Effect of humidity on the time to breakdown of polymers subject to partial discharges

Abstract

Three polymers, polyethylene terephthalate, a polyimide, and polyamide‐6, were subjected to surface partial discharges up to electrical breakdown under varying ambient humidity conditions. It was found that increasing humidity increases lifetime of the samples until a critical value of relative humidity is attained, after which the polymers' lifetime dramatically decreases. This critical value depends on the hydrophylicity of the polymer and is lower as the ability of the polymer to absorb water increases. The evolution of the electrical time to breakdown with the relative humidity is explained in terms of changes in surface conductivity following variations in the ambient humidity.

Effects of ambient humidity and temperature on partial discharge characteristics of conventional and nanocomposite enameled magnet wires

“…As Guastavino [7] mentioned, it could be considered that hydrophilicity of insulating material is one of the key factors to determine PD characteristics. The detail consideration will be described in section 4.3.…”

“…Therefore, the above results are verified in the present work. On the other hand, Guastavino [7] investigated influences of humidity on lifetime of organic insulation materials. It was shown that increasing humidity increases the lifetime of the insulating materials until a certain critical relative humidity is attained, after which the lifetime significantly decreases.…”

Charge decay on polymers subjected to ageing by partial discharges

“…As explained in Ref. 8, all the curves in Fig. 5 follow the models which relate time to breakdown with the time derivative of the apparent current of the discharges.…”

Influence of mixed-frequency medium-voltage and environmental stress on the aging of epoxy

“…This was mainly attributed to a spreading of PDs over a larger area due to the increased surface conductivity, thus leading to less impact on concentrated locations [33]. On the other hand, also a decrease in lifetime with increasing RH is reported, which, in some cases was only observed above a critical threshold RH c [32][33][34][35]. The lifetime reduction is ascribed either to a removal of surface charge, which should allegedly reduce the number of discharges and average charge, hence reducing the intensity of the aging [32], or to more severe chemical reactions (generating chemical by-products, such as ozone and nitric acids) in the presence of high RH [36,37].…”

“…The influence of humidity on the PD behavior is not straightforward. On the one hand, an increasing relative humidity (RH) was found by several authors to decrease the PD activity [29][30][31] and to increase the insulation lifetime [32][33][34]. This was mainly attributed to a spreading of PDs over a larger area due to the increased surface conductivity, thus leading to less impact on concentrated locations [33].…”