The microcomputer based power transformer voltage control scheme provides a modern form of distribution substation voltage control showing economic benefits, simplicity and advantages of self-monitoring and equipment fault indication. Very complicated forms of voltage control can be accommodated where load flow across busbar interconnecting reactors occur; also where tap discrepancies between different makes of power transformers exist. Master/Follower control of a group of transformers is provided to cater for operation under normal or abnormal power system conditions. The microcomputer uses a negative reactance compounding method for line drop compensation calculations. These mathematical software routines are reusable on future schemes which will reduce the cost of such installations. Microcomputer based control schemes provide flexibility in the form of plugin function modules and reprogramming facilities. The future trend for distribution substation control would most probably be to integrate all control functions into a station control microcomputer.