Analysis of self-healing performance of metallized

2022-08-02
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Analysis on self-healing performance of metallized capacitors Abstract: in recent two years, China's power capacitor manufacturing industry has introduced metallized products in the field of low-voltage capacitor manufacturing to replace the original oil immersed paper products. The remarkable feature of metallized capacitors is the so-called "self-healing", that is, when the dielectric breakdown occurs, the breakdown point can instantly restore the insulation performance like the wound healing line...

key words: analysis of self-healing performance of metallized capacitors in recent two years, China's power capacitor manufacturing industry has launched metallized products in the field of capacitor manufacturing with higher low-voltage axial tension to replace the original oil immersed paper products. The remarkable feature of metallized capacitors is that they have so-called "self-healing", that is, when the dielectric breakdown occurs, the breakdown point can instantly restore the insulation performance like the wound healing line. Because of this valuable self-healing performance, metallized capacitors can use very thin single-layer film dielectric. In this way, the capacitor can adopt a high working electric field strength, so the volume and weight of the capacitor are greatly reduced. However, there is a certain limit to self-healing. In some cases, the loss of self-healing performance will lead to capacitor failure. Therefore, it is important to understand the self-healing performance of metallized capacitors for product design and use. Next, we analyze the self-healing process of metallized capacitors when breakdown occurs and the factors affecting the process. 1. Analysis of the self-healing process 1.1 for the description of the self-healing process, please refer to figure 1a, B and C. the whole process from dielectric breakdown to insulation recovery can be described step by step as follows: Step 1: under the action of applied voltage, the dielectric breakdown of the breakdown capacitor is caused by the existence or development of defects such as impurities or air gaps in the dielectric to form a conductive path; Step 2: then, a sharp pulse current flows through the metal layer in a small range near the conductive path. The current on the metal layer near the breakdown point rises suddenly and is inversely distributed according to the distance from the breakdown point. At instant T, the temperature of the metal layer in the region with radius RT reaches the melting point of the metal, and the metal in this range melts and generates an arc. This current causes the capacitor to release energy, resulting in a sudden increase in temperature and pressure in the local area of the arc path. Step 3: insulation recovery with the effect of discharge energy, the metal layer in the area with radius RT evaporates violently and splashes. In the process of increasing the radius of this area, the arc is broken, the metal is blown away, oxidized and cooled, and finally the conductive path is destroyed, forming a circular insulation area with the metal layer lost centered on the breakdown point on the dielectric surface. Thus, the self-healing process is completed. The circular insulation area where the metal layer is lost is called the self-healing halo area. Generally, the lubricating oil with wear particles is extracted from the machine equipment, and its area is usually within the range of 1-8mm2. The typical self-healing halo type is shown in Figure 2. It should also be pointed out that the evaporation of the metal layer in the halo area is not the heat released by the arc path, but the direct heat generated by the current passing through the metal layer. In the process of self-healing, the current passes through the gas medium along the surface of the medium, and the whole process proceeds quickly. According to the research [1], when the surface resistance of the electrode plate is in the range of 1.4 ~ 4.5 Ω/□ the self-healing time under atmospheric pressure and 400V is about 10 ~ 20 μ S。 When the applied voltage is high, the corresponding self-healing recovery time is long. 1.2 electric equivalent circuit when self-healing occurs in the container in recent years. The equivalent circuit of the capacitor in the self-healing process is shown in Figure 3. The breakdown point s in the figure simulates the evaporation area of the metal layer on the discharge channel and the two adjacent plates; c. R and H represent the equivalent parameters of scientific and technological innovation scores achieved by the isolation technology of Kunming new airport terminal of the capacitor intact department. S can be regarded as a nonlinear active component. Its static and dynamic resistance at a certain moment is related not only to the current and voltage at the moment, but also to the previous process. At the beginning of self-healing, the voltage on s will soon reach o from the starting voltage on the capacitor plate, and then rise slowly according to the exponential law until the end of self-healing. The self-healing process is very fast, and the voltage Uc on the capacitor has no time to drop, so the influence of the external circuit can be ignored. On the calculation of parameters R and l of capacitor equivalent circuit when self-healing occurs, tuhah et al. [2] deduced the following expression through analytical operation: r=0.67nrolnb/rh=4.2 × W2d lnb/r: W -- number of element turns B -- width of electrode plate D -- thickness of medium n -- a coefficient equal to 1 or 2, which refers to single-sided or double-sided metallized paper ro -- surface resistance of electrode plate R -- radius of self-healing halo area. We can calculate that if b=100mm, r=1 ~ 4mm, ro=3, then R is%. 47~9。 Within 26 Ω. IO. C. The calculations and experiments carried out by qatuhah et al. Also show that when the R diameter is the maximum. The relationship between radius r of self-healing halo region and electrode surface resistance is shown in Fig. 4. 2. Factors affecting the self-healing process 2.1 effect of applied voltage on self-healing in order to achieve self-healing, a certain amount of energy must be applied around the breakdown point to form a circular area with metal removed. However, if too much energy is released, the adjacent medium will be damaged and cause new breakdown. Such development will lead to repeated breakdown of the medium, which will lead to burning, nodulation and self-healing failure of the medium at the breakdown point. It can be seen that the self-healing discharge energy must be controlled within a certain range in order to obtain enough self-healing corona region and prevent the adjacent dielectric from being damaged. The energy dissipated in the self-healing zone is an important parameter affecting the self-healing performance. Ywang[3] after a series of tests, it is found that the self-healing energy is proportional to the 4th power of the applied voltage, i.e. E α U4shaw d.g[1] uses two sides with a surface resistance of 1.4 Ω

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