Depression of narrowband interference in partial discharge signals of transformers with combined generalized morphological filters

In order to depress narrowband interference in partial discharge signals of transformers, combined generalized morphological filters were designed based on morphological open-close and close-open filters according to the difference between partial discharge and narrowband signals. In frequency domain, every spectral line of periodic narrow bandwidth noise could be smoothed, and partial discharge signal could be reserved by the morphological filters. The effectiveness of noise depression on simulating signals was evaluated by SNR and NCC, and results show that the filters designed can eliminate narrowband interferences effectively.