Hydrophobicity evaluation of silicone rubber insulator using DC discharge induced acoustic wave

In HVDC transmission lines, corona discharge could occur even on well-designed hardware and insulators, which can significantly damage the polymeric insulators. Under dc voltage, compared with ac voltage, the electrostatic force due to the constant electrostatic field makes more ions bump against the insulator surface. Due to these influence, the decrease even the loss of hydrophobicity will take place, which may cause flashover to affect operating reliability of power system. Much attention has been paid on the accurate evaluation for the insulator hydrophobicity. In this paper, the acoustic characteristics of surface discharge, based on the static droplet test (SDT) and the dynamic droplet test (DDT), were investigated to evaluate the hydrophobic properties of silicone rubber (SiR) insulator at different ageing degrees. The specimens were prepared by dc corona degradation. The acoustic signal of surface discharge was captured through applying using an acoustic sensor above the specimen surface. In order to quantify the acoustic signals, statistic methods were employed to establish the relationship between the pattern characteristic of signal waveforms and the hydrophobicity condition. The relationship among the flashover voltage, the signal power, the pulse number, and the corona degradation time was obtained via the static droplet test. For the dynamic droplet test, it is found that the pulse number, the voltage range, the maximum slope and the signal energy present an obvious tendency with the hydrophobicity deterioration or loss. Weibull distribution parameter (β) of the data distribution reflects the difference of specimen surface hydrophobicity. Therefore, the obtained results indicate that the acoustic characteristic of discharge is sensitive to the hydrophobic properties in the laboratory tests, which can be applied as a non-contact method for hydrophobicity evaluation of SiR insulator under dc voltage in the future.