This paper aims at characterizing and improving the metrological performances of Current (CT) and Voltage Instrument Transformers (VT) in harmonic measurements in power system. A theoretical analysis is carried out to demonstrate that, due to the iron core non linearity, CT and VT output signal is distorted even when the input signal is a pure sinusoidal. Starting from this analysis, a new method for CT and VT characterization and compensation is proposed. In a first step, they are characterized in sinusoidal conditions and the harmonic phasors of the distorted output are measured; in the second step, these phasors are used to compensate the harmonic phasors measured in normal operating conditions, which are typically distorted. The proposed characterization and compensation techniques are called SINDICOMP (SINusoidal characterization for DIstortion COMPensation). Several experimental tests, using high accuracy calibration setups, have been performed to verify the proposed methods. The experimental results showed that the SINDICOMP technique assures a significant improvement of CT and VT metrological performances in harmonic measurements.

BackgroundMicrobial population dynamics in bioreactors depend on both nutrients availability and changes in the growth environment. Research is still ongoing on the optimization of bioreactor yields focusing on the increase of the maximum achievable cell density.ResultsA new process-based model is proposed to describe the aerobic growth of Saccharomyces cerevisiae cultured on glucose as carbon and energy source. The model considers the main metabolic routes of glucose assimilation (fermentation to ethanol and respiration) and the occurrence of inhibition due to the accumulation of both ethanol and other self-produced toxic compounds in the medium. Model simulations reproduced data from classic and new experiments of yeast growth in batch and fed-batch cultures. Model and experimental results showed that the growth decline observed in prolonged fed-batch cultures had to be ascribed to self-produced inhibitory compounds other than ethanol.ConclusionsThe presented results clarify the dynamics of microbial growth under different feeding conditions and highlight the relevance of the negative feedback by self-produced inhibitory compounds on the maximum cell densities achieved in a bioreactor.

The electrical arc occurring in the sliding con-1 tact between the supply contact line and the current collector 2 (pantograph) of an electrical locomotive is a fast transient 3 phenomenon able to degrade progressively the line-to-pantograph 4 contact quality and, consequently, the continuity of operation.

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Nowadays, the interest in low-cost and increasingly accurate Phasor Measurement Units (PMUs) for active distribution systems is steadily growing. In this paper, an algorithm for synchrophasor, fundamental frequency and ROCOF estimation tailored for processing platforms with limited computational resources is described and characterized extensively in terms of both accuracy and processing time. The proposed solution harnesses the main advantages of two state-of-the-art algorithms, i.e. the Interpolated Discrete Fourier Transform (IpDFT) and the Taylor-Fourier Transform (TFT). Such algorithms are combined and implemented in a computationally-efficient manner to reduce processing time as much as possible, while ensuring good accuracy in the main testing conditions specified in the IEEE Standard C37.118.1-2011 and its Amendment C37.118.1a-2014. Estimation accuracy has been evaluated not only through simulations, but also experimentally. The good consistency between simulationbased and experimental results provides clear evidence that the uncertainty contributions due to transducers, acquisition and synchronization systems can be reasonably kept under control. The processing times of the algorithm, implemented on an embedded platform suitable for PMU prototyping, are compliant with the mandatory reporting rates of Class M PMUs.