This work gives methodology for Total Costs of Reliability (TCR) calculation taking into account both customer and utility reliability costs. Previously mentioned methodology of TCR calculations includes new approach for finding electrical power interruption costs depending on the share of customers in electricity consumption and their geographical allocation. As a result of analysis of sectors of customers, substations with typical load or Typical Substations are defined. Definition of such substations is simplifying considering of different types of load that are located in different regions of country. The work shows that the new approach allows one to estimate non-supply costs for customers more precisely comparing with situation when average non-supply costs are used. Taking into account reliability improvement costs and the share of customers in electricity consumption combined with costs of electrical energy not supplied, TRC calculation methodology allows to find optimal reliability costs with high accuracy and in such way defines optimal reliability level that in its turn increase society benefits.