Review of Accuracy Assessment Methods for Current Transformers: Errors, Uncertainties, and Dynamic Performance

Accurate electric current measurement is fundamental to the safe and efficient operation of modern power systems. Current transformers (CTs), which serve as a critical interface between high-voltage power networks and measuring or protection devices, are susceptible to various errors and uncertainties that can significantly impact the reliability of measurement results. This article provides a critical and comprehensive review of the current literature concerning the types and causes of errors in CTs, with particular emphasis on current ratio error and phase displacement. Special attention is given to the role of international standards in defining accuracy classes and permissible error limits. Methods for evaluating measurement uncertainty are also discussed, in accordance with the guidelines outlined in the Guide to the Expression of Uncertainty in Measurement (GUM), highlighting their decisive impact on the credibility of measurement results. Modern approaches—such as the application of artificial intelligence in estimating measurement errors—are also considered. This review serves as a comprehensive resource for engineers, metrologists, and researchers seeking to enhance the accuracy of CTs, particularly in measurement and protection applications.