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

Abstract

mechanically in service by rod fracture. One of the mechanical failure modes of the insulators is a failure process called brittle fracture [1]-[31], which is caused by the stress corrosion cracking (SCC) of the GRP rods [32]-[51]. The process is catastrophic and unpredictable, leading to the drop of energized transmission lines [13], [18]. Several attempts have been made over the years [1]-[31] to understand this process and provide potential remedies to avoid it in service. In Fig. 2(a-d), some examples are presented of brittle fracture failures of failed nonceramic insulators operated at 115 kV (Fig. 2a, b), 345 kV (Fig. 2c), and 500 kV (Fig. 2d). It should be noted that all insulators in Fig. 2 were made by the same manufacturer and were based on the epoxy

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

“…The first two models (Models I and II) have been thoroughly discussed in the recently published work [20], [21]. It was concluded, based on experimental evidence, polymer chemistry, in-service experience, etc., that Models I and II could not explain all of the characteristic features of brittle fracture already presented in [1].…”

“…T Introduction he most important characteristics of the brittle fracture process in nonceramic high voltage insulators have been presented in Part I of this article [1]. In this work, a significantly improved version of a brittle fracture model, based on the formation of nitric acid in service through corona discharges, ozone, and moisture, is presented and used to explain several different modes of brittle fracture.…”

“…The model based on the formation of nitric acid in service (Model III) was constructed based on the initial observations made by the first author of this article during the failure analysis of the 345-kV insulator failures already described in [1], [7]- [10], [13]. Additional brittle fracture failures, which have occurred over the years, further supported the model based on the nitric acid formation process (Model III) and that the model was the most suitable explanation of brittle fracture.…”

Hybrid composite rods subjected to excessive bending loads

“…Since carbon Table 1 Constituent material properties used to determine composite material properties [11,14,15]. All specimens were prepared per the guidelines set out in [27].…”

“…To avoid potential stress corrosion cracking (SCC) of the glass fiber/epoxy layer in acidic environments [6][7][8][9][10][11], the presently used glass fibers are boron free low-seed ECR fibers [9][10][11]. In particular, a failure process called by international utilities as brittle fracture [11][12][13][14][15] and based on SCC of E-glass fibers in nitric acid solutions is eliminated by using ECR fibers.…”