KNOMAD’s Thematic Working Group ‘’Integration Issues in Host Communities” (Chaired by Howard Duncan, Metropolis Project at Carleton University, Ottawa, and Co-Chaired by Gervais Appave, International Organization for Migration) has proposed a five-year long project to KNOMAD’s Secretariat to look at the means by which immigrant integration can and does enhance homeland development and to draw out of these explorations some ideas including best practices that governments and other agencies can consider. As part of this undertaking, an Experts Advisory Committee, composed of global experts in immigrant integration and in development, was formed to support the development of knowledge products and related activities over the proposed five-year period.
These keynote discusses the following: IoT and Interactive Design; TSUBAME3.0 towards 4.0 and Toward Convergence of Extreme Computing and Big Data; Personalized Smart Health and Big Data Cyber Infrastructure.
About the Cover : Electron beam scattering diffraction (EBSD) image revealing the unique microstructural patterns in nickel (Ni) superalloy by selective laser melting (SLM). These colorful patterns captured by diffraction techniques are the um-scale “fingerprint” for different alloy systems and their processing history. SLM, as a novel additive manufacturing technique, facilitates the Ni superalloy fabrication and creates their distinct microstructures for property enhancements. The beauty of advanced manufacturing and materials science coalesces here when the EBSD beam shines.
Time domain simulations can be used to study complex problems such as resonant overvoltages following transformer saturation. However, it is often too time consuming to use time domain tools to assess the risk. Therefore, this work develops an impedance-based criterion for efficient analysis of resonant overvoltages in the Swedish transmission system. To develop the impedance-based criterion, two study cases are considered: a heavily cablified urban network, and future connection of offshore wind in a weaker part of the network. The overvoltage stress is evaluated considering thermal and dielectric sensitivities of the various components. The selected impedance limits were found to be in line with those used by other transmission network operators.
Towers in overhead power lines should be accurately modelled as to enable representing the wave effects when endangered by lightning impulse currents, for discharges striking the tower or the shield wires, or for flashover occurring between the phase conductors and the tower. Several tower models have been developed over the years and, recently, the authors have proposed a new approach based on the Sommerfeld-Goubau wave formalism. The new approach allows to accurately explain the main physical phenomenon associated with the transient behaviour of towers, attempting to clarify some of the assumptions advocated by researchers in this field in a simple way.
Facing the rapid evolution that the electrical system has gone through, with the massive and growing insertion of inverter-based generators, the inclusion of renewable energy sources in the electrical system has allowed us to investigate the possible functionalities of these generators in different situations. In this scenario, the application of photovoltaic generators used as an active filter has been shown a promising solution for mitigating harmonics on the grid. Thus, emphasizing the multifunctionality of these generators. In this paper, we present an analysis of the application of a photovoltaic generator as an active filter for harmonic mitigation. We analysed the harmonic distortion caused by non-linear loads inserted in a medium voltage microgrid to evaluate the filter operation. The results presented illustrate the use of the inverter-based DG in the mitigation of harmonic distortion in the grid, showing the importance of the multifunctionality of DG in modern distribution networks.
Operation of 6-10-35 kV power transmission lines (PTL) under a double earth fault is characterized by significant currents flowing in the ground, which increases the magnetic effect and can result in dangerous voltages on extended metal structures, for example, pipelines passing near these transmission lines. The paper presents the results of studies conducted to develop a method for computer modeling of induced voltages on an above-ground pipeline due to the electromagnetic effect of power lines during double earth faults. This problem was solved using algorithms relying on phase coordinates and implemented in the Fazonord software. Obtained results suggest that under double earth faults, the pipeline parts can be exposed to significant induced voltages, which are close to values that are limiting for emergency conditions. The proposed method and the developed computer models can be used in practice to ensure the electrical safety of personnel working on pipelines located near 6-10-35 kV high-voltage transmission lines.
