726 



BELL SYSTEM TECHNICAL JOURNAL 



losses (item G). It will, therefore, be of some interest to discuss their 

 performance in the light of the more complete knowledge. 



Performance of D. P., C. W., and C. S. Insulators. The leakage of 

 these three types, as measured on the insulator test line at Phoenixville, 

 Pa., in a moderate rain, is given in Fig. 23. This measurement does not 

 give a true picture of the relative efficiency of the three types because 

 no two of them are aged alike. Besides, the relative efficiency varies 

 considerably with different weather conditions. However, the meas- 

 urement will serve our present purpose, which is to analyze the total 

 leakage of each design and thus give a perspective which could not 

 well be brought out in the detailed discussion of the several sources of 



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 O 



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FREQUENCY -KILOCYCLES 



Fig. 25 — Estimated allocation of leakage for C. W. insulator. 



leakage. It should be pointed out and emphasized that the allocation 

 of the total leakage to its component parts can be only very approx- 

 imate. 



Fig. 24 shows an estimate of the leakage contributed by the several 

 sources for the D. P. design. The leakage directly through the insula- 

 tor material is negligible and item A, therefore, does not appear. 

 Similarly, the leakage due to unbalanced displacement currents flowing 

 in crossarms, poles, etc., is considered negligible and, therefore, item F 

 does not appear. 



At a frequency of 30 kc, for example, B, the direct surface leakage 

 or d.-c. leakage, is about 5 per cent of the total. The dielectric absorp- 

 tion in the glass C is about 10 per cent. The dielectric absorption in the 

 wood pins B is about 20 per cent. The crossarm losses E contribute 

 about 10 per cent and, finally, the losses on the insulator surfaces G 

 contribute about 55 per cent. 



