DC vs. AC: Exploring the Use of DC in Large-Scale Electrical Projects

In summary, ABB was awarded the contract to build a large DC line from mainland Europe to the UK, but the decision to go with DC rather than AC is odd. There are several reasons why a DC system might be more appropriate on a large scale, such as the fact that it is easier and less expensive to convert high voltages to low voltages.
  • #1
chem123
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Im not formally trained in electrical engineering but have recently been forced in the last 6 months or so to get up to speed on many elec eng power type subjects. One of which is AC versus DC. I understand the history/science of it and why AC eventually won out. However, one story I encountered some months ago was the large electrical technology company ABB being awarded the contract to build a large DC line from mainland Europe to the UK. After all of my reading this story struck me as odd (based on what little I knew).

Anyone have any insight/reasons why a large project like this would be designed in DC and not AC? Also, are there in fact cases where a DC system is more applicable/appropriate than an AC system, on a large scale anyway? One reason I thought of was that since its electricity being generated on one grid and being sent to another, packaging it as DC would be akin to just wrapping up a 'product' and shipping it off and then not having to worry about as much from the supplier's side. But I am not sure.
This is a massive mult million euro project so I am sure there exists a good reason. Just curious to know how it might tie in with the AC versus DC argument.
 
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  • #2
The main reason AC won out over DC is because at the time, it was much easier and less expensive to convert high voltages (necessary for long distance transmission since low currents/high voltages are less lossy than high currents/low voltages) to low voltages (necessary because 1) it's safe for people and 2) it's easier and less expensive to design equipment to use lower voltages) for AC--since you need only an efficient, reliable , simple and relatively inexpensive transformer. Today, however, it's fairly easy and inexpensive to build efficient DC-DC step-down and step-up converters and there are several HVDC transmission lines in use today.
 
  • #3
Ah okay. This makes perfect sense. I am not sure why it never occurred to me that the necessary conversion devices were not developed at the time of AC being chosen as the main distribution current. I guess now with these devices being well developed a HVDC system has as much chance as a HVAC system to be put into use, depending on the circumstances.
Thanks for the answer.
 
  • #4
Oh, they had them, even back them. One of the earliest ones was the motor-generator (called a mo-gen or just mg for short) which, as the name implies, was simply a DC motor driving a DC generator. But these were expensive, noisy, inefficient and unreliable since they were mechanical and had moving parts which could wear out or break.
 
  • #5
DC links are still commonly used for long distance lines.
It makes the cable slightly cheaper, since you only have to design for the constant voltage rather than the peak, but the main advantage is that you don't have to have the two grids in sync. If you have an AC line the swedish and UK systems would have to be in phase - with a DC line it doesn't matter. The existing links between the UK and France are DC because of this.
 
  • #6
It is very to interesting to read these things. Really it is a news for me that d.c. can also be stepped up or down. Many high school level physics textbooks still say that the one of the differences between ac and dc is that the former can be stepped up or down while the latter can not be. Will you please brief me what is the principle behind this new techniqe of stepping up or down dc?
 

1. What is the difference between AC and DC current?

AC (alternating current) is a type of electrical current that changes direction periodically, while DC (direct current) flows in only one direction. AC is commonly used for household electricity, while DC is used in batteries and electronic devices.

2. Which is more efficient, AC or DC?

Generally, AC is considered more efficient for long-distance power transmission due to its ability to be easily converted to higher or lower voltages. However, DC is more efficient for shorter distances and in some specific applications, such as electric vehicles.

3. Can AC devices run on DC and vice versa?

Many electronic devices are designed to work with either AC or DC power. However, some devices are specifically designed to only work with one type of current. It is important to check the specifications of a device before attempting to use it with a different type of current.

4. Why is AC more commonly used for household electricity?

AC is more commonly used for household electricity because it is easier to generate and transmit over long distances. It can also be easily converted to different voltages, making it more versatile for various household appliances.

5. Is one type of current safer than the other?

In general, AC is considered more dangerous than DC because it can cause muscle contractions and heart problems at lower voltages. However, both types of current can be dangerous if not handled properly.

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