Principal Research Results

Reduction Method of Audible Noise from HVAC Transmission Lines− Development of Weatherproof Low-Noise Spiral Wires−
BackgroundTwo types of sound noise are sometimes generated from high-voltage AC overhead transmission lines. One is “audiblenoise” caused by corona discharge; the other is “aeolian noise” that is generated under strong-wind conditions. Thin spiral wires aretwisted around the conductor of HVAC transmission lines to reduce aeolian noise. The spiral wire easily accumulates rainwater, therefore the overhead transmission line with spiral wires have many waterdrops that become the source of corona discharge in rainy conditions. At CRIEPI, it was clarified that a super-hydrophilic spiral wire produced by plasma thermal spraying of TiO2 could reduce
audible noise, because it had characteristics that caused water to be quickly exhausted. However, it was also clarified that the superhydrophilic spiral wire with an aluminum substrate is easily deteriorated.

Objectives
The purpose of this study is to develop a weatherproof spiral wire that decreases both audible noise and aeolian noise(hereafter, low-noise spiral wire).

Principal Results
1. Audible noise reduction effect of low-noise spiral wires
It was clarified that the level of audible noise from low-noise spiral wires was lower than that from conventional spiral wires
on the basis of full-scale corona examinations with artificial rain. The audible noise reduction effect of the low-noise spiral wire wasexcellent particularly for hum noise, which is less than that in not only conventional spiral wires but also in conductors that were nottwisted with spiral wire (refer to Fig. 1).
2. Selection of substrate material and mechanical characteristics of prototype spiral wire
A low-noise spiral wire was made of a light titanium pipe to achieve weatherproof characteristics. The spiral wire hasmechanical characteristics similar to those of the conventional spiral wire made of aluminum (refer to Table 1).
3. Evaluation of weatherproof characteristic by atmospheric corrosion test
Two types of low-noise spiral wire, made of a conventional aluminum rod and a titanium pipe produced by plasma thermal
spraying TiO2, were exposed outdoors for 234 days (refer to Fig. 2). The aluminum substrate and nickel intermediate were eluted on tothe surface of the exposed low-noise spiral wire made of aluminum. However, there was no change in the surface of the exposed lownoise spiral wire made of titanium (refer to Fig. 3). Thus, a weatherproof spiral wire can be realized by using a titanium pipe as thesubstrate of spiral wires.
Main Researcher: Kiyotomi Miyajima,
Research Scientist, High Voltages & Electromagnetic Environment Sector, Electric Power Engineering Research Laboratory
Reference
K. Miyajima, et.al., 2008, “Development of Low-noise Spiral-Wires for HVAC Transmission Lines and Evaluation of Weather-Proof
Characteristics”, CRIEPI Report H07007 (in Japanese)784. Power Delivery

Hum noise level [dB(A)]60

Conventional spiral wire (A)Conventional spiral wire (B)No spiral wire
Low-noise spiral wire

50
4030
20
10101112131415
1617Maximum surface gradient of the conductor [kV/cm]

18

Above 10dB, the hum noiselevel of the low-noise spiralwire is lower than those of thetwo types of conventional
spiral wires. (When four
conductor bundles ofACSR410mm2 are used as
500kV HVAC overheadtransmission lines, the typicalmaximum surface gradient ofthe conductor level is about
15kV/cm.)Fig.1 C omparison of hum noise level

Table 1 Mechanical characteristics of prototype spiral wire
Substratematerial
Aluminum(Conventional)

Length[mm]Diameter[mm]

Thickness[mm]

Weight[g]

Remarks

2554

6

Solid

206

-Titanium

1834

61138

Good
construction

4Low-noise spiral wire
Conductor(aluminum)Fig.2 Low-noise spiral wire on titanium substrate

Fig.3 Proportions of component elements of surface(obtained using energy dispersive X-ray spectrometer)

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