Although the first electric power system, Edison's Pearl Street system, was based on direct current (dc), the advantages of alternating current (ac) systems were obvious by the turn of the 20th century. The voltage drop in an electrical circuit limited the distance from the source of electricity to where it was consumed. The Westinghouse transformer made it possible to boost and lower voltage levels in ac systems, making it possible early on to bring electricity into Buffalo, NY, and Portland, OR, from generators at waterfalls many miles away. Further, the Tesla induction motor replaced all steam-driven manufacturing machinery because it was more clean and flexible, thus ensuring the usage of ac as the preferred technology. Despite this, some pockets of dc power systems survived until after World War II. The choice of a three-phase transmission and distribution system over a single-phase system also came very early because of the increased efficiency of transmitting power. Although the use of electricity at the consuming end is in one phase low voltage (except for very large industrial use), transmission and distribution are always done in a three-phase system. To understand the efficiency of transmitting power, consider the discussion following section.
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