The emergence of solar Photovoltaic (PV) generation has been one of the biggest changes in the Power Grid in the past decade. Such generation plants are generally inverter based and these devices are known sources of harmonics of the fundamental frequency and ‘supraharmonics’ (distortion in the frequency range 2 to 150 kHz). It has long been observed that the service transformers that interface solar PV plants to the grid attenuate supraharmonics and hence such frequencies are localized and generally do not couple to the grid. This paper shows that in solidly grounded systems, such as the ones used in the United States (U.S.), application of conventional grounding schemes to PV plants can lead to the unintended consequence of coupling of supraharmonics to the grid. It describes a case study in which supraharmonics due to inverter switching led to telephone interference for customers located around a solar PV plant. The investigation that followed and its results are presented in this paper.
An increasing number of unbalanced customers can affect the voltage unbalance. To estimate possible effects in the future by e.g. simulations as well as to compare field measurements, it is important to have a reference for unbalanced power and voltage unbalance levels in real low voltage (LV) networks. The paper shows the measurement results of an extensive measuring campaign in German LV networks. The focus of the campaign was the voltage unbalance at transformer busbar, at feeders end and the unbalanced power of the whole LV network as well as the calculated voltage unbalance of the medium voltage (MV) network and the contribution of the LV network to the voltage unbalance at feeders end.
This paper reevaluates the active power direction method for locating the distortion sources in the power distribution network. The inaccuracies in the earlier analysis challenging the active power direction method are identified and the earlier claim of the inconsistency of the method is reconsidered.
Importance of harmonic interactions between installations containing power-electronic based sources and loads has grown in recent years. Such interactions of voltage and current harmonics within a typical low-voltage network and an islanded microgrid with different LEDs are analyzed in this paper. The analysis is based on measurements of two laboratory setups representing a LV network and microgrid with an island-capable power electronic source. The interactions between voltage and current harmonics, which are mainly dependent on the frequency dependent network impedance, are analyzed. The differences between the harmonic interactions in typical networks and in power-electronic based networks are discussed.
This paper presents a harmonic domain (HD) model of a high-voltage direct current (HVDC) system including controls for DC voltage and reactive power via the secant method. The proportional-integral (PI) control scheme is used to verify the results by the secant method. It is shown that the latter achieves computational savings compared to the PI control scheme. A case study is presented and verified with the PSCAD/EMTDC software tool in terms of harmonics and steady state waveforms.
With the advent of outbreaks, health waves, and the advancement of electromedical equipment technology, the concern with the power quality in electrical installations has gained greater attention to the perfect performance of medical equipment. However, effective techniques have been developed that allow the necessary technical requirements to ensure compliance with these facilities. The study investigates the harmonic resonance frequency from reactive power compensation through banks of automatic capacitors applied in an electrical circuit consisting of imaging magnetic resonance (MRI) equipment. Methodologically, the concepts of reactive compensation with comparations to IEC60831-1 are applied for the current of circulating work in capacitors, above 30% of the nominal and the mitigation of the system’s harmonics with implementation ant-resonant filter. However, after compensating the power factor penalty, there was a need for filter dimensioning due to the emergence of harmonic resonances. Thus, for a correct dimensioning of compensations, the concern with harmonics and their consequences are of paramount importance.
Increase in the amplitude of current harmonics at a resonance frequency could lead to high voltage harmonics in the distribution network due to resonance. As these voltage harmonics could potentially damage the insulation of network elements, preventive actions need to be taken. To take preventive actions, investigating the possibility of resonance occurrence in network is necessary. For that purpose, the resonance frequencies of the network can be estimated by employing the equivalent circuits of circuit elements, such as cables or transformers. This indicates that the accuracy of these equivalent circuits significantly affects the estimated resonance frequencies. Consequently, this paper studies the equivalent circuits of grid elements in terms of resonance frequency calculation. Also, the impacts of skin effect and parallel capacitor in cable, and the high frequency model of transformers on the estimated resonance frequencies are analysed. These investigations show that skin effect changes the value of parameters at different frequencies nonlinearly, which further complicates the estimation of resonance frequencies. Therefore, Reduced Least Squares (RLS) method is developed to estimate resonance frequencies based on Least Squares method. Finally, the RLS method is verified by the results of different case studies.
