A statistical method of improving the resolution of time-delay of UHF signals for PD location in transformers

It´s important to make an accurate PD location in transformers for fault diagnosis and maintenances of power systems. Theoretically it´s possible to locate the PD source by measuring the differences in the arrival time at the UHF sensor array. The propagation velocity of EM wave in air is 30 cm/ns, which is extremely fast, so the resolution of the time-delay of UHF signals detected at the UHF sensor array is one of the key points to make an accurate PD location. Here, we propose a mathematical method: cross-correlation-shifting-averaging algorithm that can improve the resolution of the UHF signal´s time-delay by increasing the signal to noise ratio and reducing the time dispersion caused by the random nature of PD. The practical processing results of experimental data from our laboratory indicate that the method can increase the time-delay resolution by nano-seconds in some cases, which improve PD location accuracy by tens of centimeters.