Development of Conductors with Reduced Wind Drag andWind Noise for Overhead Power Transmission Linesby Naoshi Kikuchi *, Yutaka Matsuzaki *2, Hideo Banse *2
Takao Kaneko *2, Akihiro Yukino *3 and Hirotaka Ishida *3

The wind load acting on the conductors of overhead power transmission lines is amajor factor impacting the designed strength of the towers, so that a reduction inwind drag can result in a decrease in construction costs and an improvement in the reliability of
the line. The authors have accordingly addressed the problem of reducing conductor wind drag,and propose a reduced-drag design featuring grooves in the conductor surface and a reducednoise and -drag design featuring grooves and protruding wires. This paper presents a clarificationof the mechanism of drag reduction by rendering visible the air flows around the conductors,
describes wind tunnel measurements of drag coefficient and field observations of a full-scale test
line under high-wind conditions, and the carrying out of a series of tests on basic conductor characteristics and accessories for the completion of a reduced-drag conductor.

ABSTRACT1.

INTRODUCTION

Designing the strength of the structures that support overhead power transmission lines is significantly influenced
by wind drag, and they are designed to withstand theloads bearing on the lines and the support towers themselves (design wind velocity 40 m/sec) imposed primarily
during typhoons. When they are situated in a topographical formation such that strong local winds arise as thetyphoon passes, the increased wind load is taken into
account 1), and this tends to increase construction costs.
The drag on the conductors often accounts for as much as
50-70% of total drag, and any reduction in conductor dragwill reduce the load on the support towers, making it possible to reduce costs without compromising reliability.
The authors noted the fact the wind velocity at which thedrag coefficient of a cylinder begins to drop is decreased
by surface roughness 2), and the fact that golf balls travel
farther because of their dimpled surface 3), and came tothe conclusion that it would be possible to reduce the dragcoefficient of a conductor within the range of wind velocities for which transmission lines were designed by focusing their attention on the surface morphology of the conductor. As a result we have proposed conductors with
reduced drag, provided with grooves in the surface (theLP 810-mm2 reduced-drag conductor and the LNP 810mm2 reduced-noise and -drag conductor). We also carriedout wind tunnel experiments up to a wind velocity of 80

m/sec using full-scale dimensions 4), clarified the mechanism of drag reduction using a water tunnel 5), 6), and fieldobservations on a full scale, verifying the aerodynamic
characteristics of the reduced-drag conductors.
In addition to the aerodynamic characteristics of the
reduced-drag and reduced-noise and -drag conductors,
this paper reports tests on basic conductor characteristics
and the results of studies on accessories.

2.

STRUCTURE OF A CONDUCTOR WITH
REDUCED DRAG

Table 1 shows the specifications and cross-section of the810-mm2 reduced-drag (LP-810) and reduced-noise and drag (LNP-810) conductors in comparison with those of aconventional conductor. The outermost layer of the LP810 (reduced-drag) conductor is a smooth wire, with 12
grooves at equal intervals around the circumference.
Similarly the LNP-810 (reduced-noise and -drag) conductor has 12 grooves in the smooth outermost layer and 4directional protrusions. Since the LP conductors shown in
Table 1 are designed to virtually the same current capacity as the conventional conductor, they have slightly smaller equivalent diameters.

3.

THE MECHANISM OF DRAG REDUCTION*

Engineering Dept., Electric Power Transmission EngineeringDiv.
*2 Engineering Dept., Bare Wire Div.
*3 The Kansai Electric Power Co., Inc.

