Search coil based condition monitoring technique for internal faults in converter transformer

This work evaluates the search coil as a magnetic sensor to detect transformer winding faults, through leakage flux monitoring. It is expected that the presence of harmonic contents in valve winding of converter transformer will pose challenge, for condition monitoring techniques. Search coil is technically and economically interesting, as they only require minimal instrumentation resources to practically implement them. Finite Element (FE) based converter transformer model has been developed, with search coils which are sensitive to leakage flux. The voltage induced in search coils were compared in frequency domain for various inter-turn faults and a fault diagnostic algorithm has been developed to localize the fault. Winding leakage flux were recorded using the custom designed search coils and analysed, with an emulated inter-turn fault in a 10 kVA lab-scale converter transformer. Method of emulating the inter-turn fault in transformer model, leakage flux distribution along transformer limbs, search coil design, experimental studies and the results for AC and DC loads are all discussed and presented in this report.