Shiling Zhang

Inner insulation structure optimization of UHV RIP oil-SF 6 bushing using electro-thermal simulation and advanced equal margin design method

The iso-margin method based on the classical analytical equations is widely used in the development of extra high voltage (EHV) bushing. Therefore, its effectiveness and feasibility have been fully validated. However, with the theoretical formula, it is difficult to evaluate the influence of stray capacitance and temperature on the internal electric stress of the ultra high voltage (UHV) bushing. Its necessary to further improve the traditional iso-margin method. Firstly, the basic principle of iso-margin method has been briefly described. After that, the E-field distribution of condenser bushing was investigated on the Finite Element Method (FEM) computing platform. Then, the mathematical model of the advanced equal margin design method was established. Furthermore, this paper presents the program flow of optimization which combines the simulation of electro-thermal coupling process and the particle swarm optimization (PSO) algorithm. The proposed methodology was applied to the design of the prototype of the UHV resin impregnated paper (RIP) oil-SF6 bushing, which realizes the uniform axial E-field distribution of the bushing condenser. Meanwhile, the partial discharge margin between adjacent foils can be equal. Moreover, the hot-spot temperature is lower than the operation limiting temperature of the RIP material. The bushing condenser was fabricated according to the optimal structure design. The prototype of bushing has passed through all the type tests. In this paper, the FEM electro-thermal coupling simulation and the advanced equal margin design method were applied to the inner insulation structure optimization of the UHV RIP oil-SF6 bushing. Meanwhile, the proposed methodology provides some theoretical guidelines for the future research and development of other types of bushing on the UHV level.

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.

Simulation study on E-field distribution and corona characteristics of composite insulator with water droplets

Silicone rubber makes composite insulators show excellent moisture dirt performance because of its hydrophobicity. In the wet environment, separated water droplets instead of continuous water film will form on the surface of composite insulators, helping curb the occurrence of arc in high-strength field. However, separated water droplets will distort the electric field easily leading to the partial discharge such as corona. Long-term corona discharge on silicone rubber surface will lead to the aging and ablation of silicone rubber, and then water will get inside the insulator, causing slow corrosion on mandrel and eventually leading to fracture. Therefore, it is essential to investigate the electric field distribution when there are water droplets on the composite insulator surface. In this paper, a simple electrode system is established to study the impact of water droplets on electric field on the silicone rubber by using finite element analysis software ANSYS. The law of the electric field distribution with the water contact angle, number and spacing changing is summed up. A two-dimensional model of a composite insulator is established to conduct calculation with water on the surface, after analysis the law of the electric field distribution in the sheds and sheath area and along the insulator surface is summarized. Parametric design language is applied in ANSYS to model, calculate and analyze, and then MATLAB and ANSYS are combined to optimize grading ring of a composite insulator, using genetic algorithm. Optimization results are applied to three-dimensional composite insulators insulator model to calculate in two cases, one is that drops on the surface have constant radius 2mm and the other is that the radius varies from 1mm to 3mm. The law of the electric field distribution is summed up and compared to the results in two-dimensional case.

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.

Optimization of corona ring structure for UHV composite insulator using finite element method and PSO algorithm

The optimization method combining Finite Element Method (FEM) and particle swarm optimization (PSO) algorithm has been applied to design of corona ring structure for composite insulator used along Ultra High Voltage (UHV) transmission line in the present work. Firstly, corona discharges have been investigated by means of ultraviolet imager (UVI) observation which indicates improper corona structure and installation. Next, E-field distributions along composite insulator and on surface of corona ring have been computed and analyzed with three-dimensional FEM calculation model of UHV tangent tower on which hangs suspension and tension composite insulators in single-circuit transmission line using commercial software ANSYS. Finally, an objective function which can evaluate nonlinear relationship between maximum electric field strength and corona ring structure parameters has been established based on initial calculating results, On the other hand, PSO algorithm also has been implemented using APDL language in ANSYS computing environment, then optimization of corona ring structure for UHV composite insulator can be converted to seek minimum value of objective function utilized programmed PSO algorithm. The results show that the proposed optimization process can be conducted automatically and efficiently, moreover, the electric field strength along insulator and around corona rings after optimization is less than that before optimization, and the optimal rings improve electric field distribution along composite insulators.

Experimental study on the electrical and thermal properties of epoxy-crepe paper composites for use in UHV DC bushing condensers

Entire performance of UHVDC resin impregnated paper (RIP) bushings in operation condition has an intimate connection with electrical and thermal properties of epoxy/crepe paper composites used in bushing condenser. Firstly, some samples of pure epoxy and epoxy/crepe composites which are identical to those used in actual RIP bushings were fabricated. Then micro morphology of these samples has been observed by scanning electron microscopy (SEM) and polarized light microscopy (PLM). Some electrical performance measurements were carried out including AC breakdown characteristics, bulk resistivity versus temperature characteristics and dielectric spectroscopy with broadband dielectric spectra. Meanwhile, thermal property containing thermal conductivity versus temperature characteristic has also been obtained experimentally. Finally, with these parameters of composites, electric field and temperature distribution inside bushing condenser has also been simulated by finite element method (FEM).

Simulation study of edge effect in high voltage condenser bushing foils

During the operation of a HVAC bushing, there exists E-field distortion at the edge of the aluminum foils where the edge effect enhances E-field. To figure out the operating performance of a bushing, its essential to analyze the distribution of E-field at the edge of foils. In this paper, computing and experimental researches are conducted to analyze the edge effect. We first investigate a 2-D model of several parallel foils using finite element method. By means of ANSYS parametric design language (APDL) in ANSYS computing environment, we systematically analyze the dependence of the E-field distribution on the geometrical variables describing the relative position and dimension of the foils, finding that E-field strength at the edge of foils and the ratio of the enhanced E-field strength and the average value each have an exponential relationship with the distance between two foils and the thickness of a foil.

Thermal Properties of Environmentally Friendly Dielectrics used in Medium Voltage Circuit Breakers

There is a need to replace an epoxy tie rod, which is used as the insulation and structural component within a vacuum circuit breaker, by an alternative environmentally friendly material. A selection process has demonstrated that glass filled thermoplastics are candidates. This paper compares the thermal performance using Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA) and Heat Distortion Temperature (HDT) of amorphous and semicrystalline polymers with the epoxy thermoset as the reference. The outcome demonstrated that the higher glass filled semi-crystalline polymers were better but there was still thermo-mechanical instability within the morphology at the lower temperatures.

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.