Investigations of dielectric monitoring on an energised transformer oil–paper insulation system

• Published in: IET science, measurement & technology measurement & technology, 2015-01, Vol.9 (1), p.102-112
• Main Authors: Yang, Xu, Nielsen, Shawn, Ledwich, Gerard
• Format: Article
• Language: English
• Subjects: Admittance; ageing; ageing signature; Aging; central time constant; chirp waveform excitation; condition monitoring; de‐energised transformers; dielectric measurement; dielectric monitoring; Dielectrics; Electrical impedance; energised transformer oil–paper insulation system; frequency domain spectroscopy; frequency‐domain analysis; imaginary admittance measurement; Insulation; insulation ageing process; insulation condition assessment; Monitoring; online FDS diagnostic application; power transformer insulation; return voltage measurement; Signatures; spectroscopy; transformer oil; Transformers; voltage measurement; waveform analysis
• ISSN: 1751-8822; 1751-8830; 1751-8830
• DOI: 10.1049/iet-smt.2013.0127

Frequency domain spectroscopy (FDS) is being used to assess the insulation condition of oil–paper power transformers. However, it has to date only been implemented on de-energised transformers, which requires the transformers to be shut down for an extended period and may cause significant costs. To solve this issue, a newly improved monitoring method based on the FDS principle is proposed to implement the dielectric measurement on energised transformers. Moreover, a chirp waveform excitation and its novel processing method are introduced. Compared with the conventional FDS results, dielectric results from the energised insulation system have higher tanδ values because of the increased losses. To further understand the insulation ageing process, the effects of the geometric capacitance are removed from the measured imaginary admittance of the insulation system to enhance the ageing signature. The resulting imaginary admittance is then shown to correlate well with the central time constant in return voltage measurements results. The proposed methods address the issues on techniques used on energised transformers and provide a clue for on-line FDS diagnostic application.