Electronic Combined Transformer for Power-Quality Measurements in High-Voltage Systems

The evolution of electronic technology and digital signal processing is making competitive methods and devices for the design and the development of measurement transformers for high-voltage (HV) systems deeply different from those based on the traditional electromagnetic principle. Several advantages are offered by these new solutions: higher metrological characteristics, cost effectiveness, compact size, and lack of the typical problems of the traditional electromagnetic transformers (magnetic core saturation, magnetic resonance, bandwidth limits, etc.). In this paper, the design criteria adopted for the development of a prototype of a novel HV electronic combined transformer are presented. Its architecture permits the implementation of both voltage and current protective and measurement functions. The starting point is the employment of a mix of well-tested traditional technologies (like those used for the voltage capacitive divider and for the current sensor) and very sophisticated electronics. In particular, the electronic devices and the employed system architecture, beyond what is conceived for obtaining high measurement performances, are also oriented to provide advanced ancillary functions such as autodiagnosis, fault tolerance, autocalibration, etc. The developed combined measurement transformer features a rated primary voltage of $145/sqrt{3}$ kV and a rated primary current of 1000 A. Moreover, it is fully compliant with IEC 60044-7 and IEC 60044-8 standards, assuring 0.1 measurement precision class and satisfying also 5P and 3P protection classes for current and voltage sections, respectively.