Connecting renewable energy and distributed generating sources has placed added emphasis on two-way flows through power transformers. This year the IEEE/PES transformer committee is considering standards that will mitigate core over-excitation and quasi-DC currents in tie transformers. Caused by frequency offsets between the grid and the source, these currents produce over-heating, harmonics, and premature insulation loss of life. Adopting lower excitation levels in all transformers on the grid will enhance reliability and expected life.
The science on this design is not new. Transformers designed for step-up/step-down operation are already built this way. Most transformers in the grid, however, are not. The additional cost of larger cross section cores for this design will mean added cost and more materials. Grid reliability may require all transformers to be built this way. Watch closely how the market reacts to this unanticipated consequence of evolving electrical energy production.