A new approach to solid-state on load tap changing transformers

This paper presents a new approach to solid-state load tap changing system. The tap changing system is comprised of solid-state devices (SCRs) and a number of transformer taps. Through judicious choice of the tap changer topology and a novel control approach, our system is able to offer up to 48 steps in place of the 16 steps associated with mechanical tap changers. Further, it is able to do this with fewer transformer tap windings and with the ability to move from one tap to another tap without passing through any intermediate taps. The tap changer concept has been experimentally verified. Examples are presented to illustrate the concepts and how they can be applied to support 34.5 kV, 30 MVA and 115 kV, 100 MVA systems. Economic analysis of these sample systems indicates that the approach presented can be 20-50% less expensive than previous efforts to realize solid-state tap changers.