HOW ELECTRICITY IS -GENERATED 



251 



cuit, and in at the other brush. Large direct current 

 generators have many more divisions in their com- 

 mutators. 



How is electrical energy generated and distributed 

 on a modern scale? Electrical generators are some- 

 times run by steam engines. The earliest forms of 

 commercial generators had the coils of their arma- 

 tures turned in the magnetic field by steam engines. 



While steam engines are still used to a consider- 



Courtesy Union Electric Light and Power Co. 



FIG. 397. A MODERN ELECTRICAL GENERATING PLANT 



able extent, the most modern method for using steam 

 for generating electricity is with the steam turbine. 

 Steam at high pressure is allowed to expand and push 

 against revolving blades. This gives a very rapid 

 whirling motion to the shaft to which they are at- 

 tached. The armature of the electric generator is at- 

 tached to the same shaft and is turned by the rapidly 

 turning vane wheels of the turbine. Figure 398 shows 

 a modern steam turbine attached to a generator. 



Exercise. Trace the energy of the electricity secured 

 from a generator by means of a steam engine or tur- 



bine, through all of its transformations, to its remotest 

 source. 



Falling water has tremendous energy. Man has long 

 utilized this energy to turn the wheels of mills and 

 factories which were built along the streams. The 

 use of falling water to generate electricity makes it 

 possible to have the factories many miles away, for 

 electrical energy can be sent long distances through 

 wires. 



At Niagara Falls there is a great industrial center 

 which makes use of the falling water for power. Great 

 dams have been built in many other places to raise the 

 water to high levels so that as it falls its energy may 

 be used to turn the armatures of great electrical gen- 

 erators. 



To get the energy of the falling water into turning 

 motion, a water turbine is used. In many ways it is 

 like the steam turbine shown in Figure 398 except 

 that water instead of steam is used to drive it. The 

 turbine is then attached to the armature of a generator 

 which turns in a magnetic field. 



Exercise. Trace the electrical energy secured from 

 a generator by means of a water turbine, through all of 

 its transformations, to its remotest source. 



Transformers are used when electricity is sent long 

 distances. Alternating current is used when electrical 

 energy is to be sent far away from the power plant to 

 be used. Electricity is just like water in that if it is to 



Courtesy General Electric Company 



FIG. 398. MODERN ELECTRIC GENERATOR AND STEAM TURBINE 



FIG. 399. PRINCIPLE OF THE TRANSFORMER 



be sent for some distance it must have great pressure 

 at the sending end to overcome the resistance of the 

 conductor which is carrying it. The pressure of al- 

 ternating current can be raised or lowered much more 

 easily and more cheaply than that of direct current. 

 To raise or lower the electrical pressure or voltage 

 of alternating current a device called a transformer is 

 used. The type that lowers the voltage is commonly 

 used to operate toy electric trains and furnish current 

 for door bells. Transformers used to raise the voltage 



