Polymer Insulator Pro and Cons
Ceramic and glass insulators have long been the materials of choice for high-voltage insulators and lightning arresters, offering good resistance to electrical stress and outdoor exposure without significant deterioration. However, they do have disadvantages such as poor hydrophobicity and low performance under contaminated environmental conditions, low seismic performance, are prone to punctures, suffer from cement growth, pin erosion, susceptible to vandalism, relative higher installations costs.
Polymer insulators were first developed by GE in 1959 and since then many manufacturers have been trying to improve their characteristics and performances.
NCIs or composite insulators designs offer lighter weight, less breakage,improved seismic performance, high hydrophobicity and withstanding contaminated condition and more flexibility in design than ceramic insulators. These features often translate into lower installation cost, greater durability and more aesthetically pleasing line design. Yet, along these benefits problems were detected such as: bonding failures leading to flashover, hardware separation of the fiberglass core leading to line drops, chalking, crazing and shed's splitting allowing humid penetration causing electrical failure.
Polymer insulators cons are their fast aging` susceptibility to UV radiation (sun & corona); handling and storage concerns and lower withstanding to mechanical loads. Often it is being stated that the lack in experience in the HV market (less than 3 decades of use) makes trending analysis of polymer insulators hard to get.
NCI's general structure:Where the end-fittings are made of metal, the core rod is made of FRP - Fiberglass Reinforced Plastic, with an outer housing made from either silicone rubber, EPDM or EPR
One of the major and most important characteristics of Silicon is hydrophobicity i.e. the capability to form beads of water allowing a resistance to wetting. When contamination build-up is exposed to moisture, an electrolytic film can develop, leading to excessive leakage current, dry band arcing and eventually to flashover. such as wetting corona activity resulting from non-uniform wetting and high electrical field mainly on the energized and ground end-fittings.
Grading rings are being introduced lately to insulators of lower voltages. The role of corona rings is to lower the e-field stress and shift it away from the end fitting. Grading rings can prevent corona and it's derives: radio interferences, audio noise, and formation of nitric acid and ozone. (read more...).
Typical failures of polymeric insulators are brittle fractures (read more...), mechanical and electrical rod failures as flashunder, end-fitting detachments, flashover and others, all of which can be detected by a UV camera such as DayCor®
Ofil's DayCor® cameras extend the advantages of NCI insulators and diminish their disadvantages because they can alert at the early stages of partial discharges before theses turn into full discharge, arcing flashover and deterioration of the insulation material.
- Ceramic vs. Polymer (Non Ceramic) Insulators, 2002, Andrew Phillips, EPRI