XinoTroN I don’t know anything anout that. How does it work?
Copyright reasons
Oberstrom limits how much amperes you can use. As you use more power, you also increase the amperes (the ammount of electricity) you're pulling from the overhead catenary. In Germany you can't use all the way up to 1000A, but are limited to 600A (or, in some conditions, just 400A). This mean you cannot use full power, because otherwise you could potentially damage the catenary system.
There are, of course, much more to this than what I explained, as this german Wiki-page will show you: https://de.wikipedia.org/wiki/Oberstrombegrenzung