Conference Agenda

Subsea cable connectors are critical components of offshore power delivery systems. The current-carrying components of these connectors are typically enclosed in solid insulation and protected by a liquid-filled diaphragm. Even though liquid dielectrics make pins and sockets more watertight and seal them from seawater, this solid-liquid interface may also be vulnerable to creepage discharges, which, by propagating over the solid insulator surface, can lead to flashover. It is therefore critical to understand the characteristics of these discharges, as well as their morphological evolution over time under sustained electrical stress. This could result in a better reference for the design and production of underwater cable connectors.

To investigate creepage discharges, a needle-to-plane electrode arrangement was adopted, and the gap distance was set at 25 mm. The sample under investigation consists of a block of Polyetheretherketone (PEEK) immersed in a synthetic ester liquid inside a 1.2 L polycarbonate test cell. The AC stress is ramped up to 30 kV at 1 kV/s and sustained for approximately 4 hours. In addition to recording PD apparent charges throughout the process, a camera captures surface tracking on the PEEK surface. Based on the results, phase resolved partial discharge patterns (PRPD) are analysed as well as PD magnitude and length of the tree growth over time.

PD magnitude and time were found to be related, indicating that the whole process can be divided into two phases. In the first stage, recordings were made above 3000 pC with a low repetition rate. At this stage of initiation, no trees were observed on the sample and the PRPD pattern was similar to that of an open liquid gap. This indicates that discharge in liquids was the primary cause of PDs. The second stage took place after approximately 65 minutes. During this propagation stage, PD magnitude abruptly decreased while tree length increased. In this phase, the number of PDs increased and the PRPD pattern changed into a turtle-like shape, with many PDs occurring at zero crossings, indicating accumulation of space charge on the PEEK surface. The final length of the tree was estimated at 14.3 mm, more than half the gap distance

This paper is about Partial Discharge (PD) measurement techniques for detecting insulation defects in oil-filled 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.