A novel approach to investigate the deterioration of insulation of oils in power transformers with terahertz time-domain spectroscopy

This article presents a non-destructive and non-contact method, based on terahertz time-domain spectroscopy measurements, for testing insulation oils which are extracted from different power transformers and in different ages. It is a novel method to investigate the changes of insulation oils at the molecular scale in terahertz region. Optical parameters such as the refractive index and absorption coefficient of samples are calculated based on the amplitude and phase information obtained from the measured terahertz spectra. Wavelet-denoising and smooth spline algorithms are employed to assist with the spectral analysis and signal processing. By comparing the experimental results with the conventional methods, it finds that the deterioration of the transformer oil contribute to existence of carbonyl and hydroxyl compounds and the intensive absorption due to stronger intermolecular interaction results in the changes of the dielectric characteristics. Terahertz time-domain spectroscopy offers insight into the deterioration of the electrical properties of insulation oil in power transformers. Hence, it is a useful technique in characterizing dielectric systems and appears capable of discovering the particle disaggregation states in the insulation oil.