Design and Characterization of a Combined Low-Power Voltage and Current Instrument Transformer for Low-Voltage Applications

Recent trends in smart substations have massively motivated the integration of low-power instrument transformers (LPITs) for the purpose of metering, monitoring, protection, and control. In this article, a novel design principle for the development of a combined low-power voltage and current instrument transformer for low-voltage (LV) applications is proposed. In specific, a capacitive voltage divider and a shielded Rogowski coil (RC) are employed for voltage and current measurement, respectively. Significantly, the RC shield is exploited as an electrode for the high-voltage (HV) capacitance of the voltage divider. A prototype featuring 400 V rated primary voltage and 500 A rated primary current has been developed. Subsequently, accuracy characterization has been carried out. Experimental results confirm the full compliance of the combined transducer with IEC 61 869 standards, assuring 0.5 and 0.1 accuracy classes for voltage and current measurement, respectively. This research provides a compact and cost-effective solution for combined LV LPITs with high precision and wide dynamic range.