# Safety Issues Referred to Induced Sheath Voltages in High-Voltage Power Cables--Case Study
## 2 Description of the Analyzed 110 kV Cable Line  
The power cable system under analysis connects a 110 kV power substation (supply service) and a dedicated consumer/load (Figure 2). The total length of the single-circuit three-phase cable line is approx. 12 km. The manufacturer's length of the cable (minor section) is equal to approx. 1 km and the points with connections of the consecutive sections are marked p.0-p.12 in Figure 2. In some of these points, earthing and bonding (including cross bonding) of the cables' sheaths are possible. Generally, cables are laid in trefoil formation without spacing. Some spacing, as well as short sections with flat formation, are applied in the cable ducts, what is included in the computer model. The type of cable used in this line is presented in Figure 3 (a simplified view). The nominal parameters of the cable/cable line are as follows [31]:  
* nominal voltage of the cable: 110 kV (line-to-line), 64 kV (line-to-earth);
* nominal cross-sectional area of the aluminium conductor (core): 240 mm\({}^{2}\); (external diameter \(D_{\rm Al}\) = 17.9 mm);
* resistance of the aluminum conductor (core): 0.125 \(\Omega\)/km (DC in 20 \({}^{\circ}\)C), 0.161 \(\Omega\)/km (AC in max temp. 90 \({}^{\circ}\)C);
* nominal cross-sectional area of the copper sheath: 95 mm\({}^{2}\) (mean diameter \(D_{\rm Cu}\) = 58.5 mm);
* resistance of the copper sheath: 0.192 \(\Omega\)/km (DC in 20 \({}^{\circ}\)C);
* inductive reactance of the cable line in the trefoil formation: 0.143 \(\Omega\)/km;
* XLPE insulation external diameter: \(D_{\rm XLPE}\) = 52.9 mm;
* PE outer sheath external diameter (the outer diameter of the cable): \(D_{\rm PE}\) = 66.6 mm;
* the current-carrying capacity in the trefoil formation: 421 A (single-point bonding), 409 A (both-ends bonding);
* short-circuit power at the supply service point: 1120 MVA. Figure 2: General data of the analyzed power cable system; p.0–p.12—possible points for earthing and bonding. On the base of the nominal parameters of the cable/cable line, it can be stated that the maximum permissible power transmitted via this line is approx. 80 MW. However, the consumer's demand is only 10 MW and the connection of other loads to this 110 kV cable line is not planned. The power cable system under analysis has been modelled with the use of the PowerFactory software [32]. The computer model takes into account all data delivered by the investor, among other: cable technical parameters, cable line layout (including the arrangement with cable ducts), possible points of the bonding or earthing. The entire model of the line consists of 161 sections, of which 61 are cable ducts with different cable arrangements. Two types of cable ducts are used: the flat formation and the trefoil formation. The participation of the flat formation ducts in the length of the line is 1.7%, and the participation of the trefoil formation ducts is 8.2%. Thus, 90% of the cable line length is the trefoil formation without spacing and without ducts--for rough calculations of the induced voltages, it is acceptable to assume such a formation along the entire length of the line. Figure 4a presents a cable route, which is reflected in the computer model--small blue dots indicate a change in cable spacing (due to ducts application). The cables' joints are marked as big red dots. The PowerFactory software allows for modelling cable lines, including cable spacing, which means that the software automatically determines the selected power line electrical parameters.