Adapting frequency domain spectroscopy as an online monitoring tool for the insulation of power transformers

This paper investigates the possibilities and limitations of the FDS method as an on-line monitoring method for the oil-impregnated-paper insulation of power transformers. Bushing taps and the earthed tank are used as feed-in and measuring points for the perturbing voltage signal and its corresponding current response respectively. All possible capacitances of a transformer (HV-LV, HV-Tank, LV-Tank, Bushings) are considered in this investigation. Special guarding configurations which are important for the FDS method especially under simulated on-line conditions were also investigated. The proposed method was first simulated using equivalent circuit models and then measurements were performed on a transformer under online conditions. The results were then compared with conventional off-line FDS measurements which showed good agreement with each other, hence verifying the feasibility of this method. Our initial investigations show that the proposed FDS method could be adapted as an on-line measuring tool to continuously monitor the insulation of a power transformer.