Partial Discharge Measurement Experiences on Field Maintenance and in Workshop Fault Investigations of Power Transformers and Shunt Reactors - Case Studies

This paper is about Partial Discharge (PD) measurement techniques for detecting insulation defects in oilfilled power transformers and reactors. Despite well-designed and properly dried insulation systems, discharges can occur due to defects such as moisture, voids, bubbles, delaminations, free or fixed particles and poor connections. The study examines both conventional (IEC 60270) and unconventional (UHF) PD detection methods, highlighting their effectiveness in identifying and localizing defects in laboratory and field conditions. However, challenges arise in interpreting results due to multiple PD sources and environmental noise. Recent advancements, particularly tools like 3PARD, have significantly improved the diagnostic capabilities for identifying PD sources. By using these tools alongside UHF and electrical PD tests, detailed analyses of measurement results can be conducted. The paper presents seven case studies that illustrate the application of these techniques in both field and laboratory settings. Results from these studies reveal various suspicious PRPD patterns, with many PD sources successfully identified using 3PARD. Subsequent visual inspections of the transformers and reactors confirmed serious insulation damages consistent with the observed PD patterns. This correlations between PD measurements and actual physical damages underscores the reliability of these diagnostic methods. Overall, the findings demonstrate that PD diagnostics are effective for identifying insulation faults, emphasizing the importance of ongoing monitoring and maintenance. The ability to clearly match PD patterns with visualized damage validates the robustness of these diagnostic tests in ensuring the reliability and longevity of power transformers and reactors. The paper ultimately highlights the critical role of advanced PD measurement techniques in enhancing the maintenance and operational integrity of electrical insulation systems.