High voltage circuit breaker is an important utility in power system

which can protect and control the power lines

so its reliability is vital to the safety of the power system. Mechanical condition monitoring system can identify the mechanical conditions of circuit breakers to some extent. Current signal of the closing coil contains important time and condition information

thus it is applicable for the condition monitoring. In this paper

a morphological filter based on the theory of mathematical morphology is proposed to denoise the coil current signal. This filter can completely eliminate the peaks and valleys of coil current waveform

and keep the characteristic structure of the current waveform as well. The coil current waveform after filtering is very smooth without sacrificing the accuracy and information content of the signal. Corresponding program is coded on the platform MATLAB to implement the proposed filtering algorithm.