**2. The current usage of covered conductors in the middle to high voltage networks**

Covered conductors for overhead power lines are meant to replace the existing bare cable power lines, especially in wooden areas where the risk of falling trees is high. Another concern is the weighing down of cables from sticking snow and ice. Reasons for using

© 2012 Voršič, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Voršič, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

covered conductors are better safety, ecology (fewer disturbances in the nature, especially less clearing of trees), better operational reliability and lower operating costs.

Polyurethane as an Isolation for Covered Conductors 383

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experiments with the voltage of 70 kV. The first was to determine the feasibility of the existent spacer (a device for spacing bundled conductors). The second was done on a distribution cable with higher voltage, to determine the criteria for building new compact high-voltage transmission lines in small corridors, especially in densely populated areas.

Since 1980, the use of covered conductors increased worldwide. The reason for this is that the covered conductors are more compact and environmentally friendlier than traditional non-insulated conductors. Also the number of failures is much lower. This development has also an impact on the characteristics of voltage drops and is an important aspect of working

The space around an electrically charged body is in a special state. This special state acts only on particles that have an electric charge. If we introduce a small electric charge that does not significantly alter the state of that space, we find that there is force acting on that small charge. This force is proportional to the electric charge *q* and the vector quantity that defines the state of the space. It is denoted as *E*. The vector *E* of the electric field intensity

For the understanding of the distribution of voltage and electric field intensity in a covered conductor, we first look at the electric field in a cylinder of charge (Voršič J., Pihler J., 2005). The electric field intensity *E*(r) of an isolated cylindrical Gaussian surface is shown in

*Q ql D rl* 2 ,

2 2 *<sup>Q</sup> ql q <sup>D</sup>*

 *rl r*

(2)

with clients, sensitive to such decrease in voltage.

has the same direction as the force.

figure 1.

where:

From the equation,

**3.1. The electric field: Cylinder of charge** 

b. the electrostatic field is a flat radial field.

*r –* is the radius of the equipotential surface,

*D–*is the electric displacement field and

*l –* is the length of the cylinder,

*Q–* is the electric charge;

In an infinitely long charged cylinder two things are true:

*q –*is the electric charge, gathered on the length of the cylinder,

we obtain the absolute value for the electric displacement field,

*A*

a. the electric charge is evenly distributed over the surface of the cylinder,

**3. Using covered conductors at the highest voltage levels** 
