Comprehensive Investigation on Service Aged Power Transformer Insulating Oil After Decades of Effective Performance in Field

Liquid-based dielectrics have been used in the electrical power components for high voltage insulation and cooling purposes for over a century. Numerous condition monitoring techniques are used for its performance analysis. Dielectric breakdown event of insulting oil is a key failure mode which adversely impacts the transformer performance. Transformer oil is a prime source of fault diagnosis of transformer and its condition monitoring. Insulation condition of the oil, acidity, chemical degradation that occurred over the period of time can be detected by modern spectroscopic techniques. Fourier transform infrared spectroscopy (FTIR) has acquired exceptional importance in determining the chemical degradation of the oil for utility professionals. In this work, service aged oil specimens were taken from a transformer with a successful operating life of 37 years in order to investigate the reason behind its internal faults. Various testing techniques such as breakdown voltage, frequency-domain dielectric spectroscopy, UV–visible spectroscopy, charge migration and mobility and FTIR were used for comprehensive analysis of oil condition. For comparative performance analysis, pristine samples of same oil were procured from the identical manufacturer. More emphasis was laid on the capability of FTIR to access the oil condition. The experimental findings of this study could provide a valuable insight to researchers and condition monitoring engineers in this field.