page_title: Folsom Powerhouse State Historic Park
section_title: Alternators
hierarchical_section_title: Folsom Powerhouse State Historic Park / Alternators
caption_attribution_description: English: Folsom Powerhouse Rotating Armature, Enlargement of Power Pickoff areas
context_page_description: Folsom Powerhouse State Historic Park is a historical site preserving an 1895 alternating current hydroelectric power station—one of the first in the United States.
  Before the Folsom powerhouse was built nearly all electric power houses were using direct current generators powered by steam engines located within a very few miles of where the power was needed. The use of rushing water to generate hydroelectric power and then transmitting it long distances to where it could be used was not initially economically feasible as long as the electricity generated was low-voltage direct current. Once it was invented, AC power made it feasible to convert the electrical power to high voltage by using the newly invented transformers and to then economically transmit the power long distances to where it was needed. Lower voltage electrical power, which is much easier and safer to use, could be easily gotten by using transformers to convert the high voltage power to lower voltages near where it was being used. DC power cannot use a transformer to change its voltage.
context_section_description: The four alternating current generators are some of the most powerful rotating armature 3-phase machines ever built. 
  Newly invented by Elihu Thomson, they weighed almost 30 tons each (57,887 pounds) and were 8.5-foot-tall (2.6 m). These original AC generators used many DC generator components in their first design. The 750-kilowatt (1,005 horsepower) alternating current generators were made in the newly incorporated General Electric plant in Schenectady, New York.
  The alternators had rotating armatures with 216 radial 4 inch slots formed into the perimeter.  Each slot holds two insulated 3 1/2 foot rectangular inductive bars of related phase, an inner circle of 216 bars and an outside circle of 216 bars. The induction bars are twice bent into offsets in the same direction. The middle of the bar has a straight section 3 feet long, to get from the front of the rotor to the back. The inner circle of bars is connected to the outer circle by small conductive jumper blocks on the front and back of the rotor.  The rotor's three phases are connected to six branch circuits.  Each of the six branch circuits make their way three times progressively around the rotor in right hand flattened spirals.
  Supplying power for the 24 stator (non-rotating) field coil magnets on the AC generators was a small direct current generator with another DC generator in standby mode for immediate substitution if needed. If one DC generator failed or needed maintenance the other one could be used.
  All four AC generators power were connected to each other, when long-term demand increased and it was found that tying generators together improved frequency control, by synchronizing action.
caption: Enlarged drawing of radial bus bar terminations.
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