Compact conductors with steel support and high mechanical resistance, also with “Penetrante * Aluminium sheath”.

In this first part, we will illustrate the compact conductors of steel and aluminum, as substitution for  copper cables, that have been developed for overhead use in collaboration with Enel and the Railways.

These have been carefully developed, in collaboration with Enel, in order to replace the crude copper conductors, frequently targeted by thieves, of overhead lines. This leads to remarkable advantages of weight, current capacity and ohmic resistance.We have also studied compact power cables for rail networks.

These are the fruits of new technologies, developed and put into use by our company, utilising the extrusion of aluminum sheaths onto cords of steel or other materials (as an example iron-nickel-molybdenum alloys or composites in spun carbon fibers and fibreglass).

*Aluminium fully extruded over the conductor to fill the outer layer interstices.

The cable types shown in the figure above have already become widely used by ENEL in Italy: Without these components, in order to dissipate vibrations caused by the wind, cables must be installed with appropriate dampers. These have been researched and developed by professor Diana of the Polytechnic of Milan after strict tests on live samples (Stockbridge type dampers characterisation).

The fastening vices and the joints have been researched and developed by the company “Gorla Morsetterie” in collaboration with our company: good results are obtained with “the preformato” type with threads in aluminum-magnesium alloy (Almelec) The substituition offers the advantages described below compared to plain copper:

	Compact cord Diameter 6.50mm Compared with plain copper conductors of 16mm2	Compact cord Diameter 8.80mm Compared with plain copper conductors of 25 & 35mm2
Lower ohmic resistance (Ω/Km)	0,947 compared to 1,118	0,507 compared to 0,720 & 0,519
Lower unit weight (kg/m)	0,111 compared to 0,141	0,205 compared to 0,228 & 0,317
Lower coefficient of thermal expansion (1/°Cx10exp-6)	13,5  compared to 17,0	13,5  compared to 17,0  & 17,0
Higher tensile load (N)	890 compared to 635	1425 compared to 1028 & 1425
Lower cost of materials (€/Kg)	1,46 compared to 2,90	1,46 compared to  2,90 & 2,90
(€/m)	0,164 compared to 0,410	0,299 compared to 0,662 & 0,918
Larger current carrying capacity at 70°C	100 compared to 90	215 compared to 140 & 190

With these compact conductors we have achieved the following objectives :

a) Optimisation of cross-sections

The result has been achieved to significantly reduce the outer dimensions with respect to traditional cords for the same resistance and mass or, vice versa, to significantly reduce the resistance for the same outer dimensions and mass.

b) Increase in operating temperature

These cords can be used in suspension, even for temperatures over 90 °C as the tensile load is taken entirely by the steel and not the Aluminium which is prone to softening at higher temperatures.

c) (Low sag)

Using high-tensile steel molybdenum in place of ferronickel, the cables can be suspended at greater mechanical tension with a resultant reduction in sag.

d) Increased performance

At a working temperature of 150 °C, compact cords of 6,50 mm and 8,80 mm diameter can carry 160 and 330 amperes respectively.

e) Reduced cost of materials

The use of aluminium in place of copper results in a dramatic reduction in costs for materials used, up to 70%.

Insulated conductors

These have been developed by our company, (always) in collaboration with Enel, for critical installations in difficult zones and have the advantage of reduced mass and dimensions with respect to traditional cables: moreover, the presence of the aluminum girdle prevents the longitudinal passage of water more efficiently, avoiding complex fillers which were previously utilised. The insulation is made from a mixture of XLPE or plastics in order to guarantee a working temperature of at least 90 °C.

On insulated conductors of this type, various types of fastening and joints of span have been tested to meet standards BSI, N° plan 2006/00714 (draft EN 50397-2: 2007; covered conductors for overhead lines and related accessories): the preformate vices, with threads in aluminum-magnesium alloy (Almelec) have given the best results and have widely exceeded the tests previewed from the cited capitolato one.

 

Compact conductors for “binary” circuits at high current.

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These conductors have been researched for the Italian Railways in order to discourage the thefts of the usual copper types. The presence of the high-tensile steel inside the aluminum sheath acts does not increase the breaking strength (which is already sufficient) but does ensure that the aluminum of the sheath and outer layers, if stolen, need to be professionally recycled: in fact, the outer layers are made of an aluminium alloy (zirconium) that makes recovery of the aluminium a difficult and expensive proccess.

The cables in question can therefore achieve a permanent working temperature of 150 °C carrying a current of:

780 A if bare                          725 A if insulated

The insulation is made from a special, scratch resistant, silicon rubber, that guarantees a working temperature of 150°C and can also be used for emergency wiring.

Conclusions

 

The innovations that we have described above have led to a substantial contribution to the resolution of some complex technicial problems of overhead lines, but above all they have allowed a drastic cost reduction of the raw materials when compared to previously specified copper cables. In addition, the ability to operate at  higher temperatures (high thermal limit) acts to increase the transmitted power, negating the losses of a higher resistance.

Plastic Insulation

14 concentric Al strands

10 concentric Al strands

Aluminium sheath

Steel wire, φ 1.25mm