Mark Fink, age ll, of Huntsville, Ala., for his question:
How much electric power can a big dam generate?
For countless ages the rivers and waterfalls squandered their mighty energy in an endless dash to the sea. The invisible might of electricity was untamed. Then about a century ago these two forceful giants were harnessed in humming generators to yield hydroelectric power.
Michael Faraday sat in class, but his mind was not entirely on the lecture. He was toying with a magnet and some bits of copper and dreaming of a great idea. He knew that magnetism and electricity were related, and he suspected that the two could be wedded to generate electric current then suddenly he saw how to do it. Later he made a small gadget, the first electric dynamo, to test his idea.
Faraday's dynamo was a horseshoe magnet with a copper disk set at right angles to turn through its open end. He fixed the two ends of a wire loop to the gadget and turned the disk with a handcrank. The disk cut through the invisible lines of force surrounding the magnet and this generated electric current through the wire circuit. On a much larger scale the same idea is used to turn the great turbines that generate our hydroelectric power.
A generator uses mechanical or moving energy to keep its copper parts cutting through the force field of a magnet. A hydroelectric power plant Uses the mechanical energy of falling water. A strong river is dammed to fill a reservoir lake and the water is guided to spill over and down a steep concrete cliff.
Our mightiest dam is the Grand Coulee that spans the Columbia River. Its man made waterfall stands 550 feet, more than twice the height of Niagara. Its 4,l73 foot span is 369 yards short of a mile. There is enough concrete in the massive dam to build a highway from the Atlantic to the Pacific. Its tumbling spillways are geared to run l8 major generators and a number of extras. The falling water provides l50,000 horsepower of energy to turn the turbine for each big generator. At full capacity, the mighty Grand Coulee can generate l,974,000 kilowatts and one kilowatt of electric power can light 20 50 watt bulbs..
A big generator can yield half a million kilowatts, enough power for half a million people. The dozen or so generators of a big dam do not hum constantly. Its output is limited by its water supply and controlled to meet the needs of the area it serves. In America, We have l6 dams of more than l00,000 kilowatt capacity and two with more than a billion capacity.
Most of our dams are built in groups to harness the energy of great river systems. In the immense TVA project some 40 dams provide power through an 80,000 square mile area in Tennessee and nearby states. The basins of the Colorado and Missouri rivers are harnessed with dams. Great Grand CouIee is part of the Bonneville system having dams in five states. This project controls floods, provides irrigation and its 20 power plants can generate 6.5 billion kilowatts of electricity.