The Grid: Electrical Infrastructure for a New Era

by Gretchen Bakke

With alternating current, in contrast, a rotating polarity at the generator causes the “direction” of the positive charge to switch. The free electrons, still passionate in their struggle to regain atoms of their own, thus also shift: surging first forward, then stopping, then surging backward. And stop. And forward. Stop. Backward. Stop. And so on and on and on. This flow of electrons is still doing work every time it passes through a machine. With AC, however, sometimes the electrons are moving in one direction through the machine and sometimes in the other direction. These stop/go, stop/go, stop/go reversals and interruptions in the direction and flow of power are so quick (in the United States, about sixty per second), that nothing much of what is plugged in even notices these directional shifts, though the buzzing of early fluorescent lights was a symptom of it. In the early days of the grid there were several types of alternating current—single phase, dual phase, and polyphase; the differences between these, while important, can be simplified for our purposes to the fact that dual phase and polyphase send multiple waves though the wires and single phase sends just one.