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.