Sh1n reposted a report from Faytuks Network stating:

Police are investigating on suspicion of terrorism following the suspected attack on a substation at the Jänschwalde coal power plant in southern Brandenburg, authorities said.

Faytuks Network also cited WELT regarding the possible perpetrators:

Sources warn against blaming Russia too quickly, noting left-wing extremists have targeted Jänschwalde infrastructure before. Both politically motivated groups and foreign agents remain possible. -WELT