Sustainable mining conditions in EstoniaValgma, Ingo; Leiaru, Maris; Karu, Veiko; Iskül, Riho11th International Symposium "Topical Problems in the Field of Electrical and Power Engineering." Doctoral School of Energy and Geotechnology II : Pärnu, Estonia, January 16-21, 20122012 / p. 229-238 : ill