above the floor. This arrangement corresponded to an average rain intensity of 3.5 mm / h upon the conductor, i. e. corresponding to light summer rain but higher than IEC standard rain. Tests were performed under both dry and rain conditions at representative maximum voltage gradients of 12, 14, 16, 18 and 20 kV rms / cm, by adjusting test voltage. The test involved: measurement of dry background noise( reference spectrum), application and stepwise increase of voltage with noise measurement at each voltage level, application of rain and measurement of noise at each voltage level, and finally, switch off and measurement of wet( rain) background noise level.
Set-up for 1000 h salt fog tracking and erosion test.
For tests under rain, the performance of all types of conductors was found similar( excluding the short acid treated conductor, because of its different length). Influence of different background levels is taken out through subtraction. Excluding the short acid treated conductor, it is clear that the super-hydrophobic conductor performs similarly to the average conductor.
One possible explanation is the appearance of water drops on the energized conductor. Photos were taken in conjunction with AN measurements and it is clear that water was present only on the top surface( in the case of hydrophilic conductors water drops normally collect on the bottom surface). Moreover, the influence of electric field can be seen as drops extend in a radial direction( and even‘ explode’) as voltage increases from level E1 to E2. Of course, it would be desirable to repeat similar tests on a test span in the field under natural wetting conditions; however early indications are that, due to its super-hydrophobic properties, the coating might behave similarly to standard conductors( which is basically different to the comparison of normal hydrophobic / hydrophilic conductors referred to earlier).
Photograph to rank visual impact of different conductors.
Typical image of tower with three different insulators( coatings) and three different backgrounds used for automatic image analysis( taken at test site).
Photos courtesy of STRI
C. Low Ageing The goal here was to study long-term performance of conductors with a super-hydrophobic coating using the 1000 h salt fog test( IEC 62217), prescribed as a typical tracking and erosion test for composite insulators.
A super-hydrophobic and an RTV coated conductor were tested in a moisture-sealed corrosion-proof chamber with 45 m ³ volume. The two conductors were mounted using composite line insulators hanging from the roof and tested at elevated voltage to ensure corona activity on the surfaces.
From a degradation point of view, the two coatings passed the 1000 h test and remained properly adhered to conductors. The super-hydrophobic
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