Controllable Network Transformers

The electric power grid is under stress, caused by increasing loads, decreasing investments, and increasing penetration of dynamic sources and loads. Grid control techniques have not changed much over the last 50 years, with generator excitation providing the only 'analog' control handle. The basic control problem on the grid is to maintain node voltages while ensuring that branch currents do not exceed defined limits. This paper proposes the possibility of converting existing load tap changing (LTC) transformers into Controllable Network Transformers (CNT) using fractionally rated direct ac converters - providing vernier control of amplitude and phase angle. This would allow dynamic control to be distributed on the grid, enhancing response and reliability. The concept can be scaled to realistic power levels.