MODELING OF TAP-CHANGER TRANSFORMERS IN AN ENERGY MANAGEMENT-SYSTEM

Tap-changer transformers are used in a power system to influence the v oltage profile as well as the distribution of power flow. The coupling of the two transformers - the main transformer and the tap transforme r - establishes a complex power system element. The correct modelling of this device has turned out to be critical for the accurate estimati on and calculation of the power system state. This paper introduces an improved model which simulates the behaviour at the different tap pos itions and loading conditions. The paper focuses on the positive seque nce system of a regulated connected group consisting of a 3-winding ma in transformer and a 2-winding tap-changer transformer. Model verifica tion against test reports and experiences gained from using the new mo del in an EMS are documented.