Poly(ethylene terephthalate) (PET) used as an insulating medium of laminated busbars is subjected to combined stresses of the dc electric field and elevated temperature. The coupling effect induces the electrothermal aging of PET, which weakens the busbar performance and thus threatens the long-term reliability of power electronics equipment. In this article, the dc electrothermal aging tests of a 50- $\mu \text{m}$ PET film are carried out at varied aging temperatures of 60 °C, $80~^{\circ }\text{C}$ , and $100~^{\circ }\text{C}$ and a fixed electric field of 120 kV/mm. The surface becomes rougher with ongoing electrothermal aging. It is found that the surface roughness Sa of samples increases from 95 to 2100 nm and the PET surface energy drops from 46.7 to 43.9 mN/m. Moreover, dc breakdown strength and volume resistivity decrease from 807 kV/mm and $6.75\times 10^{{16}}\,\, \Omega \cdot \text{m}$ to 556 kV/mm and $3.97\times 10^{{16}}\,\,\Omega \cdot \text{m}$ , respectively. The aging performance of dc breakdown strength and volume resistivity is discussed based on trap characteristics, which are involved in the evolution of aggregation structure and molecular chain during electrothermal aging. The results of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) reveal that in the initial aging stage, recrystallization leads to the increased deep trap depth and the crystalline region destruction, and the molecular chain scission results in the decreased deep trap depth in the late aging stage.

中文翻译：

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电热老化对层压母线中聚对苯二甲酸乙二醇酯表面形态和介电性能的影响

用作叠层母线绝缘介质的聚对苯二甲酸乙二醇酯 (PET) 承受直流电场和高温的组合应力。耦合效应引起PET的电热老化，削弱母线性能，从而威胁电力电子设备的长期可靠性。在本文中，50- 的直流电热老化测试 $\mu \text{m}$PET薄膜在60°C的不同老化温度下进行， $80~^{\circ }\text{C}$， 和 $100~^{\circ }\text{C}$和 120 kV/mm 的固定电场。随着持续的电热老化，表面变得更粗糙。发现样品的表面粗糙度Sa从 95 增加到 2100 nm，PET 表面能从 46.7 下降到 43.9 mN/m。此外，直流击穿强度和体积电阻率从 807 kV/mm 下降到 $6.75\times 10^{{16}}\,\, \Omega \cdot \text{m}$至 556 kV/mm 和 $3.97\times 10^{{16}}\,\,\Omega \cdot \text{m}$， 分别。基于陷阱特性讨论了直流击穿强度和体积电阻率的老化性能，它们涉及电热老化过程中聚集结构和分子链的演变。差示扫描量热法（DSC）和傅里叶变换红外光谱（FTIR）结果表明，在初始时效阶段，再结晶导致深阱深度增加和晶区破坏，分子链断裂导致深阱减小老化后期的深度。