This paper describes the development of an algorithm suitable for automatic tap changer control (ATCC) system. It is specifically designed to control the voltage of high voltage substation using an object-oriented technique. The considered substation consists of six bus-sections; three are classified as main buses while the other three as reserves. The six buses can be interconnected in various different configurations using switchgear that are installed between them. By opening and/or closing various switchgears bus sections can be interconnected in various ways to form groups (or bus groups). Each group may contain number of transformers, which may be up to seven connected in parallel. In order to correctly perform the process of automatic voltage control, it is vitally important that the algorithm has the ability to: (i) identify the bus-groups which are formed as a consequence of switching operations in the substation; (ii) identify the transformers which are connected to individual bus groups; and (iii) perform automatic voltage control (AVC).