Optical Spectroscopy Techniques for Condition Assessment and Fault Diagnosis of Power Transformer Insulation: A critical Review on Technologies, Methods and Standards

Power transformers are critical components in power grids, whose main role is maintaining the required voltage levels throughout the grid. Thus, continuous condition monitoring of their status is crucial. Otherwise, catastrophic repercussions would occur. Diagnosis and condition assessment of power transformers ensure that the power transformer operates safely without service interruption and allow to schedule preventive maintenance. Optical spectroscopy has gained considerable attention over conventional condition assessment techniques due to its simplicity, speed, accuracy, non-destructiveness approaches, and cost-effectiveness. This paper reviews various optical spectroscopy technologies applied to condition assessment and fault diagnosis of insulation systems inside power transformers to predict their quality. These techniques include ultraviolet-visible spectroscopy, photoluminescence spectroscopy, near infrared spectroscopy, and infrared spectroscopy. First, transformer insulation parameters correlated with aging are highlighted. Then, the technologies used in optical spectroscopy approach are discussed. After that, the detailed application of these technologies and possible correlation between their characteristic parameters and insulation condition are discussed. Finally, further needs for future research, development and standardization are identified.