Diagnostic challenges in dielectric loss assessment and interpretation: a review

In any sustainable electrical systems, various high‐voltage (HV) power apparatuses such as electrical cable, transformer etc. play a pivotal role to transfer electrical energy from the generation end to the consumer end. The degradation due to electrical stress is very unlikely to avoid in operation. Prominently, the insulation system is mostly expected to be strong enough, and its degradation always provides a constant threat to the reliable operation. Moreover, the continual deterioration can gradually lead to the complete breakdown of HV equipment. To assess the overall dielectric properties, the regular monitoring/diagnosing of electrical insulation has a paramount importance in power systems. One of the potential tools for diagnostic assessment is the tan‐delta (tan δ ) measurement. Considering different aspects at various frequencies, this study elucidates a comprehensive review of tan δ measurement. First, a detailed review and explanation of multiple challenges associated with dielectric loss measurement are presented. Various dielectric losses, their contribution to tan δ , measurement techniques and their comparisons are also discussed. This study further reviews the analogy of different physical dipolar theories, modelling and a brief analysis of commercially available measurement instruments.