Artigo AUDIBLE NOISE GENERATION OF INDIVIDUAL SUBCONDUCTRS OF TRANSMISSION LINE CONDUCTOR BUNDLES

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IEEE Transactions on Power Apparatus and Systems, Vol. PAS-95, no. 2, MarchiApril 1976 
AUDIBLE NOISE GENERATION OF INDIVIDUAL SUBCONDUCTORS 
OF TRANSMISSIa LINE CONDUCTOR BUNDLgS 
M. G. Comber 
General Electric Co. 
Pittrfield, Uarr. 
Audible noiu due to corona 011 high-wltage trans- 
PPirrion line conductors can be reduced by introducing 
an a m t r y into the conductor bundle gemtry. Pre- 
determlnatioa of the opthum arrangemat of conductorr 
can be extremely involved and ir bent iwertigated by 
analpring the porfomance of individual tubconductorr 
in the bundle. An experinmtal technique ured for the 
determination of individual subconductor foulweather 
noire generation ir described. The rerultr obtained 
allow one to compute the noire parformPnce of any 
bundle configuration. Calculation8 are compared to the 
maarured perfonmncer for two different bundle arrange- 
mento. 
INTRODUCTION 
Audible noise from corona har been identified a8 
one of the mort important factor6 in the derign of con- 
ductor configuration8 for high-voltage trandrrion 
liner, 500-kV and above and ha8 been the subject of 
several recent rtudier.1'5 Aa more rertrictionr in the 
fonn of mtate and local regulations on noire emirrionr 
are being introduced, the utility industry IB obligated 
to Investigate techniques by which audible noire from 
tranmdssion lines can be limited to acceptable lwelr. 
In each of the referenced studier,l'5 the influ- 
ence of the n d e r of subconductors in a bundle and/or 
the influence of rubconductor diamcter was examined. 
Results denunrtrate that audible noise lwelr can be 
controlled by careful relection of there par.meters. 
Hawver, for trandrrion voltages in the ultrahigh 
voltage (UHV) range - 1000-kV and above - the rolution 
to the audible noire problem may require additional 
technology. Limiting noire to rpecified levels merely 
by increaring the subconductor d i m t e r or the n d e r 
of tubconductorr may result in a very uneconomical de- 
sign and may introduce additional problems, such as 
line-stringing and, in certain areas, ice and wind 
loading. 
One technique which presently prondrer to be the 
most economical =ann of reducing the noire level of a 
bundle in bundle geometry optimization. Most inverti- 
gatorr have concentrated on "regular" bundle geometries; 
that is, with conductorr evenly spaced around a circu- 
lar section. It has been demonstrated, however, that 
audible noise generation could be reduced by introduc- 
ing an arymmtry into the bundle geollrtry.6 and, fur- 
ther, that there umy in fact be a particular optiaum 
geometry for which audible noise is a animmn. The 
early theoretical work6 war based on rouewhat limited 
laboratory tests but, neverthelerr, was rearonably 
well-supported by results of outdoor tarts on full- 
sized 6-conductor bundles. Subrequent investigatiow, 
hovaver, have pointed out the limitations of this par- 
Distribution Committee of the IEEE Power Engineering Society for presentation at 
Paper F 75 4804, recommended and approved by the IEEE Transmission & 
the IEEE PES Summer Meeting, San Francisco, Calif., July 20-25, 1975. Manu- 
m i p t submitted February 3,1975, made available for printing April 30,1975. 
R. Cortina 
Milan, Italy 
ENEL 
ticular theoretical approach and have identified the 
need for further research. 
In order to fulfill thin need, a program of tert- 
lag war formdated by which the audible noire perform- 
ance of realirtically-rized, rtranded conductorr could 
be evaluated in an enviromant sinulating that of actu- 
al operating conditionr. Conniderable insight into the 
behavior of different subconductor8 within a bundle war 
obtained from there tertr, the reaultr of which have 
been conrolldated into a digital computer program which 
has the capability of determining the audible noire 
perforaunce, for average foulweather conditiotu, of 
any bundle configuration, and specifically, pcmdtr the 
opthimtion df bundle geomatry. 
It ir recognized that the use of anymetrical bun- 
dler may require the solution of other problem, both 
machanical and electrical, not encountered in the ure 
of regular bundle configurationr. For eunple, the 
clore proximity of adjacent conductorr that m y be re- 
quired for an arymactrical arrangenent nmy also rerult 
in conductor vibration which nuat be eliminated; un- 
equal distribution of heavy load current8 anwngst a r p 
mattically positioned rubconductors may lead to differ- 
ences in rubconductor temperatures and rag8 which m s t 
be minimized. Although such problem are outride the 
scope of thin paper, it is anticipated that they can be 
ratirfactorily overcome and will not detract greatly 
from the advantages of a8pnmrtrical bundle geomctrier. 