The paper contains a set of observations on the fast charging of electric vehicles (EV’s) on Swedish low voltage networks in rural/commercial and urban areas. The emphasis of the study has been to analyze the impact of EV charging on the electric grid and particularly on the observed waveform distortion. The paper focuses on the observation of harmonics on the grid and the variation in the observed harmonics with time as the charging current increases from a small value associated with limiting the inrush current, to the value required by the EV’s for the fast charging of the battery pack. Observations from a bus charging station at Gothenburg are also discussed.
In many countries, the proportion of high-voltage cables is increasing to address the issue of public resistance to transmission system extensions. A major technical challenge in this is the propagation and amplification of existing background harmonics caused by system resonances at lower frequencies.This paper presents a method to explain harmonic propagation in transmission systems using theory of standing waves. By analyzing the characteristics of standing waves, one can find useful information on the nature and extent of harmonic propagation. It is shown that the presented method describes the standing harmonic voltage on power system lines with different topology and therefore, how a simple change in grid configuration affects the harmonic propagation. The results are verified with good agreement against simulations with commercial power system software. Guides to advance this study to meshed systems is given.
This work shows an application of a deep learning-based graphical tool for analyzing waveform distortion in wind power plants. The tool consists of a deep autoencoder followed by a clustering algorithm. Previous applications of such a tool have covered harmonic emission which follows daily patterns. The challenge of measurements in wind power plants is the intermittence of the power production, which can vary in a time frame of minutes and hours. To this point, this work proposes a modification of a DL method presented in the literature to address measurements from wind power plants. The method can automatically obtain the number of clusters. The method is applied to harmonic measurements from H2 to H50 and active power in a Brazilian wind power plant. The graphical results allowed obtaining the correlation between patterns of odd and even current harmonic with the active power generated by a wind power plant.
Waveform distortions are Power Quality (PQ) disturbances with harmful impacts on power system components, and planning engineers and system operators are deeply interested in new methodologies able to provide a support to limit this impact. The forecasting of PQ indices on voltage and current waveforms is nowadays considered one of the most important tools to provide this support. In this paper, probabilistic forecasting methodologies are proposed, investigated and compared to predict waveform distortion indices with different intervals. The Quantile Regression (QR) model is considered as the underlying forecasting model for predicting the considered PQ index level, and the Principal Component Analysis (PCA) is considered to mitigate the high dimensionality of the forecasting problem that could arise by exploiting data collected by dedicated PQ measurement systems. Numerical applications based on actual data and developed for different lead times give evidence of the suitability of the methodologies and the interest in the obtained results.
The waveforms distortion assessment nowadays requires great research efforts due to the contemporaneous presence of low- and high-frequency harmonics and interharmonics (up to 150 kHz). In this paper, a new multi-method approach allowed accurate and fast analysis of such waveforms. The method profitably integrates the performances of some basic methods: the Discrete Wavelet Transform, the sliding-window modified ESPRIT method, and the sliding-window Discrete Fourier Transform which uses a Nuttal window whose length is accurately calculated thanks to the application of the Prony method or the Particle Swarm Optimization. The accurate calculation of Nuttal window length guarantees a good performance in the high-frequency spectral components assessment while reduced computational efforts are obtained parallelizing the calculation of low- and high-frequency harmonics/interharmonics. Numerical applications on synthetic and measured waveforms demonstrate that the proposed method improves the performances of high-performing methods proposed in the recent relevant literature, in the examined cases.
This paper shows an application of a deep learning method to a solar installation with a solar tracking system. The method consists of a deep autoencoder followed by clustering. The deep learning method allows defining the most dominant component in harmonic spectra during long-term measurements. Power Quality measurements were accessed over two years in 3ϕ PV installation of 6 kVA with 2-axis tracking in northern Sweden. The deep learning results indicate that the third harmonic of current is the component that changes most over the two years. This paper demonstrates that there is a correlation between the daily and seasonal variations of the third harmonic with the solar elevation angle at the location. The main conclusion for this cause was associated with the operation of the solar tracking systems which are based on single-phase motors. The paper also discusses the possibility of correlation of the third harmonic with cloud coverage, snow on the panels, and reactive power unbalance.
