The effect of mutual induction is to induce surges in the line where a difference of frequency exists between the two currents, and to induce high electrostatic charges in lines carrying little or no current, such as telephone lines.

Size B.&S. Diam.
(inches)
Distance
d
(inches)
Self Inductance
L
(henrys)
0000 .46 12.00234
18.00256
24.00270
48.00312
000 .41 12.00241
18.00262
24.00277
48.00318
00 .365 12.00248
18.00269
24.00285
48.00330
0 .325 12.00254
18.00276
24.00293
48.00331
1 .289 12.00260
18.00281
24.00308
48.00338
2 .258 12.00267
18.00288
24.00304
48.00314
3 .229 12.00274
18.00294
24.00310
48.00351
4 .204 12.00280
18.00300
24.00315
48.00358
5 .182 12.00286
18.00307
24.00323
48.00356
6 .162 12.00291
18.00313
24.00329
48.00369
7 .144 12.00298
18.00310
24.00336
48.00377
8 .128 12.00303
18.00325
24.00341
48.00384
9 .114 12.00310
18.00332
24.00348
48.00389
10 .102 12.00318
18.00340
24.00355
48.00396

This effect may be nullified by separating the lines and by transposing the wires of one of the lines so that the effect produced in one section is opposed by that in another. Of two parallel lines consisting of two wires each, one may be transposed to neutralize the mutual inductance.

[Fig. 2,678] shows this method. The length L' should be an even factor of L so that to every section of the line transposed there corresponds an opposing section.

Fig. 2,681.—Capacity effect in single phase transmission line. The effect is the same as would be produced by shunting across the line at each point an infinitesimal condenser having a capacity equal to that of an infinitesimal length of circuit. For the purpose of calculating the charging current, a very simple and sufficiently accurate method is to determine the current taken by a condenser having a capacity equal to that of the entire line when charged to the pressure on the line at the generating end. The effect of capacity of the line is to reduce the pressure drop, that is, improve the regulation, and to decrease or increase the power loss depending on the load and power factor of the receiver.

Fig. 2,682.—Capacity effect in a three phase transmission line. It is the same as would be produced by shunting the line at each point by three infinitesimal condensers connected in star with the neutral point grounded, the capacity of each condenser being twice that of a condenser of infinitesimal length formed by any two of the wires. The effect of capacity on the regulation and efficiency of the line can be determined with sufficient accuracy in most cases by considering the line shunted at each end by three condensers connected in star, the capacity of each condenser being equal to that formed by any two wires of the line. An approximate value for the charging current per wire is the current required to charge a condenser, equal in capacity to that of any two of the wires, to the pressure at the generating end of the line between any one wire and the neutral point.

The self inductance of lines is readily calculated from the following formula:

L = .000558 {2.303 log (2A ÷ d) + .25} per mile of circuit