AUDIBU NOISE GENERATION OF A SUBCONDUCTOR IN A BUNDIE 
The audible noire round prerrure level due to 
transadreion-line corona can be determined from a know- 
ledge of the noire generation of each phara bundle.7 
The generation, expreseed ar generated acourtic P-I, 
dB(A) above 1 WW per mater of conductor length, can in 
turn be found from sunming the generations of indlvidu- 
a1 subconductore in the bundle. 
The generation of corona of an individual subcon- 
ductor, and therefore its associated effects, including 
audible noire, is a function of the electric field dis- 
tribution i n the vicinity of the subconductor. It can 
be demonstrated analyticall# that the field distribu- 
tion close to the rubconductor surface is practically 
determined by four paramcters; namcly, 
d, the rubconductor diameter 
the maximum voltage gradient existing 
on the surface of the subconductors 
the average voltage around the rurface 
of the subconductor 
the angular position of the maxilrmm 
gradient measured from some reference 
point. 
be noted that a11 references to voltage 
gradients in this paper imply quantitier. 
- 
Thus, if rubconductors in two different bundles 
have Identical values of there four paruaters, the co- 
rona generation will be practically identical. For ex- 
ample, consider subconductor #1 of each of the two bun- 
dles shown in Fig. 1. These subconductors share the 
ram values of d and CT and, if energized such that they 
525 
d 1 I in. 
Fig. 1. T w different bundle configurationr with eub- 
conductors having the ~ r m ) field paramtern. 
have equal values of &, they also have equal values 
of Em. Then, ar shown in Reference 6, the field in 
the W d i a t e vicinity of nubconductor #1 is the u ~ e r 
for each bundle. Under these condition8, corona gen- 
eration of this subconductor will be practically iden- 
tical for each case. 
For cormenience, a ratio k can be defined as 
and then the C O ~ O M generation of a rubconductor can 
be erpresred as a function of four parsnrters 
The calculation of the generation of a bundle is 
therefore rcZluced to a determination of the function 
f. 
EXPSRIbSNTAL EVALUATIW OF SUBCONDUCTOR GJiNERATIW 
The determination of the dependence of subconduc- 
tor generation on the various parameters, expressed by 
equation (2), is best perforned experimentally. To 
approach realistic conditions as closely as possible 
and still maintain sufficient flexibility to cwer a 
wide range of paramatera, a test program utilizing one 
of the Project W testcagea7 war formulated. The 
cage, 26-ft. (7.92-m) square and 45-ft. (13.7-m) in 
length, permitted the use of conventional, stranded 
conductors, which could be exposed to an artificial 
rain-spray or, whenever possible, to natural rain con- 
ditio-. 
The basic problem consisted of determining a me- 
thod of subjecting a rubconductor to the conditions it 
would experience in a bundle while at the same time 
being able to discriminate between its audible noise 
and that of other conductors which are required to er- 
tablish the required field conditions. Several di- 
ferent approaches to this problem were considered be- 
fore a rather unique solution was adopted. 
Test Arrarsc-ts 
One approach which was investigated involved the 
placement of large-diameter nonconducting tubes on all 
but one subconductor of a regular bundle configura- 
tion. When tasted under natural or artificial rain 
conditione, water would collect on the tubes away from 
the actual surfaces of the conductors in a relatively 
low field region. The noire generated by the tube- 
cwered conductors was, consequently, of very low lev- 
el. In this vay, the noise measured was due practi- 
cally entirely to the uncovered conductor upon whose 
surface vater drops could form uninpeded. By suitable 
selection of the uncovered conductor and by variation 
of the bundle d-iow, a wide range of paranrters 
could be exumiued. However, this approach vas found to 
have reveral inherent drawbaclu, and an alternative 
technique was sought. 
Other pathod. cmidered included a s y s t a to wet 
only one nubconductor of a bundle, and a technique 
which required the use of an extremely directional mi- 
crophone. Thene, however, were rejected in favor of 
the 8pproach finally adopted. 
