Complete FEM-based model of a bulk-glass optical current transformer

This paper is focused on digital substation technologies, with a further attention to optical current transformers and their impact on differential protection performance. Optical current transformers (OPCT) have become more readily available in recent time. This transition from conventional current transformers requires the development of models to verify and evaluate the performance aspects of OPCTs. This paper presents a complete model of an open-core bulk-glass optical current transformer. The model is based of 2-D FEM design for the optical part and an experimentally obtained transfer function for the electronic part. The model is used to explore performance, interoperability with other current sensing technologies and error inducing nonlinearities caused by external sources. These external sources are vibration, temperature irregularities and external magnetic fields. In addition the complete OPCT model performance is compared to a model of a conventional current transformer. This comparison is executed in a real-time differential protection setting using playback of simulated transients over IEC61850 Sampled measured Values (SMV) protocol.