The assessment of the power quality could be a valuable tool to foster the efficiency of the railway systems. Power quality is a well-addressed topic in conventional AC 50/60 Hz power systems and many procedures, algorithms and measurement systems were presented in the international standards and widely discussed in the scientific literature. A less explored research field is the assessment of the power quality in the railway traction supply systems, in particular with reference to the DC and 16.7 Hz systems. The paper explores this theme, proposing an extension of the definitions and of the standard measurement procedures for some of main power quality indexes, well defined and widely used for conventional power systems, in order to be used also in all railway traction supply systems. The limits or difficulties of applicability are discussed with reference to measurements performed both on-board and in substation. The proposed procedures are applied to an experimental case of a real DC railway system with a large measurement campaign.

A setup for the measurement of the frequency response of voltage measurement transformers under actual waveform conditions is presented. It is based on a two-step procedure that makes use of high voltage gas insulated capacitors and a digital bridge. It allows calibrations using distorted waveforms, with a fundamental tone at medium voltage level and superimposed harmonics up to 20% and 15 kHz. Combined standard uncertainty in the measurement of the voltage transformer (VT) error is estimated at 200 μV/V for the ratio error and 300 μrad for the phase displacement up to 10 kHz. First applications to the measurement of the frequency response of VTs with different rated primary voltages up to 50 kV are presented.

In this paper, the authors propose a methodology to guide the verification of single-phase energy meters under sinusoidal and nonsinusoidal conditions. At first, a brief review is presented about definitions of the quantities that should be measured or monitored for revenue purposes and their relationship with electrical quantities that are recognized to be important in terms of metering accuracy. Then, a design of an experiment that allows the testing meters under a combination of disturbances showing positive and negative correlations are described. Finally, a hardware and software system to perform verification procedures in complex situations is presented with some preliminary analyses.

Calibration of electrical energy meters is coming up as a metrological concern. The latest European Union (EU) directives about measuring instruments adopted for commercial transactions state that their accuracy has to be verified in actual operating conditions. This requirement is leaving all laboratories involved in energy meter calibration in serious difficulty because this kind of metrological verification is, at the moment, still not fully developed or even clarified in all involved aspects. In this paper, a measurement equipment for the calibration of energy meters is presented. Its structure and metrological characterization are discussed. To improve its performances without increasing its costs, two online digital compensation procedures have been realized and are shown: one increases the spectral purity of test signals and one corrects the transducer frequency response. Experimental results relating metrological characterization have shown that the so-realized calibrator is suitable for the onsite calibration of energy meters.

The advance in power electronics causes, over the years, an increasing diffusion of nonlinear loads. Moreover, electrical generation systems are going to include a growing amount of solar and wind energy, characterized by time-variant flow of energy and, very often, with a relevant distortion. These aspects give more and more emphasis to the monitoring of conducted disturbances on power systems over a wide frequency range, and consequently, voltage and current transducers adopted for this aim must have a proper frequency bandwidth. Voltage transformers (VTs) and current transformers (CTs), which are the most installed transducers in electrical power systems, are typically constructed to operate only at the industrial frequency, i.e., 50/60 Hz, but it is clear that their substitution would require an unsustainable cost. Therefore, in this paper, a method for real-time digital compensation of the CT frequency response over a wide range is presented. An implementation of the proposed method is shown, and the compensated CT is characterized and tested in some practical situations, with waveforms affected by typical power quality disturbances.