Even though today most of the electricity transmission lines are alternating current ones, in some cases direct current lines are also used. Scientists have been working to improve the technology needed for this conversion. The aim has been that this transmission should be done in a more straightforward, smoother and consequently less expensive way.
Electricity is normally transmitted by means of alternating current, but it is not the only way and not always the best one.In some cases, high voltage direct current (HVDC) is used. In Spain, for example, there is only one direct current line, the one that connects mainland Spain with the Balearic Islands; all the remaining ones transmit electricity by means of alternating current. Direct current continues to be highly suitable for underwater and underground lines.
However, as most of the lines in the power grid are alternating current ones, converters are needed to change the type of electricity transmission, and they are very costly.That is why direct current lines are appropriate beyond a certain length.
Bearing in mind that right now most of the transmission of electricity is done by means of alternating current lines, “our aim is in no way to replace these lines by direct current ones. Our proposal is based on using direct current as a solution in cases where there are problems with the alternating current lines..Renewable energies are produced in a very irregular way; the wind, for example, could blow very strongly at some moments and very lightly in others.And the output may not coincide with moments of peak energy consumption.”One way of solving the problem caused by this situation for the electricity supply could be to connect the farms or parks of various countries where renewables are produced. That way, if at one moment one region has a high consumption of energy but is not producing renewable energy, its demand could be met by using renewable energy which is being produced somewhere else,” explained the researcher.
The AIM, to assist transmission :
The GISEL group is working to improve the energy exchange converters between direct current lines and alternating current ones.Specifically, they are working on new technology for converters known as VSCs (Voltage Source Converters).Compared with conventional technology, “the VSC has many advantages; among others, it is easier to control the power that is transmitted, and that is very important on wind farms, for example. At the same time, given the fact that direct current has great economic advantages in underwater lines, it is very appropriate for them.
In the future HVDC grids are expected to coexist with alternating current grids, which are in the majority nowadays.Transmitting direct current via the currently existing lines could be a first step towards building HVDC grids.
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