The effect of voltage and material age on the electrical tree growth and breakdown characteristics of epoxy resins

Abstract

Electrical tree growth (a long-term electrical breakdown process) has been investigated in Araldite CT200 and CT1200 epoxy resins as a function of voltage and material age (defined as the time between manufacture and testing of pin-plane samples). Reproducible and predictable electrical tree growth was obtained for both CT200 and CT1200 epoxy resins provided that (i) the essentially random tree initiation time is removed and (ii) the samples tested were of the same age. The tree growth and time to failure (defined as the time to breakdown from a pre-initiated 10 mu m tree) characteristics as a function of both voltage and sample age show large step changes at a critical voltage and critical age. In particular, the resin physical ageing has a large effect on the tree growth behaviour, with the time to failure varying by three orders of magnitude over a time span of 3 years. Measurements of some of the physical properties (residual internal mechanical stress, surface refractive index, glass transition temperature and dielectric loss) of CT200 epoxy resin all indicate the occurrence of physical ageing of the resin, with structural (network) relaxation as the most important ageing process. However, these measurements are unable to account for the step change (critical age effect) found in the time to failure of tree growth. The fractal nature of tree growth and its relationship with voltage and the long-term changes in the properties of the resin are briefly commented upon.

Dielectric breakdown of epoxy-based composites: relative influence of physical and chemical aging

“…This author forecasted that the physical aging could hence facilitate the electrical degradations in the form of partial discharges similar in nature to those observed in semi-crystalline polyethylene. On the contrary, Champion and Dodd [16] have studied the effect of this physical aging on the tree growth of unfilled epoxy anhydride networks. These authors have, in particular, established that the fractal dimension of trees increased with the materials age.…”

Electrical treeing in a glassy epoxy resin — The filamentary tree and the PD tree

“…A report of filamentary tree growth is found in Champion and Dodd's work [8] on electrical treeing in a glassy epoxy resin (Araldite CT 200). They reported that for AC stressed samples of needle-plane geometry, trees grew in 'young' specimens (23-33 days after samples were fully cured) of fine diameter (~ 1 μm) and low fractal dimension.…”

Transmission Electron Microscopy Study on Microstructure of Ag-Based Conductive Adhesives

“…On the basis of transmission electron microscopy (TEM) studies, they reported a close relationship between the morphological changes in the Ag fillers (probably caused by application of electric current) and the irreversible I-V characteristics of the specimen. We further expect that a microscopy observation offers a clue to understand the process of electric breakdown [11][12][13] which is caused by an excess voltage. For example, TEM observations may provide useful information about the conduction paths and/or the region of the specimen showing a significant temperature increase when excess current is applied to the specimen.…”