HOW TO INCREASE THE CAPACITY OF AN HVAC TRANSMISSION GRID
In broad terms, there are four ways to increase the capacity of an HVAC transmission grid:
- Remove blockages or reduce or remove bottlenecks by adding transmission capacity at appropriate points, either HVAC or HVDC depending on the local conditions. For example, a new transmission link between Tunisia and Sicily would increase transmission capacity between North Africa and Europe. Likewise, the addition of one or more HVDC submarine cables between Morocco and Spain would relieve or remove that bottleneck. Since the distances are fairly short, costs should be quite low. In general, removing blockages and removing or reducing bottlenecks should be relatively cheap.
- Upgrade the HVAC transmission system using technologies of the Flexible Alternating Current Transmission System (FACTS).
- Upgrade the HVAC transmission system by converting some of the longer HVAC lines into HVDC transmission lines. Since this merely involves changing the equipment at the ends of the lines and making some adjustments to insulators and pylons, it should be relatively cheap and easy to do. Each HVAC circuit uses 3 cables but an HVDC circuit uses only 2, so the two circuits (6 cables) that are often used for HVAC transmission may be converted into three HVDC circuits, each with 2 cables. This change, combined with increases in efficiency, can increase transmission capacity of a double-circuit HVAC line by a factor of 3 or more (see Transmission and distribution networks: AC versus DC (PDF, 176 KB, D. M. Larruskain et al., Department of Electrical Engineering, University of the Basque Country, Bilbao, Spain).
- Upgrade the HVAC transmission system by the addition of long-distance HVDC transmission lines. These may be seen as providing relatively efficient transmission of electricity between local grids that are not geographically contiguous, thus creating a hybrid system that combines the cascading principle with long-distance HVDC transmission. Alternatively, these transmission lines may be seen as a way of increasing the size of each local grid without a correspondingly large impact on the efficiency with which electricity may be transmitted across the grid.
With these kinds of upgrades, a system that originally relied entirely on HVAC transmission and the cascading principle may evolve progressively towards a fully-developed HVDC grid that provides for long-distance transmission between local HVAC grids, as described in the TRANS-CSP report.
Last updated: 2009-08-20