Wow, I didn't know continental Europe is a single synchronized area. Here in the Nordics (Finland) our grid is separated from the neighbours via DC stations to eliminate the need to synchronize with everyone. Here you can see our grid info: https://www.fingrid.fi/sahkomarkkinat/sahkojarjestelman-tila... - "Sähköverkon aikapoikkeama" is actually the cumulative difference between the 50Hz reference and the actual frequency in the network. When that stays zero, AC clocks keep their time.
edit: I stand corrected, we are in the same frequency domain with Sweden and Norway. I must have confused myself with the DC submarine cables under the Baltic.
Eliminating the need for synchronization isn't the only benefit of high tension DC power lines. DC is also sometimes used for long-distance transmission lines to avoid hysteresis losses. The downside to DC is that voltage step-up and step-down equipment is more complicated/expensive and (at least generally) less efficient.
In high school, I was told that a lot of the power for Minneapolis was sent over high tension DC lines from coal power plants in the neighboring Dakotas for this reason. This was part of the lesson about how the lakes in northern Minnesota had very little pH buffering capacity due to limestone being scraped down to bedrock by glaciers and therefore being particularly sensitive to SO2 emissions from coal power plants in the Dakotas, but most of the electrical demand for that power also coming from Minnesota.
That's interesting! According to this map [0] the AC connections are only between Sweden, Norway, Finland and a large part of Denmark. At least under the assumtion that the frequencies are separated in the "converter station back-to-back" in Vyborgskaya, Russia.
edit: I stand corrected, we are in the same frequency domain with Sweden and Norway. I must have confused myself with the DC submarine cables under the Baltic.