Evaluation of Partial Discharge Signatures Using Inductive Coupling at On-Site Measuring for Instrument Transformers

This paper describes the use of conventional and unconventional partial discharge tests by capacitive and inductive coupling in Instrument Transformers (IT). The objective of this work was to evaluate Phase-Resolveld Partial Discharge (PRPD) signatures features obtained during on-site (online) and laboratory (offline) measurements, by comparing results with state-of-the-art patterns and standard recommendations. The analysis of the results showed that is possible to obtain partial discharge (PD) patterns - corona, background noise, internal PD, free potential and surface PD - at on-site measurements but those are compromised by the pulse attenuation, difficulties in performing measuring system calibration and the absence of reference voltage. Suitable range of on-site measuring was above 1 MHz up to 5 MHz. The results reached in on-site measuring can be used as image preprocessing methodology to perform automatic pattern recognition of partial discharge signature. It is also described the parameterization of the HFCT for different frequency filter values though carrying out HFCT parameterization for different types of high voltage equipment was not objective of this work.