Applied Science 801 



bonded conductors back to the source of supply. In itself an 

 insulated conductor carrying current is not dangerous. A bird 

 may perch on it with immunity, and men who repair the overhead 

 wires of tramways handle them safely with bare hands, because 

 the platforms on which they work are insulated from the ground. 

 But if a person touches both the insulated conductor and the earth 

 or the other conductor, he completes the circuit, and may be killed 

 at once. 



In continuous-current circuits for traction purposes it is 

 usual to insulate the positive conductor, and use the rails as the 

 "return" or negative conductor. 



Generating Power Stations 



Before considering how electrical energy is transmitted and 

 distributed from the generating station to the points where it is 

 required, let us see what goes on at one of the great electrical 

 power-stations. As a general rule they do not convey to a visitor, 

 who is no expert, any adequate impression of the scale on which 

 such vast energy is being produced. There is no bustle and little 

 visible movement, and not much from a spectacular point of view 

 to excite one's wonder. The three principal central power- 

 stations in London are at Chelsea, at Wood Lane, and at Neas- 

 den. From these power-stations the various underground 

 railways receive the electrical energy which enables them to 

 transport 571 million passengers a year. An enormous volume 

 of fuel is required; one station alone consumes no less than 

 260,000 tons of coal per annum for the production of electric 

 current. 



We shall see great steam turbines driving huge dynamos 

 and alternators. At the Chelsea Power Station the power is 

 .equal to 78,000 kilowatts, or about 100,000 horse-power. Currenl 

 is supplied from these to twenty-seven sub-stations scattered 

 about London ; at these sub-stations the power is transformed into 



