Diagnosis of Inter-Turn Shorts of Loaded Transformer Under Various Load Currents and Power Factors; Impulse Voltage-Based Frequency Response Approach

Inter-turn short circuits within the transformer winding are diagnosable through the impulse voltage based frequency response analysis (IFRA). If the diagnosis is made Online, interruption to the power network can be avoided. However, the transformer's load may influence the frequency response based diagnostic process, and this aspect has not yet been investigated. Motivated by this research gap, experimental investigations were carried out on a three-phase 5 kVA, 440 V/440 V Star/Delta transformer and a three-phase 315 kVA, 11 kV/433 V, Dyn11 distribution transformer, when they were supplying power to loads of different magnitudes and power factors. The influence of the load current and its power factor on the IFRA was observed under the transformer's healthy condition and with inter-turn short circuits in one of the windings. Investigations under these different loaded conditions revealed that a signature FRA plot developed at a particular load condition cannot be directly used for assessing the condition of the transformer at a different load. Both the magnitude and the power factor of the load are found to influence the frequency response. A careful interpretation of the Frequency response of the transformer, based on its load, was found effective in detecting and locating the inter-turn shorts.