环氧树脂高频松弛的交流电导与双极性方波击穿特性

doi:10.19595/j.cnki.1000-6753.tces.222129

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Abstract

As one of the solid insulation materials of high frequency transformer (HFT), epoxy resin presents good performance under high frequency non-sinusoidal electrical voltage. Its insulation performance depends strongly on voltage frequency. Due to the local temperature rise in high frequency transformer, electrothermal effect can increase the conductivity of epoxy resin. Nevertheless, the AC conductivity from the dielectric spectrum measurement cannot be equivalent to the AC conductivity characteristics under high-frequency non-sinusoidal voltage. Therefore, this paper studies the AC conductivity characteristics under high-frequency square voltage by the Fourier decomposition. By improving the free volume breakdown theory, the mechanism underlying the AC conductivity of epoxy resin on breakdown at high frequency is discussed. The relationship between the AC conductivity and the high frequency breakdown of epoxy resin is analyzed by the high frequency relaxation characteristics and high frequency and high field conduction theory.
Two kinds of epoxy resin samples E1 and E2 were prepared using the same preparation process and method. According to the results of glass transition temperature T_g and AC conductivity, the Almond-West (A-W) model and Havriliak-Negami (H-N) multi-dispersion relaxation polarization model were used to fit and analyze the AC conductivity spectrum at different temperatures, and the DC conductivity of epoxy resin at different temperatures was also obtained. Then, the temperature and frequency dependence of relaxation process α and relaxation process δ are analyzed according to the fitting results of H-N model. According to the insulation breakdown measurement results, the breakdown characteristics of two epoxy samples within 500-3000Hz were analyzed. Based on the statistical results of three-parameter Weibull distribution, the relationship between the featured breakdown field strength and the frequency was obtained. According to Jonscher's universal dielectric response model, Poole-Frenkel effect, DC conductivity, the effects of frequency and electric field on AC conductivity under bipolar square wave voltage are analyzed. The free volume breakdown model under high frequency electric field is proposed to analyze the influence of frequency on the AC conductivity and high frequency breakdown in the epoxy resin samples.
According to the fitting results of the A-W model and the H-N model, the AC conductivity is mainly determined by the polarization loss caused by the relaxation process α above T_g. The relaxation process α depends on the dipole turning polarization, and the dipole concentration in the epoxy resin sample with high epoxy value is higher. The relaxation process δ is determined by the DC conductivity process, and δ process is related to the carrier migration across the barrier. The breakdown strengths of two epoxy resin samples decrease with the increase in frequency. The breakdown strength of E1 sample is greater than that of E2.
According to the measured results, fitting results and model analysis, we can obtain the conclusions. (1) The AC conductivity at high frequency and high field includes dipole conductivity at low field, Poole-Frenkel emission of charge carriers under high frequency electric field and the DC conductivity. The AC conductivity increases with the increase in frequency or electric field. (2) The hysteresis effect of movements of molecular chain segments under high-frequency electric field become obviously as the frequency increases. The maximum length of the unoccupied equivalent free volume between the molecular chains increases, resulting in the reduction of breakdown strength at high frequency voltage. In addition, the molecular group spacing decreases with the increase in frequency, leading to the decrease of carrier hopping potential barrier and the increase in AC conductivity of epoxy resin samples.

Key words： Epoxy resin AC conductivity bipolar square wave voltage free volume high frequency breakdown

Received: 11 November 2022

PACS:

TM215.1

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	Jiang Qihang
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	Zhong Yu
	Li Shengtao
	Xu Yongsheng

Cite this article:

Jiang Qihang,Wang Weiwang,Zhong Yu等. AC Conductivity with High Frequency Relaxation and Breakdown Characteristics of Epoxy Resin Under Bipolar Square Wave Voltage[J]. Transactions of China Electrotechnical Society, 0, (): 124-124.

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https://dgjsxb.ces-transaction.com/EN/10.19595/j.cnki.1000-6753.tces.222129 OR https://dgjsxb.ces-transaction.com/EN/Y0/V/I/124

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