This iS illustrated by the diagram of Fig. 2. The 
S 
2 
Emax 
Fig. 2. Illuntration of conductor arrangeuent for sub- 
conductor generation tests. 
tert conductor was strung at a known spacing S from a 
rmlticonductor bundle. The multiconductor bundle, ini- 
tally 12 x 1.823 x 30-in (12 x 4.63 x 76.2-cm), vas 
centered in the cage and energized at the same voltage- 
to-ground as the test conductor. By varying the angu- 
lar position of the test conductor as indicated, while 
the spacing S and the voltage are kept constant. the on- 
ly parameter varied is a, the angular position of the 
point of maximum gradient, which is directed radially 
outward from the center of the cage. The referonce 
point used for the measurement of a was taken to be the 
bottomPost point on the conductor surface. An increase 
of the spacing S decreases the shielding effect of the 
bundle on the test conductor, thereby cawing E- to 
increase; but, at the same time, the distribution of 
gradient around the conductor is changed, approaching a 
more uniform distribution (a single conductor in space, 
not influenced by other conductors, has an entirely u- 
niform gradient distribution). Thus the parameter k, 
the ratio of nruinum to average surface gradient, ir 
reduced. Couversely, a decreare in the spacing S re- 
duces * but increases k. The absolute value of rur- 
face gradient is more precisely controlled by adjust- 
m n t of the test voltage. Finally, the parameter d is 
varied by the ure of different diameter test conductors 
Thw, this test arrangement permits the variation of 
each of the generationdefining parameters: d, b, k 
and a. Figures 3 and 4 n h w one of the configurations 
actually tested. With the asarmption that corona gene- 
ration is uniquely defined by the four parameters de- 
scribed abwe, the validity of the approach is further 
dependent on the fact that the generation of the uulti- 
conductor bundle is negligible compared to that of the 
test conductor, and the measured audible noise is due 
entirely to generation on the tert conductor. This v.8 
verified both by visual obsemations and by quantita- 
tive meamureuentr. During heavy rain and wet-conductor 
526 
Fig. 4. Close up of end-connections for arrangement in 
which d = 1.427 in, k 1.304, Cy = 45'. 
Fig. 6. Test arrangement using a 4 x 1,823-in bundle. 
conditions at night, it was observed that corona activ- 
ity was practically confined to the test conductor, as 
illustrated in Fig. 5. Subsequent measurements of the 
audible noise of the uulticonductor bundle alone, ener- 
gized over the ~(UIT voltage range as for the individual 
subconductor tests, shoved that the conttibution from 
the bundle to the total noise was negligible. 
Calculations indicated that the parameter k was 
very sensitive to -11 changes in conductor position 
when the spacing S was small. Extreme care was taken, 
therefore, to insure that conductors were spaced apart 
by the correct distances. 
The physical dimensions of the end hardware re- 
stricted the ranges over which the parameter k could be 
varied. These ranges were e y n d e d by replacing the 
12 x 1.823 x 30-in bundle vit a 4 x 1.823 x 10-in 
It should be emphasized, at this point, that m e 
of the =in objectives of this work was to provide data 
which could be used for the optimization of bundle ge- 
Ometry, the concept of which is applicable for "aged" 
conductors; that is, conductors whose surfaces have a 
hydrophilic, or wettable, property similar to that of 
conductors which have been exposed to the elements for 
a considerable period of time. Water accunulates as 
drops on the bottom of such conductors rather than in 
beads all around the surface as is the case for new 
conductors. The aged property can be artificially pro- 
duced, and for these tests was obtained by sandblasting 
the surfaces of all conductors. 
Test Procedure 
For each test configuration, measurements of audi- 
527 
ble noise, &(A), were t a w for a vide range of appli- 
ed voltages under conditions of heavy artificial rain 
and at 30-second intervals after the rain-spray system 
vas shut off. A General Radio (GR) one-inch ceramic 
microphone, type 1560P7, located at bundle height and 
14.4-ft. (4.391~) from the center of the bundle, v a s 
used in conjunction with a GR precision sound-level me- 
ter, type 156u. The averages of readings at the 1-1/2 
and 2-minute points after rain Yere taken as wet-con- 
ductor levels, representing levels observed under con- 
ditions of natural light rain, or mnximm levels ob- 
served under fog. Through comparisons with results of 
natural rain and fog tests, the vet-conductor condition 
has been shown to be representative of the conditions 
described above. 
The ranges of parameters tested are indicated in 
Table I. 
I. RANGES OF PARAMETERS TESTED. 
Subconductor 1.165-in 1.427-in 1.823-in 
diameter, d (2.959-cm) (3.625-cm) (4.630-cm) 
Maxknwn gradi- 16-23-kV/cm 14-21-kV/cm 13-20-kV/cm 
ent E,, 
Maxinnun/average 1-1.260 1-1.304 1-1.356 
gradient, k 
Angular position, ---------- 0, 45, 90, 120"----------- 
01 
Test Results 
era1 different forms of data could be considered. I d - 
Because of the rider of parameters involved, sev- 
tially, the actual measured noise values were plotted 
against maxiram test conductor surface gradient. For a 
given d and k this yielded a family of curves with CY as 
a parameter. Examples are shown in Figs. 7 and 8. 
