The harmonic current and vibration of a converter transformer are effective pieces of information for detecting mechanical faults in the winding. In this paper

the ratio of vibration acceleration to the current squared is defined as the vibration frequency response function (VFRF) of the winding

and then

a novel online vibration frequency response analysis (VFRA) method is constructed. A harmonic load platform is built to simulate the real operating environment of the converter transformer

and it is verified by experimental methods that online VFRA is a simpler and more convenient method for winding mechanical condition detection than offline VFRA. The effects of different factors such as current magnitude and harmonic content on the online VFRA are investigated

and the converter transformer winding mechanical condition is detected by combining the VFRF trace with two numerical indices of Lin's concordance coefficient (LCC) and improved comparative standard deviation (CSD). Laboratory experiments demonstrate that online VFRA has high stability and can effectively diagnose winding looseness faults of different degrees. In contrast to the traditional frequency response analysis (FRA) and short-circuit impedance (SCI) methods

online VFRA has higher sensitivity and detection capability

and is a better method for online monitoring of the winding mechanical condition.