MUTUAL IMPEDANCES Of GROUND-RETURN CIRCUITS 645 



of which could be used to predict the coupling coefficients in advance of 

 the construction of the power or telephone line. An obvious method is 

 to determine an experimental coupling curve by performing tests simi- 

 lar to those made at Cross Keys, using short-length disturbed circuits 

 and either an existing power or telephone line, or a specially laid out 

 conductor, as the disturbing line. 



0.07 



0.05 

 0.04 



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a. 



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5 



0.03 



0.02 



0.01 



0.007 



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z 



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(£ 0.002 



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z 



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O 0.001 



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S 0.0007 



in 



tt 0.0005 



-" 0.0004 

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K 0.0003 



D 

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30 50 100 200 300 500 1000 2000 3000 5000 



HORIZONTAL SEPARATION IN FEET 



Fig. 16 — Glens Falls tests. Experimental values of mutual resistance and reactance. 



This experimental curve would then be used to compute the coupling 

 between power and telephone lines. One advantage of using an experi- 

 mentally determined coupling curve is that it obviates the necessity of 

 knowing or assuming a structure and conductivity of the earth; the 

 coupling curve can be used directly without reference to any theoretical 

 formulas. To determine the practicability of such a scheme, 60-cycle 

 tests have been made in two locations where existing exposures were 

 present, for the purpose of determining the accuracy with which experi- 

 mental observations could be predicted. 