Note thatfor the CaRe of a single conductor the value 
of ~y is not uniquely definable, since the marimnn gra- 
l- I 
d = 1.427- in 
k = 1.0 
k 
I 
I 
I 5 16 17 18 19 20 21 2 2 
MAXI WM SURFACE GRADIENT - kV/cn 
MAXIMUM SURFACE GRADIENT- kV/cm 
Fig. 8. Example of audible noise results for 
d = 1.165-in, k - 1.200. 
dient exists e v e m e r e around the conductor surface. 
With a full complement of such curves, the effect of 
variation of all parameters can be nore closely ex- 
amined by translation to a different format. A parti- 
cularly informative presentation vas found to be curves 
of noise levels versus the parameter k, for different 
values of d and k. Figs. 9-20 shov the results pre- 
sented in this marmer for several different h, with 
measured noise levels converted to generation quantiti- 
es; i.e. generated acoustic pwer.7 
This form of data presentation provides consider- 
able insight into the behavior of different conductors 
within a bundle, and clearly deuvmstrates that the 
noise from the lover conductors (mall CY) in a regular 
rmlticonductor bundle generally dominates that of the 
upper conductors (large e). The effect is more pro- 
nounced for the higher values of k. This corresponds 
to increased n-et of subconductors in a bundle or de- 
creased bundle diameters, the value of k for regular 
bundles being given by 
k a 1 + (n - 1) d/D (3) 
where n is the n-er of subconductors in the bundle, 
and D is the bundle diameter. 
Also of particular interest is the behavior of the 
subconductors for high values of surface gradient. The 
effect described above becomes less pronounced, with 
all subconductors approaching the same noise character- 
istic, irrespective of their positions in the bundle. 
Fig. 7. Example of audible noise results for 
d = 1.427-in, k = 1.0 (single conductor). 
528 
‘,a = 45 
\< - 
1.0 1 . 1 1.2 I .3 
k 
Fig, 9. Wet-conductor generation vs. k; d = 1.165-iny 
E,,, = 16-kVlcm. 
c 
% - 2 0 . 
8 a = O 
I 
d = 1.165-in 
Emax= 18 Wlan 
W > 
a 
a - - - 
--c------ ---- 
- 
W - - 
I .o 1.1 1.2 1.3 
k 
Fig. 11. Wet-conductor generation vs. k; d = 1.165-iny 
E,,, = ZQ-kV/cm. 
d = 1.165 - in 
E,,, = 22 kV/m 
- k 
Fig. 10. Wet-conductor generation vs. k; d = 1.165-in, Fig. 12. Wet-conductor generation vs. k; d = 1.165-iny 
Emax = 18-kVIcm. E,, = 22-kVIcm. 
529 
U 
k 
I .2 13 
Fig. 13. Wet-conductor generation VS. kg d = 1.427-in, 
Emax = 15-kVf~m. 
I 1 I 
d = 1.427411 
E 
\ E M X I7kV/a 
%20 a = 0 - 
a = 45 5- -- -- ------ 
- 
w 
- 
I .o 1.1 I .2 I .3 k 
I I I I 
3 10. 
g 
I \ 
3 d = 1.427-in \ 
Emx = 19kV/cm Y 
\ 
\ 
\ 
\ 8 0 . 
t s 
\ 
s - \\ 0 120 I I I 1 - 
ID 1.1 I .2 I .3 
k 
Fig. 15. Wet-conductor generation vs. k; d = 1.427-in, 
Em, = 19-kVfcm. 
3 10. 
g 
I \ 
3 d = 1.427-in \ 
Emx = 19kV/cm \ E - \ 
0 
Y \ 
8 0 
t \ s 
\ 
s - - I 1 I I 
ID 1.1 I .2 
k 
Fig. 15. Wet-conductor generation vs. k; d = 1.427-in, 
Em, = 19-kVfcm. 
I .3 
r w 
W 
ID 1.1 I .2 
k 
13 
Fig. 14. Wet-conductor generation VS. k; d = 1.427-in9 Fig. 16. Wet-conductor generation vs. k; d = 1.427-in, 
Emax = 17-kVfm. E,,, = 21 -kV/cm. 
- 
530 
w d = 1.8% in 
E,: I4kVVlcm 
I 
0 - 0 
k 
Fig. 17. Wet-conductor generation v& k; d = 1.823-in, 
Emax 1 4 - k V I m 
k 
Fig. 18. Wet-conductor generation VS. k; d = 1.823-in, 
E,, = IS-kV/cm. 
1.0 1.1 1.2 1.3 
k 
Fig. 19. Wet-conductor generation vs. k ; d = 1.823-in, 
Em, = 1 7 - k V I ~ . 
d = 1.823 - in 
Emax- 19kVlcm 
- 
I 
- 
I 
1 
k 
I. 2 I .3 
Fig. 20. Wet-conductor generation vs. k; d = 1.823-in, 
Em- = 19-kVIcm. 
