Experimental investigation on the breakage in earth wire suspension string with winding preformed armor rods

Overhead earth wire breakage accident may occur frequently, which can seriously affect the reliable operation of the power grid. The main reason of the earth wire breakage is the contact resistance inside the clamp as short-circuit current flows through it. To understand the mechanism of the earth wire breakage, this paper conducts the theoretical study on the skin effect and contact resistance of the wire suspension string with winding preformed armor rods. The temperature rise experiments using of the new and old earth wire suspension string are performed to verify the theoretical analysis. The results show that the hotspots locate in the fracture of the preformed armor rods and the inside the clamp when short-circuit current flows through the earth wire suspension string. The reason could be the increase of the contact resistances in these two locations due to rust of the suspension string. Comparing with the earth wire suspension string without wrapping preformed armor rods, the number of hotspots in the earth wire may increase and accordingly the possibility of earth wire breakage can increase