To reach a clear understanding of the mechanism of dragreduction, a program of visualization of air flow and dragmeasurement using the water tunnel of the Central

50

Table 1

Characteristics of conductors.
Specification

Characteristic

Unit
Reduced-drag LP-810

Conventional TACSR-810

Reduced-noise & -drag LNP-810

Type of conductor

Tensile load

kN

180.9

184.1

187.2

{kgf}

{18,450}{18,770}{19,090}

mm

38.4

37.2

Protrusions: 38.8
Outer diameter

Declivities: 37.2
Equivalent: 37.9

mm2
Calculated

836.6 (TAL)

814.5 (TAL)

858.3 (TAL)mm256.29 (ST)56.29 (ST)56.29 (ST)mm2870.8 (Total)

892.9 (Total)

914.6 (Total)

Calculated weight

kg/km

2,700

2,761

2,821

Electrical resistanceΩ/km

0.03630.03530.0344

Gpa

71.1

70.9

70.6

{kgf/mm2}{7,250}{7,230}{7,200}Coefficient of linear expansion/°C

20.8×10-6

20.9×10-6

20.9×10-6

Current capacityAcross-sectional area

Modulus of elasticity

1,998 (continuous at 150°C, 60 Hz) 2,003 (continuous at 150°C, 60 Hz) 2,041 (continuous at 150°C, 60 Hz)
2,007 (continuous at 150°C, 50 Hz) 2,011 (continuous at 150°C, 50 Hz) 2,050 (continuous at 150°C, 50 Hz)

Research Institute of Electric Power Industry, together
with oil flow tests using wind tunnel facilities was carriedout to obtain information on the nature of flows over thesurfaces of LP and LNP conductors.
3.1 Conductors with Reduced Wind Drag
Figure 1 shows a visualization, using a water tunnel, offlows over conductor surfaces. In the case of the conventional conductor, separation occurs approximately 100
deg downstream from the upstream stagnation point, irrespective of wind velocity (Figure 1a). In contrast, it can be
confirmed (see Figure 1b) that in the case of the LP conductor, when the drag coefficient is reduced, the separation point of the flow shifts to the downstream side
(approximately 120 deg). This represents a rearward shift
in self-excited vibration in a free-shear layer (or cavity
tone phenomenon), occurring in cavities in the vicinity of
70 deg, by which the after-flow region on the back surfaceof the conductor becomes smaller and drag is reduced.
Even if the conductor is rotated so that the position of thegrooves relative to the flow is changed, the same kind of
phenomenon occurs confirming that for conductors of thisconfiguration, the position of the grooves has no effect.
3.2

Conductors with Reduced Wind Noise and Wind
Drag
When visualized in the water tunnel test, the drag is
reduced as the main flow approaches the conductor due
to the vortexes generated at the protrusions. At thegrooves, in the region where Re exceeds 7.6×104 (windvelocity 30 m/sec) the separation point shifts rearward asa result of a cavity tone in which multiple vibration modes
are superimposed. At the same time, due to the overall

51a) Conventional conductor

Figure 1b) Reduced-drag conductor

Visualization of flows over conductor surfaces atpoint of separation.

turbulence occurring toward the rear side, the mainstream contacts the conductor and drag is reduced.
In oil flow tests using actual conductors, it was also
found that since protrusions and grooves alternate in the
conductor axial direction, a forced separation of the flow
due to protrusions and a rearward shift in the separation
due to the grooves are present alternately along the axisof the conductor.
By these results it was possible to explain the mechanism by which drag was reduced.

4.

FEATURES OF CONDUCTORS WITH
REDUCED WIND DRAG

4.1 Drag Coefficient
4.1.1 Wind Tunnel Facility
The wind tunnel tests were carried out using three facilities: Research Center for Advanced Science andTechnology, University of Tokyo, Canada's National
Research Center, and Furukawa Electric.

Furukawa Review, No. 21

20023-component force detector

Low-Noise Wind Tunnel, Bare Wire Div.,
Furukawa Electric

940 mmWind tunnel outlet aperture size:
1m x 1 m

Wind velocity m/sec
Conductor sample

Sealed measuring section
10-kgf 3-component force gauge

Stable section

Wind tunnel from above

Goettingen-type
wind tunnel

CL direction
Conductor
sampleCY direction(conductor axis)
Cd direction

Direction of air flow

3-component force
detector

Figure 2

A/D converter
board

Adder and calibrator
ch1--ch2--ch3--

Recording of
average values

Schemata of directionsof 3-component
force measurement

Computer

DC amplifier

Layout of test equipment in Furukawa Electric's wind tunnel.