531 
APPLICATION OF RESULTS TO CALCuLhTION OF 
AUDIBIg NOISE GEMERATION OF A BUND= 
To c-ute the audible noise generation of any 
bundle using the technique of individual subconductor 
generation, one mwt f i rs t calculate the parameters 
E-, k and CT for each subconductor in the bundle. A 
suggested approach, valid for single-phaae cases, is 
described i n Appendix I of Reference 6. With s l igh t 
modification this approach can be used also for uulti- 
phase si tuations. With these parametric values and the 
subconductor diamater, d, one can find the subconductor 
generation from curves such a s given i n Figs. 9-20, in- 
terpolating or extrapolating as necessary. When the 
generation of each subconductor has been determined, 
the to ta l bundle generation is obtained by s&ng the 
individual subconductor contributions. 
It is recognized that this calculation, particu- 
la r ly for a bundle of many mbconductors, can becamc 
somewhat arduous. Thus, for simplification, the re- 
su l t s were incorporated into a computer program which 
computes the parameters h, k and cy for any specifi- 
ed bundle geometry, whether i n a single-phase or 3- 
phase l ine , and then determines the generated acoustic 
power of the individual subconductors and the bundle as 
a whole. 
Comwrison with Experimental Results 
AB s ta ted ear l ie r , one of the main objective. of 
t h i s w r k was t o provide more valid data for the appli- 
ca t ion to bundle gcometry optimization. Figure 2 1 
shows the results of cage t e s t s on aaymmatric 6-conduc- 
t o r bundles, superinposed on cumes calculated by the 
described technique. A l l data r e f e r t o t h e Center 
p b r e of a 3-phase l ine having an average height of 
70 f t . (21.3-m) and phase spacing of 50 f t . (15.2 m). 
It should be noted that the experimcntal results were 
obtained from t e s t s i n a cage significantly different 
namely, 17.5 f t . (5.3 m) square and 190 f t . (57.9 m) 
from tha t used for the eubconductor generatian t e s t s ; 
long. The degree of asyPmetry, Eo, is a measure of how 
f a r reauved a bundle is from a regular configuration 
(Eo 1). For a given n h e r of subconductors and sub- 
conductor diameter there is no unique mean8 of asylmmt- 
r i s ing t he gemt ry . For the case described here, the 
bundle gemt ry vas va r i ed according to t he diagram of 
Fig. 22. Subconductors l i e on a c i rc le , and adjacent 
arc distances are in geometric proportion.; that is 
Good agreenrnt between test resu l t s and camputa- 
t ions is observed. Also of note is the behavior of the 
bundle for increa8ing system voltage. For increasing 
voltage, the benefit of bundle a8yamtry diminishes 
and, a t t he same time, the opt- geometry tends to- 
vards a regular configuration. This again illustrates 
the point which has been repeatedly observed at Project 
W V ; namely, t ha t i f a bundle is operated a t very high 
gradients (the mar- gradient for the 1150-kV regular 
bundle i n Fig. 22 is 17.5 kV/cm) , then there is very 
l i t t l e one can do, i n any respect, to improve the audi- 
ble noise performance. 
%@ % 
I 
DEGEGREE OF ASYMMETRY E I - A4 
O AI 
Fig. 22. Asyrrmetrical arrangement of a 6-conduc- 
tor bundle. 
The techniques of calculating audible noise per- 
formance from individual subconductor generations is 
not confined to bundle optimization as described above, 
but can be applied to any bundle geometry. Figure 23 
shows computations for a rather atypical 6-conductor 
bundle using three different subconductor diameters. 
Generations for each subconductor a re shovn, along with 
the bundle total , for the center phase of 3-phase lines 
w e r t h e range 800 - 1100-kV. Also shovn are tha re-r a in and a r t i f i c i a l , "wet-conductor," conditions. I t 
E U l t 8 of cage tests on t h i s bundle, for both natural 
is apparent that the calculations are somewhat on the 
pessimistic side for higher voltages and on the opt* 
istic s ide for lower voltages. Nevertheless, the a- 
greement with test resu l t s is good. In addition one 
53 2 
I I I I 
800 900 lo00 1100 
THREE-PHASE LINE VOITAGE. kV 
Fig. 23. Test resu l t s and calculated performance of 
a 6-conductor bundle using three different subcon- 
ductor diameters. 
may observe the good correspondence between resu l t s of 
natural ra in tests, obtained in l i gh t t o medium rains, 
and those obtained from t h e a r t i f i c i a l r a i n t e s t s . It 
should be noted that the bundle configuration eramined 
was not chosen for practical applications, but merely 
to i l l u s t r a t e t he ve r sa t i l i t y of the calculation tech- 
nique. 
