Condition assessment of Oil-filled Rectifier Transformers in a Smelter Plant by On-line Acoustic Emission Technique – Case studies

DC current of high magnitudes in the range of 30kA to 120kA are being used in the electrolytic process in aluminium smelting plants. These high currents are generated with the help of rectifier modules with oil filled high voltage-high current rectifier transformers in tandem with high voltage - high power regulating transformers. High current rectifier modules with the oil filled rectifier transformers form an important link in the aluminium smelting process. Need exists to know the condition of these rectifier transformers in order to maintain continuous and uninterrupted currents to the smelting process. Condition of rectifier transformers of 83.3MVA, 89.7kV/887V(Y)-897V(Δ),3ph, OFAF are considered for the case studies. On-line acoustic emission (AE) technique is employed to ascertain the condition of 8 numbers of rectifier transformers operating in one of the oldest smelter plant. On-line AE technique is used for detection of partial discharges and hotspots within the insulation system of the rectifier transformers. Analysis of the AE signals captured from the identical rectifier transformers at different DC currents of magnitude of 40kA and 60kA and comparison of the relative performance are discussed along with DGA of the oil of the rectifier transformers.