An Attempt to Identify the Faulty Phase in Three-Phase Transformer Windings Using an Advanced FRA Measurement Technique

Although FRA method is very popular and well-known for its accuracy in fault-detection in three-phase transformer, it has not become an adept so far in fault localization. Fault-localization in transformer winding is undoubtedly an important aspect in fault diagnosis and providing a solution to any extent for this problem would be certainly a worthwhile contribution. Towards this approach, even identifying the faulty winding could be a substantial contribution to enhance the diagnostic performance of FRA method. To this context, this paper presents an innovative FRA measurement technique to identify the faulty phase (whether the middle or either of the two outer phases) in 'delta-connected' HV windings. Proposed technique imposes an apparent 'second-delta' from the terminals together with the presence of original 'delta' inside and measures the two desired output current responses simultaneously for an excitation to the middle phase. A mere observation of symmetry or asymmetry between the two responses determines whether the fault exists in the middle phase or in any of the two outer phase windings. Proposed technique is first evaluated by the simulation results followed by experimental measurements on actual three-phase transformer windings. Results reported in this paper are also found very promising and encouraging.