An investigation on the relation between PRPD patterns acquired by conventional and UHF nonconventional PD measuring technique for power transformers

Summary

Partial discharge (PD) signal propagation in the ultrahigh frequency (UHF) range is one of the aspects that can be used to characterize PD inside high voltage equipment. The UHF PD measuring technique has some advantages in comparison to the conventional method according to IEC 60270 including the possibility of online application, localization and improved immunity against external noises. Phase resolved partial discharge (PRPD) patterns method, in which the PD pulses are displayed with respect to the phase of power frequency of the AC cycle is a widely used and effective technique to analyze the PD data. Based on the phase and charge magnitude of PD occurrences, a pattern is obtained, which, according to theory, can be used to distinguish the types of PD. However, practical experiences, especially for onsite measurements, indicate, that the PRPD pattern technique is not always successful in identifying the cause of PD, particularly in case of using nonconventional PD measuring techniques, such as the UHF method. In this contribution, the alternative approach of applying the PRPD technique to the captured UHF signals generated by PD in order to obtain an UHF PRPD pattern as a complementary PD cause analysis is investigated. For this purpose, different fault scenarios were created inside a specially designed transformer tank. The UHF signals were captured via different antennas using several measuring setups to determine how the position and the surrounding material of the PD source affects the sensitivity of the UHF measuring technique using a PD fault model with a constant electric PRPD pattern. Furthermore, the correlation between the captured PRPD patterns using the electrical measurement according to IEC 60270 and the UHF measuring technique were analyzed and compared. Finally, the results are presented and the advantages and flaws of the PD cause identification via the UHF PRPD technique are discussed.

Additional informations

Keywords

UHF Measuring Technique, Phase Resolved Partial Discharge, UHF PD, IEC60270, Power Transformer