Modeling and Analysis of Under-Load Tap-Changing Transformer Control Systems

This paper considers the problem of modeling and analysis of under-load tap-changing (ULTC) transformer control systems. A nonlinear system model is derived, suitable for analysis of voltage and reactive power flow control applications of ULTC transformers in the consideration of mid-term and long-term dynamics and steady-state behavior of power systems. The model is verified with the example of a distribution ULTC transformer, used for the voltage control. As an illustration of the feasibility of the model in various voltage and reactive flow control applications, some digital simulation results of such a distribution voltage control are also presented.