Denoising neutral current of a power transformer measured during impulse test by framelet technique

Condition monitoring of the insulation of the windings of a power transformer depends on the accuracy with which the neutral current is measured during impulse test both at full and at reduced voltage. The most common problem faced while measuring neutral current is that it contains noise that causes ambiguous fault signatures. This paper presents an effective means for filtering out the noise from the neutral current using framelet technique. A fast and yet simple algorithm has been used here to calculate the framelet coefficients. Results presented are for an electromagnetic transient program (EMTP) simulated model of a 3 MVA transformer mostly used up to 33 kV. Studies have been carried out with both high and low frequency synthetic noises. Comparison of the results with that obtained from wavelet technique based method has also been reported in the paper.