Presented by Shah Farhang & Charles Nybeck, Megger

Power transformers play an essential role in the transmission of electrical energy. Most of these transformers have been in operation for decades. Even with proper maintenance, the insulation will degrade over time. However, the older models tend to be of higher quality and more robustly designed, making them more valuable to keep in service. In addition to periodic maintenance, monitoring the insulation of power transformers is a key factor in increasing the reliability of the entire grid. PD monitoring and oil condition monitoring by way of dissolved gas analysis, or DGA, are two common methods used to assess the health of transformer insulation. This presentation will compare the standard offline tests recommended by NETA with these two online monitoring methods to demonstrate how online monitoring methods can improve the reliability and life of transformers. In addition to the comparison, this presentation will explain each method and how they addresses issues in the early stages of transformers. Each method has its advantages and disadvantages. While the industry still relies on offline test results, online monitoring influences the frequency of maintenance tests (see Appendix B, NETA MTS). If online monitoring indicates developing defects, an offline test should be conducted sooner rather than later. Moreover, the details provided via online monitoring will improve the efficiency of offline testing. The presentation will briefly explain the DGA and PD monitoring and expectations from these monitoring techniques then correlate the results to the offline test recommended by NETA.