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Effect of nano-additive size on the space charge behaviour in LDPE/SiO 2 nanocomposite

The distribution of space charge in polymer nanocomposite material is related to the properties of nano-additive, such as size. In this paper, nanocomposites of low-density polyethylene (LDPE) and nano-SiO2 with different size were prepared, respectively. The space charge behaviors of all samples were investigated with pulsed electro-acoustic method (PEA). After pre-stressing under an electric stress of 50 kV/mm for 1 h, samples filled with different size of nano-SiO2 were shorted, and space charge was measured. It is shown that the distribution and amount of space charge in the nanocomposites has a strong relation relation with the size of nano-SiO2. The potential barrier between nanocomposite and electrodes materials attenuates with decreasing of nano-SiO2 size. And the mean attenuation rate of space charge decreases when the pure LDPE is filled with nano-SiO2. However, the mean attenuation rate of LDPE/SiO2 rises with increasing of nano-SiO2 size.

The thermal conductivity and electrical strength of epoxy resin with different filler content of micro and nano alumina

Epoxy resin is widely used in high voltage apparatus, electrical machines etc due to its excellent mechanical, electrical and chemical properties. Great progress has been made in application on electrical insulation, casting and potting. The epoxy resin containing nano-size and micro-size Al₂O₃ of various contents are prepared. The purpose of efforts we engaged in is to study the efforts of nano Al₂O₃, micro Al₂O₃ and nano-micro Al₂O₃ on the characteristics of epoxy resin on electrical and thermal properties. The epoxy resin(UVR6105) is used as the base material and Methyl six hydrogen anhydride is used as the curing agent. Various nanocomposites, microcomposites and nano-microcomposites are prepared and fabricated properly through three roller grinding machine. Breakdown strength experiments are done through JNC801 breakdown voltage tester. Nano Al₂O₃ enhances the electrical characteristics of epoxy resin on breakdown strength while micro Al₂O₃ lowers it. The thermal properties of thermal conductivity of the epoxy resin are tested through LFA477. The thermal conductivity of epoxy resin is increasing with the filling contents of the Al₂O₃ while there is a comparatively lower value if nano Al₂O₃ is added due to its high thermal interface resistance between epoxy resin and Al₂O₃.

Study on the Online Dissolved Gas Analysis Monitor based on the Photoacoustic Spectroscopy

According to the principle of Photoacoustic Spectroscopy, HPAS-1000 Online Dissolved Gas Analysis Monitor is developed to monitor the dissolved gas in the power transformers online, which can directly extract the oil sample from the running transformer and measure the content of Hydrogen, Acetylene, Ethylene, Methane, Ethane, Carbon monoxide and Carbon dioxide dissolved in the oil sample in real time. Field Gas Monitor-INNOVA 1412 module is employed for it only takes a few milliliters of gas to achieve the measurement and the sensitivity of Acetylene, Ethylene, Methane, Carbon monoxide can reach to less than 0.5ppm. In order to separate the gas from the transformer oil a vacuum pump is used in the degassing module with TEFLON AF 2400 polymer membrane. For every fault gas has cross-interferences with each other including water vapor when measuring, INNOVA 1412 module should be calibrated by the fault gases of known standard concentrations before it can be used for measuring. Then several experiments were designed in order to study the characteristics of capillary negative pressure oil gas degassing system, and found the most efficient way of degassing. The experimental results show that, under the same conditions, the longer the degassing time, the higher the degassing efficiency; the greater the pressure difference, the higher the degassing efficiency; as the flow rate increases, the degassing efficiency increases first and then decreases, and the optimum flow rate is between 20ml/min and 30ml/min. Based on these results, the performance of HPAS-1000 Online Dissolved Gas Analysis Monitor is optimized, thus it subsequently passed the certification of CEPRI successfully and installed in the substations.

One novel type of UHF antenna for locating partial discharge and simulation of UHF signal propagation within transformer

In recent years, ultra high frequency (UHF) method has become a widely used method to detect partial discharge (PD) in transformers. For this method, we should pay attention to two crucial problems: (i) How to detect the UHF signals radiated from PDs; (ii) How to confirm the PD locations accurately. In this paper, a new type of antenna, named multi-element monopole antenna or Goubau antenna, is introduced to the area of PD detection. The antenna was designed using electromagnetic simulation software. The simulation software computed return loss shows a reasonable agreement with tested data. Both of the results turn out that operating frequency range of the antenna is about 400-1000MHz. To study the influence brought by inner structures of transformer, the time-delay effects caused by core and winding respectively were simulated using FDTD method. It is concluded that time-delay effect caused by core is obvious, while the effect caused by winding is not.

The three-layered core model permittivity of polymer nano-composites in electrostatic field

Multi-layered core model of nanoparticle was supposed to have advantage in analyzing dielectric characteristic of polymer nano-composites by many researchers. However this model cannot be verified effectively from the view of mathematic. This paper focused on solving this problem. First the three-layered core physical model was built based on physical phenomenon and former research results, and then mathematical model was built by taking different densities into Maxwell Garnett Approximation (MGA). Permittivity of each layer was established by integrals mean value point of supposed three different functions in respective thickness. At last three-layered core mathematical model of diffusion system was built and the equivalent permittivity was calculated. The calculated results have a better coincidence with experimental result and all of this show that three-layer core model and arc-tangent function have a good description of character of interaction zone.

Apparatus for on-line monitoring of transformer winding deformation using leakage inductance identification

Windings of power transformer may suffer short circuit currents or mechanical forces, which lead to different winding displacements such as axial displacements and radial displacements. Measurement of leakage inductance is one of the most effective methods to identify these mechanical displacements. In this paper, an on-line detection system based on WinCE platform for transformer winding deformation is proposed. Based on the equivalent circuit of the transformer for low frequencies, the formula to calculate the leakage inductance on-line is derived. In practice, using the signals gained from the voltage transformers and current transformers, with the help of proper signal filtering method, leakage inductance is calculated in our program. Both the signal processing theory and the algorithm of online leakage inductance estimation are presented. To evaluate the feasibility of the detection system, experiments with and without winding displacements were made using a small transformer and the results of on-line detection were discussed.

Finite element simulation of LDPE/SiO 2 nanocomposite

A three-dimensional three-phase model intended to describe the current behaviors of LDPE/SiO2 nanocomposite under DC voltage is presented. The polarization current and depolarization current are simulated by finite element method based on this model. In order to verify the feasibility of this model, practical currents in LDPE/SiO2 nanocomposites filled with different content of nano silica are measured, respectively. It is shown that the trends of simulated currents and practical currents are the similar, especially under low doping concentration (below 1%wt in this article). However, the current decay rate of simulated results and experimental results has a little difference, especially under high doping concentration (above 2%wt in this article). Thus, this three-phase model is useful in calculating the current behavior of nanocomposite, although it is not perfect and still needs to be improved.