An investigation of moisture and leakage currents in GRP composite hollow cylinders

Abstract

The applicability of using flat composite plates and hollow core composite cylinders for moisture absorption testing of unidirectional glassr r r r rpolymer composites ( ) used in high voltage composite non-ceramic insulators was examined. Two main ( issues were addressed in this work. First, the effect of specimen geometry cylin-) ders vs. plates on moisture absorption by the composites was investigated both numerically and experimentally. Both classical Fickian and non-Fickian diffusions ( ) were considered. Subsequently, hollow core cylinders made up of ECR low seedglass fibers and epoxy resin were tested for their high voltage properties under controlled moisture diffusion conditions. The specimens were exposed to warm, moist air and their high voltage properties were ascertained using a modified ver-( ) sion of the ANSI test standard C29.11 Section 7.4.2 for water diffusion electrical testing. It was found that the behavior of the hollow core cylinder and flat plate composite specimens subjected to moisture compared reasonably well experimentally and very well numerically. From the high voltage tests, a direct correlation was found between the amount of moisture that had been absorbed by the specimens and the amount of leakage current that was detected. It was shown that using the thin walled composite cylinders leakage currents could be predicted based on the amount of absorbed moisture in the insulator composites. The predictions can be made based on relatively short term moisture data even if the diffusion process in the composites is anomalous in nature with long times required for full saturation. After additional verifications, considering other composite systems, the hollow core cylinder testing under controlled moisture and high voltage conditions could become a screening test for selecting suitable glassr r r r rpolymer composites for insulator applications.

Failure analyses of nonceramic insulators. Part 1: Brittle fracture characteristics

“…This makes the evaluation of the effects of the manufacturing process, design, selection of materials, and in-service conditions on the mechanical and electrical integrity of the insulators very difficult. The authors' observations presented in this article are based on a large multidisciplinary study of the failure analysis of insulators performed between 1992 and 2004 [13]- [21], [23], [26], [29]- [31], [37]- [61]. The three primary goals of the study have been 1) to identify mostly mechanical failure modes of the insulators (including brittle fracture); 2) to evaluate the effect of various manufacturing techniques, material selections, insulator designs, loading conditions, etc.…”

Failure analyses of nonceramic insulators: part II - the brittle fracture model and failure prevention

“…The seeds are gaseous voids left in the fibers from the fiber-manufacturing process. If present, the seeds can increase leakage current in a NCI [39]- [41], [43]. …”

“…If boron-free fiber rods are not available or if their quality is not high because of the presence of seeds, which might compromise the electrical properties of the insulators [39]- [41], the obvious choice is between E-glass epoxy and E-glass/vinyl ester. Certainly, the second system has much better resistance to SCC and, thus, brittle fracture.…”

Effects of electric partial discharges on the rheological and chemical properties of polymers used in HV composite insulators after railway service

“…However, despite all these advantages, composite insulators have suffered in service from different failure modes [1]. Indeed, the overall quality of the composite insulators is strongly dependent on many factors such as the type of filler and the resin matrix [2,3], the interfacial properties [4,5], the polymer surface roughness [6,7] or the manufacturing conditions [8,9]. Besides structural parameters, 7 April 2009. the immediate environmental stresses can also be responsible for the electrical failure of composite insulators.…”

“…Besides structural parameters, 7 April 2009. the immediate environmental stresses can also be responsible for the electrical failure of composite insulators. For instance, epoxybased insulators are prone to water absorption in wet atmosphere, contributing to anomalous production of leakage currents [10][11][12] resulting in degradation. A more complex phenomenon called 'brittle fracture' is described by many researchers.…”