| The results of an investigation concerning the brittle fracture in Glass Reinforced Plastic (GRP) rods for Nonceramic Insulators (NCI) are presented. GRP rods used in NCI were investigated for microscopic defects in order to evaluate their role in causing brittle fracture. It was confirmed that the rods experience voids, capillaries and cracks. Assuming a spherical void geometry, Niemeyer's generalized approach to Partial Discharge (PD) modeling was used to investigate the development of electrical discharges inside the rods. The results indicate that for rods used in NCI ranging from 115 kV through 500 kV, the inception voltage was well above the applied system voltage. Thus, it was concluded that the reactive species required for the formation of acids could not be developed inside the rods. In addition, a brittle fracture in an epoxy cross arm, which was installed in a region where the natural formation of acids can be neglected, was analyzed. Furthermore, GRP rods with different types of resin systems and reinforcing fibers were tested for brittle fracture development under the concurrent action of flexural mechanical stresses and different attacking chemicals. It was observed that the fracture proceeds faster when the rods were exposed to Ultra-Pure Water (UPW) than when exposed to acids. Moreover, a relative ranking of the brittle fracture resistance, which correlates with the field experience, was obtained for the rods evaluated. The overall results of this investigation indicate that chemicals other than acids promote the fiberglass stress corrosion cracking that causes the brittle fracture in GRP rods for NCI. To the author's knowledge, this has never been reported in literature and hence, can be considered as an original contribution to the science of NCI. |
