Simulative and experimental investigation of transfer function of inter-turn faults in transformer windings

• Presentation of an improved lumped circuit model of transformer windings.
• Simulation and experiments of inter-turn faults in varying degree.
• Interpretation of transfer function variations caused by the inter-turn fault.
• Investigation on the sensitivity of transfer function method to the fault.

The transfer function (TF) method is a powerful tool to detect inter-turn faults. Correct interpretation of the TF variations is significant to distinguish the inter-turn faults from less urgency defects. This paper investigates transfer functions of inter-turn faults in transformer windings using simulative and experimental approach. An improved lumped circuit (ILC) model was developed to investigate the detailed energy transmission mode between adjacent turns. Actual experiments of inter-turn faults in different levels were carried out on a purpose-made winding by shorting the adjacent turns with different value resistors to verify the simulative results. Simulative and experimental results show the same characteristics of TF variations. The resonance frequency increases with rising transmission energy in shorting resistance. The amplitudes of resonance frequency vary in a U-shaped trend, which is determined by the energy consumed in the shorting resistance.