Overhead power line#Bundle conductors

A bundle conductor is a parallel and spatially closely spaced arrangement of two or more conductor cables of the same potential. Bundle conductors are used for overhead lines for power transmission at high voltages from 110 kV to reduce line losses. The individual conductors of a bundle are grouped together with spacers to ensure a substantially constant spatial distance between the individual conductors to each other.

In Germany eligible for the maximum voltage of 400 kV usually four bundles to use, but sometimes three bundles are used, for example, in numerous 380 kV lines of EnBW AG and some newly built lines in the new federal states. In some cases, such as the 380 kV circuit of the line Hoheneck - Herbertingen come from structural reasons also two bundles used. Individual conductors come in the 380 kV level only in some overhead line crossings wider waterways with large span, such as the Little Belt in Middelfart in Denmark, for use as conductor bundle easier to wind-induced vibrations tend to be single conductor. In the 220 ​​kV distribution predominantly coarse come -one bundle for use. Triple and quadruple bundles are here usually only encountered when in the future conversion of the pipeline is planned to 380 kV. On the other hand, there are numerous older normally, 220 - kV lines with single conductors. In the 110 kV and the traction power network can be found bundled conductor (usually two bundles, rare triple and quadruple bundle ) only for heavily loaded lines.

The same applies to low voltage lines where the conductor bundles are only found in special cases at the heavily loaded lines as Erdrückstromleitungen of new railway lines or HVDC lines. Cables at extremely high voltages also bundles come with more than 4 sub-conductors are used. So used the three-phase line Ekibastus - Kokshetau in Kazakhstan, which can be operated with voltages up to 1150 kV, bundle of eight individual conductors in a circular arrangement.

Calculation principles and advantages of bundled conductors

From the telegraph equation, the so-called natural power can be derived. The lower the characteristic impedance of a line is, the higher the natural performance describes the optimal operating condition of a line. The wave impedance of the line can be reduced by increasing the conductor diameter - this increase is achieved expediently with bundle conductors.

The use of bundle conductors leads to the reduction of the surface field intensity along the surface of the conduit. Too large an edge field strength leads to increased losses due to corona discharges, which cause noise and electromagnetic interference along the line. A bundled conductor with n strands, which are at a distance R and a rope radius r0, is a cylindrical conductor of radius R ' with the following relation equivalent:

The fringe electric field strength is thus compared with the single conductor cable, neglecting the ground potential by a factor of

Reduced. The parameter a expresses the distance of the outer conductor on poles from each other.

For example, for a bundled conductor having four individual parts ( n = 4) which are arranged at the corners of a square 20 cm on a side in cross-section and a cable radius of r0 = to 5 mm, and a distance between the outer conductor of a = 10 m, the edge field strength is reduced at the surface of the conductor bundle by a factor of 0.4 as compared to a single conductor cable. The cylindrical wire of radius R 'of the replacement conductor with the same edge field strength in this case is 86.5 mm, which is only a lead rope of 5 mm is more than a tenfold increase compared to the radius.

Another advantage of the bundle conductors is that a bundle of conductors, with the same cross-section has a larger surface area than a single circuit, allowing for better heat dissipation, so that the bundle of conductors can carry more current than a single cross-section of the same conductor. An example of a transmission line with bundled conductors and high current load is the compact transmission line Lutsk.

Application Examples

Six- bundle conductor with an operating voltage of 765 kV. Operators Eskom in South Africa.

Quad - bundle conductor on a 735- kV high- voltage line of the Hydro- Quebec.

Six- bundle conductor for high power transmission line between the generator and generator transformer