Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Direct current, another option to improve the electrical power transmission


A UPV/EHU engineering group has optimized the technology for converting alternating current lines to direct current ones

Even though today most of the electricity transmission lines are alternating current ones, in some cases direct current lines are also used. And researchers are becoming aware that in some cases direct current lines are more suitable than alternating current ones. In this area, the GISEL research group of the Department of Electrical Engineering of the UPV/EHU-University of the Basque Country has 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.

In fact, "direct current continues to be highly suitable for underwater and underground lines," asserted Marene Larruskain, one of the engineers in the UPV/EHU's GISEL group. Furthermore "less investment is needed to build direct current lines, and there are fewer losses in electricity transmission. "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," specified Larruskain. And this is in fact the use that is made of high voltage direct current lines, to transmit electricity over very long distances; indeed, the longest lines that exist are direct current ones. "There are facilities worldwide thattransmit direct current electricity.The typical examples are the transmission lines of large hydraulic power stations: the Itaipu power station in South America, the Three Gorges power station in China, etc.

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," explained Larruskain. Renewable energies could could an example of this. 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 metby using renewable energy which is being produced somewhere else," explained the researcher. As there is a global grid, the variability in production of renewables could be balanced. The UPV/EHU's GISEL group is proposing that these global grids should be direct current ones.

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."

However, VSC technology has a number of drawbacks: firstly, its capacity to transmit energy is lower, the energy losses are greater and it does not respond well when problems arise. For example, if there is a short circuit, the system has problems. That is why "we're working to minimize those problems," explained the researcher.

Secondly, the researchers want to make use of the advantages of both means of transmitting electricity to be able to address growing power consumption. And it is a fact that "even though more and more energy is being produced to meet the demand, problems may arise when it comes to transmitting that energy. It is not always possible to incorporate the surplus energy produced into the already existing lines owing to their limits. In these cases, the use of direct current could solve the problem of the alternating current lines already installed, because, among other things, the HVDC lines can transmit more electrical power," explained Larruskain.

The GISEL research group has studied how to make the features of the alternating current and direct current lines compatible. The electricity lines of alternating current are three-phase. For example, the number of conductors are three, or multiples of that number. On the other hand, HVDC lines have two poles: a positive one and a negative one. "How are we going to divide two poles into three conductors?" wondered Larruskain. If we use one pole for each phase, one of the conductors of the original line will remain free and part of the power will be lost. That is why a line and a half of alternating current corresponds to each pole of direct current. Even though it looks impossible, there are various ways of making this distribution.

"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," explained the UPV/EHU engineer.

Additional information
This study was conducted in the Department of Electrical Engineering of the University School of Mining and Public Works Engineering.The head of the department is Professor Inmaculada Zamora, and the research group is made up of the PhD holders Marene Larruskain, Oihane Abarrategui and Araitz Iturregi. The group has published six papers in several scientific journals and has given as many presentations in connection with this subject.What is more,they have filed two patents in Spain:one for a current limiting device, and another for a device to limit the voltage in converter stations.

M. Larruskain, I. Zamora, O. Abarrategui, A. Iturregi. January 2014. "VSC-HVDC configurations for converting AC distribution lines into DC lines". International Journal of Electrical Power & Energy Systems54: 589 -597 040 0142-0615
M. Larruskain, I. Zamora, O. Abarrategui, A. Iturregi. 2013. "A Solid-State Fault Current Limiting Device for VSC-HVDC Systems". International Journal of Emerging Electric Power Systems, Volume 14, Issue 5: 375-384, ISSN (online version) 1553-779X, ISSN (print) 2194-5756, DOI: 10.1515/ijeeps-2013-0017.

Matxalen Sotillo | Eurek Alert!
Further information:

Further reports about: Electrical Engineering HVDC ISSN electricity lines means underwater voltage

More articles from Power and Electrical Engineering:

nachricht New polymer creates safer fuels
02.10.2015 | California Institute of Technology

nachricht Making batteries with portabella mushrooms
30.09.2015 | University of California - Riverside

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: New Sinumerik features improve productivity and precision

EMO 2015, Hall 3, Booth E06/F03

  • Drive optimization called automatically by the part program boosts productivity
  • Automatically switching the dynamic values to rapid traverse and interpolation...

Im Focus: LZH presents additive manufacturing at the LABVOLUTION

The Laser Zentrum Hannover e.V. (LZH) will present how laser-based technologies can contribute to the laboratory of the future at the LABVOLUTION in Hannover in Hall 9, Stand E67/09, from October 6th to 8th, 2015. As a part of the model lab smartLAB, the LZH is showing how additive manufacturing, better known as 3-D printing, can make experimental setups more flexible.

Twelve partners from science and industry are presenting an intelligent and innovative model lab at the special display smartLAB. A part of this intelligent...

Im Focus: New polymer creates safer fuels

Before embarking on a transcontinental journey, jet airplanes fill up with tens of thousands of gallons of fuel. In the event of a crash, such large quantities of fuel increase the severity of an explosion upon impact.

Researchers at Caltech and JPL have discovered a polymeric fuel additive that can reduce the intensity of postimpact explosions that occur during accidents and...

Im Focus: 3-D printing techniques help surgeons carve new ears

When surgical residents need to practice a complicated procedure to fashion a new ear for children without one, they typically get a bar of soap, carrot or an apple.

To treat children with a missing or under-developed ear, experienced surgeons harvest pieces of rib cartilage from the child and carve them into the framework...

Im Focus: Walk the line

NASA studies physical performance after spaceflight

Walking an obstacle course on Earth is relatively easy. Walking an obstacle course on Earth after being in space for six months is not quite as simple. The...

All Focus news of the innovation-report >>>



Event News

EHFG 2015: Securing healthcare and sustainably strengthening healthcare systems

01.10.2015 | Event News

Conference in Brussels: Tracking and Tracing the Smallest Marine Life Forms

30.09.2015 | Event News

World Alzheimer`s Day – Professor Willnow: Clearer Insights into the Development of the Disease

17.09.2015 | Event News

Latest News

Infrared thermography can detect joint inflammation and help improving work ergonomics

02.10.2015 | Medical Engineering

Semiconductor nanoparticles show high luminescence in a polymer matrix

02.10.2015 | Materials Sciences

New Sinumerik features improve productivity and precision

02.10.2015 | Trade Fair News

More VideoLinks >>>