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For several years at the Tomsk Polytechnic University the probabilistic methods and algorithms for technical efficiency of the electric network relay protection has been developed. Among the relay protections, line distance relay protections have a large proportion. Distance relay protections have some special features compared with the current relay protections. The most representative and reliable results of making losses: refusals of operation, false and excessive actions take place at definition of their expressions as products of probabilities of corresponding conditions (faults on a protected line and in an external network, normal working operational conditions, asynchronous and open-phase modes, etc.) on conditional probabilities of losses in these conditions. The conditional probabilities are formed on new modification of the method SBID (selection the borders of intervals of the in and out data) allowing to define the full probability distribution law (PDL) of all determined or random functional dependences of any dimension on one-dimensional PDL of arguments of these dependences. The new modification of the method SBID is determined based on the possibility that PDL parameter response (which is measured by the distance relay protection of the resistance) can be approximated; even PDL has allowed simplifying the calculation of the losses of the technical effect. Determining the criteria for technical efficiency is an objective indicator quality of functioning relay protection. Therefore on its extremum it is possible to define the optimum values of interest of practical problems, in particular the optimal settings of relaying.