Monitoring voltage harmonics represents one of the most important tasks in power quality assessment. In particular, the employed instrument transformer plays a key role in the achieved accuracy. Its harmonic measurement performance is typically evaluated by measuring its frequency response function. However, nonlinearities may have a nonnegligible impact on measurement uncertainty; for example, this occurs as far as the inductive voltage transformers are considered. This paper proposes a simple technique allowing the compensation of the most significant nonlinear effect that is the harmonic distortion produced by the large fundamental primary voltage. The method is first derived and introduced by means of numerical simulations and then implemented through a proper experimental setup. Results highlight remarkable accuracy improvements when realistic voltage waveforms are measured.

Voltage instrument transformers are usually tested at the rated frequency. In order to assess their performance in measuring harmonic components, typically, the frequency response function (FRF) is evaluated. Therefore, this conventional characterization does not consider nonlinear effects that may have a nonnegligible impact on the accuracy, especially when the transducer under test is represented by an inductive voltage transformer (VT). In this paper, a simple procedure for the characterization of voltage instrument transformers is presented. The method is based on the concept of best linear approximation of a nonlinear system. It requires applying a class of excitation signals that resembles the typical voltage waveforms found in power systems. Results consist of the FRF that permits the best linear compensation of the transducer response, and sample variances that allow quantifying the impact of noise and nonlinearities on the accuracy. The method is presented and explained by means of numerical simulations. After that, it has been applied to the characterization of a conventional inductive VT. Experimental results show how the accuracy of the transducer under test is heavily degraded by nonlinear phenomena when low-order voltage harmonics are considered.

The need for high-current transducers featuring wide-band and high-insulation levels is becoming a more and more impelling need in the electric power network, as the current distortion increases due to the proliferation of nonlinear, time-variant loads. The closed-loop Hall-effect current transducers show a good compromise between cost and metrological performance. On the other hand, they may introduce an unacceptable nonlinearity error when the dynamic range of the input current is a reduced portion of the dynamic range of the transducer and may show a large drift of their gain with temperature. The paper proposes a simple method for reduction of the nonlinearity error when the input signal is an unbiased sinewave and the automatic calibration of the gain. Experimental results are also reported, showing the method effectiveness.

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/√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.

Steel-fiber-reinforced concrete is a composite material which is becoming more and more widely employed in building construction, due to its better resistance to cracking and to crack propagation with respect to plain concrete. Its mechanical behavior strongly depends on the choice of fiber properties and their volume fraction in the concrete mixture. As any material used in building construction, the “on-site” test of its properties represents a very important task. Often, this requires the employment of noninvasive and nondestructive measurement procedures that have to be carried out directly in situ. In this paper, a new method for the estimation of the fiber density and their average orientation is presented. The measurement technique is based on the employment of a probe that is sensitive to the magnetic properties of the steel fibers. The performance of the method has been theoretically and experimentally analyzed.

The number of nonlinear devices in distribution grids has rapidly grown in the last years, and this trend is likely to increase in a near future. In this scenario, power quality monitoring and identification of disturbance sources are critical aspects. Inductive transformers are often employed for this purpose, although their metrological performances are guaranteed only near rated frequency. Secondary voltage harmonics are affected by the filtering behavior of the transformer, but also by nonlinearities due to the iron core that may have remarkable impact. In this work a novel post-processing technique allowing to dramatically reduce the detrimental effects of nonlinearities is proposed and discussed. After explaining the methodology, it has been applied to enhance the harmonic measurement accuracy that can be obtained by using an inductive medium voltage instrument transformer. Experimental tests carried out in laboratory show the significant performance improvement achieved thanks to the proposed approach.