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Narrow Band Dielectric Frequency Response: Theory and Applications

It is imperative that transformers in distribution and transmission substations function properly in order to avoid any damage or unnecessary system outages. There are diagnostic tests recommended in various international standards that can provide early evidence of possible issues within the equipment's overall health. The primary goal is to provide continuous and reliable operation throughout the life expectancy of a transformer, which relies mainly on the condition of the insulation system. Traditional power factor testing is performed at line frequency and is used to assess the condition of an insulation system. However, power factor measurements conducted at line frequency have limitations such as low sensitivity, lack of data, and incorrect temperature correction that can lead to a delayed response to an issue in the insulation system. It is suggested that the test be performed utilizing a narrow frequency band from 1 to 500 Hz. Performing the test using this frequency band offers higher sensitivity, specifically at 1 Hz. This strengthens the ability to trend results and to identify issues in a deteriorating insulation system at an earlier stage. This paper will discuss the theory behind power factor and narrow band dielectric frequency response, as well as discuss recommended applications and include a section for results analysis.