A diagnosis model and a diagnosis method for looseness fault of transformer winding are proposed based on the surface vibration signal of the transformer in operation. Firstly

the relationship between the amplitude of the winding vibration and the current

the preload

the vibration of the iron core and the nonlinear factor is analyzed. And the characteristic frequency of the 100 Hz is determined. Then the method for separating winding vibration amplitude and vibration amplitude of iron core is proposed. A diagnosis model of winding and the average safety allowance based on the model are proposed. The average safety allowance is calculated using the amplitude of the windings detected in a set of load current to determine the state of the winding. Finite element simulation and experiment are used to test the diagnosis model and method. Experimental results show there is a loosening fault when the average safety allowance is beyond the range. The farther away the allowance is from 1

the greater the degree of loosening. The method solves two problems of the transformer in operation: the problem of the transformer at the same fundamental frequency and vector superposition of the winding and the iron core's vibration in actual operation; the load and the current changes

the problem of accuracy being limited is judged only by the amplitude of a current

which is easy to do thanks to quantification of the degree of looseness.