The assurance of power quality depends on factors which influence the performances of the availability: the reliability and its support - the maintenance. This paper deals with the interactions between the indicators of reliability, maintenance, availability and with the methods for the calculation of the reliability indicators. For an overhead line of 110 kV the characteristics of the reliability of the system are determined by modeling and analyzing its functionality by the Markov process of continuous time. The value of the availability index and the maintenance function function contributes to ascertain for the studied case that the value of the availability coefficient has the same value with the probability of success and the probability of repairing an equipment is closely connected to the maintenance function.