Design & Development of Zero-Flux Type Current Transformer

Abstract

The need for high-current transducers featuring wide-band and high-insulation levels is becoming a more and more impelling need in the electric power network, as the current distortion increases due to the proliferation of nonlinear, time-variant loads. While sense resistors may have previously represented the state of the art in current sensing, the need for safe, isolated detection of electrical current has spurred the development of non-intrusive current sensing methods and devices. Among a handful of alternative current-sensing methods, zero-flux current transformer(ZFCT) based on Hall-Effect principle may be implemented in high volume with relatively low cost for many of these applications. This report is based on designing of a Zero-Flux Type Current Transformer. The ZFCT is a kind of electronically compensated current transformer based on the principle of zero ux. These types of device are referred to as active current transformer because of the use of electronic amplifier and feedback circuits. When current is passed through the conductor placed inside of the core, magnetic field established around it is caught by the core and a flux is circled in the Hall sensor. The output of the Hall Effect sensor is proportional to the magnetic field. The hall voltage is amplified through the power amplifier and it drives the feedback circuit in such a way that the ux in the core remains zero throughout the measurement range of the current transformer. The report presents the design procedure of different parts of the ZFCT. It contains the design of Magnetic core, Feedback winding, Offset remover circuit, Phase error compensation circuit, Pre-amplifier and Power amplifier circuit. The Finite- element analysis of gapped toroid core used in ZFCT is done in NISA software to analyze the behavior of gapped toroid core. The analysis results shows the effect of the air gap length on the performance of gapped toroid core. The prototype of ZFCT is fabricated and tested in open loop and close loop operation with AC/DC current. The results shows that the prototype gives satisfactory results with 0.5% accuracy.