The 3-m diameter Goettingen-type wind tunnel at Tokyo
University's Research Center for Advanced Science andTechnology was used for the investigation of optimum
configurations at the onset of the research, and for tests of
the aerodynamic characteristics of multi-conductor
arrangements for selected prototype reduced-drag configurations. The 2×3-m sealed Goettingen-type wind tunnel
at Canada's NRC in Ottawa was used for aerodynamic
characteristic tests for single conductors (including incident angles other than 90 deg) up to 80 m/sec. Furukawa
Electric's 1×1-m Eiffel type wind tunnel was used for measuring overall aerodynamic coefficients, including suchconditions as rain, turbulence, conductor aging, surface
fouling and so on. Figure 2 shows the layout of the test
equipment in Furukawa Electric's wind tunnel testing facility, in which the measuring section can be either sealed oropen, according to the purpose of the test.
A comparison was made between the drag characteristics obtained at the three facilities, and despite differences
attributable to the procedures and conditions of measurement a high degree of accuracy was confirmed.
4.1.2 Drag Coefficient When Dry(1) Conductors with reduced wind dragFigure 3 shows the relationship between drag coefficientand standard wind velocity at two incident angles (90 deg
and 60 deg) for TACSR-810 and LP-810 conductors. At
wind velocities from about 25 to 60 m/sec, the LP conductor shows a decrease in drag coefficient of approximately
30% compared to the conventional conductor.
Figure 4 shows the relationship between the incident
angle of wind and drag coefficient. The drag coefficient of
the LP-810 conductor, like that the TACSR-810 conductor,

decreases as sin2θ of the incident angle, so design withrespect to oblique winds can be done by the same method
as before.
(2) Conductors with reduced wind noise and wind dragFigure 5 shows the relationship between drag coefficientand standard wind velocity for TACSR-810 and LNP-810
conductors. At wind velocities from 27 about to 40 m/sec,
the LNP conductor shows a decrease in drag coefficient ofapproximately 20% compared to the conventional conductor. Figure 6 shows the relationship between the incident
angle of wind and drag coefficient. Although as a result of
the protruding filament this conductor has an incident
angle vs. drag coefficient curve with a different trend fromthat of the conventional conductor, it is somewhat lower
than that of the conventional conductor even at an angleof 60 deg.

5.

FIELD TESTS

To obtain in-the-field verification of the drag-reduction
effect in LP conductors, conventional and LP conductors
were installed during fiscal 1998 at the Miyakojima Test
Line, an actual-scale facility located in Okinawa
Prefecture, where typhoons are frequent, and the swing
angles of the conductors were compared during the strong
winds that accompany the passage of typhoons.
5.1 Description of the Miyakojima Test Line
This test facility is located on the island of Miyakojima
approximately 150 m from the shoreline, and consists ofthree towers and two spans. Although the terrain aroundthe test line is somewhat hilly along the line, it is flat to

52

1.4

1.4
Wind at 90 deg

1.2

Drag coefficient Cd

1.2

Drag coefficient Cd

Wind at 90 deg

Conventional
Reduced-drag

1.0

0.8

1.0

0.8

0.6

0.6
Wind at 60 deg

Wind at 60 deg

0.4
0

20.0

40.0

60.0

0.4

80.0

0

10.0

Standard wind velocity (m/sec)

Figure 3

Conventional
Reduced-noise & -drag

20.0

30.0

Drag coefficient vs. standard wind velocity for
TACSR-810 and LP-810 conductors.

