![]() ![]() Similarly, the affected lines ran along coastal and inland plains instead of traversing snow-covered mountains. This blackout event was induced by heavy, high conductivity snow combined with strong winds – a climatic condition quite different from that which usually deposits ice accretion or snow cover. Impact on Insulators of Wet Snow with Sea Salt completed change-out of the long rod insulators of one circuit in the affected area to cap & pin strings and have since adopted the same countermeasure in other regions where similar events seem possible in the future. 1b: Example of packed snow on vertically mounted long rod insulator strings and gap type arresters. For example, the volume density of the packed snow ranged from 0.54 to 0.94g/cm 3 while its maximum conductivity was approximately 0.2 mS/cm.įig. These shapes of snow on insulator strings are quite different from those that result from simple ice accretion or snow cover. The shapes of packed snow on insulators in some cases were cylindrical while in other cases were eccentric pennant into the wind direction. Figs.1a and 1b show examples of this on insulator strings as well as on a gap-type arrester. Maintenance workers discovered that many of the porcelain long rod insulators used on the affected 66 kV and 154 kV lines were packed with wet snow. Eventually, 30 transmission lines and 49 circuits were affected. At the same time, some 275 kV transmission lines also began to trip out due to conductor galloping. Cascading electrical failures on 66 kV and 154 kV lines started just before 09:00 and resulted in numerous tripped lines. average wind velocity were 26 mm and 14 m/sec respectively (with an overall maximum wind speed of over 25 m/sec). Ambient temperatures in the Niigata Kaetsu area, on the island’s northwest, stabilized in the range of 0 to +2☌ with a combination of heavy precipitation and wind. ![]() In late December 2005, a powerful low-pressure system from the Pacific moved south to north along the east coast of Japan’s main island while another similar system in the Sea of Japan crossed the island. All this was part of a larger project also dealing with wet snow accretion on conductors as well as conductor galloping. It also discussed the properties of wet snow accretion on insulator strings based on the results of artificial wet snow tests. This past INMR article, contributed by Manabu ‘Gaku’ Sakata of Tohoku Electric Power and Hiroya Homma of Japan’s Central Research Institute of Electrical Power Industry (CRIEPI), provided a brief overview of the event. More research is therefore necessary to clarify the mechanisms of failure and establish the most effective countermeasures. While much research has been performed on ice accretion/snow accumulation on insulators, knowledge related to the effect of wet snow containing contamination such as sea salt is still comparatively rare. Because the snow contained large amounts of sea salt, the insulation strength of the strings deteriorated rapidly and led to numerous flashovers – but in a way quite different from the better-known phenomena of ice accretion or snow cover on insulator strings. ![]() In this case, the wet snow accreted on insulators and filled the gaps between sheds due to the effect of strong winds. Conductor galloping along 275 kV transmission lines also contributed to the scale of the problem. ![]() The massive blackout was induced by wet snow mixed with sea salt that had packed the sheds of porcelain long rod insulators on both 66 kV and 154 kV lines. For a country such as Japan, with among the highest reliability levels in the world, this was truly an extraordinary event. About 650,000 households were affected over a maximum duration of as much as 31 hours. A severe snowstorm in northern Japan a decade ago led to one of the country’s worst long-term outages in decades and impacted the Niigata Kaetsu region supplied by Tohoku Electric Power Co. ![]()
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