Overhead ground-wire cable
Overhead ground-wire cable
One or more cables are mounted depending on the location, the number of wires on the power line supports, ground resistance, voltage class of the line, the required degree of lightning protection. The ground wire suspension height is determined depending on the angle of protection, that is, the angle between the vertical passing through the cable, and the line connecting the cable and the end wire, which can vary widely and even be negative.
Ground wires are usually not used at high-voltage transmission lines with a voltage of up to 20 kV. High-voltage transmission lines of 110-220 kV on wooden poles and high-voltage transmission lines of 35 kV (regardless of the material of the supports) are most often protected with a rope for approaches to substations only. Lines of 110 kV and higher on metal and reinforced concrete supports are protected with a cable throughout the length.
Steel ropes are used as ground wires or sometimes steel-aluminum wires with a steel core of increased cross-section, as well as PS steel wires. Steel ropes are conventionally denoted by the letter S and numbers indicating their cross-section (for example, S-35), and the steel wires are conventionally denoted by letters PS and numbers indicating their cross-section (for example, PS-70). As a rule, ropes 8,0-N-120-1-SS GOST 3062 (ТК 8.0) are used as ground wires on high-voltage transmission lines 35 kV, ropes 9,1-G-1-SS-N-140 GOST 3063-80 (TK 9.1) on high-voltage transmission lines 110 and 150 kV, ropes 11,0-G-1-SS-N-140 GOST 3063-80 (ТК 11.0) on high-voltage transmission lines 220 kV and higher.
Since July 1, 2009, during the construction and reconstruction of high-voltage transmission lines, the Federal Grid Company PJSC and MRSK should use ground wires (steel ropes) of MZ-V-OZH-N-R brand, made under technical specifications 71915393-TU 062-2008 and ground wires of GTK brand according to technical specifications TU 3500-001-86229982-2010, for protection against direct lightning strikes.
The ground wire can be suspended on insulators. In this case, the lightning current passes to the earth electrode through a special spark gap. Isolated ground wires are used on a high-voltage transmission line with automatic ice melting.
At a high-voltage transmission line of 150 kV and below, if ice melting or channels of high-frequency communication is not provided on the cable, the isolated fastening of the cable should be done only on metal and reinforced concrete anchor supports. Fastening of cables at all supports of high-voltage transmission lines of 220-750 kV must be provided with insulators shunt with a spark gap.