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DC Power Production, Delivery and Utilization

3000-volts and then back down again was exactly the same concept as employed in present day power systems where a “generator step-up” transformer is used to raise the system voltage to a very high level for long distance transmission, and then “large substation” transformers are used to lower the voltage to some intermediate level for local distribution.

Similar alternating current systems that use transformers eventually replaced Thomas Edison’s direct current systems. Stanley’s installation in Great Barrington was the first such sys- tem to include all of the basic features of large electric power systems as they still exist more than one hundred years later.

Centralization dictates AC instead of DC

Other factors led to the preference for AC power transmission instead of DC power delivery —most notably a desire for large- area grids relying on centralized power plant, such as hydro- electric dams. Having a transmission and distribution system that could provide hydro-electricity to cities or to remotely located industries such as gold or silver mines in the Rocky Mountains was also an economic imperative.

Such development relied not only on transformers, but on de- velopment of polyphase alternating current generators. Per IEEE:

Niagara Falls represented a showplace of a very different sort. Here electrical engineers were confronted with one of the great technical challenges of the age—how to harness the enormous power latent in Niagara’s thundering waters and make it available for useful work.Years of study and heated debate preceded the start-up of the first Niagara Falls Power Station in the summer of 1895, as engineers and financiers argued about whether electricity could be relied on to trans- mit large amounts of power the 20 miles to Buffalo and, if so, whether it should be direct or alternating current.

The success of the giant polyphase alternating current genera- tors made clear the directions that electric power technology

June 2006

An EPRI White Paper

would take in the new century.

In the 25 years following the construction of the Niagara Falls Power Station, various technological innovations and other factors led away from the early small-scale DC systems, and toward systems based upon increasingly larger-scale central- station plants interconnected via transmission lines that car- ried alternating current. Now cities and towns could be inter- connected, and power could be shared between areas. During this period, transmission voltages as high as 150 kV were being introduced, and so relatively large amounts of power could be transmitted efficiently over long distances.

In addition to technical and market forces, the government also played a role in development of centralized power systems and thus reliance on AC transmission. Public policy and legislation

Figure 25. Adams Hydroelectric Plant, 1895

When the Adams Plant went into operation on August 26, 1895, it rep- resented a key victory for alternating-current systems over direct-cur- rent.The clear advantage of high voltage AC for long distance power transmission and the unprecedented size of the plant (it reached its full capacity of ten 5,000-HP generators in May 1900) influenced the future of the electrical industry worldwide.

Photo courtesy of The Smithsonian

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