Study on Temperature-Frequency Partial Discharge Characteristics of Polyimide under High Frequency Electrical Stress Based on Improved Variational Modal Decomposition Denoising
Xu Huangkuan, Zhang Li, Bilal Iqbal Ayubi, Zou Liang, Wang Guan
School of Electrical Engineering Shandong University Jinan 250061 China
Abstract：Partial discharge (PD) is a significant reason for the deterioration of polyimide (PI) insulation in high-frequency power transformers (HFPT). In order to study the partial discharge mechanism of polyimide under high-frequency voltage and explore the influence of temperature and frequency on the partial discharge characteristics, a high frequency partial discharge test platform was established. Spherical plate electrode was selected to simulate the actual electric field distribution of polyimide in HFPT, and ETS-93686 high-frequency pulse current sensor was used to collect PD signal. Teck MDO3024 oscilloscope was used to simultaneously collect high-frequency sinusoidal signal and partial discharge signal. Four temperatures (25℃, 50℃, 75℃, 100℃) and five frequencies (10kHz, 20kHz, 30kHz, 40kHz, 50kHz) were selected for the experiment. The partial discharge inception voltage (PDIV) was recorded at a boosting speed of 200V/s. The test selected 1.5~2 times of PDIV as the partial discharge test voltage, which means keeping each experiment at a constant voltage of 2.5kV. There are a lot of noise signals in the data measured by the pulse current sensor. Because it is difficult to adaptively select decomposition parameters of variational mode decomposition (VMD), equilibrium optimizer (EO) algorithm was used to obtain the optimal number of modal decomposition K and the penalty factor α. First, initialized the parameters of the EO algorithm and generated n initial particles randomly. Limited K to an integer ranging from 1 to 10, and constrained the penalty factor α ranging from 100 to 7 000. Second, decomposed the initial particles by VMD, and obtained the minimum envelope entropy as the fitness value. Evaluated the fitness value, then selected the best four terms and the arithmetic mean value of these four terms as candidate solutions to build a balance pool. Updated the concentration to determine whether the maximum number of iterations has been reached. Finally, the optimal parameter K and α of VMD decomposition was obtained. The result of experimental data denoising shows that the EO-VMD algorithm proposed in this paper can remove the experimental noise very well. The experimental results show that temperature and frequency have positive correlation with the characteristic quantity of partial discharge, such as the maximum discharge amplitude, the total discharge amplitude and the discharge times. At the same time, with the increase of temperature or frequency, the phenomenon of "clustering" and "delamination" of discharge decreases gradually. The influence of frequency on the characteristic quantity of PD is greater at high temperature, while the influence of temperature is greater at high frequency. These two variables have a coupling promoting relationship. In this paper, the mechanism of temperature-frequency synergy is analyzed. At high frequency and high temperature, the tangential electric field at the gas-solid interface increases, and the discharge develops to the weak electric field region. Therefore, the phenomenon of "clustering" and "delamination" of the discharge gradually weakens. High frequency will lead to the increasing times of space charge injection and extraction per unit time, which means the increase of displacement current and local temperature. High temperature will make it easier for carriers to overcome the work function and cause more hot electron emission. Therefore, under high-frequency sinusoidal voltage, temperature and frequency have a coupling promoting relationship to partial discharge.
徐黄宽, 张黎, BilalIqbal Ayubi, 邹亮, 王冠. 基于改进变分模态分解去噪的高频电应力下聚酰亚胺局部放电温-频特性研究[J]. 电工技术学报, 2023, 38(3): 565-576.
Xu Huangkuan, Zhang Li, Bilal Iqbal Ayubi, Zou Liang, Wang Guan. Study on Temperature-Frequency Partial Discharge Characteristics of Polyimide under High Frequency Electrical Stress Based on Improved Variational Modal Decomposition Denoising. Transactions of China Electrotechnical Society, 2023, 38(3): 565-576.
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2023, Vol. 38 
