A Method for Correcting Distorted Current Waveforms at Air-Gapped Current Transformers

A new technique for the correction of distorted current waveforms in the secondary windings of protective current transformers (CTs) is presented. The technique is based on the integration of the induced voltage in a tertiary winding. The exciting current is determined using a function that describes the magnetization process in the core, and by adding it to the distorted secondary current. In this way, a more faithful reproduction of the primary current wave is obtained. The initial magnetic flux in the core is determined by analogical integration of the voltage across the tertiary winding, from the pre-fault state up to the instant in which the current reaches 150% of the load current. Due to the large air gap length, the remanent flux in the core is ignored.