Feature Cabling & Cable Management
Satisfying the appetite of modern power hungry cities
Addressing the challenge of supplying more electricity to congested urban centres is becoming increasingly challenging. Here, Francis Debladis, overhead lines corporate technical manager at Nexans, explains how new technology is helping to solve the problem
existing cable towers with minimal modifications, reducing both project delivery times and costs. Lo-Sag is also expected to have a lifetime of at least 40 years, similar to, or even better than conventional conductors.
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cross the globe large urban centres are becoming more and more power hungry - particularly in fast growing economies where the availability of power is crucial for eco- nomic growth. In turn, the creation of new power routes in areas with a high population density leads to major bot- tlenecks, both in land and equipment costs and the extended timescales required to obtain the necessary permits and rights of way. However, using a new alternative approach, existing power transmission routes can be up-rated to carry the extra power required. A five year development pro- gramme involving Nexans’ technol- ogy centres in France and Belgium has produced the Lo-Sag conductor. This overhead line technology con- sists of a thermal resistant aluminium conductor wrapped around a compos- ite carbon core. Compared with the traditional ACSR (Aluminium Conductor Steel Reinforced) design, based on a steel core, the composite carbon core of the same diameter is much lighter and 50% stronger. Most importantly, the carbon core’s coefficient of thermal expansion is roughly one tenth of that of steel, so it expands (and therefore ‘sags’) much less when heated by the high current flow- ing in the conductor, enabling the vital safety clearances to be maintained
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between the conductor and the ground, even at high operating temperatures. These properties enable the new overhead lines to be driven much harder by an electricity utility, running at significantly higher temperatures to carry around twice as much power.
Proof of the pudding The world’s first Lo-Sag installation was carried out for Light, Rio de Janeiro’s electric utility. It has been operating in the field for over a year on a 138kV transmission line that connects SE Cascadura to SE São Jose in the Pavuna district - one of the areas of Brazil with a specific need for more electricity - where it has been proved to increase the power trans- mission capacity by over 70%. While Lo-Sag has been developed to meet the particular needs of power transmission upgrading projects, the concept also offers important advan- tages in the construction of new transmission lines. In particular for long spans (over the 1km required for river crossings), Lo-Sag could help to reduce the height of the towers by up to 30%.
Dynamic Line Rating
Upgrading existing routes As an example, we can consider a typical 400m span between towers with a 322mm2
conductor cross-sec-
tion. A conventional ACSR conduc- tor, at a typical safe limit, might operate at 90°C with a sag of 14.9m, while Lo-Sag could operate at 150°C with a sag of just 10.8m.
This makes Lo-Sag well suited for upgrading existing routes to higher powers, using established routes and
The correct choice of conductor is just part of an overall system approach required to optimise the performance of overhead lines. Rather than regarding them as a static commodity, they should be viewed as an active system that changes its operating behaviour minute by minute as wind, weather and load conditions vary. To operate this system to maximum effect it is useful to have access to real time Dynamic Line Rating (DLR) information that shows exactly how the transmission lines are responding to these varia- tions. It is then possible to make them work smarter and harder with- out compromising safety margins.
Nexans
www.nexans.co.uk T: 01908 250 848
Above: Francis Debladis, overhead lines corporate technical manager at Nexans
Left: Lo-Sag has a carbon core and its coefficient of thermal expansion is roughly one tenth of that of steel, so it expands (and therefore ‘sags’) much less when heated by the high current flowing in the conductor
Left: the Lo-Sag conductor is the result of a five year development programme
involving Nexans’ technology centres in France and Belgium
Enter 205 SEPTEMBER 2013 Electrical Engineering
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