EVN, which is a 49 percent shareholder in a project company for the construction of the Walsum 10 coal plant in Duisburg, said it wanted to start arbitration proceedings against a Hitachi consortium and a court action against an insurer.
It said expected its partner in the project company, western German power generator Steag, to consent to pursue the claims in the next few days, and that the total amount of damages was about 600 million euros ($821 million).
Hitachi was not available to comment, while Steag had no immediate comment.
The Duisburg Walsum 10 unit, an advanced coal-fired power plant, was supposed to be reaching full power by the end of this year but is well behind schedule after new steel types proved problematic and had to be swapped.
The plant produces power and also heat for a Norske Skog (NSG.OL) paper mill nearby.
EVN shares were down 0.6 percent by 1022 GMT (5:22 AM EST), underperforming a 0.5 percent rise in the European utilities index .SX6P.
($1 = 0.7308 euros)
Reporting by Georgina Prodhan; Editing by Mark Potter and Louise Heavens