Abstract: In order to diagnose and locate the core loose failure of oil-immersed power transformer, this paper studies the vibration signals measured on the surface of the transformer tank. Firstly, the characteristics of vibration signals with different locations of the tank surface is theoretically analyzed under the condition of no-load operation of transformers and the variation of the vibration signals of the transformer tank surface before and after core loosening is discussed. And then experiment on an oil-immersed transformer is carried out and the variation of characteristic frequency of the vibration signals before and after core loosening is analyzed. Experimental results show that the value of fundamental component amplitude of the vibration signal is in linear with the value of the square of no-load voltage. When one phase core of the three phases A, B, C loosens, the fundamental frequency component amplitude of the vibration signal increases with the degree of core loosening of the corresponding position measuring point above the phase iron core. And the vibration amplitude of the other two points firstly decreases and then increases. The core loose fault can be diagnosed and located according to this principle.

Key words: transformer, core loosening, fuel tank vibration, fault location, fault diagnosis, transformer experiment