Relaxation studies to identify aging with oil filled transformers - experiments

Requirement of reliable condition indicators is needed in the energy sector with web based information structure and with increased number of aged power apparatus operating in digital switching and loading environment. This project for oil-filled power transformers is taken up by Cooperative Research Centre for Integrated Engineering Asset Management (CIEAM) to develop knowledge models for prediction of remaining life of operating transformers. The aims at Queensland University of Technology (QUT) are to come up with partial discharge (PD) and relaxation condition indicators. In this paper, part of the promising results on relaxation measurement is presented. Two 11 kV/220 V dasiaSWERpsila (Single Wire Earth Return) and one 70 kV/220V HV test transformers were tested. They were tested with Step Polarization and Low Frequency Domain Spectroscopy techniques. The collected time and frequency domain polarization responses provide the aged and new status of transformers. The dynamic variation of the relaxation responses with heating reveals the aging status information of the transformers. With heating, NEW transformer´s leakage current magnitude and changes with heating time are significantly less.