**Author details**

404 Polyurethane

fibbers.

*C* = 12.6 nF/km.

element method.

**7. Conclusion** 

Figure 22 shows the calculation for points 1 m above the ground transverse to the power line in the area of the maximum sag of the cable using the analytical method and the finite

The Slovenian power system designers tend to reduce the number of voltage levels. In the future, only four levels will probably exist: 0.4; 20; 110 and 400 kV. The 10 kV levels are in the middle of the range and are present only in large towns (Ljubljana, Maribor). One of the major problems is abandonment of the 220 kV voltage level in the transmission network. The designers are thinking about preservation of the 220 kV power line platforms and the transition to 400 kV conductors. The simplest solution seems to be the erection of new overhead power lines, yet this would involve substantial funds and new permissions. The proposition is the use of covered conductors. The purpose of this chapter was to determine whether it is possible to use the existing platforms and transmission towers of the 220 kV power lines with the new 400 kV conductors. We proposed a covered conductor with a carbon fibber core and a conductive layer made from aluminium, surrounded by in insulation made from polyurethane. The insulation thickness was calculated as the double insulation of the conductor was made from two layers, the one being polyurethane and the other air. We determined a radius at which the electric field intensity at the edge of the insulation is not high enough to cause breakdown of the surrounding air (the electric field intensity has to be lower than the dielectric strength of air). For the reduction of weight of the conductor we assume that we can replace the steel core with a core made from carbon

We attempt to calculate the electric field intensity in the air (at the edge of the insulation) with the following values. For the radius of the conductor we take the radius of the current 220 kV conductor, which is 15.3mm. For the thickness of the insulation we use 15mm and its dielectric strength εr = 3.4. For the voltage we use 400 kV. The result we get with these

The proposed conductor will have a core made from carbon, a conductive layer made from aluminium and the insulation made from polyurethane. According to the usual labelling of conductors we named the suggested conductor PUAC 2150/490/65 mm2. Here 2150 mm2 stands for the cross section of the polyurethane mantel, 490 mm2 for the aluminium and 65 mm2 for the core made form carbon fibber. The electrical resistance of the covered conductor doesn't change in comparison with a normal conductor and is R = 0.0592 Ω/km. Likewise the dielectric strength of the insulation mantle does not affect the electrical reactance of the conductor, which is = 0,414 Ω/km. For the proposed conductor PUAC 2150/490/65 mm2 with a 15 mm thick insulation layer made from polyurethane (εr= 3.4) the capacitance is

The over ground conductors are used to transfer electricity between two points and they lead through various parts of the area. We calculated the mechanical properties of the proposed cable and the sag in the middle of the imaginary span and over obstacles. With

values is 2.39 MV/m, which is less than the dielectric strength of air.

Žiga Voršič *University of Maribor, Slovenia* 
