Influence of the stoichiometric ratio on the material properties and the aging behavior of anhydride-cured epoxy systems
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Date
2023-11-02Type
- Journal Article
ETH Bibliography
yes
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Abstract
When partial discharge (PD) and dielectric heating effects can be excluded, comparatively little is known about the aging behavior of polymeric insulation materials under combined environmental and electric field stress. Since it was found in an earlier study that hygroelectrical stress leads to a strong reduction in the residual breakdown strength of anhydride-cured epoxy samples, the goal of this contribution is to determine if a material modification could enhance the insulation performance under hygroelectrical stress. For this purpose, epoxy samples of different stoichiometric ratios (SRs) were manufactured and hygroelectrically stressed. The material properties were evaluated by AC breakdown strength measurements as well as by Fourier-transform infrared (FTIR) spectroscopy before and after each aging sequence. Gravimetric analysis quantified the water diffusion behavior and the (steadystate) water absorption during exposure to different relative humidity (RH) levels at room temperature. The breakdown strength decreases for both increasing and decreasing SR compared to SR = 95 %. Moreover, FTIR measurements revealed that an increase of the SR leads to a higher amount of unreacted anhydride which correlates with an increasing amount of absorbed water. Thus, the mutual presence of water in the atmosphere and of unreacted anhydride in the epoxy material is identified as the main risk factor for epoxy degradation under the influence of electrical stress, since unreacted anhydride favors stronger water absorption and the presence of water inside the material is attributed to a lowering of the potential barrier for molecular bond breaking. Remarkably, the breakdown strength of non-aged samples is lower at SR = 80 % compared to SR = 95 %, but the long-term performance with respect to insulation aging is enhanced, which correlates with the non-/less-existing unreacted anhydride in the material. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000625088Publication status
publishedExternal links
Journal / series
Journal of Physics D: Applied PhysicsVolume
Pages / Article No.
Publisher
IOP PublishingSubject
Insulation aging; Epoxy; Hygroelectrical stress; Water absorption; FTIR; Breakdown strength; Stoichiometric ratioOrganisational unit
03869 - Franck, Christian / Franck, Christian
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ETH Bibliography
yes
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