Abstract
This paper investigates the dynamic behaviour of tap changing operations in Tap Change Under Load (TCUL) transformers. Interactions among multiple TCUL controls will cause oscillatory behaviour in tap changing actions, which unnecessarily increases tap operations before reaching equilibrium point. Conditions for the interaction are derived and features of the phenomena are examined through theoretical analysis as well as through numerical simulation. It is shown that various types of oscillations exist depending on the obtained conditions. The validity of the proposed analysis is verified through numerical simulations in an example system having three TCUL transformers, where sustained and transient type oscillations are observed as predicted by the derived stability conditions.
