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The use of composite insulators on TERNA overhead lines is nowadays standard practice. After some troublesome trial application in the late ’80s, these components presently show a very good service performance, especially under heavily polluted conditions. Their lower weight, their shape and material allow lower cost installation procedures and ensure long lasting safe operation. However, in contrast with glass insulators (which shatter in presence of defects showing the presence of a failed unit to the naked eye from ground level or to a helicopter-based operators), composite insulators may be subject to internal or surface defects without showing any sign visible from a distance. This fact rises problems in all cases where live maintenance practices must be applied, because the lack of knowledge on the residual dielectric strength may inhibit any live line operation under safe and reliable conditions. A diagnostic method to ascertain that the residual strength of insulators is sufficient for live line maintenance operations is therefore strongly needed. RSE is a public company entitled to carry out research activities on the lifecycle of electricity (generation, transmission, distribution and end-use) on the base of a Contract Agreement with the Italian Ministry of Economic Development. The experts of RSE have set up a diagnostic protocol for composite insulators, using models and tests in the UHV laboratories. Fundamental research was initially carried out to characterise the residual withstand characteristics of insulators with different types and lengths of defects and to verify under which conditions and distances live maintenance procedures could be applied. The diagnostic protocol developed is based on the combination of ground level visual inspections, UV and IR checks able to ascertain that the insulator under investigation has no critical defect such as to jeopardize its possibility to safely undergo live maintenance. A thorough detailed assessment of the presence of internal or external defects is carried out, using the electrical field profile measurement live-line techniques. The package, developed in laboratory and tested in many different simulated configurations appeared to be very promising, but needed validation and calibration in the field. A team of experts from the two companies was formed to learn from each other’s experience: researchers accompanied linemen in the field to apply the diagnostic protocol. Critical lines, based on TERNA service experience, were inspected from the ground level with visual aids, UV and IR cameras, and potential defected insulators were selected, checking that live maintenance operations could be applied safely. Electric field measurements were carried out by TERNA linemen and common elaborations were conducted to point out pieces of interest for the validation of the protocol. These pieces were removed from service, subjected to the diagnostic protocol in laboratory to confirm the field findings and finally thoroughly tested to assess the real residual dielectric strength and analyse the actual defects. Cross-fertilisation between service and research expertise was achieved, on one hand validating and calibrating in the field a diagnostic protocol initially developed in the laboratory, on the other hand delivering to service personnel an innovative approach to live line maintenance and data analysis. The protocol is nowadays applied on a regular basis and its principles are presently under discussion within standardisation organisations. Continuous developments and updates are envisaged considering other equipment, with special reference to composite insulators for station equipment, leveraging on this winning combination of research and application synergy.
31 Dicembre 2011
Impatto sul sistema elettrico della potenziale diffusione dei veicoli elettrici (P10 USI)