1. 
2. 
3. 
4. 
coNcLus1oNs 
A means by which individual subconductor genera- 
t ions can be derived experimentally has been de- 
veloped. 
Results clearly demonstrate the different noise 
generating characteristics of different subconduc- 
tors within a bundle. I n a regular bundle, the 
lower subconductors are dominant for low to moder- 
ate surface gradients. For increasing gradients, 
t h i s e f f ec t is reduced,all subconductors approach- 
ing the sam characterist ic of behavior. 
The audible noise genetation of bundled conductors 
of any configuration can be calculated through a 
knowledge of the generations of individual subcon- 
ductors in the bundle. 
Very satisfactory agreement between computer gen- 
erations and those derived through bundle t e s t s 
has been obtained. Further, a good correlation 
between the "wet-conductor" levels determined from 
a f t e r ( a r t i f i c i a l ) r a i n tests and levels obtained 
in natural rain has been observed. The wet-con- 
ductor condition is considered t o be representa- 
t i ve of average foul-veather conditions; that is , 
5. 
1. 
2. 
3. 
4. 
5 . 
6. 
7. 
the 50% level on a crmulative foul-weather d i s t r i - 
bution curve. 
Bundle aspmetry offers one of the most a t t rac t ive 
means of reducing audible noire leva18 of high- 
voltage transmission lines to acceptable levels. 
However, the degree to which aryamatry is benefic- 
i a l is very nu& depmdent on the surface gradient 
a t which the bundle conductors are operated. 
Greater reductions in noise are posnible as the 
operating etress i s reduced. Very l i t t l e can be 
done t o reduce the noise levels of a bundle which 
is highly stressed and already very noisy. 
D. E. Perry, "An analysis of transmission-line au- 
dible noise levels based upon f i e ld and three- 
phase tes t - l ine measurements," IEEE Trans. (Power 
Apparatus and Systems), vol. PAS-91, no. 3, pp. 
857-865, Eley/June 1972. 
A. Cocquard, C. Gary, "Audible noise produced by 
e l ec t r i ca l power transmission lines a t very high 
voltage," Paper 36-03 presented at CIGRE In te r - 
national Conference on Large High Tension Elec t r ic 
System, Paris, France, Aug. 28 - Sept. 8, 1972. 
N. Kolcio, B. J. Ware, R. L. Zagier, V. L. C h a r t i - 
er, F. M. Dietrich, "The Apple Grope 750-kV Project 
e ta t i s t ica l ana lys i s of audible noise performance 
of conductors a t 775-kV," IEE Trans. (Power A m - 
ratue and Systems), vol PAS-93, no. 3, pp. 831-840 
May/June 1974. 
N. G. Trinh, P. S. Marwada, B. Poirier, "A com- 
parative study of t h e corona performance of con- 
ductor bundles for 1200-lcV transmission lines," 
IEEE Trans. (Power A D R a r a t U and Systems), vol. 
PAS-93, no. 3, pp. 940-949, May/June 1974. 
M. Sforzini, R. Cortina, G. Sacerdote, R. Piazza, 
"Acoustic noise by ac corona on conductors: Re- 
su l t s of an experimental investigation in the an- 
echoic chamber," Paper T74 402-4, presented a t t he 
IEEE PES Summer Meeting and Energy Resources Con- 
ference, Anaheim, California, July 14-19, 1974. 
M. G. Comber, L. E . Zaffanella, "Audible noise re- 
duction by bundle geometry optimization,'' I E E 
Trans. (Power Apparatus and Systeme), vol. PAS-92, 
pp. 1782-1791, Sept./Oct. 1973. 
M. G. Comber, L. E . Zaffanella, "The use of single- 
phase overhead t e s t l i nes and t e s t cages to walu- 
a te the corona e f fec ts of ehv and uhv transmission 
lines," IEEE Trans. (Power Apparatus and Syst-), 
vol. PAS-93, no. 1, pp. 81-90, Jan./Feb. 1974 
ACKNowLeDGEMNTS 
The work cwered in th i s paper is a portion of an 
ultrahigh voltage transmission research program spon- 
sored by the Electric Power Research Ins t i tu te . The 
help and encouragement of the Project UHV Steering 
Comnittee is gratefully acknwledged. The authors al- 
so wish to acknowledge the encouragement and support 
of Dr. M. Sforzini of Ente Nazionale per 1'Energia E l - 
e t t r i c a (ENEL), I ta ly . 
