Frequency Response Technique to Recognize Turn-to-Turn Insulation Deterioration in Transformer Winding

One of the most important failure issues in transformers is the turn-to-turn short circuit fault. Turn-to-turn fault can be occurred due to the inter-turn paper insulation deterioration, or due to removing thin layer coated insulation between the winding turns. To date, there is no specific pre-determined method to find (or at least suspect) a deteriorated turn-to-turn insulation medium before catastrophic failure. Frequency Response Analysis (FRA) as a method introduced for transformer mechanical defect recognition, may be able to recognize the turn-to-turn fault potential and assist on this case. Hence, this study has concentrated practically on FRA capability to find turn-to-turn insulation degradation as well as inter-turn aging rate. To this end, two different test objects are used and FRA signatures in various conditions are recorded. FRA results are provided and technically discussed.