Understanding Power Transformer Frequency Response Analysis Signatures

The majority of transformers currently in service worldwide were installed prior to 1980, and consequently most of them are approaching or have already exceeded their design lifetimes [1], [2]. This poses a significant risk for utilities and other power network stakeholders, since the impact of in-service transformer failure can be catastrophic. One of the most serious problems with an in-service transformer is movement of its windings due to electromagnetic forces generated during short-circuit faults. Reduction of clamping pressure due to insulation aging can also cause winding movement and may result in an explosion [3]¿[6]. There are many causes of mechanical faults, e.g., earthquake, explosion of combustible gas in the transformer oil, short-circuit currents, and careless transportation [7], [8]. While a transformer with minor winding deformation may continue to work satisfactorily, its capability to withstand further mechanical or electrical faults will gradually decrease [9]. Therefore it is essential to detect any minor winding deformation as soon as possible and to take appropriate remedial action. Winding deformation has various forms, e.g., spiral tightening, conductor tilting, radial/hoop buckling, shorted or open turns, loosened clamping structures, axial displacement, core movement, and collapse of the winding end supports. It is difficult to differentiate between these internal faults using conventional testing methods [10]. © 2006 IEEE.