Electrical Tree in HTV Silicone Rubber With Temperature Gradient Under Repetitive Pulse Voltage

High temperature vulcanized silicone rubber (HTV SIR) is important insulation for high voltage direct current (HVDC) cable accessories. The pulse voltage in the HVDC system may initiate an electrical tree in SIR insulation. During the operation, there is a temperature gradient in SIR caused by the different temperatures of conductor and external environment. So it is necessary to research the electrical tree initiated by pulse voltage under the temperature gradient. In this paper, electrical trees in SIR with different temperature gradients were recorded. The inception voltage, tree length, and accumulated damage (AD) distribution were analyzed. The experiment results indicate that tree inception voltage decreases with the increase of temperature of the ground electrode when the needle temperature is 90 °C, it also decreases with the increase of needle temperature when the ground temperature is 90 °C. All the trees are in bush structure when the ground temperature is 90 °C, the structure changes from branch to bush with the increase of ground temperature when the needle temperature is 90 °C. When the needle temperature is 90 °C, AD distribution changes obviously with the increase of ground temperature. The conductivity of SIR under different temperatures and electric fields was tested. The effect of changing conductivity on tree inception was discussed. Surface potential decay (SPD) at different temperatures was tested. The trap characteristics and charge kinetic properties influenced by temperature may be the main reasons for the change of tree structures in the growth process

Effect of water on electrical properties of Refined, Bleached, and Deodorized Palm Oil (RBDPO) as electrical insulating material

This paper describes the properties of refined, bleached, deodorized palm oil (RBDPO) as having the potential to be used as insulating liquid. There are several important properties such as electrical breakdown, dielectric dissipation factor, specific gravity, flash point, viscosity and pour point of RBDPO that was measured and compared to commercial mineral oil which is largely in current use as insulating liquid in power transformers. Experimental results of the electrical properties revealed that the average breakdown voltage of the RBDPO sample, without the addition of water at room temperature, is 13.368 kV. The result also revealed that due to effect of water, the breakdown voltage is lower than that of commercial mineral oil (Hyrax). However, the flash point and the pour point of RBDPO is very high compared to mineral oil thus giving it advantageous possibility to be used safely as insulating liquid. The results showed that RBDPO is greatly influenced by water, causing the breakdown voltage to decrease and the dissipation factor to increase; this is attributable to the high amounts of dissolved water

Physics of electrical treeing in Silicon Gel

Silicone gel is commonly employed in electrical insulation, especially in power module encapsulation. In the recent years, the increase of the operation voltage of this application led to a higher electrical stress on the silicone gel, thus, electrical treeing has become a serious issue to the reliability of power modules. In this research, the degradation produced by the electrical treeing has been evaluated dividing it into two main parts: the tree inception and the tree growth, which have been assessed for different waveforms of the applied voltage. The tree inception, the preliminary stage of this phenomenon, has been tested and an innovative model has been proposed explaining this stage. The tree growth has been evaluated in function of the waveform voltage obtaining useful comparisons between the possible electrical stresses. This thesis highlights the peculiar behavior of silicone gel under high electric field and furnishes useful guidelines for designing and testing the electrical insulation made by silicone gel

Model of electrically stimulated hernia mesh electrode for soft tissue healing

Hernia repair is a common surgery that repairs tissues that have torn due to strain, allowing the internal organs to protrude from the body cavity [1,2]. Hernioplasty, which is hernia repair surgery with incorporation of a mesh to prevent retearing by mechanically supporting the tissues, has various levels of success. Factors such as infection, comorbidities, and age all play a role in how quickly the body can recover. To allow the tissues to be strengthened more naturally, an incorporation of electrical stimulation of the tissues would encourage faster cellular proliferation and therefore wound healing for strengthening the soft tissues [3]. An alternating current (AC) that creates an electric field in the region surrounding a wound has shown in other studies to encourage cellular proliferation and faster healing [3-5]. Previous related research utilized piezoelectric materials to output small amounts of voltage by stimulating the piezoelectric material [6]. This output voltage has been shown to be achievable in soft tissues through transcutaneous medically safe 1MHz ultrasound waves stimulation of the piezoelectric material that mimic the effect of mechanical loading [7]. A literature review of stimulation of cells within soft tissue indicates that fibroblasts proliferate within a sinusoidal AC electric field range of 20-300 mV/mm [3-6]. In this study, the output created by ultrasound loaded piezoelectric device was incorporated into a computational COMSOL® model of a conductive hernia mesh. COMSOL®, a multiphysics finite element analysis software, was used to model the conductive electrode, determine voltage inputs and their resulting electric fields, and to test designs for creating a clinically relevant electric field stimulation within the proliferation range for fibroblasts. The model shows an electrically stimulated hernia mesh devised from the current methods of implanted polypropylene (PP) hernia mesh, by overlaying a thin gold surface onto the polymer mesh, which is proposed to be connected to a small piezoelectric device. For maximized area of stimulation, one of the electrode connection points is insulated from the body environment to conduct the positive and negative electrode points to opposite sides of the wound, creating an electric field across the wound site. Electrode materials for the mesh conductance layer were tested within the model, which showed similar electric fields for each material. The small differences were shown to be based on the material properties, which allowed higher or lower conductance through the surrounding solution, phosphate buffered saline. Gold was chosen to be the conductive metal based on its moderate electric field and biocompatibility. A range of possible output voltages from the piezoelectric device were also modeled in a voltage sweep to show the maximum and minimum electric fields the tissues would experience within the previously set range. When several set points in the electric field were measured at a value of Vin=100 mV, the electric field average was 5.93 ± 1.24. The overall electric field showed maximum values at the anode and cathode, but there was also stimulation midway between the nodes that could supply moderate stimulation to cells wherever they may lie within the electric field. It was concluded from these computations that a voltage of 20mV – 250mV should allow for increased tissue healing through cellular proliferation when connected to gold coated polypropylene hernia mesh