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.

With the proliferation of harmonic sources in power systems, current transformers (CTs), which are the most widely used current transducers in power systems, will have to measure and monitor signals with increasing levels of distortion. The accuracy of the measurement can be affected by the nonlinear response of the CT, which is dependent on the distortion in the measured signal, but nonlinear mathematical models can be used to compensate the measured value. In this paper, the complex ratio of the CT is modeled using a frequency domain model based on tensor linearization, obtaining a real-valued compensation matrix. An accurate measurement setup has been built to characterize the CTs performance in distorted conditions. Experimental results using the proposed compensation technique are presented and discussed for two commercial CTs of accuracy class 0.5 and 1. It is demonstrated that the proposed technique can accurately reconstruct the harmonic components (up to several kilohertz) of the CT primary current from the measured CT distorted secondary current.

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.

In this paper, the design and the prototype implementation of a power-quality (PQ) measuring and monitoring instrument based on an embedded controller with reconfigurable I/O are described. The instrument performs the calculation of main PQ indexes according to the latest standards, and it can be reconfigured for future standard developments. It is properly implemented to operate in stand-alone mode, and it is interfaced with hardware modules to exchange information and data, locally, with RS-232 connection or, remotely, with Transmission Control Protocol/Internet Protocol communication. The design includes enhancing of transducer performances through the correction of systematic errors with digital filters implemented by a field-programmable gate array module. This instance allows better performance without increasing cost. Finally, the whole accuracy of the proposed measurement system is evaluated by experimental tests that were performed in agreement with the specification of a class-A instrument for some of the main PQ indexes. The tests are performed, including the transducers, although that component is not required by the standard, to evaluate the behavior of compensated transducers. The test results are compared with those obtained by a commercial PQ instrument and show a good agreement.