In the paper the generalized mathematical model for estimation of the efficiency of measures on the increasing of reliability of the transformer equipment’s functioning is developed. The particular mathematical models for economic estimation of measures on purchase and modernization of transformer equipment are given also on the base of generalized model. This task is solved under the conditions of deficit of the investments in the Latvian Power Company. The search for the optimum solution for the considered task is made among the set of modernization alternatives of the transformer base and prolongation of transformer lifetime. The total annual discounted costs for transformer whole life cycle are offered as the objective function for estimation of measures on modernization.