Time delay estimation for UHF signals in PD location of transformers

Time delay estimation (TDE) is essential for PD location using the UHF technique. However, noise and effects of multi-path propagation are two main problems affecting the accuracy of the estimate. Comparing two methods, which are based on cumulative energy curve and power curve respectively, a cross correlation based method is employed to achieve the estimation. A high-pass filter is applied to the UHF signal to eliminate operating noises. The phase characteristic of the filter is designed to be linear for making the time delay a constant in terms of frequency. A window in the time domain is selected to reduce the effect of multi-path propagation.