The conclusion of the generating equipment for repair, in the optimal way, is the main one when planning repairs. But to consider this issue, it is necessary to understand the essence of the problem and find ways to solve the identified problem. It is necessary to start with the concept of "reliability", namely the reliability of electrical power systems. The article deals with power systems in general, properties of power systems, elements of power systems. The ratio of the functions and properties of energy systems is analyzed, where the main functions of the objects under consideration are: a function associated with the purpose of production equipment, a function associated with the fact of its creation. The meaning of the assignment function is that the object has some task that is performed. In turn, the fulfillment or non-fulfillment of the task is directly related to reliability. Reliability is the property of an object to perform a specified function related to its purpose, subject to specified constraints.