Papers by Keyword: Electrical Tree

Abstract: Electrical tree is a topic that has been extensively studied in recent years. Electrical tree is considered a deterioration of the electrical insulator due to the high voltage field's distortion. Solid insulating materials used in high voltage applications, such as epoxy resin are widely employed due to their high dielectric strength and excellent mechanical properties. This research studies the effect of micro and nanoparticles of Al₂O₃ and SiO₂ on electrical tree inhibition in epoxy resin insulators. Electrical tree inhibition is achieved by incorporating micro and nanoparticles into the polymer material, which possess different properties. Following ASTM D 3756-97, the experiment is conducted with a constant 22 kV voltage and frequency of 50 Hz. Both Al₂O₃ and SiO₂ possess the ability to inhibit the growth of the electrical tree. Experimental results revealed that the addition of Al₂O₃ and SiO₂ to the epoxy resin affected the formation of electric trees. As the quantity of filler increases, fewer electric trees are produced. Additionally, It has an effect on the initial formation time of electric trees. The initial time of the electric tree with the addition of micro/nano(1/3) Al₂O₃ additives at a ratio of 0.1 wt% was 3.5 times longer when compare with pure epoxy resin.

Abstract: Epoxy resin is widely used in high voltage insulator material because of its high dielectric strength. Electrical tree phenomena are one of an electrical insulation degradation. It is easily initiated due to the distorted high electrical field. In this study, graphene nanoplatelets (GNPs) with the contents of 0.003-0.010 wt.% (2.6-8.8 mg) were filled into epoxy resin to improve electrical tree inhibiting ability. Treeing experiments were conducted at a fixed voltage of 15 kV, 50 Hz. LCD digital microscope was used to observe the electrical tree inhibition of GNPs in epoxy resin. The digital image of insulators sample was then analyzed by MATLAB program. The percentage of electrical tree damages of GNPs content of 0.007 wt.% was found at 2.75 %. Experimental results showed that electrical tree has propagated from main branch tree to many small branches. The distributed electrical tree around the main branches occurred after the addition of GNPs. Filling GNPs content of 0.005 wt.% will result to a complex branch tree structure with much longer branches than others. Nevertheless, the average tree length was inhibited at the GNPs filling contents of 0.003 to 0.007 wt.%.

Abstract: Electrical tree phenomenon commonly occurred in solid insulator material resulting from the inconsistency of stresses during the manufacturing process. The treeing phenomenon will degrade the characteristic of insulator and may lead to breakdown. The use of filler in the manufacturing process in order to enhancing the insulation property is a popular approach. This paper presents the use of coconut shell powder (CSP) filler in epoxy resin for inhibition of electrical tree growth. The particle sizes of CSP varied from 62, 75 and 125 µm. The CSP is filled with the ratio of 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 2.0 and 3.0% by weight. We aim to observe the effects of varying the combination of CSP particle sizes and the ratio of epoxy resin for an inhibition of electrical tree growth. The electrical tree was tested by applying AC voltage of 15kV to the test sample and conducted for 360 minutes in this experiment. When the epoxy resin using CSP filler of 1% by weight is fixed for the particle size of 62, 75 and 125 µm, electrical tree length is at 1.24mm, 1.382 mm and 1.78 mm respectively. Whereas, when the particle size of CSP at 62 µm is fixed, a tree length is 1.98 mm and 1.24 mm for the ratio of 0.1 and 1% by weight respectively. Our study demonstrates that the epoxy resin using CSP filler at a ratio of 0.1% by weight can shorten length of electrical tree when compared with a ratio of 1.0% by weight. The electrical tree length was affected through the changes of permittivity by addition of CSP compound.

Abstract: Electrical tree phenomenon is a long term degradation and can be found in solid insulator material. Its phenomenon will degrade the characteristic of insulator and may lead to breakdown. The use of filler in the process of manufacturing for the insulation is very popular method. This paper presents the use of coconut shell powder (CSP) filler in epoxy resin for inhibition of electrical tree growth. The CSP is filled with in ratio of 0.1, 0.3, 0.5, 0.8 and 1.0% by weight. The electrical tree was tested by AC voltage of 15kV and conducted for 30 minutes in this experiment. Experimental results shown that, the pure epoxy resin using as a controlled has tree length of 3.20 mm. While the epoxy resin using CSP filler of 1% by weight has a tree length propagation of 2.10 mm. The shorten length of electrical tree may be affected by the combination of modified permittivity (Ɛ) value of an insulator. Also, this study has shown that the CSP may be a potential candidate as a filler compound to be used as electrical tree inhibition for electrical insulation system.

