Westinghouse Transformer, Used by Rensselaer Polytechnical Institute, 1886-1889

Transformers increase or decrease voltage and are essential to alternating current (AC) power systems. In the late 1800s, with the help of transformers, AC power systems proved more efficient and economical than their direct current competitors. Transformers helped convert electricity to high voltage for transmission across long distances, then reduced it to lower, safer voltages for use in homes and factories.