Performance Evaluation of Optical Fiber Current Transformer

Abstract

The requirement for reliability and security in power system is increasing every day with the increase in complexity of the power system networks. In order to ensure highest level of reliability and protection, relays have to receive correct and accurate measurement values. Conventionally, currents and voltages in protection system are measured using inductive-type instrument transformers. Due to their design, conventional instrument transformers introduce distortions to the current and voltage signal replicas, which may cause mal-operation of protective relays. The aim of this thesis is to develop new optical fiber current transformer (OFCT). The performance of power system protection is evaluated using an OFCT instead of conventional CT through dynamic simulation studies. Additionally, the thesis focuses into development of an experimental model of an OFCT, and investigation of its application in power system protection. Derivations a mathematical model of the optical fiber current transformer from its principles of operation indicating the various detection configurations provided. Various assumptions are taken into considerations to reduce the complexity of the OFCTs model whilst maintaining an acceptable level of accuracy of dynamic performance of OFCTs. Jonse Matrix is used to redesign the OFCT with Faraday Rotation Mirror to eliminate linear birefringence and other effects. Multifunction numerical relay model is developed including fault detection algorithms. The operating performance of the numerical relay with OFCT is evaluated using various simulation scenarios based on operating characteristic, and trip-times. The simulation evaluation is carried-out using MATLAB / SIMULINK. An experimental model is configured to implement and test the OFCT, the numerical relay is implemented using PIC16F877A microcontroller. The simulation and experimental results prove that OFCTs are capable to measure current with very high accuracy over wide dynamic range with acceptable errors that match the IEC 0.2 class accuracy requirements. Furthermore, OFCTs has extraordinary features, which makes it more suitable for replacing conventional CTs. Additionally, OFCTs are providing direct to digital outputs according to the IEC 61850 standard, these outputs are immediately compatible with modern digital substation communication.