Influence factor on sweep frequency impedance to detect winding deformation within power transformer

As the heart of a power system, the safe running of a power transformer is important. The rate of transformer failures caused by the winding deformation remains high, therefore the study on detecting the transformer winding deformation is of great significance to avoid unexpected failures and improve the reliability of the operation in power systems. To detect the winding deformation within a power transformer effectively, people develop lots of non-destructive methods, such as frequency response analysis (FRA), short circuit impedance (SCI), sweep frequency impedance (SFI), low voltage impulse (LVI), and so on. As a novel detection technique, the SFI method is widely used for onsite tests due to its anti-jamming ability and definite standard code, but its characteristics still need be studied further. In this paper, a fast, economical, and nondestructive testing system was established to study influence factors, which included the length of the grounding line and the inside short circuit line, on SFI method during detecting winding deformation within a power transformer. The experimental results show that: 1) the longitudinal change of the short circuit line between two disks affect the tendency of the SFI curve at medium frequency band during simulating a short circuit fault within a power transformer. 2) the change of the grounding line length leads to the change of the SFI curve at high frequencies, which results in the misjudgment of the transformer winding deformation.