The necessity of self-checking technology for arc transmission channel in arc flash relay of medium-voltage and low-voltage switchgears is described. The principle and methods realizing self checking for arc transmission channel by superimposing pulse light are introduced. It is theoretically analyzed that the recursive median filter algorithm can eliminate the influence of pulse light

and the deviation of pulse light to background light is also estimated. The test shows that in the premise of no misoperation of the device

the method can realize real-time self-checking for arc transmission channel

which can improve the reliability of arc flash relay.