Simulating the vibration increase of the transformer iron core due to the DC bias

Transformers in the power systems are sometimes influenced by the DC bias and produce abnormal vibration or noise. This paper presents a method to simulate the transformer vibration increase due to the DC bias. A three-dimensional finite element model coupling the circuit - magnetic field - mechanical field is established for the simulating. Firstly, the 3D magnetic field in the iron core is calculated through combing the circuit equation and magnetic field equation. Secondly, the magnetostrictive force derived from the magnetic field is used to establish the transient structural force field model, so that the vibration displacement can be calculated. Based on the method, the vibration at different positions of the transformer iron core with different DC bias is investigated. The simulation shows that the vibration of the iron core is quite sensitive to the DC bias. The vibration amplitude significantly increases and the vibration waveform becomes asymmetrical and sharp with the increase of DC current. The odd frequency component, represented by 50 Hz and 150 Hz, appears and grows faster than the 100 Hz and 200 Hz component. The model and the simulation results can be used to guide the structural designing of transformers and promote the fault diagnosis method of transformers based on the vibration signal monitoring.