Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Direct current, another option to improve the electrical power transmission

30.04.2014

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.

References
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 http://www.sciencedirect.com/science/article/pii/S0142061513003360
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. http://www.degruyter.com/view/j/ijeeps.2013.14.issue-5/ijeeps-2013-0017/ijeeps-2013-0017.xml

Matxalen Sotillo | Eurek Alert!
Further information:
http://www.ehu.es/p200-hmencont/en/contenidos/noticia/20140415_corriente_continua/en_20140415/20140415_corriente_continua.html

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

More articles from Power and Electrical Engineering:

nachricht Filter may be a match for fracking water
26.09.2017 | Swansea University

nachricht Fraunhofer ISE Pushes World Record for Multicrystalline Silicon Solar Cells to 22.3 Percent
25.09.2017 | Fraunhofer-Institut für Solare Energiesysteme ISE

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: The fastest light-driven current source

Controlling electronic current is essential to modern electronics, as data and signals are transferred by streams of electrons which are controlled at high speed. Demands on transmission speeds are also increasing as technology develops. Scientists from the Chair of Laser Physics and the Chair of Applied Physics at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have succeeded in switching on a current with a desired direction in graphene using a single laser pulse within a femtosecond ¬¬ – a femtosecond corresponds to the millionth part of a billionth of a second. This is more than a thousand times faster compared to the most efficient transistors today.

Graphene is up to the job

Im Focus: LaserTAB: More efficient and precise contacts thanks to human-robot collaboration

At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.

Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Nerves control the body’s bacterial community

26.09.2017 | Life Sciences

Four elements make 2-D optical platform

26.09.2017 | Physics and Astronomy

Goodbye, login. Hello, heart scan

26.09.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>