IEEE Std 2652:2021 pdf free download – IEEE Guide for DC Inclined PlaneTracking and Erosion Test forOutdoor Insulation Applications
5.2.1 Electrowetting
During the initial stages of the test and prior to the dry-band formation, the applied voltage causes electrostaticforces at the interface between the liquid-contaminant and the tested surface. With high voltages applied, theseelectrostatic forces overcome capillary forces, causing the expulsion of the droplets from the contaminantrivulet. This expulsion,which has been shown to be dependent on the voltage type and polarity, reduces thevolume of the contaminant rivulet,thus its conductance(Cherney, et al. [B2]). Since the magnitude of the dry-band arcing current and thus the impinged power on the surface is limited by the conductance of the liquid-contaminant, electrowetting of the liquid-contaminant has a consequent biasing effect on the severity of thedry-band arcing on the tested surface depending on the voltage type and polarity. Therefore, the level of theapplied voltages needs to be modified as discussed in 6.2 in order to help ensure that such a biasing effect iseliminated.
5.2.2 Polarity effect
Generally, it is recommended to use new electrodes with each new ac test; therefore, it is valid to have the samerecommendation applied for the dc test. Extensive corrosion has been reported for the upper electrode underpositive polarity of dc voltages, and remarkable oxidation was reported for the bottom electrode.However,experimental studies have not reported electrode corrosion or oxidation as a governing factor altering theoutcomes of the inclined plane tracking and erosion test(Ghunem, Jayaram, and Cherney [B3), thus thiseffect has not been considered in the development of effective de voltage levels for the test (Cherney, et al.[B2]).Further investigation on this effect is useful in order to confirm whether or not this corrosion has asignificant biasing effect on the inclined plane tracking and erosion test outcomes under dc voltages(Cherney,et al.[B2]).
6. Aspects of the dc inclined plane tracking and erosion test
Bias outcomes may be produced when the dc voltage in the inclined plane racking and erosion test is set equalto the corresponding standard root mean square ac (ACrms)voltage.Therefore, the dc inclined plane trackingand erosion test must be conducted with effective de voltages(Cherney, et al.[B2]).Constructing a completelynew test with a new concept, setup, and circuitry could be a valid alternative in order to eliminate any potentialbiasing influential factors under dc.However, developing such a new test may require a rigorous and lengthyprocess, and the inclined plane tracking and erosion test has already been widely accepted among industryand academia.Applying the proper value of dc voltage could further enhance the practical usefulness of theinclined plane tracking and erosion test that is now widely accepted among industry and academia.
Different approaches have been taken in using the inclined plane tracking and erosion test under dc voltages.Many of these approaches are linked to the electrical performance of outdoor insulators in dc as compared toac. For example, it has been proposed for the inclined plane tracking and erosion test to set the ratio of the dcvoltage to the corresponding ACrms voltage to the same ratio as the respective flashover voltages. Althoughthis approach has a practical merit, it does not take into consideration that the inclined plane tracking anderosion test is a laboratory test that is not designed to account for the difference in material surface properties,i.e., hydrophobicity.Although the outcomes of the ac inclined plane tracking and erosion test have been shownto well correlate with field experience, the test conditions are far from resembling actual field conditions. Thisguide describes the three main aspects of the dc inclined plane tracking and erosion test as follows