MUTUAL IMPEDANCES OF GROUND-RETURN CIRCUITS 647 



large difference in this section is reflected in the rather poor check in the 

 overall coupling (Section 0-5). 



Tests at Massillon, Ohio. Tests made at Massillon, Ohio, were similar 

 to those at Glens Falls, except that the arrangements were somewhat 

 more elaborate. The layout of the circuits involved is shown in Fig. 

 17. The exposure is about 16 mi. long with separation between the 

 power and telephone line ranging from a crossing to about 4200 ft., a 

 large part of the exposure being at a separation of about 3000 ft. A set 

 of "exploring wires," each 200 ft. in length, was laid on the ground 

 parallel to the telephone line as shown in the detail of Fig. 17. These 

 were arranged in four groups and were distributed over an area approx- 



TO 



5HLAN0 



N 



s 1 ' n 1 



•^ ¥ '^1 ?• S: 2i ' S CHICAGO- 



._! ^yiL.''' _^£Ll. •" PHILADELPHIA 



TO MANSFIELD \MASSILLON-ASHLAND I '• "T"""^ ; f ",''^^~ 1°'"^ "^'^^ 



• 1-^ ! ' 1 '^^>^V "'t 3PHAS F LINE 



I DEf^iU^A" I I ;«0 CYCLES -^ 



EXPLORING WIRE I DFTAIL "A- S 



I r NETWORK -j . DETAIL A ^^^^^ « 



* I I . IN MILES ■" 



J > EXPLORING 1^ as 10 



< ; SCALE WIRES :2 " 1 



P'. r IN FEET ->) "St 



" ; 1000 1 / It ' 



-■J: ^_ i lOy-^ I 



" "_/["CHICAGO"-j;;PHiLADELPHIA LINEfj I CIRCUIT POWER 



I SI ttl J 5 HEIGHT 50-80 FEET 



: ""r hI^ ^ & ■ FREQUENCY 60 CYCLES 



i 5i '-^A 



!— " 'ImSsL Iw- ASHLAND LINE J 



Fig. 17 — Massillon tests — circuit arrangements. 



MASSILLON 



SUBSTATION 



y 



TO 

 ^CANTON_ 



TELEPHONE 

 22 FEET 



imately 1>^ by 2 mi. Coupling curves were determined from measure- 

 ments of the voltage induced in the exploring wires for the condition of 

 the telephone line energized with 6 amperes ground-return current, and 

 also for the condition of the power line energized with 40 amperes 

 ground-return current. The mutual impedances derived from the two 

 sets of measurements are practically identical. Fig. 18 shows the 

 resistive and reactive components of the coupling curve using the aver- 

 age of all measurements made on the exploring wires. A comparison 

 of the measured curves with curv^es calculated by Carson's formulas for 

 a value of earth conductivity of 3.6 X 10~^^ abmhos per cm. cube show 

 the same type of agreement as that observed at Cross Keys and Glens 

 Falls. 



The principal reason for using such a large number of exploring wires 

 on this particular test was to investigate the effect of local irregularities 

 of the earth upon an experimental coupling curve and to determine the 

 minimum number and length of exploring wires which it is necessary to 

 use in order to be reasonably confident of the accuracy of the results. 



