On-line condition assessment of high voltage current transformers

This paper presents the development of an ultrawideband (UWB) PD technique that allows on-line diagnostic of 400 kV CT's. The measurements carried out on 130 CT's were qualitative on-line measurements and included PD and thermal imaging inspection. PD measurements were carried out on CT's ground connection using a clamp-on Rogowski coil whose output is centered at UWB frequencies and then processed and fed into a standard PD detector using a frequency stretcher. Evaluations were performed on CT's installed at seven transmission substations of main Mexican Utility. The diagnostics were performed establishing three levels of partial discharges magnitude (tow, medium and high). Over 5% of CT's were detected with high PD level. Those will be retired from service and evaluated in laboratory through power factor, capacitance, PD and DGA analysis.