Are there any databases containing some statistics of power transmission networks of different countries? e.g. length of transmission network for 380kV in Germany is 5000km. thanks
The best page for the European system is probably: https://www.entsoe.eu/data/data-portal/Pages/default.aspx
As an example, look at NORDEL: https://www.entsoe.eu/fileadmin/user_upload/_library/publications/nordic/annualstatistics/Annual%20Statistics%202008.pdf
There you see the kind of numbers you ask for.
Also, Google "entsoe order grid map" (I can't post more than two links). There you can get a detailed 26MB map of the european grid.