HVDC > HVDC for laypersons > HVDC can link different power systems
One of the classic HVDC applications is to provide links between electric power grids (networks).
The AC networks are in most cases large; the map below shows the European situation.
European interconnected power grids.
There is one grid in Western Europe, one in Eastern Europe, one in the Nordic countries. Islands like Great Britain, Ireland, Iceland, Sardinia, Corsica, Crete, Gotland, etc. also have their own grid with no AC connection to the continent. The other continents on the globe have a similar situation.
This leads us to one of the traditional applications for Direct Current (DC) in power systems. HVDC systems (classical HVDC and HVDC Light®) can be used to interconnect the different grids or networks so that power can be exchanged between them! For example, there are underwater cables with direct current between i.e. Norway - Denmark (Jutland), Sweden - Germany, Sweden - Poland, England - France, etc.
Even if the networks in Europe have the same nominal frequency, 50 | 
The Scandinavia - Northern Europe HVDC interconnections |
cycles per second or Hertz (Hz), there is always some variation, normally less than ± 0.1 Hz, and in certain cases it may prove impossible to connect them with AC! And in other parts of the world (South America and Japan) 50 and 60 Hz networks are bordering each other and it would be impossible to exchange power between them with an AC line or cable.
The use of direct current for this application depends on two significant factors:
- Cables for DC costs less than for alternating current (AC)
- The use of direct current as an intermediate power carrier makes it possible to convert DC to AC at the exact frequency of each network.
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