A STUDY OF TELEPHONE LINE INSULATORS 



719 



The curves of Fig. 18 show that E may be large in dry weather. In 

 fact, it is generally several times the magnitude of item C in dry weather 

 and at the upper frequency range. Therefore, E is the controlling 

 factor in dry weather. 



As to the effect of weather conditions on E, the increase in insulator 

 capacitance brought by wet weather tends to greatly increase the losses. 

 On the other hand, the large decrease in the crossarm impedance re- 

 sulting from rain tends to decrease the losses. As a net result of these 

 opposing effects, E is generally less in wet than in dry weather. In 

 fact, after several hours of rain, E has been found to be almost negli- 

 gible. 



The upper curve in Fig. 20 shows E for the insulator of Fig. 1 foil- 

 coated and mounted on steel pins with composition cobs. This curve 



tn- 



o 



in 



o 



r 



o 

 cr 

 o 



u 

 o 

 < 



< 



10 



20 30 



FREOUEINCY- KILOCYCLES 



40 



50 



Fig. 20 — Measured leakage due to (E). 



was obtained in dry weather. The lower curve of Fig. 20 shows the 

 magnitude of E for the same insulators after \y^ hours of rain. 



The equivalent conductance of the crossarms varies over a wide range 

 depending on the weather. For instance, values of d.-c. conductance 

 40 times as great as that recorded on Fig. 17 have been observed and the 

 data indicated that still higher values are probable. The smallest 

 observed value was one tenth of that recorded in Fig. 17. 



The experimental determination of the magnitude of E for insulators 

 on wood pins is a difficult problem, because E cannot be readily 

 separated from D. 



The importance of insulator capacitance on E has already been es- 

 tablished, so a knowledge of this factor for insulators on wood pins en- 

 ables an estimate of E to be made. 



