Magazine | Issue 1 2024 developing faults using electrical testing, monitoring, and a direct visual inspection inside the transformer. Advanced electrical testing and diagnostic tools, such as Dielectric Frequency Response (DFR) testing, Sweep Frequency Response Analysis (SFRA) testing, and Partial Discharge (PD) testing and monitoring, are now widely used to assess and diagnose the insulation condition of power transformers by detecting certain faults that conventional testing methods are unable to detect. In this article, we will focus on PD testing and monitoring. Partial discharge testing on power transformers According to the IEC 60270 standard, a PD is a localized dielectric breakdown of a small portion of a solid or liquid electrical insulation system under high-voltage stress. PD is a reliable indication and an accelerator of fault development in electrical asset insulation. This is why PD measurement and monitoring play an important role in assessing insulation condition to maintain the health and reliability of electrical equipment, such as power transformers. PD measurements on power transformers are initially performed at the factory as a quality control tool to assess transformer insulation condition according to specified acceptance criteria. During commissioning, PD measurements are performed to check the power transformers’ installation condition after transport. During the power transformer’s service life, PD measurements and monitoring are regularly performed for troubleshooting to detect and localize potential faults. Increasing hydrogen (H2) levels were indicated after performing a DGA analysis on a 154/31.5 kV (100 MVA) 3-phase power transformer. «After we opened the transformer for visual inspection, it became clear that our assumptions based on the PD test results were correct.» Mükremin Yanan, Chief Engineer, TEİAŞ Turkish Electricity Transmission Corp. CO 0 20 40 60 80 100 % H2 CH4 C2H6 C2H4 C2H2 PD T1 T2 20 40 60 80 80 60 40 20 20 40 60 80 T3 D2 D1 DT % CH % C H % C H C H C H C H CH H PD S D1 D2 T2 T3 T1 D1 Discharges of low energy D2 Discharges of high energy DT Mixed thermal and discharge faults PD Partial discharges S Stray gasses T1 Thermal faults (<300 °C / < 572 °F) T2 Thermal faults (300–700 °C / 572–1,292 °F) T3 Thermal faults (>700 °C / >1,292 °F) 23
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