Resistance and reactance of 3 conductor cables
1
Discussions Of A.I.EE Papers as RecommenJeJ for Pmitlicaiiom Ly Technical Committees this and the following 8 pages appear 2 additional authors' closures of papers presented at the 1935 A.I.E.E. winter convention, New York, . Y., January 22-25, and the first discussions submitted of papers presented at the general technical and the insulation and protection sessions of the South West District meeting, Oklahoma City, Okla., April 24-26, 1935. Authors' closures, where they have been submitted, will be found at the end of the discussion on their respective papers. Members anywhere are encouraged to submit written discussion of any paper published in ELECTRICAL ENGINEERING, which discussion will be re- viewed by the proper technical committee and considered'for possible pub- lication in a subsequent issue. Discussions of papers scheduled for presenta- tion at an A.I.E.E. meeting or convention will be closed 2 weeks after presenta- tion. Discussions should be (1) concise; (2) restricted to the subject of the paper or papers under consideration; and (3) typewritten and submitted in triplicate to C. S. Rich, secretary, technical program committee, A.I.E.E. headquarters, 33 West 39th Street, New York, . Y. Resistance and Reactance of 3 Conductor Cables Authors* closing discussion of a paper pub- lished in the December 1934 issue, pases 1581-9, and presented for oral discussion at the cables session of the winter convention New York, . Y . , January 24, 1935. Other discussion of this paper was published in the March 1935 issue, pages 324-6, and in the April 1935 issue, pases 436-7. . H. Salter, G. B. Shanklin, and R. J . Wiseman: In reference to the comments by R. W. Atkinson in regard to the difference found when the phase rotation of current was reversed, analysis of these data did not give a logical reason why a difference should be found. We could not explain it on the basis of accuracy of test methods because the difference is in the same order of magni- tude as was found for other factors which we knew did influence a-c losses. It was decided to include the data in the paper with the hope that someone could offer a reason for that which we found. Atkinson's comments on the disruptive effect of heavy currents are quite interesting. We are glad to see that his tests confirm that which is reported in the paper, namely, that for the expected values of short circuit currents, it is not necessary to provide for special binders to hold the conductors in place. As we must use a binder of some form in manufacture and a lead sheath, we do provide a reinforcing for those instances where extra heavy currents are likely to occur. It may be that the effects of short-circuit currents on belted cables weaken them electrically and, therefore, eventually re- sult in failure. However, to get a short circuit a failure must first ^take place, and in view of the speed with which circuits are opened, it seems a bit difficult to picture a permanent effect in the cable which eventu- ally causes further failures. It would seem as though effects of oil migration are more readily responsible for the poor showing of belted cables as compared to shielded cables. Louis Meyerhoff's comments are greatly appreciated. It would have been helpful to the committee handling the preparation of the paper if his ideas of proximity effect had been given them for consideration as possible explanations of the experimental data. As far as it was possible theoretical reasons for the total increase in conductor resistance were given and theoretical calcu- lations checked remarkably well, except in thoses cases where the strands were all laid in the same direction. By eliminating the calculated proximity effect, the theoretical increase in resistance very closely equalled the actual; in other words, proximity effect was zero. Meyerhoff's reason is logical, but it must be remembered that the oxidized surface of the strands also aids normal stranding in reduction of proximity effect when the strands are highly crushed. Referring to W. H. Cole's statement that the extra losses in his 3 conductor cable represented a deficiency of the order of from 5 to 8 per cent, or approximately $25,000, this is presumably based on the maximum carrying capacity of the cable line. Whether it is an actual deficiency or not, of course, depends upon whether the present or future peak loads required of this line become equal to the maximum allowable carrying capacity. This in turn depends upon how much reserve capacity this cable line was laid out for in the beginning. The fact that magnetic binder cable has about 20 per cent higher reactance than nonmagnetic cable is of no particular im- portance so far as voltage regulation