Composite housings are fast becoming a standard solution implemented in power grids worldwide and especially preferred for application in severely polluted service environments. To ensure performance under such conditions, the following design tests are generally performed:
• IEC 60587  – Inclined plane test
• IEC 61462  (§7.3.2) / IEC 62217  (§9.3.2) – Accelerated weathering test
• IEC 61462  (§7.3.3) / IEC 62217  (§9.3.3) – Tracking and erosion test at different shed profiles and dimensions
• IEC 62217 (2005-10) First edition  – 5000 hour multiple stress test
Design depends mainly on factors such as pollution, diameter, shed profile, material and creepage distance to avoid rain bridging, prevent local short circuiting between sheds, aid self-cleaning, avoid pollution traps and control localized electric field stress. Recommendations for shed profiles are summarized in IEC TS 60815-3 for AC composite insulators and in IEC TS 60815-4 for DC composite insulators in uncontrolled environments.
Compared to porcelain insulators, the hydrophobic properties of silicone housings improve pollution performance and that means less creepage distance is necessary. Moreover, composite insulators can reduce weight by up to 40% compared to porcelain for large dimension units. Finally, the manufacturing process for composite insulators allows also single piece units with very large dimensions. Indeed, in high pollution areas and for UHV applications, composite insulators may be the only practical solution given the high creepage distances required.
In regard to AC applications, IEC standards are available for design and testing of such composite insulators and there is practical field experience covering decades. For DC applications, pollution is generally more critical because of polarization and charge accumulation with possibly higher accumulation of contaminants. In addition, a missing voltage zero crossing leads to different discharge behaviour. Standards still do not exist for pollution testing of composite insulators under AC and especially under DC applications. This has lead to special customer tests with increased requirements that are are not widely accepted and that are based only on initial experience. Additional long-term ageing tests under severe service conditions are therefore needed to complete a total overview of pollution behaviour.
Attend the 2017 INMR WORLD CONGRESS in Barcelona-Sitges from November 5 to 8 to hear a paper by Eric Moal of Reinhausen Power Composites who will review pollution tests on composite insulators, including:
• Artificial pollution test under DC stress;
• Long-term outdoor test under AC stress.