Medium Voltage Divider Coupled With an Analog Optical Transmission System

Similar to low-voltage power systems, also in medium voltage networks there is a growing need for power quality (PQ) analyses, required by the increasing diffusion of distributed generation sources equipped with switching converters. This leads to the employment of transducers and measurement techniques able to convert and acquire voltage signals with better accuracy on a wider frequency range than conventional voltage and current instrument transformers. Voltage dividers (VDs) are expected to become the most used transducers in PQ assessments, since, with respect to conventional voltage transformers, they show higher frequency bandwidth and better linearity. The main disadvantage of the VDs is the absence of galvanic insulation between the transducer and the measurement/protection devices. Therefore, in this paper, a prototype of a VD for phase-to-ground connection with an insulating transmission system is presented. It is constituted by a high-impedance resistive-capacitive VD and by an analog electronic insulation interface. Such an electronic interface, inserted between the output of the divider and the input of a measuring instrument, realizes the galvanic insulation by means of an optical transmission system ensuring, simultaneously, wide frequency bandwidth and high accuracy. The design, simulation, and characterization of the realized insulated equipment are presented. Its performance well fit the prescription of the international standards about instrument transformers for PQ measurements.