of the system is concerned and becomes only of importance when an attempt is made to parallel magnetic and nonmagnetic cables. Everything else being equal, a nonmagnetic cable should be preferred, but there would still be a demand for magnetic binder cable for purposes of paralleling in those systems where the practice of using magnetic binder cable is already being followed. The last part of Cole's discussion seems to be based on the misconception that mini- mum proximity effect is realized with solid bar conductors. A comparison of the data in our paper will show that solid bar conduc- tors cause maximum and not minimum proximity effect. Compact rolling of the strands results in minimum proximity effect, although in physical appearance this type of stranding approaches nearest to solid bar. The reason for these 2 cases representing ex- tremes of proximity effect is fully explained in the paper. Rolling of the strands gives much larger contact area between strands and a more uniform distribution of cross currents. Tnese currents in turn are re- duced in total value by the contact resist- ance as represented by the natural oxide film on the surface of each strand. V Constant-Current D-C Transmission Authors' closing discussion of a paper pub- lished in the January 1935 issue, pases 102-8, and presented for oral discussion at the general overhead line problems session of the winter convention, New York, . Y . , January 23, 1935. Other discussion of this paper was published in the March 1935 issue, pases 327-9, and in the April 1935 issue, pases 447-9. C. H. Willis, B. D. Bedford, and F. R. Elder: In answer to the questions regard- ing the operation of the monocyclic network, the following simple vector analysis of its operations is submitted. The balanced monocyclic network, com- posed of pure inductive and capacitive ele- Fig. 1. Monocyclic vector diagram, special resistive load ments, theoretically produces an absolute constant voltage-constant current trans- formation. In practice the losses are small, and results closely approaching the theo- retical are obtained. When an inductance and capacitance of equal impedance are con- nected in series across a constant voltage source, a constant current must flow out the common connection of the 2 impedances. For simplicity consider 2 special loads of 882 ELECTRICAL ENGINEERING
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Transcript of Resistance and reactance of 3 conductor cables
D i s c u s s i o n s O f A . I . E E P a p e r s a s R e c o m m e n J e J f o r P m i t l i c a i i o m L y T e c h n i c a l C o m m i t t e e s
this and the following 8 pages appear 2 additional authors' closures of papers presented at the 1935 A.I .E.E. winter convention, New York, Ν. Y., January 22-25, and the first discussions submitted of papers presented at the general technical and the insulation and protection sessions of the South West District meeting, Oklahoma City, Okla., April 24-26, 1935. Authors' closures, where they have been submitted, will be found at the end of the discussion on their respective papers.
Members anywhere are encouraged to submit written discussion of any paper published in ELECTRICAL ENGINEERING, which discussion will be reviewed by the proper technical committee and considered'for possible publication in a subsequent issue. Discussions of papers scheduled for presentation at an A.I .E.E. meeting or convention will be closed 2 weeks after presentation. Discussions should be (1) concise; (2) restricted to the subject of the paper or papers under consideration; and (3) typewritten and submitted in triplicate to C. S. Rich, secretary, technical program committee, A . I .E .E . headquarters, 33 West 39th Street, New York, Ν. Y.
Resistance and Reactance of 3 Conductor Cables
Authors* closing discussion of a paper p u b l ished in the December 1 9 3 4 issue, p a s e s 1 5 8 1 - 9 , and presented for oral discussion at the cables session of the winter convention N e w Y o r k , Ν . Y . , January 2 4 , 1 9 3 5 . O t h e r discussion of this paper was publ ished in the March 1 9 3 5 issue, pages 3 2 4 - 6 , and in the A p r i l 1 9 3 5 issue, p a s e s 4 3 6 - 7 .
Ε. H. Salter, G. B. Shanklin, and R. J . Wiseman: In reference to the comments by R. W. Atkinson in regard to the difference found when the phase rotation of current was reversed, analysis of these data did not give a logical reason why a difference should be found. We could not explain it on the basis of accuracy of test methods because the difference is in the same order of magnitude as was found for other factors which we knew did influence a-c losses. It was decided to include the data in the paper with the hope that someone could offer a reason for that which we found.
