LIGHTNING — PEEK 



]71 



The mechanism of the corona is of extreme theoretical interest. 

 There is also a practical interest because the laws of corona are 

 very important in the design of high-voltage transmission lines. 

 It is important to select the conductors so that a large percentage 

 of the energy is not lost in the corona. A physical idea of what 

 this means may be of interest. A 220,000-volt transmission line 

 requires a conductor about 1 inch in diameter to prevent corona 

 loss, while a million-volt line would require a conductor about 6.5 

 inches in diameter. 



High voltages are economical when there is considerable power 

 to transmit a considerable distance; 220,000 volts is economical 

 when power of the order of 50,000 to 100,000 kilowatts is available 

 to transmit distances of the order of 200 miles. With a million 

 volts it would be possible to transmit 3,000,000 kilowatts 1,000 miles 

 with about 12 per cent loss, using copper section equivalent to 

 the 1 inch, 220-Kv. cable. The copper would of necessity be put 

 in the form of a hollow tube to obtain the 6.5 inches diameter re- 

 quired by corona loss. There is, at present, no apparent economic 

 need for 1,000,000- volt transmission. 



The laws of corona established at the lower voltages were found 

 to hold at the higher voltages. 



Figure 1 shows the corona discharge from one of two parallel 

 wires, while Table 1 shows good agreement between measured and 

 calculated corona starting voltages for different electrodes. 



Table 1. — Corona on parallel brass tubes (GO cycles). 



