Discrete Models of Slow Voltage Dynamics for under Load Tap-Changing Transformer Coordination

In this paper, an approach to modeling, analysis, and design of slow distributed voltage control schemes is proposed. In particular, a dynamical voltage model governed by the under load tap-changing transformers as control tools is studied. Rigorous conditions are derived to predict when the LTC based scheme may be poorly coordinated and not able to maintain voltages within the limits. The proposition is that nonconvergence of LTC control scheme is one of the causes of a systemwide voltage collapse.