Determination of power transformer’s technical condition is directly dependent upon the diagnostic measurements included in maintenance strategy. Projections of capital needed in future required to maintain reliable service across the power system, are enormous and beyond the financial capacity of many of the relatively newly formed transmission and distribution companies. For that reason condition-based maintenance strategy (CBM) is useful along with prognostics and health management (PHM). Therefore this paper describes cooperation between two mentioned maintenance strategies wherewith lifetime assessment properties.