Many utilities worldwide have established maintenance programs based on periodic PD testing and monitoring of their power transformer fleets since PD is a reliable indication of aging and developing faults in the insulation. Corrective actions can be taken before a developing fault eventually causes the asset to fail. PD testing, inspection, and repair of a 100 MVA transformer I am the Chief Engineer responsible for field test evaluation and test method development at TEIAS Turkish Electricity Transmission Corp. My team and I have developed a holistic approach to condition assessments and a solid maintenance plan for our grid assets, particularly power transformers. If potential faults are detected in the field, the transformers are taken out of service and sent to our central workshop facility in Ankara, Türkiye. Medium and large power transformers are tested and diagnosed in our workshop’s HV lab to determine if repairs and refurbishments are needed to return the transformers to reliable service. In one case, our test engineers investigated a 154/31.5 kV (100 MVA) 3-phase power transformer, which has been in service since 1996. A DGA analysis initially performed on the transformer in the field displayed a continuous increase of hydrogen (H2) and methane (CH4) gasses, which indicate potential PD activity and damage to the insulation in the transformer. Due to these increasing gas levels, we removed the transformer from the grid and sent it to our central workshop for further inspection and repair. Different 3PARD diagrams were obtained that indicated various potential PD sources. 3PARD diagrams showing the possibility of voids in the insulation material before and after the vacuum was applied. According to CIGRE 676, this PRPD pattern is very close to the one related to voids in glue. Traces of carbonization were found on various components. 24
RkJQdWJsaXNoZXIy NTkxNzY=