Condition assessment of porcelain and toughened glass insulators from residual strength tests
Transmission and distribution networks of most utilities worldwide have a substantial quantity of porcelain and toughened glass insulators that have been in service for over 30 years; a number that has been traditionally considered as useful life for planning purposes. Many utilities are implementing programs to replace older or defective insulators for improving reliability and also for upgrading their lines. In order to help prioritize line maintenance it is important to identify the condition of insulators and replace those insulators whose performance has reduced significantly from their new condition, hence threatening reliability. In this project, porcelain and toughened glass insulators that were in service for periods ranging from 10-30 years were removed from several locations. Electrical (puncture strength, flashover voltage) and mechanical (tensile strength) tests were performed to assess any reduction in performance. Diagnostic tests such as analysis of bonding agents, identification of internal failure paths were performed to understand failure causes. A sufficiently large number of samples were evaluated and this permitted condition assessment with statistically significant confidence limits
In-Lab Evaluation of Composite Insulators following their Withdrawal from the Network
This chapter is dedicated to the in-lab evaluation of aged, “old” or failed line composite insulators. The term in-lab evaluation is used, because the state of the insulators or the insulator strings/sets is evaluated as off-line diagnosis, which is different to the inspection method of an on-line diagnosis. It describes various methods, philosophies and resources that make it possible to evaluate their technical state and thus estimate the remaining time of use of composite insulators that are the same type as those being tested. The composite insulators to be evaluated are specifically withdrawn from the line in order to obtain representative results for this generation of insulators. Frequently, analyses are also conducted if old composite insulators are available as part of scheduled replacement schemes. If a certain behaviour has already been identified as being critical to operations, it is recommended to evaluate at least ten insulators. If the line route includes various pollution zones or loads that are otherwise different, a sufficient number of each insulator must be inspected representative for the corresponding in situ conditions. When withdrawing insulators from the network, it is important to ensure that the installation conditions are adequately documented and can be clearly assigned. In many cases, the manufacturer of the composite insulators can provide additional data to identify the product (technical state of a particular generation of insulators, production date, material batches, etc.). In critical cases, it is recommended to perform the evaluation in conjunction with the manufacturer and a specialist independent laboratory. The identification of intensive ageing phenomena that effectively signify the end of service life for an insulator can prompt the withdrawal of other insulators of the same type/generation.
Solitary Orbital Paget Disease: A Case Report
Purpose: To describe the clinical findings in a patient who had developed painless supraorbital prominence. Methods: Clinical and histopathological findings of the case are reviewed and presented. Results: The patient had an isolated histologically confirmed Paget disease of the orbit. Local excision of the lesion was performed. Conclusion: Paget disease can present not only as a diffuse process but also as a painless, solitary lesion of the orbit.