Study On Vibration Signal Analysis Method Of Amorphous Alloy Drytype Transformer Under Mechanical Fault State

Amorphous metal distribution transformer（AMDT）is a new type of energy saving transformer,and its no-load loss is only one fourth of that of ordinary silicon-steel transformer.Therefore,it is widely used in distribution network,especially in rural power network.However,AMDT is prone to faults during its operation,so it is necessary to adopt on-line fault diagnosis measures to ensure the normal operation of AMDT.In this paper,the SCBH15-200/10 amorphous alloy dry-type transformer was taken as the research object.Firstly,the finite element analysis（FEA）simulation was used to carry out modal simulation calculation and analysis on the transformer model,and then the transformer operating state for three different mechanical faults was analyzed through experiments.Finally,the fault state information of the transformer is decompose and diagnosed using wavelet packet transform（WPT）.The main research contents of this paper are as follows:（1）The simulation calculation model of amorphous alloy dry-type transformer is established.The three-phase core model of amorphous alloy dry-type transformer is established.The magnetic flux density distribution,modal analysis and harmonious response analysis of the three-phase core are carried out by FEA software.It can be concluded that the magnetic flux density of the inner chamfering of the three-phase core,B-phase core column and the upper yoke are higher through analysis,and the maximum value of the magnetic flux density is 1.41 T.The vibration of three-phase core is mainly concentrated on the upper yoke based on the modal analysis of three-phase core.The analysis of three-phase core harmonic response mainly focuses on three frequencies of210 Hz,470 Hz and 510 Hz.In these frequency bands,the core is easy to produce resonance.（2）The vibration test platform of amorphous alloy dry-type transformer was built,and vibration sensors were arranged in different areas of the transformer body to obtain the vibration signals on different parts of transformer.The largest vibration area of transformer surface is the upper clamp of transformer through the analysis of frequency-domain signal of transformer vibration.The vibration of upper yoke on the transformer core is transmitted to the upper clamp through air,so the vibration of the upper clamp is the largest among the transformer clamps,and its maximum vibration amplitude is at 300 Hz.（3）The mechanical fault states of amorphous alloy dry-type transformers were studied:nut loosening,the application of pressing stress and nut loosening combined with compression force applied.The maximum vibration amplitude and noise pressure of the transformer are increasing when the number of loosening of the upper clamp nut is increasing.When the clamping stress applied by the upper clamp increases,the maximum vibration amplitude and noise pressure of the transformer first decrease and then increase.When the nut of the upper clamp is loosened and the compression force is increased,the maximum vibration amplitude and sound pressure level of the transformer decrease.（4）Three-layer WPT is used to decompose and reconstruct the vibration signals of the transformer,and the energy eigenvalues of each frequency component was extracted.The variation trend of energy eigenvalue E₃₀of vibration signals in the above three different mechanical fault states is similar to the variation trend of maximum vibration amplitude and noise value.It can be judged that the transformer is in fault state by comparing the energy eigenvalue threshold of the transformer in normal no-load operation with the energy eigenvalue in different mechanical fault states.