TRANSMISSION OF POWER BY ALTERNATING CURRENT 401 



Lightning arresters should be connected to the incoming 

 line when- it enters the- station, or even outside the station. 

 Choke coils, consisting of a few turns of hare wire, are connected 

 between the arresters and the station bus-bars, Fig. 365. When a 

 -lies the station, it has a choice of two paths, the in- 

 ductive path through the choke coil into the station and the 

 condensive path through the arrester to ground. Obviously, a 

 heing of high frequency, will take the path to ground 

 through the arrester, whose condensive reactance is low at high 

 frequencies. 



^ Choke Coil 



To Hich Tension 

 Bua-ban 



Fio. 365. High-voltage entrance and COIUKM tion> to linhtninn arresters and 



bus-bare. 



TRANSMISSION LINE CONSTRUCTION 



170. Pin-type Insulators. -The success of any transmission 

 line depends to a largo extent on the insulators. Little or no 

 difficulty is encountered in insulating lo\\ -\ <>lta<j;e lines. Pin- 

 type insulators are always used for such lines. because they are 

 cheap, are easy to install and act as rigid supports for the con- 

 ductors. Pin-type insulators are made of ulass. of porn-lain, and 

 of pai nted compounds. 



(ila.-s i- HiitaNe for lino of lijrht construction, such as tele- 

 phone lines, and for power lim- <>f moderate voltage. Its ad- 

 vantages up to 10,000 or 15,000 volts are its cheapneM and the 

 'hat cra< tlaus are readily detected. < >n the other 



hand, it is hygroscopic and lreaks readily. 



26 



