UHF characteristics of silent discharges

Summary

Power Transformers are one of the main assets in power transmission and distribution systems. Partial discharges (PD) are known as one of the early sources of insulation failures in power transformers. Therefore, PD measurements are used as the main quality assessment of power transformers. Localization of PDs could reduce the maintenance cost intensely. Due to some limitation in localization via electrical methods, other PD detection such as ultra-high frequency (UHF) and acoustical methods became more favourable due its immunity against noises. In recent years numerous investigations have been done to prove the reliability of these methods. Previous investigations show the possibility of silent discharges in insulation materials. Silent discharges are a special kind of PD, which happens in high voltage insulation components and despite of their electric signals no detectable acoustic signals were measured with the acoustical sensors. Therefore silent discharges could cause uncertainty in terms of localization and monitoring via acoustical methods. In this contribution UHF characteristics of silent discharges were discussed, produced in a needle-plane configuration. PD-signals were captured electrically together with acoustic emission (AE) and UHF sensors simultaneously. Due to the significant differences between frequency and speed of AE signals compared to the electric and UHF signals, different devices have been used to evaluate this correlation at different time scales. The used piezoelectric AE sensors has resonant frequencies in the range of 30 kHz up to 400 kHz with peak frequencies of 75 kHz and 150 kHz. The relation of electric and UHF signals of silent discharge was investigated. Advantages and disadvantages of UHF method versus acoustical method are discussed. The results could be helpful to develop a combined UHF/acoustical PD localisation method, which uses advantages of both methods.

Additional informations

Authors

H. SAADATI, P. WERLE, E. GOCKENBACH, H. BORSI

Keywords

UHF, Silent PD, Partial Discharge, Acoustic Emission