Cracks under the coating of overcurrent components of hydropower station will directly lead to a decrease of the components' fatigue strength and affect the safety of the hydroelectric units. In order to realize crack detection under the coating

eddy current detection is selected as the detection method of over-current components in this paper

through comparison of multiple non-destructive detection methods. Three kinds of eddy current testing methods are analyzed. The results show that

the detection efficiency of pulsed eddy current testing is low and easy to be affected by the crack direction

which is difficult to meet the requirements of rapid detection on site. The ACFM testing can not penetrate the coating

and is not able to carry out crack detection. The array eddy current testing can effectively detect the cracks under the coating

which is suitable for the detection of cracks under the coating of overcurrent components on site.