533 
Disclrrson 
N. Giao Trinh (HydroQudbec Institute of Research, Varennes, Qudbec, 
Canada): The authors are to be commended for the experimental work 
showing clearly the contribution of the individual subconductor to the 
audible noise generation of conductor bundles. 
At IREQ, we have been working toward a method of predicting 
the corona performance of conductor bundle by evaluating the con- 
the corona performance of single conductors and takes into account 
tribution of individual subconductors. The computation method uses 
the actual distribution of the field intensity at the surface of individual 
subconductors in the bundle. The calculated results are found to agree 
reasonably with the experimental data obtained from cage tests. 
- not only the AN, but the RI and corona loss of conductor bundle 
in the bundle. 
can be evaluated from the contribution of individual subconductors 
- the contribution of individual subconductors can be extrapolated 
from test results on single conductors. 
These results are essentially in agreement with the authors’work, 
and they even suggest that the conclusions of the paper can be ex- 
tended to the cases of RI and corona loss of conductor bundles. 
The results of our study indicated that: 
Manuscript received August 8,1975. 
D. E. Perry, S. H. Sarkinen, and A. L. Courts (Bonneville Power Admin- 
istration; Portland, Oregon): Asymmetric arrangement of bundled con- 
ductors is an interesting means of reducing audible noise generation. 
larly at UHV transrmssl 
This scheme has potential for reducing conductor requirements particu- 
’on levels, however, solutions to several mechan- 
ical problems must be developed to make the scheme practical. 
Ostrander Audible Noise Test Line and also investigated the mechanical 
We have investigated the effectiveness of the technique on the 
problems associated with u n e q d distribution of load currents. The 
Ostrander Test Line section with 4 x 1.382” bundled conductor (de- 
metrical configuration for three-phase evaluation. The original s y m - 
scribed in the author’s Reference 1) was rearranged into an asym- 
metrical bundle with 18” subspacing was in effect rotated 90” and the 
lower conductors spaced 12”, the upper conductors spaced 24”, F d 
the legs of the trapezoidal shaped bundle being 18”. A 5-6 dBA 1111- 
provement was predicted for this modification, however, the long term 
1 2 3 4 5 
ASYMMETRYFACTOR 
Fig. 1 - Ratio of Maximum and Minimum Subconductor Currents for 
7 x 1.6” 42-Inch Diameter Bundle as a Function of Degree of 
Asymmetry. 
Manuscript receivedAugust 1 1,1975. 
tests showed a 2-3 dBA improvement over the original configuration. 
The line voltage varied between 505 and 525 kV during the test period. 
Do the authors have any comments on the discrepancy between the 
predicted and measured value? 
Regarding Conclusion 5, BPA studies indicate the asymmetrical 
bundling causes an unbalance of the subconductor reactances of a given 
phase bundle which for the range of degrees of asymmetry offering 
maximum audible noise reduction results in a significant unbalance of 
the subconductor currents as shown in Figure 1. 
As a confmation of our computational model, we tested in the 
laboratory a 120’ length of 8conductor bundle with varying degrees of 
lated in all cases. Although this unbalance increases line losses slightly 
asymmetry. The current distributions were within 5% of those calcu- 
(1 to 4 percent depending on the degree of asymmetry), we believe that 
the most serious consequence is the effect on mechanical performance. 
The unequal current loading among the subconductors will result 
in unequal sag, the amount depending upon line loading, spacer loca- 
tion, etc. Greatest currents are carried in the upper subconductors. This 
unequal loading and sag unbalance can cause rotation of the bundle dis- 
placing the conductors from their optimum position and affecting their 
resulting noise performance. Under wind load, a rotational moment will 
be applied to the bundle due to the centroid of the transverse forces 
not coinciding with the center of mass of the bundle. A rotational oscil- 
lation can result. 
We have studied various solutions to the problem of unbalanced 
currents. One of the most feasible seems to be subconductor transposi- 
tion, thereby forcing equal currents through each subconductor. This, 
ing the insulation of the required insulated spacers. Design of such 
however, results in a build-up of voltage between subconductors stress- 
spacers would have to account for this continuous stress as well as as- 
suring arc deionization should the insulation spark over under transient 
conditions. 
metric configurations may result in problems of subconductor oscilla- 
The decreased spacing between the lower subconductors of asym- 
tion. Increased bundle diameters may be required to offset this reduced 
mechanical aspects of asymmetric bundles. 
spacing. We would be interested in the authors’ comments regarding the 
M. G. Comber, and R. Cortina: We would like to thank the discussers 
for their comments. 
