Impact of Optical Instrument Transformer Characteristics on the Performance of Protective Relays and Power Quality Meters

This paper evaluates the influence of optical instrument transformers (OIT) characteristics on the performance of protection and power quality metering intelligent electronic devices (IED). Lab research and experience from field application have shown that instrument transformer characteristics may affect the performance of relays, revenue metering systems and power quality meters. Recently, optical voltage and current instrument transformers have become readily available. Optical transducers measure changes in properties of some materials as a result of the surrounding electrical or magnetic field instead of directly measuring currents and voltages. A quantitative relationship between this change and the current or voltage can be obtained. OIT provide several benefits for protection and metering applications: wider frequency bandwidth and better dynamic performance. A previous study has presented a methodology for assessing the influence of instrument transformer characteristics on relay performance. The methodology presented in this paper uses some of the aspects presented in the previous studies and defines criteria and procedure for evaluating the influence of OIT characteristics on the performance protective relays and power quality meters. OIT models obtained from laboratory testing of actual sensors have been used along with simulation environment to quantify the influence. Results of simulation are presented