Atkinson's comments on the disruptive effect of heavy currents are quite interesting. We are glad to see that his tests confirm that which is reported in the paper, namely, that for the expected values of short circuit currents, it is not necessary to provide for special binders to hold the conductors in place. As we must use a binder of some form in manufacture and a lead sheath, we do provide a reinforcing for those instances where extra heavy currents are likely to occur.
It may be that the effects of short-circuit currents on belted cables weaken them electrically and, therefore, eventually result in failure. However, to get a short circuit a failure must first ^take place, and in view of the speed with which circuits are opened, it seems a bit difficult to picture a permanent effect in the cable which eventually causes further failures. It would seem
as though effects of oil migration are more readily responsible for the poor showing of belted cables as compared to shielded cables.
Louis Meyerhoff's comments are greatly appreciated. It would have been helpful to the committee handling the preparation of the paper if his ideas of proximity effect had been given them for consideration as possible explanations of the experimental data. As far as it was possible theoretical reasons for the total increase in conductor resistance were given and theoretical calculations checked remarkably well, except in thoses cases where the strands were all laid in the same direction. By eliminating the calculated proximity effect, the theoretical increase in resistance very closely equalled the actual; in other words, proximity effect was zero. Meyerhoff's reason is logical, but it must be remembered that the oxidized surface of the strands also aids normal stranding in reduction of proximity effect when the strands are highly crushed.
Referring to W. H. Cole's statement that the extra losses in his 3 conductor cable represented a deficiency of the order of from 5 to 8 per cent, or approximately $25,000, this is presumably based on the maximum carrying capacity of the cable line. Whether it is an actual deficiency or not, of course, depends upon whether the present or future peak loads required of this line become equal to the maximum allowable carrying capacity. This in turn depends upon how much reserve capacity this cable line was laid out for in the beginning.
The fact that magnetic binder cable has about 20 per cent higher reactance than nonmagnetic cable is of no particular importance so far as voltage regulation of the system is concerned and becomes only of importance when an attempt is made to parallel magnetic and nonmagnetic cables. Everything else being equal, a nonmagnetic cable should be preferred, but there would still be a demand for magnetic binder cable for purposes of paralleling in those systems where the practice of using magnetic binder cable is already being followed.
The last part of Cole's discussion seems to be based on the misconception that minimum proximity effect is realized with solid bar conductors. A comparison of the data in our paper will show that solid bar conductors cause maximum and not minimum proximity effect.
Compact rolling of the strands results in minimum proximity effect, although in physical appearance this type of stranding approaches nearest to solid bar. The reason for these 2 cases representing extremes of proximity effect is fully explained in the paper. Rolling of the strands gives much larger contact area between strands and a more uniform distribution of cross currents. Tnese currents in turn are reduced in total value by the contact resistance as represented by the natural oxide film on the surface of each strand.
V
Constant-Current D-C Transmission
A u t h o r s ' c losing discussion of a paper p u b l ished in the January 1 9 3 5 issue, p a s e s 1 0 2 - 8 , and presented for oral discussion at the general overhead l ine problems session of the winter convent ion , N e w Y o r k , Ν . Y . , January 2 3 , 1 9 3 5 . O t h e r discussion of this paper was publ ished in the M a r c h 1 9 3 5 issue, p a s e s 3 2 7 - 9 , and in the A p r i l 1 9 3 5 issue, p a s e s 4 4 7 - 9 .
C. H. Willis, B. D. Bedford, and F. R. Elder: In answer to the questions regarding the operation of the monocyclic network, the following simple vector analysis of its operations is submitted.
The balanced monocyclic network, composed of pure inductive and capacitive ele-
F ig . 1. M o n o c y c l i c vector diagram, s p e c i a l resistive load
ments, theoretically produces an absolute constant voltage-constant current transformation. In practice the losses are small, and results closely approaching the theoretical are obtained. When an inductance and capacitance of equal impedance are connected in series across a constant voltage source, a constant current must flow out the common connection of the 2 impedances.
For simplicity consider 2 special loads of
882 ELECTRICAL ENGINEERING