Figure 5

Drag coefficient vs. standard wind velocity for
TACSR-810 and LNP-810 conductors.

40 m/s

40 m/sConventional

Conventional

1.0

1.0
Design value

Drag coefficient Cd

sin2θ

Drag coefficient Cd

40.0

Standard wind velocity (m/sec)

0.8[ Cd=0.68 ]at 90 deg
0.6

sin2θ

0.8
[ Cd=0.68 ]at 90 deg

0.6
Reduced-noise & -drag

Reduced-drag

0.4

0.4
50.0

60.0

70.0

80.0

90.0

50.0

Incident angle of wind (deg)Figure 4

Incident angle of wind of 40 m/sec vs. drag coefficient for TACSR-810 and LP-810 conductors.

both left and right, so that there are no obstacles to crosswinds that might impede measurement for LP conductors.
The towers are approximately 25 m in height, and the lowest point of the conductors being measured was 14.2 m
above ground (see Figure 7).
Measurements of swing angle were made in the 100-m
span between towers #1 and #2. The conventional and LP
conductors were strung in parallel with a sag of 5 m, andwith no insulators installed.
Generally speaking the static swing angle θ of a transmission line is determined by the mass of the conductor
and the wind load and may be stated as:

θ =tan-1

Wm
Wc

70.0

80.0

90.0

Figure 6

Incident angle of wind of 40 m/sec vs. drag coefficient for TACSR-810 and LNP-810 conductors.

of a target attached to the conductor at mid-point in the
span was found by processing the images obtained by
VCR during high winds, and from this displacement (theobserved swing angle,) the swing angle of the conductor
under static conditions was calculated geometrically. Wind
velocity was measured by a 3-component ultrasonic windgauge and a vane-type wind gauge mounted atop a 16-mhigh concrete tower at the mid-point of the span, datafrom which were subjected to analog-digital conversion at
0.05-sec intervals and recorded by the computer. The
VCR for recording conductor swing was activated whenever wind speed exceeded a set value.

(1)

where:
θ is the swing angle of a transmission line,
Wm is the wind load on the conductor(=1/2 . ρ . V 2 . C d . D . L) (kg/m),
where, in turn:ρ air density (kg . sec2/m4),
V is the wind velocity (m/sec),
Cd is the drag coefficient,
D is conductor diameter (m)L is unit length of conductor (1 m), and
Wc is conductor weight (kg/m)
On the other hand as Figure 8 shows, the displacement

53

60.0

Incident angle of wind (deg)Tower #1

Tower #2
Tower #3

Figure 7

Miyakojima test line.

Furukawa Review, No. 21

200210-min ave. swing angle (deg)Position during swing
Position at rest

TargetSwing angle

Figure 850
Conventional (observed)
Reduced-drag (observed)
Conventional (Cd =1)
Reduced-drag (wind tunnel)

40
30
20
10
0
0

5

10

15

20

25

30

35

40

10-min ave. wind velocity component at 90 deg to line (m/sec)

Schematic showing swing angle of conductor.

Conventional

Reduced-dragWind velocity

0

100

200

300

400

500

110
100
90
80
70
60
50
40
30
20
10
600

50

10-min ave. swing angle (deg)

50
45
40
35
30
25
20
15
10
5
0

Wind velocity (m/s)

Swing angle (deg)Figure 10 Swing angle vs. wind velocity (10-min ave.) for
TACSR-810 and LP-810 conductors.

Time (sec)Figure 9

Conductor swing angle vs. wind velocity for TACSR810 and LP-810 conductors.

