Failure analysis of transmission line tower subjected to combined wind and dust loads

Towers play a vital role in the transmission line (TL) system. The main objective of the present study is to analyse the failure of towers subjected to dust storms. This study, analyses the failure of a 765 kV single-circuit delta-type horizontal configuration tower in the river delta region near Agra. TL towers are designed based on IS 802 Part 1/Sec 1 and 2 standards. Dust particles of soil may be lighter individually, but have definite density. The wind carrying dust particles may increase the wind pressure on the tower line system. The increased wind pressure significantly affects the sag and tension of ground wire and conductor and results in additional loads on the tower, thus causing failure. It also increases wind load on the tower body and insulator string. There is literature related to numerical and wind tunnel studies on the combined effect of wind and rain loads, but no information is available on the wind and dust loads at present. The density variation method is used in the present study for calculation of additional wind pressure due to dust particles during storms. A relation between density of air mix, volume fraction of dust and density of dust particles is considered. Using FEM software, the tower is analysed for existing design loads and verified for its strength adequacy. The tower stability is studied by analysing for additional loads considering the presence of dust particles in the wind for three different volume fractions of 0.01%/m(3), 0.02%/m(3) and 0.03%/m(3). The wind pressure increases by about 10% for an increase of every 0.01% of dust particles in the wind. The tension in the conductor and ground wire increases by 8%. The existing tower design is inadequate to withstand the additional forces from wind storms associated even with a small fraction of dust particles and may be the reason for the failure of towers in northern India during a particular period of the year.