Denoising UHF signal for PD detection in transformers based on wavelet technique

Although the UHF technique is immune from electrical interference; communication noises, thermal noise from the detection system, and periodic pulse-shaped noise from thyristor operation are usually found in the UHF signal. In this paper, a method based on discrete wavelet transforms is introduced. Three steps in the de-noising process are studied and discussed. Hundreds of combinations involved in the process are compared. An artificial signal is created by mixing the specific noise with a ´clean´ UHF signal. The optimal process and corresponding parameters are defined by comparing the ´clean´ signal and the de-noised version of the artificial signal.