Conventional (Cd = 1)
Reduced-noise & -drag (Cd = wind tunnel)
Conventional (observed)
Reduced-noise & -drag (observed)

40

30

20

10

0
0

5

10

15

20

25

30

35

40

10-min ave. wind velocity component at 90 deg to line (m/sec)

5.2 Results of Observations
Figure 9 shows typical time sequence data for wind velocity and the swing angle of the two conductors over a 10min period during Typhoon 10 in 1998. It can be seen that
conductor swing angle closely follows changes in windvelocity.
Figure 10 plots the wind angle against wind velocity
using the averages of several 10-min sets of data during
the passage of Typhoon 10. Also shown are the curves
calculating the respective swing angles taking the dragcoefficient of the conventional conductor as 1 and that of
the LP conductor as the coefficient curve obtained in windtunnel experiments. It can be seen that the plotted points
for the swing angle of the TACSR are in good agreementwith the calculated curve. In the case of the LP conductor,
on the other hand, the plot is in good agreement with thecalculated curve around 30 m/sec, but at lower windvelocities are below the curve. This is thought to bebecause, when an LP conductor is placed in a naturalwind, the effects of turbulence shift the transitional windvelocity to a lower value than that obtained in wind tests.
Figure 11 plots the 10-min average values of swing
angle and wind velocity for TACSR-810 and LNP-810 conductors during the passage of Typhoon 18 of 1999. The
10-min average wind velocity ranged between 15 and 21
m/sec, and the LNP conductor shows good agreementwith the curve for swing angle calculated using the dragcoefficient obtained in the wind tunnel experiments.
Next, to investigate the response of the LP conductor towind gusts, the relationship between wind velocity andswing angle was determined for periods of 4 sec, chosenbecause this represented the period of swing for the conductors strung to this test line, by the following method.
Time sequence data on wind velocity and imageprocessed swing angle (sampling frequency 20 Hz) was

Figure 11 Swing angle vs. wind velocity (10-min ave.) for
TACSR-810 and LNP-810 conductors.

divided up at 4-sec intervals producing 80 sets of data
which were the averaged, yielding 150 average data for 4sec periods in 10 min. These data were then segmented
using breakpoints every 1 m/sec, the average within eachsegment was found and wind velocity was plotted against
swing angle. Figures 12 and 13 show the results of thisprocessing.
As can be seen from the two figures, the 4-sec ave.
wind velocity was from 15 to 40 m/sec, in virtually complete agreement with the curves calculated on the basis of
the drag coefficient obtained in the wind tunnel experiments. Thus it was verified that even under typhoon conditions on the field test line, the LP conductor agreed withthe drag coefficient measured in the wind tunnel experiments.

6.

ENVIRONMENTAL CHARACTERISTICTESTS

Since the outermost layer of the LP conductor is smoothwire, its wind noise characteristics are inferior to those of
the conventional conductor. Accordingly an LNP conductor was developed for use on lines that traverse areas
where wind noise is a concern.
Wind noise characteristics were investigated as theenvironmental characteristics of the LNPconductor. Figure
14 shows the wind noise spectrum in the wind noise test,
and it can be seen that noise from the LNP conductor was
dramatically lower (10 dB(A) or more) than for the conventional conductor.

54

4-sec ave. swing angle
at breakpoints of 1 m/sec (deg)60

8.
Conventional (observed)
Reduced-drag (observed)
Conventional (Cd = 1)
Reduced-drag (wind tunnel)

50
40
30
20
10
0

5

10

15

20

25

30

35

40

45

4-sec ave. wind velocity (m/sec)

Figure 12 Swing angle vs. wind velocity (4-sec ave.) for TACSR810 and LP-810 conductors (16 Oct. 1998 21:58-22:08
hrs).

