Abridgment of mutual impedances of ground return circuits: Some experimental studies

Abstract

the new angles are used instead of the new impedances. V. Find T en from (22) using e Qn just obtained. VI. Determine e in from ( %dn %dn \ / % dn % qn \ T _ ~ , j -β *η I -_ χ i J ( 56 )qn ·»άη / \ * qn ^ an / This formula is obtained by combining (8) and (9) VII. Calculate change in e* n from where Δ t is the increment of time used for one step; Ε n is the average slip ring volts, during the Δ t con sidered; ei"is the value of the synchronous stator voltage at the beginning of the Δ t considered; T on is the open circuit time constant of the machine; and Δ e* n is the change which takes place in e* n during the Δ t con sidered. This formula 9 comes directly from the well known relation that the applied voltage is equal to the resis tance drop plus the inductive drop, the quantities being all in per unit values.VIII. Calculate new value of e* n from e* n found in II and Δ e* n found in VII. e* n = e* n + Δ e*n (58) new II.VII.IX. Calculate change in angle from (55). The other angular changes are to be calculated as explained in the discussion of (55), (54), and (51).X. Allow the angle to shift and repeat IV to X. Appendices I and II of the paper will be devoted to illustrating the procedure by means of a special exam ple. The general procedure is modified in this special case for convenience in illustrating fully each step. Synopsis.-This paper describes some of the results of the work of the Joint Development and Research Subcommittee of the National Electric Light Association and Bell Telephone System on the mutual impedances of ground return circuits.The first part of the paper deals with some experiments which were performed to establish an experimental background for the testing of theoretical ideas. Different theories, one involving an "equivalent ground-plane, 11 a second, a d-c. distribution in the earth, and a third, an a-c. distribution in the earth, are discussed in the light of the experimental results.While none of these is adequate to explain all the observed phenomena, each has afield in which it can be made useful The second part of the paper is devoted to a description of practical means for predetermining the mutual impedances of power and telephone lines.This involves an experimental determination of a curve of mutual impedance as a function of separation in the region of the proposed exposure and the calculation of the over-all mutual impedance between the proposed lines from this curve and the dimen sions of the exposure.The results of trials of this method in two locations are given indicating that it should be of sufficient accuracy for engineering purposes.