In work it is analyzed a condition 110 кV transformer base of the Latvian power system, the possible reasons of damage of transformers and tendencies of their ageing. The complex methods for a choice of technical measures is developed for increase of reliability of work of transformer base. The methods include the analysis of its actual condition, the profound technical and economic analysis of possible technical measures and a substantiation of their choice. Within the limits of methods the generalized technical and economic model and models for concrete technical measures on its basis are created. For an economic estimation of technical measures criterion functions on the basis of the total discounted annual costs (NPV) for all service life (life cycle) of the equipment are used. Optimum value NPV is economic criterion of a choice of technical measure. In work the profound technical and economic analysis of measures on purchase new and replacement become outdated 110 кV transformers, modernization of the basic units and prolongation of equipment service life is lead. For all technical measures practical calculations are lead, their technical and economic feasibility is estimated and recommendations at their choice are given.