IREQ. The approach outlined by Dr. Trinh is somewhat different to 
It is of interest to us that similar work is being conducted at 
that adopted by us in that computations of the corona performance of 
a conductor bundle is based on experimental results obtained from tests 
on single conductors. It is not immediately clear to use how the effect 
of surface gradient distribution (described by us by the parameter K) is 
taken into account, since the distribution around a single conductor is 
essentially uniform (K = 1). It is with great interest, therefore, that we 
look forward to the reporting of the results of Dr. Trinh’s investigation. 
In addition to audible noise measurements we also recorded RI and 
corona loss data for all the test configurations. However we have con- 
developed a computational procedure for determining the RI and 
centrated our efforts on the audible noise aspect and we have not as yet 
conductor performances. I t is encouraging that Dr. Trinh’s investigation 
corona loss performance of conductor bundles from individual sub- 
indicates that such an evaluation can be made. 
Mr. Perry reports the results of tests on a konduc to r asym- 
metrical bundle. From the data presented in this paper, the expected 
noise reduction from the original diamond configuration is around the 
achieved is reported to have been only 2-3dB(A). Without more de- 
5-6 dB(A) mentioned by Mr. Perry. However, the reduction actually 
tailed information concerning the conditions under which this 
2-3 dB(A) reduction is applicable it is difficult to pinpoint the primary 
presented apply to well aged conductors for which water drops only a p 
cause of the apparent discrepancy. We must reemphasize that the data 
pear in a single row on the bottom of the conduton. For conductors 
with a poorer wetting property the calculated noise reduction will be 
on the optimistic side. In addition, the data refer specifically to the 
“wet-conductor” condition. Through comparisons of our calculations 
with field measurements reported in references 1 and 3 and, more re- 
cently, with measurements on Project UHV’s three-phase test line, we 
have concluded that “wet-conductor” conditions represent very well 
the 50% level on a cumulative distribution curve of noise in natural rain 
conditions. For conditions between “wet conductor” and “heavy rain,” 
Manuscript received September 25,1975. 
534 
which we relate to the 95% level on the cumulative distribution curve, 
reductions in noise level would be less than those calculated on the 
basis of data presented in this paper. For "heavy rain" conditions no 
reduction at all may be experienced. (From a recent analysis of approx- 
imately 62 hours of rainfall at Project UHV we found that the 50% 
rainrate level was 0.06 in/h, while the 95% level was 0.4 inlh). 
conductors will result in an unequal distribution of load current. How- 
We agree with Mr. Perry that asymmetrical arrangements of sub- 
ever, the consequences may not be as severe as Mr. Perry indicates. For 
example, we made a calculation for the case of an 1100-kV line carry- 
ing a maximum load of lOOOqMW under conditions of zero wind and 
ambient temperature of 25'C. The bundle considered was an optimized 
8 x 1.302 x 40-in. (degree of asymmetry = 2.3). A span length of 1250 
ft was used, with spacers positioned at invervals of 250 ft. The ratio of 
maximum to minimum subconductor current was 1.44. Under these 
extremely unfavorable conditions, the maximum differential sag was 
calculated to be 11 in., occurring at midspan. In practice, such ex- 
treme conditions (maximum loading, zero wind) would occur very rare- 
ly. However, the consequences of this occurrence would be consider- 
ably diminished by addition of spacers, which would generally prove 
to be a relatively inexpensive proposition when compared to the al- 
ternative of adding more conductor material t o a regular bundle to 
achieve the same noise reduction. The temperature differences between 
subconductors, and thus the differential sag, will be reduced appreci- 
ably in the presence of wind and thus the wind-induced rotational os- 
cillation mentioned by Mr. Perry should not be of major concern. 
sult in a balanced current situation. This of course would result in a dif- 
Transposition of conductors, as suggested by Mr. Perry, would re- 
ference in voltages between subconductors but, again, this is not con- 
sidered a major limitation. We have calculated that, for the transmission 
line used in the example above, a transposition every 6 spans would re- 
load at 1100 kV the current per subconductor would be 656 A and the 
sult in a maximum voltage difference of 0.16 V/A. For a 10000 MW 
maximum voltage difference between subconductors would be 105 V. 
Insulating spacers and suspension hardware could be designed to with- 
between subconductors it is considered that the current drawn through 
stand this relatively low voltage. In the event of momentarycontact 
the contact resistance would be neghgible. 
The problem of subconductor oscillation due to decreased sub 
conductor spacing is an aspect which we have not studied in depth. 
Certainly, it is an area which deserves further investigation. However, 
we feel that this, and other mechanical problems arising out of asym- 
metrical bundles do not pose problems which cannot be relatively 
easily and relatively inexpensively overcome. Obviously there is a trade- 
off between the cost of ensuring satisfactory mechanical performance 
of an asymmetrical bundle and the cost of achieving the same noise re- 
duction by conventional means. Each case must be evaluated on an 
individual basis. 
535