Feasibility Study on Simultaneous Detection of Partial Discharge and Axial Displacement of HV Transformer Winding Using Electromagnetic Waves

Recently, axial displacement detection of transformer winding has been performed using synthetic-aperture radar (SAR) imaging, as an online method, in ultra-wideband frequency band. Another important problem in power transformers is partial discharge (PD), which emits signal in the ultra-high-frequency (UHF) frequency band. If detection of axial displacement using SAR imaging can be applied to the UHF band, both defects can be detected using only one set of antennas and application of these methods can be more economic. However, as shown in this paper, using the same frequency band for detection of both defects leads to wrong conclusions about winding conditions, if PD is occurred during the application of SAR imaging. As a solution, UHF stepped-frequency imaging method and generalized likelihood ratio test method are proposed for detection of axial displacement. Finally, on a three-phase real transformer both defects are simultaneously detected using designed monitoring system.