Saturation of current transformers and its impact on digital overcurrent relays.

摘要

A current transformer transient model was implemented, using Electromagnetic Transient Program (EMTP), nonlinear inductor (Type-96) in order to investigate the effects of CT's saturation on digital overcurrent relays. The model was validated by testing in laboratory and found to be effective, reliable and accurate for evaluations of digital overcurrent relays, during CT's saturation. Factors that lead to CT's saturations were comprehensively discussed and evaluated.; A typical digital overcurrent relay was tested in the laboratory to investigate the effects of secondary burden, short circuit level, asymmetrical fault with dc offset components and remenant flux on CT's saturations and digital overcurrent relays operations. Evaluations of test results against the rules, specified by IEEE Standard C37.110-1996 were evaluated. The research includes studying the impact of CT saturation on both the instantaneous and time-delayed element of digital overcurrent relays. The results were satisfactory and guidelines and recommendations for CT's selection were presented.