Tap Changer

A tap changer is a mechanism built into a transformer that lets its turn ratio be adjusted in discrete steps by connecting to different points along its windings, so the transformer output voltage can be regulated as conditions on the grid change. A no load tap changer must be de-energized before it can be adjusted and suits applications where the setting rarely needs to change, while an on load tap changer can be adjusted while the transformer stays energized, typically by dividing its tap selector switches into even and odd banks and using a heavy duty diverter switch to move current between them without interruption. On load tap changers commonly provide around 33 taps spanning plus or minus 10 percent of rated voltage in steps of about 0.625 percent each, and they are standard equipment on large power transformers used in transmission and distribution networks to keep voltage within range as load and generation vary.