Particle Swarm Optimization-based BP Neural Network for UHV DC Insulator Pollution Forecasting

In order to realize the forecasting of the UHV DC insulator's pollution conditions, we introduced a PSOBP algorithm. A BP neural network (BPNN) with leakage current, temperature, relative humidity and dew point as input neurons, and ESDD as output neuron was built to forecast the ESDD. The PSO was used to optimize the the BPNN, which had great improved the convergence rate of the BP neural network. The dew point as a brand new input unit has improved the iteration speed of the PSOBP algorithm in this study. It was the first time that the PSOBP algorithm was applied to the UHV DC insulator pollution forecasting. The experiment results showed that the method had great advantages in accuracy and speed of convergence. The research showed that this algorithm was suitable for the UHV DC insulator pollution forecasting

Electric Field Distribution and Switching Impulse Discharge under Shield Ball Surface Scratch Defect in an UHVDC Hall

The dimension and surface state of shielding fittings in ultra high voltage direct current (UHVDC) converter station valve halls have a great influence on their surface electric field and switching impulse characteristics, which are important parameters confirming the air gap distance in the valve hall. The characteristics of impulse discharge under different lengths, dent degrees and burrs around the scratches of Φ1.3 m shield balls with a 2 m sphere-plane gap length were tested, in the UHVDC testing base of the Hebei Electric Power Research Institute. The discharge characteristics under the influence of the surface scratches of the shield ball were obtained. The results demonstrate that the discharge voltage of sphere-plane gap decreases obviously when there are unpolished scratches on the surface of the shield ball. However, when the scratches are polished, the discharge voltage has no significant impact. At the same time, a 1:1 full-scale impulse test model was established based on the finite element method. The electric field intensity and the space electric field distribution of the shield ball were obtained under the influence of scratches with or without burrs. The results of the simulation show that when the surface of the shield ball is smooth, the electric field distribution around it is even. The electric field intensity on the surface of the shield ball increases obviously when there are burrs around the scratches. When there is no burr around the scratches, the length and depth of the scratches have no obvious effect on its electric field distribution. Meanwhile, calculation results are consistent with test results. The results can provide an important basis for the design and optimization of shielding fittings, and technical support for its localization

Constitutive Characteristics, Microstructure, and Texture Evolution of As-Cast 42CrMo Alloy in Nonisothermal Multipass Compression

The nonisothermal multipass deformation behavior of as-cast 42CrMo alloy was studied with declining temperature, constant pass strain, varying strain rate, and interval time. The stresses are used to develop the constitutive model. As the finishing temperature increases from 990°C to 1070°C, the stress decreases gradually and the softening effect increases, which results in a large grain size and inhomogeneous microstructure. The low angle grain boundaries transform into high angle grain boundaries through absorbing dislocations. The noticeable stress softening in a high strain rate is attributed to the thermal softening, dynamic recovery, and dynamic recrystallization. The thermal softening is no longer considered to be the main interpass softening mechanism at a low strain rate. The interval time has a negligible effect on the stress, but the significant changes in grain size and texture component are caused by the interpass softening. The average grain size is approximately 40 μm, and the distorted grain boundaries and small fine grains are found in the interval times of 0.5–5 s, implying the dynamic recovery and grain growth. The near {001} and {110} orientation exerts an important influence on the grain refinement

Experimental Study on Breakdown Characteristics of Transformer Oil Influenced by Bubbles

Bubbles will reduce the electric strength of transformer oil, and even result in the breakdown of the insulation. This paper has studied the breakdown voltages of transformer oil and oil-impregnated pressboard under alternating current (AC) and direct current (DC) voltages. In this paper, three types of electrodes were applied: cylinder-plan electrodes, sphere-plan electrodes, and cone-plan electrodes, and the breakdown voltages were measured in both no bubbles and bubbles. The sphere-sphere electrodes were used to study the breakdown voltage of the oil-impregnated pressboard. The results showed that under the influence of bubble, the breakdown voltage of the cylinder-plan electrode dropped the most, and the breakdown voltage of the cone-plan electrode dropped the least. The bubbles motion was the key factor of the breakdown. The discharge types of the oil-impregnated pressboard were different with bubbles, and under DC, the main discharge type was flashover along the oil-impregnated pressboard, while under AC, the main discharge type was breakdown through the oil-impregnated pressboard

Preparation of magnetic-conductive Mn06Zn04Fe2O4-CNTs/PANI nanocomposites through hydrothermal synthesis coupled with in situ polymerization

A facile chemical method through hydrothermal synthesis coupled with in situ polymerization to prepare the Mn0.6Zn0.4Fe2O4-carbon nanotubes (CNTs)/polyaniline (PANI) nanocomposites has been reported in this paper. The structure of samples has been characterized by the Fourier transform infrared and X-ray diffraction. The shape and size of samples have been observed by the scanning electron microscopy and transmission electron microscopy. The conductive properties of the Mn0.6Zn0.4Fe2O4-CNTs/PANI nanocomposites have been tested by a four-probe conductivity tester at room temperature. And the magnetic properties are measured by a vibrating sample magnetometer. When the mass ratio of the Mn0.6Zn0.4Fe2O4-CNTs to aniline (m(Mn0.6Zn0.4Fe2O4-CNTs)/m(An)) is 0.15, the Ms, Mr and Hc achieves 15.44emu/g, 5.06emu/g and 308.68Oe, respectively. At the same time the probable formation mechanism of nanocomposites is also investigated based on the experimental results. ? 2014 Elsevier Ltd