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| The Growth of Electrical Trees and Partial Discharge Characteristics at the Interlayer Insulation Interface of Epoxy Resin |
| Ma Xianwei1, Shang Yingqiang1, Zhao Yang1, Song Jianhong2, Lü Zepeng2 |
1. State Grid Beijing Electric Power Company Beijing 100031 China;
2. State Key Laboratory of Electrical Insulation and Power Equipment Xi'an Jiaotong University Xi'an 710049 China |
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Abstract With the increasingly widespread and in-depth application of power electronics technology, the requirements for power density, efficiency, and cost of power electronic devices are also constantly increasing. The insulation performance of traditional materials has become increasingly difficult to meet the needs. The partial discharge (PD) and electrical tree of epoxy resin under the electric-thermal environment are important factors that restrict the safe and stable operation of equipment, and the study of the PD characteristics during the growth process of electrical tree is particularly important. At present, there is a relative lack of research on the characteristics of electrical tree and PD in epoxy resin multilayer structures. Therefore, this paper uses epoxy encapsulated printed circuit boards (PCBs) as multilayer samples to study the characteristics of electrical tree growth and PD on V-shaped electrodes at the interface between epoxy resin and PCB.
Firstly, a sample was designed with a bottom made of copper-clad laminate, electrodes made of copper wire, and an upper layer made of epoxy encapsulation. The electrode structure adopted a V-shaped design to facilitate the growth of electrical trees. The PD and changes in the morphology of the electrical tree were recorded until the sample breakdown at 12 kV. The typical phase-resolved partial discharge (PRPD) patterns of electrical tree at different stages of growth process were analyzed. By analyzing the trend in applied voltage difference between adjacent PDs in the partial discharge sequence, it was found that the voltage difference plots of electrical tree changed from a rhombus shape to a double hooked hexagonal shape during the growth process. Based on the characteristics of non-conductive electrical trees, it was found that the change in needle tip potential corresponds to the change from the PD extinction electric field to the PD inception electric field in the electric tree. A method was proposed for estimating the partial discharge inception voltage (VI) and extinction voltage (VX) based on the voltage difference of PD.
Furthermore, by comparing the length of non-conductive electrical tree, l, with the difference between the VI and VX, as well as the maximum magnitude of partial discharge, Q, it was found that Q and l and VI -VX are approximately linear. Considering the partial discharge propagation characteristics of non-conductive electrical tree, the relationship between PD propagation length and partial discharge magnitude was obtained by analyzing the electric field and potential distribution of the tree before and after PDs take place. Due to the randomness of the PD in the electrical tree, the propagation path of each discharge is also different, and each partial discharge cannot cover all the branches. Therefore, the maximum discharge propagation length can be equal to, but is more likely to be less than, the total length of the electric tree.
Specifically, the following conclusions can be drawn: (1) At lower voltages, the electrical tree and discharge characteristics in PCB and epoxy encapsulation are similar to those of needle plate electrodes. Through partial discharge pulse sequence analysis, it was found that the VI and VX of the electrical tree growth process decreased overall, with fluctuations in the middle. (2) In the early stage of electric tree growth, there is a linear relationship between discharge magnitude, VI -VX, and electrical tree length. The ratio of partial discharge magnitude to VI -VX and electrical tree length is approximately equal to a constant, close to πε0. (3) A narrow channel partial discharge model based on non-conductive electrical tree is used to explain the linear relationship between partial discharge magnitude, VI -VX, and electrical tree length.
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Received: 16 October 2024
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2025, Vol. 40 
