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.