Partial or complete bridging of insulator dry arc distance by ice or snow can lead to greatly reduced electrical reliability,particularly in the transition temperature range between -2 to 0℃.As example,a severe snowstorm in northern Japan a decade ago led to one of the country's worst outages and affected 650,000 households for up to 31 hours.In a country with one of the highest levels of reliability,this was truly extraordinary.The massive blackout was induced by wet snow mixed with sea salt that had packed the sheds of porcelain long rod insulators on 66 KV as well as 154 KV lines.
Ice and snow flashovers even when not of such scale- have long been known to cause sporadic problems on 115 KV and 230 KV systems.Then,during the late 1980s, such events also came to be recognized as a factor limiting reliability of EHV and UHV systems-especially when coupled with existing surface contamination.New icing test methods for such situations were therefore standardized as part of the IEEE Dielectrics&Electrical Insulation Society as well as the Power and Energy Society Guide to Test Methods and Procedures to Evaluate the Electrical Performance of Insulators in Freezing Conditions(IEEE Standard 1783TM-2009).According to this standard, icing tests must incorporate normal line voltage stress up to 100kV AC line-to-ground per meter of dry arc distance in the ice accretion and flashover processes.
Service experience in several countries subsequently led to further design guidance on exposure factors such as weight of ice per unit length,ice conductivity and surface pollution prior to any icing event.These factors were then combined to establish suitable insulator dry arc and leakage distances in IEEE's Standards Project P1820(Guide on the Selection of Transmission and Distribution Insulators with Respect to icing).
This article,based on a past contribution by INMR Columnist,William Chisholm,and Masoud Farzaneh,UQAC Industrial Chair on Atmospheric Icing of Power Network Equipment(CIGELE) and Canada Research Chair on Atmospheric Icing Engineering of Power Network (INGIVRE),reports on
additional progress in this area.
From:INMR Issue 111-Quarter 1-2016 www.inmr.com
