The solution of the secondary circuits effect consideration problem during electrical network calculation is presented in the paper. The analysis of statistical operational data concerning primary and secondary equipment failures taken directly from the plant was performed. It follows from the analysis results that relay protection and automation consideration during the reliability calculation is appropriate. The model which permits to solve the reliability assessment problems of the elementary electrical substations circuits with the use of the probabilistic methods and classical reliability theory was developed on the base of statistical data. The basic problems of reliability calculation method application under the conditions of real branched networks were considered and the method importance and further development were also evaluated.