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In this paper, we show that the field-induced electromechanical stress cannot be the Maxwell stress, as we had assumed in former models. In fact, high field electrical aging seems to be another case of electrostriction. This does not change the more or less linear relation between log time and the square of the applied field but the activation volume (i.e. the inverse of the broken C-C bonds concentration)...
It is shown that under high fields, molecular straining becomes significant and that it affects the energy barrier equation for electrical aging of polymers. This implies that at high fields the time to go over the barrier varies not only with the stress (i.e. with the square of field) but also with the square of the stress. Examples are shown along with the corresponding calculated activation volume...
Rain with a pH <; 5.6 is known as acid rain. Acid rain can deteriorate high voltage outdoor polymeric insulators and affect their performance over time. Presented in this paper are the results of a long term (2544h) performance study of 28kV Thermoplastic elastomeric (TPE) and silicone rubber (thermoset) insulators under acid rain multistress conditions of Mexico City, Mexico. The results indicate...
The influence of the strain energy on high field electrical aging of polyethylene and various other polymers is briefly reviewed. It appears that molecules strained by high fields store a significant energy and this modifies the endurance characteristics. An equation adding this term to the energy dissipated by the Maxwell stress describes very well the electrical aging of several polymers. Difficulties...
Salient considerations of insulation behavior when fillers are utilized are reviewed. The authors seek to clarify the current supporting science for engineering filled polymeric systems specifically for rotating electric machines. Included is a brief discussion of possible property improvements with the use of fillers. An expanded micro-mechanical approach to describing insulation behavior would be...
In this paper, we show that the electrical aging equation for polyethylene and polypropylene under high fields (above 100 kV/mm) require and additional term, which is the strain energy (sometimes called the electromechanical energy). This term becomes significant at high fields when the electromechanical stress thus generated compress the tested sample. From a practical point of view, this means that...
In this paper, we address some poorly explained problems associated with electrical properties of dielectric polymers. Charge injection is often unclear due to metal-polymer interfaces phenomena including poor contacts, asperities and electrochemical reactions. We also review some difficulties involving the sample bulk, the most important being the influence of the sample size on aging and breakdown...
Most semi-conductor devices are encapsulated by epoxy moulding compound (EMC) material. Even after curing at the prescribed temperature and time in accordance with the supplier's curing specifications often the product is not yet 100% fully cured. As a consequence, the curing process of a product continues much longer, leading to curing effects of the EMC during the lifetime of the package. In this...
We have shown elsewhere that the Eyring equation can describe the electrical aging of several polymers. This equation has two main activated parameters, namely the activated energy DeltaG and the activated volume DeltaV. In this paper, we confirm our previous supposition that DeltaG is related to the C-C bond strength by providing examples deduced from the electrical aging of polyethylene and polypropylene...
The differences between AC and DC aging are pointed out and are partly due to the different dissipated energy under the two types of field and partly due to the fatigue induced by the alternating stress. In addition to these effects, the sample size has also a considerable impact on both aging and breakdown. It is shown, from well known existing data, that the aging characteristics of polyethylene...
Unlike semi-conducting organics, insulating polymers exhibit electroluminescence features that cannot be interpreted on the basis of the photo physical properties of the material. In particular, it is shown that the spectral components observed in electroluminescence in three different classes of insulating polymers -polyolefin, polyester and epoxy, can only be reproduced when the material is irradiated...
The complex estimation of polypropylene (PP) based plastic products on the basis of strength reliability at the stages of design, manufacturing and exploitation is offered in the paper. The strength reliability of polymer products is assessed through the probability of failure-free performance.
After a discussion of the concepts of ageing of insulations and of the endurance of insulating materials, the importance of verifying the relevance of ageing to insulation failure in equipment is pointed out. Information regarding frequency distributions of service stresses and of the stress dependence of insulation strength is also required. After a discussion of ageing versus changes of property,...
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