Abstract: Nonlinear insulated materials can uniform electric field distribution in non-uniform electric field. In order to inhibit the electric tree initiation and propagation inside high-voltage cross-linked polyethylene (XLPE) insulated cable, a kind of 220kV high-voltage XLPE insulated cable with new structure is designed by embedding nonlinear shielding layer into XLPE insulation layer of high-voltage cable with traditional structure in this study. Experimental and simulation results indicate that the nonlinear shielding layer can effectively inhibit electrical tree propagation inside the XLPE specimens, and obviously extend the breakdown time caused by electric tree propagation. When the electrical tree propagates into the nonlinear shielding layer sandwiched between insulation layers of cable, the electric field distribution near the tip of electrical tree is obviously improved. These findings prove the feasibility and the effectivity of inhibiting electrical tree propagation inside high-voltage cable by adding nonlinear shielding layer into the insulation layer.

Abstract: Electrical tree aging is one of the leading factors causing degradation and breakdown of insulation performance of high-voltage cross-linked polyethylene (XLPE) cable. A lot of attention has been paid to inhibiting electric tree initiation and propagation inside high-voltage cable. In this study, insulation composites with nonlinear electrical conductivity are prepared. Experimental results show that these composites are helpful for enhancing the apparent breakdown electric field strength of XLPE in the pole electrode system. A kind of high-voltage XLPE insulated cable with new structure is designed by using these composites as nonlinear shielding layer. Numerical simulation results indicate that nonlinear shielding layer can obviously improve the distribution of electrical field at the defect of insulation surface of high-voltage XLPE cable, and decrease the maximum electrical field strength at the defect. This new structure is potential for effectively inhibiting electrical tree initiation inside high-voltage XLPE insulation cable, thus increasing life span and operational reliability of the cable.

Abstract: In high voltage equipments, insulation systems are the most vital parts to prevent any discharges from occurs around the protected systems. However, the discharges in the form of electrical treeing can easily occur when there are existences of impurities, voids or defects in the insulation bulk. This phenomenon can lead to the insulation breakdown when subjected to prolonged electrical stresses. This paper discusses about the effects of silica nanofillers on the electrical treeing growth in epoxy resin. The silica nanofillers were dispersed in epoxy resin matrices homogeneously by using ultrasonication method based on weight percentage (wt %) which the weight percentages used in this study were 0 wt%, 1 wt%, and 3 wt% respectively. The influence of these nanofillers on the electrical tree breakdown resistance was investigated experimentally. The electrical tree data such as tree inception voltage, tree breakdown voltage and tree propagation time were tabulated and appropriate comparative analysis were made and presented. Last but not least, scanning electron microscopy images were captured and discussed based on its dispersion state and also the morphological features of the epoxy nanocomposites. In this study, it was found that the existence of different silica nanofiller concentrations have profound effects on insulation strength and could exhibit significant improvement of tree characteristics of epoxy nanocomposites.

Abstract: The failure of magnet wires used in inter-turn insulation of inverter-fed motor winding is the main cause which leads to the motor insulation breakdown. This paper conducted electrical tree breakdown experiments on magnet wire insulating film (FCR 100) used in the inter-turn insulation of JD117 inverter-fed motor and meanwhile combining with energy spectrum analysis and scanning electrical microscope (SEM), by which type and content of elements, breakdown main body and electrical tree channel could be clearly observed, the corresponding failure mechanisms were analyzed. The experiment results reveal that all the breakdown main bodies are located at the pointedness and insulation joint of magnet wires, of which dielectric strength is relatively lower; they are the insulation “weak point”, which should be paid enough attention and strengthened at the manufacturing period. The electrical tree breakdown time is quite long and the life span of magnet wire is 11 hours. The electrical breakdown strength of envelope is very low when containing metal impurity. It is also found that the aluminum occupies the highest content tested by energy spectrum analysis.

Abstract: Effects of additive powders on the machining mechanism of powder mixed EDM were researched. The whole discharging process was discussed based on theory of plasma and dielectric. Experiments, oscillograms and energy spectrum analysis gotten in experiments were performed in order to examine the changes of discharge between EDM and powder mixed EDM.