General

Earth wire in EHV transmission lines is used to provide safeguard against lightening other transient surges and efficient operation of protection system under fault conditions. It serves the dual purpose of protecting the power conductors from lightening strokes and of conducting fault currents away to ground. apart from problems of lightening protection and power loss considerations, the earth wires must be of the suitable magnitude to withstand maximum possible ground fault currents. After accurate determination of currents in earth wire in the event of faults in the line and the resultant temperature rise the following optimum economic sized of earth wires are being used in various EHV transmission lines of UPSEB-

• 132 KV Transmission Lines...................7/3.25mm GS Earth wire (95kg/mm2 Quality)
• 220 KV Transmission Lines...................7/3.67mm GS Earth wire (95kg/mm2 Quality)
• 220 KV River Crossings...............7/3.67mm GS Earth wire (110kg/mm2 Quality)
• 400 KV Transmission Lines...................2x7/3.67mm GS Earth wire (95kg/mm2 Quality)

The finished earth wire has minimum brittleness as it is subjected to continuous aeolin vibrations while in use on lines throughout its life. The steel wires (Strands) used in the manufacture of earth wire are hard drawn from high carbon steel wire rods. the electrolytic high grade zinc of minimum 99.95% purity conforming to IS:209 is used for the coating of steel wires. The steel wires are hot dip galvanized as per IS:2629.

Technical Particulars