The new operation algorithm of the automatic input device of a reserve (AIR) together with the system of relay protection of power transformers of substation is offered. The increase in reliability and speed of the automatic input of a reserve is provided due to use of signs and algorithms of identification of emergencies and collaboration of a system of relay protection and automatic equipment of substation. The sign of identification of level of undervoltage on tires of the distributing device with automatic input of a reserve and also type of the relay protection which switched-off the equipment in emergency operation is entered. The formulas for calculation of parameters at which operation of AIR is provided are offered. The proof of efficiency of the offered signs and algorithms is executed on the basis of the analysis of oscillograms of parameters of emergency operation. The program realization of the offered algorithm on the basis of the microprocessor terminal of relay protection Sepam 1000+ is presented.