4-sec ave. swing angle
at breakpoints of 1 m/sec (deg)60
Conventional (observed)
Reduced-noise & -drag (observed)
Conventional (Cd = 1)
Reduced-noise & -drag (wind tunnel)

50
40
30
20
10
0

5

10

15

20

25

30

35

40

45

4-sec ave. wind velocity (m/sec)

Figure 13 Swing angle vs. wind velocity (4-sec ave.) for TACSR810 and LNP-810 conductors (21 Sep. 1999, 00:0200:12 hrs).
80
Conventional
Reduced-noise & -dragBackground noise

Noise level (dB(A))

70
60
50
40
30

CONCLUSION

We have developed a reduced-drag (LP) conductor having reduced conductor wind load and a reduced-noise and-drag (LNP) conductor combining the two functions of conductor wind load reduction and conductor wind noise
reduction, and through a variety of tests have demonstrated its serviceability.
The LP conductor, when used on new power transmission lines, can contribute to savings in construction costs,
and when used to replace existing lines will improve reliability with respect to wind load. They have a number of further advantages. If existing lines are replaced with thosehaving the same maximum tension it will, of course, benecessary to consider decreases in vibration fatigue characteristics resulting from increased ordinary tension, but it
will be possible to string them with a smaller ordinary sag,thus making it possible to reduce sag and increase capacity. We are confident that they will become widely
employed.
In connection with the development of the LP conductor
we would like to express our appreciation to the late
Mitsuda, professor emeritus, and Masaru Matsumoto, professor, of Kyoto University; to Yozo Fujino, professor ofTokyo University; to Sachio Tamura, professor of Tokyo
Institute of Polytechnics; to Yoshirharu Iwatani, professorof Nihon University; and to Hideji Nakamura, associate
vice president at The Abiko Research Laboratory and
Yuzuru Eguchi, researcher, of the Central ResearchInstitute of Electric Power Industry for their guidance andassistance in research on aerodynamic characteristics; to
The Okinawa Electric Power Co., Inc. for their cooperationin field testing; to Asahi Electric Works for their cooperation in research on accessories; and to all others involved.

20
10
0
100

1000

10000

Center frequency of 1/3 octave band (Hz)Figure 14 Wind noise for TACSR-810 and LNP-810 conductors(20 m/sec, single conductor).

7.

CHARACTERISTICS OF ACCESSORIES

Among the accessories considered for the LP conductor
were span-spacers and jumper spacers for multiple conductors, suspension clamps, and dead-end clamps. Thus
since the cross-sections of the LP conductor and LNP
conductor were either round or nearly round (with a protruding filament that was low), the spacer clamp required
no collar or other special structures, and the clamp for theconventional conductor could be adapted by merely
changing the diameter of the hole to fit. Similarly the compression-type dead-end clamp and wedge type dead-end
clamp can engage by the same method as with the conventional conductor, without the use of collars. It has thus
been confirmed that no special structure is required foraccessories for the LP conductor, making it superior to theconventional conductor in terms of construction costs.

55

REFERENCES
1) Japan Electric Association: Research Committee for ElectricTechnology Standards, Regulations for Overhead Power
Transmission, (JEAC 6001-1993) (in Japanese)2) CHENBACH,E.HEINECKE: On vortex shedding from smoothand rough cylinders in the range of Reynolds number 6×103 to
5×106, J. Fluid Mech, vol. 109 (1981)
3) Kimura et al.: Flow around a circular cylinder with circular arc
grooves on the surface, Visualization Information, Vol.10 Suppl.
No.1 (1990-7) (in Japanese)4) Ishikubo et al.: Study on wind-load reduction of overhead transmission lines, Part III, Conference of Electric Power and Energy
Division, IEEJ, No.494, (1997) (in Japanese)
5) Eguchi and Nishihara: Basic study on low wind-load wires -Investigation on the wind load reduction mechanism of wires
through hydrodynamic experiments, Report of CRIEPI, U96516,
March 1997 (in Japanese)
6) Eguchi and Nishihara: Basic study on low wind-load wires -Detailed visualization and theory of the mechanism of wind load
reduction, Report of CRIEPI, U97515, March 1998 (in Japanese)
7) Hiratsuka et al.: Results of field tests on low wind-load wires, Part2, General Conference of IEEJ, No.1623, 1999 (in Japanese)

Manuscript received on November 6, 2001.

Furukawa Review, No. 21

2002