History of Voltage and Frequency
The system of three-phase alternating current electrical generation, transmission, and distribution was developed in the 19th century by Nikola Tesla, George Westinghouse and others. Thomas Edison developed direct-current (DC) systems at 110 V and this was claimed to be safer in the battles between proponents of AC and DC supply systems (the War of Currents). Edison chose 110 volts to make high-resistance carbon filament lamps both practical and economically competitive with gas lighting. While higher voltages would reduce the current required for a given quantity of lamps, the filaments would become increasingly fragile and short-lived. Edison selected 100 volts for the lamp as a compromise between distribution costs and lamp costs. Generation was maintained at 110 volts to allow for a voltage drop between generator and lamp.
In the 1880s only carbon-filament incandescent lamps were available, designed for a voltage of around 100 volts. Later metal filament lamps became feasible. In 1899, the Berliner Elektrizitäts-Werke (BEW), a Berlin electrical utility, decided to greatly increase its distribution capacity by switching to 220 volt nominal distribution, taking advantage of the higher voltage capability of metal filament lamps. The company was able to offset the cost of converting the customer's equipment by the resulting saving in distribution conductors cost. This became the model for electrical distribution in Germany and the rest of Europe and the 220-volt system became common. North American practice remained with voltages near 110 volts for lamps.
In 1883 Edison patented a three wire distribution system to allow DC generation plants to serve a wider radius of customers. This saved on copper costs since lamps were connected in series on a 220 volt system, with a neutral conductor connected between to carry any unbalance between the two sub-circuits. This was later adapted to AC circuits. Most lighting and small appliances ran on 120 V, while big appliances could be connected to 240 V. This system saved copper and was backward-compatible with existing appliances. Also, the original plugs could be used with the revised system.
At the end of the 19th century, Westinghouse in the US decided on 60 Hz and AEG in Germany decided on 50 Hz, eventually leading to the world being mostly divided into two frequency camps. Most 60 Hz systems are nominally 120 volts and most 50 Hz nominally 230 volts.
Read more about this topic: Mains Electricity
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