Introduction
The late 19th century was a period of rapid technological development and innovation. Thomas Edison's incandescent lightbulb, patented in 1879, helped kickstart the era of electrification. However, a major battle soon emerged between Edison's direct current (DC) system and Nikola Tesla's alternating current (AC) system over which was superior for power transmission. This became known as the "War of the Currents." Edison favored DC while Tesla championed AC. In the end, Tesla's AC system triumphed over Edison's DC system due to its ability to transmit electricity efficiently over long distances.
Edison's Direct Current System
Thomas Edison was one of America's most famous inventors and businessmen. In 1879, Edison patented the first commercially viable incandescent lightbulb. To power these new electric lights, Edison developed the first electrical power distribution system using direct current (DC).
In Edison's DC system, electricity flowed in one direction from a generation station along copper wires to the customer. This allowed for electric lighting as the steady uni-directional flow of current could power bulbs connected to the system.
Benefits of Direct Current
Edison's DC system had several key benefits:
- Simple and established technology - DC systems were already in use and well-understood at the time.
- Local power distribution - DC could economically distribute electricity within a city or populated area.
- Supported electric motors - DC could power electric motors which were important for industry.
Limitations of Direct Current
However, Edison's DC had some major limitations:
- Low voltage - DC could only be transmitted at low voltages of 100 Volts before power losses became prohibitive.
- Power loss - At higher voltages, DC transmission over long wires leads to substantial power losses due to resistance.
- Expensive copper - Thicker copper wires were needed to carry power over long distances without losses.
Due to these factors, DC systems were impractical for generating and transmitting electricity over long distances such as between cities. The low transmission voltage also meant a power plant needed to be located every mile or so.
Tesla's Alternating Current System
Working under George Westinghouse, Nikola Tesla pioneered the use of alternating current (AC) for electric power systems. In an AC system, the current periodically reverses direction many times per second, often 60 cycles per second (60 Hz) in the U.S.
Advantages of Alternating Current
Tesla's AC had major advantages over Edison's DC:
- High voltage - AC can be transmitted at extremely high voltages (10,000 - 750,000 Volts) using transformers.
- Low power loss - Higher voltages mean lower currents and much lower losses over long distances.
- Cheap transmission - AC could be transmitted hundreds of miles cheaply and efficiently.
By using very high voltages, alternating current could be transmitted over long distances with acceptable power loss levels. This allowed large central generating stations to be located far from customers and still provide power economically.
Tesla's Innovations
Tesla made major innovations that allowed practical AC power transmission:
- Induction motor - Tesla invented a simple AC induction motor to run on AC current. Previously only DC motors existed.
- Transformer - Transformers "step up" low AC voltages to extremely high levels for transmission then "step down" again for use by customers.
- Polyphase - By using multiple phase shifted currents, Tesla created polyphase AC that improved efficiency.
The War of the Currents
The advantages of AC quickly led to competition between the Edison DC system and Tesla/Westinghouse AC system. The "War of the Currents" broke out to determine which system would dominate electrification of America.
Edison's Campaign
Edison launched a propaganda campaign against the dangers of AC power, sponsoring public demonstrations of animals being electrocuted to show AC was deadly:
- He held public executions of animals using AC generated negative PR to portray AC as dangerous.
- Edison proposed using AC for the first electric chair to discourage use of AC in homes.
Triumph of Alternating Current
Despite Edison's efforts, AC proved superior and was rapidly adopted:
- Westinghouse won the bid to light the 1893 Chicago World's Fair with AC, demonstrating its feasibility.
- AC systems were used to transmit hydroelectric power from Niagara Falls in 1896.
- Alternating current allowed large, efficient central power plants located far from demand centers.
- AC could power lights as well as motors, allowing entire cities and factories to run on electricity.
Within a decade, AC virtually replaced DC for generation and transmission of power across the country. J.P. Morgan's merger of Edison General Electric and Thomson-Houston created General Electric in 1892, which converted its systems over to AC.
Conclusion
In the "War of the Currents," alternating current defeated direct current due to its ability to transmit power over long distances efficiently. Tesla's innovations like induction motors and transformers enabled AC to be transmitted at high voltage then used at safe low voltages. This allowed the generation and distribution of electricity on a national scale. Though it took years to be convinced, even Edison's company ultimately adopted AC as the superior system.