Abstract
The paper presents the development of a model-based Smart Power Plant Supervisor, a digital tool targeting the optimization of the operation and maintenance of hydroelectric units to improve ...ancillary services provision to the power system. The paper focuses on a control-oriented modelling methodology which allows integrating the operational parameters of the hydroelectric unit in an optimization algorithm steering the advanced control of the units. The technique to develop analytical functions representing the behaviour of the hydropower plant is presented and validated by comparing numerical simulations with measurements of the real time operation of the run-of-river hydropower plant Vogelgrun. The results show a good performance of the modelling technique able to correctly predict the power generation of the power plant over one month of operation.
•PMU characterization needs a reference with TVE of 0.00x% in steady-state conditions.•Metrological analysis of the hardware uncertainty contributions.•Uncertainty propagation due to internal ...time-source inaccuracy.•Deterministic routine for the evaluation of PMU reporting latency.
The effective deployment of Phasor Measurement Units (PMUs) in Distribution Networks (DNs) requires an enhancement in terms of estimation accuracy beyond the limits of IEEE Std C37.118.1 (IEEE Std), aiming at a Total Vector Error (TVE) in the order of 0.0x% in steady-state test conditions. As a consequence, a rigorous metrological characterization of PMU performance requires a validation system whose accuracy is at least one order of magnitude better than the one of the device under test, i.e. it requires a TVE in the order of 0.00x% in steady-state test conditions and 0.0x% in distorted or dynamic test conditions. In this paper, we consider the hardware and software architecture of a previously published PMU validation system specifically designed for PMUs operating in DNs. In this context, we evaluate the quality of the generated test waveforms, and we carry out a thorough metrological characterization of the uncertainty contributions due to generation, acquisition and synchronization stages. In this sense, the proposed analysis provides a rigorous methodology for the evaluation of such low uncertainty levels, and enables us to identify and discuss the most challenging aspects in the implementation of a high-accuracy PMU validation system.
In this paper, we investigate the effect of periodically-grounded shielding wires and surge arresters on the attenuation of lightning-induced voltages. We discuss the adequacy of the commonly made ...simplification of assuming the shielding wire at ground potential, instead of being treated as one of the conductors of the multiconductor system. We also compare then the mitigation effect of shielding wires with that achievable by the insertion of surge arresters along the line. The computation results are first validated by means of calculations obtained by other authors referring to a simple line configuration, and then by means of experimental results obtained using a reduced-scale line model illuminated by a nuclear electromagnetic pulse (NEMP) simulator. One of the main conclusions is that the effectiveness of shielding wires and surge arresters depends mostly on the spacing between two adjacent grounding points or surge arresters.
The evaluation of electromagnetic transients in overhead power lines due to nearby lightning return strokes requires accurate models for the calculation of both the incident lightning electromagnetic ...pulse (LEMP) and the effects of coupling of this field to the line conductors. Considering also the complexity of distribution networks in terms of their topology and the presence of power system components and protection devices, the implementation of the LEMP-to-transmission-line coupling models into software tools used to represent the transient behavior of the entire network is of crucial importance. This paper reviews the most significant results obtained by the authors concerning the calculation of lightning-induced voltages. First, the theoretical basis of advanced models for the calculation of LEMP-originated transients in overhead power lines is illustrated; then, the relevant experimental validation using: 1) reduced-scale setups with LEMP and nuclear electromagnetic pulse (NEMP) simulators and 2) full-scale setups illuminated by artificially initiated lightning are reported. Finally, the paper presents comparisons between simulations and new experimental data consisting of measured natural lightning-induced voltages on a real distribution network in northern Italy, correlated with data from lightning location systems.
We report on new p(e,e′p)π∘ measurements at the Δ+(1232) resonance at the low momentum transfer region, where the mesonic cloud dynamics is predicted to be dominant and rapidly changing, offering a ...test bed for chiral effective field theory calculations. The new data explore the Q2 dependence of the resonant quadrupole amplitudes and for the first time indicate that the Electric and the Coulomb quadrupole amplitudes converge as Q2→0. The measurements of the Coulomb quadrupole amplitude have been extended to the lowest momentum transfer ever reached, and suggest that more than half of its magnitude is attributed to the mesonic cloud in this region. The new data disagree with predictions of constituent quark models and are in reasonable agreement with dynamical calculations that include pion cloud effects, chiral effective field theory and lattice calculations. The measurements indicate that improvement is required to the theoretical calculations and provide valuable input that will allow their refinements.
This paper deals with the calculation of lightning-induced overvoltages on medium-voltage (MV) and low-voltage (LV) distribution networks taking into account the presence of MV-LV distribution ...transformers and, in particular, the surge transfer through them. The influence of the high-frequency model adopted for the representation of the power transformer on the calculation results is analyzed, with regards to two different models, both identified and validated by means of laboratory measurements: namely, a simple pi of capacitances, and the more complex one introduced by Morched, Marti, and Ottevangers in 1993. Accurate simulation results provide information on the adequacy of both models for the calculations of interest. Additional results, useful to evaluate the expected level of power quality and the benefits achievable by a proper installation of protection devices, are presented making reference to a realistic and complex configuration of an overhead distribution system.
•The use of vacuum circuit breaker models for transient recovery voltages simulation is presented.•The models are validated against measurements in a water-pumping plant and in an offshore wind ...farm.•Detailed vacuum circuit breaker models significantly improve the agreement between measurement and simulation results.•The adjustment of the VCB model parameters is necessary to fit the simulations for both opening and closing manoeuvres.
Vacuum circuit breakers (VCBs) are widely used for medium voltage applications when low maintenance, long operating life, and large number of allowable switching cycles are required. The accurate estimation of the transient recovery voltages (TRVs) associated with their switching operation is indispensable for both VCB sizing and insulation coordination studies of the components nearby the switching device. In this respect, their accurate modelling, which is the object of the paper, becomes crucial. In particular, the paper illustrates two applications of a VCB model, which show the model capabilities of simulating TRVs due to opening/closing operation, namely the switching of large electrical motors and the switching of cables collecting offshore wind farms (OWFs). Data from digital fault recorder (DFR) in a water-pumping plant and from a measurement campaign in an OWF using a high-bandwidth GPS-synchronised measurement system, respectively, are used for model validation. It is shown that the inclusion of detailed VCB models significantly improves the agreement between the measurements related to both pre- and restrikes and the corresponding simulation results obtained by using two well-known electromagnetic transient simulation environments, namely, EMTP-RV and PSCAD/EMTDC. The procedure adopted for the identification of the VCB model parameters is described.
The paper deals with the evaluation of the indirect-lightning performance of overhead distribution networks. The novelty of this contribution is that it takes into account the inherent complexity of ...distribution networks. These networks are indeed characterized by a plurality of lines (main feeder and laterals) and also by the presence of typical power components (e.g., transformers and surge arresters); they consequently differ considerably from the straight line configuration generally adopted in this type of studies. To accomplish such an evaluation we have extended the general procedure already presented in a previous paper based on the use of the LIOV code along with the Monte Carlo method. The extended procedure combines the advantage of the LIOV-EMTP computer code-that allows the calculation of lightning-induced voltages in complex distribution networks-with a heuristic technique specifically developed and integrated in the Monte Carlo routine in order to reduce the computational effort. The application of the proposed procedure to a set of distribution overhead networks characterized by different topologies, but all of the same length, shows that, in general, the usual single straight-line approach may result into a misestimation of the indirect-lightning performance. The paper also analyzes and discusses the influence of both the line terminations, and the position of the line poles.
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