646 BELL SYSTEM TECHNICAL JOURNAL 



Tests at Glens Falls, N. Y. Fig. 15 shows the arrangement of circuits 

 involved in tests made at Cilens Falls, N. \ . A section of the Saratoga- 

 Glens Falls telephone line about six miles in length was energized with 

 ground-return current. Measurements were made of the voltages 

 induced in short ground-return circuits laid on the ground parallel to 

 the straight section of the telephone line. The resistance and reactance 

 components of the mutual impedance derived from these measurements 

 are given on ¥{g. 16. As a matter of interest the mutual resistance and 

 reactance computed by the use of the Carson formulas for an earth 

 conductivity of 1.75 X 10~^^ are also given. This earth conductivity 

 gives the best agreement between the calculated and observed magni- 

 tudes of the mutual impedances. The general agreement between the 

 computed and observed quantities is much like that found from the 

 Cross Keys tests. 



Earth return current was then sent over the power line from Spier 

 Falls to Tower 99, and induced voltages measured in the entire exposed 

 section of the Saratoga-Montreal telephone line, and in several parts of 

 the exposure as indicated on the sketch. In Table II, the observed 



TABLE II. 



Glens Falls Tests 



Measured Mtitual Impedances of Power and Telephone Circuits and Comparison with 

 Values Calculated from Coupling Curves of Fig. 16. 



Section of Measured mutual Calculated mutual 



telephone line impedance — ohms impedance — ohms 



0-1 .0586 /68.5° .0614 r^3.3° 



1-2 .0294 /52.4° .0564 /49.8° 



2-3 .0476 /73.4° .0382 /69.6° 



3-4 .107 /56.4° .113 /49.2° 



4-5 .100 /44.4° .0117 /35.8° 



0-5 .347 /5 .8° .267 /55.3° 



mutual impedances determined from this latter test are compared with 

 values calculated by using the experimental coupling curve given on 

 Fig. 16. The agreement between computed and observed values is, in 

 general, only fair, although for two of the parts, the agreement is 

 excellent. It is thought that the rather poor check for Sections 1-2 and 

 2-3 is due to the inductive effect of currents set up in the ground wire 

 on another power line which extended through these sections. With 

 regard to the extreme departure of the measured mutual impedance 

 for Section 4-5 from that calculated it is impossible to decide the cause 

 from the experimental data available. A possible explanation is that 

 it is due to a large difference in earth conductivity in this region from 

 that in the region in which the coupling curve was determined. The 



