Abstract
AbstractIt is desired to establish an insulation diagnosis method for cast resin transformers (CRTrs), which is often used in distribution systems. Partial discharge (PD) detection is considered to be an effective method, but its phenomenon has not yet been clarified. This paper presents investigation on the frequency characteristics of PD generated inside CRTrs to improve PD detection technology. It is clarified that dominant frequency of PD signal detected by a high frequency current transformer (CT) depends on the frequency characteristics of the impedance between the primary and secondary windings. It is suggested that the dominant frequency could be predicted in advance by analysis using a high‐frequency equivalent circuit model of CRTrs. PD diagnostic technology that utilizes the frequency characteristics of the CRTrs impedance has also been proposed. It is found that a PD generated external to CRTrs does not have resonance at the dominant frequency of the CRTrs itself, even though it passes through the CRTrs. In conclusion, it is suggested that the frequency analysis of CRTrs impedance could identify degraded CRTrs and external noise.
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