national standard, an available test voltage is corrected by previous coefficient considering interactions of three-dimensional environment. Finally, the corona test of a type of grading ring for UHV suspension composite insulators is performed using above method as an example. This method shows good effect by field observation on tangent towers with an ultraviolet camera and the tested grading rings have been applied in the UHV pilot project in China successfully.

Electric Field distribution on four-bundle conductors in 750 kV AC substation

In high altitude areas of northwest China, the corona activity of conductors is serious in 750 kV AC substations, which may lead to severe electromagnetic environmental problems. According to the research and field experience, determination of adequate parameters of conductors is intended to solve these problems. In this paper, the critical E-Field value is obtained by Peeks empirical formula and this provides a reference for the optimization. Using a three-dimensional FEM model, factors that affect the E-Field distribution on four-bundle conductors are discussed and recommendations on diameter and bundle spacing are obtained. The optimization can result in reduction of the corona discharge on the conductors. The derived conclusions can provide experiences and references for the design of conductors in 750 kV AC substation.

E-Field distribution of circuit with value controlled reactors in 750 kV substations

Since 750 kV transmission lines locate in the high altitude areas of northwest China where the environment condition is comparatively severe, the electromagnetic environmental problems in substations appear to be more prominent. As can be seen from the field observation results of the in-service substation, the frequent or permanent presence of corona discharge is obvious adjacent to the corona rings and end fitting hardware. This can result in distinct consequences of radio interference and audible noise, thus it may necessitate reasonable design of corona rings to improve the E-Field conditions. In this article, using a three-dimensional finite element method model, the E-Field distribution of circuit with value controlled reactors in the 750 kV substations is researched. According to both actual knowledge of phenomena and practical experiences form test facilities and lines in operation, a viable value of E-Field intensity is ascertained to control the electric field, and the configurations of some corona rings are optimized subsequently to diminish the corona discharge. And then an exhaustive suggestion about the design and arrangement of corona rings is proposed. The results could provide experiences and references for the design of 750 kV AC substation, and better technical performance and economic competitiveness is predicted to be implemented.