Current transformer error correction

This paper presents the development of micro-processor based device with ability to decrease protection-type current transformer measurement error in the area of small currents. Measurement transformers are available with a high precision class of 0.2 and 0.5 and maximal measurable current up to double rated value. Transformers, produced for relay protection purposes, are with error classes of 3, 5 and 10 meaning error rates of 3, 5 and 10 % respectively. Our idea consists in a new way for joining the characteristic curves of relay-type and measurement-type current transformers. The micro-processor based device may “teach” itself by forming some error correction table in it´s memory on the basis of core outputs compare during normal operation. In case of fault device may operate with much higher sensitivity thus sensing fault on it´s early stage.