combination of both type dem, some efficacious conclusion is reached, Which provides reliable provement for the optimal design of inverse plummet system, and posses high practiceu value.

It is pointed out that shed bridging of insulator and the pollution in the ice cause the icing flashover frequently,and the thickness of icing is signifcant above the design value,the excess icing load cause the tower falling down and wire broken,and the differential i.

The heavy icing damages the weak part of tower and meteorological condition causes the tower falling down.

Because of its large scale and intensity,as well as long duration,the bad weather severely damaged power grid facilities by causing many tower collapses and line disconnections within short period of time.

The damage of the transmission lines in Hunan during the 2008 ice storm is surveyed and the main causes for the tower collapses and line failures are analyzed.

Distribution laws of the collapsed towers about tower type, terrain and its features, and design factors are shown according to the statistical figures of 500 kV transmission lines of SGCC.

At the beginning of 2008,an infrequent and serious ice cover disaster in the South resulted in bad ice transmission lines,large-scale collapsed tower and long-playing power breakdown.

The forming course of tower failure in 220 kV Zhaoqi line in the north of Shanxi power network on July 3,2004 was introduced.