Energies

Editorial

8 pages, 211 KiB

Open AccessEditorial

Editorial for the Special Issue “Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020)”

by Gianfranco Chicco, Andrea Mazza, Salvatore Musumeci, Enrico Pons and Angela Russo

Energies 2022, 15(15), 5752; https://doi.org/10.3390/en15155752 - 8 Aug 2022

Viewed by 1306

Abstract

The 55th International Universities Power Engineering Conference (UPEC 2020) has been held on 1–4 September 2020 in the Virtual Conference mode because of the limitations due to the pandemics, hosted by Politecnico di Torino, Torino, Italy [...] Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

Research

Jump to: Editorial, Review

17 pages, 558 KiB

Open AccessArticle

Trichel Pulse Analysis: Physical Calculation and Validation by Using Broadband Measurements

by Kerstin Friebe and Frank Jenau

Energies 2021, 14(15), 4512; https://doi.org/10.3390/en14154512 - 26 Jul 2021

Cited by 1 | Viewed by 2115

Abstract

Partial discharge measurement is part of the monitoring of equipment in power engineering systems. It provides important information about the condition of the equipment and in particular the condition of the insulation components. This information serves to take necessary preventive measures at an [...] Read more.

Partial discharge measurement is part of the monitoring of equipment in power engineering systems. It provides important information about the condition of the equipment and in particular the condition of the insulation components. This information serves to take necessary preventive measures at an early stage to avoid failures of the affected energy system and thus ensure a high level of energy supply security. Possible causes of partial discharges in energy technology equipment include high field strengths at edges with small radii or defects within insulation materials itself. Depending on the location and extent of the occurrence, partial discharge events may cause lasting damage to components of equipment. In order to be able to interpret the measurement results of partial discharge monitoring with regard to the exact cause and, if necessary, to evaluate them automatically, a precise understanding of the physical phenomena that occur during a partial discharge is necessary. The physical replication of a partial discharge pulse helps to better understand, evaluate, and interpret measurement results and thus create a synergy between measurement data and model-based results. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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31 pages, 8039 KiB

Open AccessArticle

Optimal Computation of Network Indicators for Electricity Market Bidding Zones Configuration Considering Explicit N-1 Security Constraints

by Cristian Bovo, Valentin Ilea, Enrico Maria Carlini, Mauro Caprabianca, Federico Quaglia, Luca Luzi and Giuseppina Nuzzo

Energies 2021, 14(14), 4267; https://doi.org/10.3390/en14144267 - 14 Jul 2021

Cited by 4 | Viewed by 1867

Abstract

In this paper an optimization problem designed to calculate electric grid specific indicators to be used within model-based methodologies for the definition of alternative electricity market bidding zone configurations is designed. The approach integrates within the framework of a bidding zone review process [...] Read more.

In this paper an optimization problem designed to calculate electric grid specific indicators to be used within model-based methodologies for the definition of alternative electricity market bidding zone configurations is designed. The approach integrates within the framework of a bidding zone review process aligned to the specifications of the Commission Regulation (EU) 2015/1222 (CACM) and Regulation (EU) 2019/943 of the European Parliament and of the Council (CEP). The calculated solution of the optimization provides locational marginal prices and allows to determine, outside the optimization problem, the power transfer distribution factors for critical elements. Both indicators can be used as inputs by specially designed clustering algorithms to identify model-based electricity market bidding zone configurations, as alternative to the current experience-based configurations. The novelty of the optimization problem studied in this paper consists in integrating the N-1 security criteria for transmission network operation in an explicit manner, rather than in a simplified and inaccurate manner, as encountered in the literature. The optimization problem is evaluated on a set of historical and significant operating scenarios of the Italian transmission network, carefully selected by the Italian transmission system operator. The results show the optimization problem capability to produce insightful results for supporting a bidding zone review process and its advantages with respect to simplified methodologies encountered in the literature. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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25 pages, 3335 KiB

Open AccessArticle

Technical Indicators for the Comparison of Power Network Development in Scenario Evaluations

by Maria Dicorato, Gioacchino Tricarico, Giuseppe Forte and Francesca Marasciuolo

Energies 2021, 14(14), 4179; https://doi.org/10.3390/en14144179 - 10 Jul 2021

Cited by 11 | Viewed by 1954

Abstract

The problem of electric network expansion has different implications concerning the definition of criteria for the comparison of different candidate projects. Transmission expansion planning usually involves a set of economic and technical influences on market framework and on network operation over defined scenario [...] Read more.

The problem of electric network expansion has different implications concerning the definition of criteria for the comparison of different candidate projects. Transmission expansion planning usually involves a set of economic and technical influences on market framework and on network operation over defined scenario evolutions, or even combining generation and transmission planning, although the application to real-sized networks usually implies cost-benefit analysis. In this paper, a methodology for performance analysis of a set of network development projects is proposed, including zonal market framework and load flow analysis, in order to individuate possible candidate projects and their influence on active power losses, admissible load increase and admissible renewable generation increase. Those merit indicators are compared among candidate projects by means of Analytic Hierarchy Process (AHP) method, aiming at determining the most promising solution under different weights of criteria. Moreover, the influence of network development investment cost on project selection is assessed by means of an extension of AHP. The procedure is applied to yearly operation of NREL-118 test system. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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19 pages, 3213 KiB

Open AccessArticle

Short-Term Load Forecasting Using Convolutional Neural Networks in COVID-19 Context: The Romanian Case Study

by Andrei M. Tudose, Irina I. Picioroaga, Dorian O. Sidea, Constantin Bulac and Valentin A. Boicea

Energies 2021, 14(13), 4046; https://doi.org/10.3390/en14134046 - 5 Jul 2021

Cited by 31 | Viewed by 3670

Abstract

Short-term load forecasting (STLF) is fundamental for the proper operation of power systems, as it finds its use in various basic processes. Therefore, advanced calculation techniques are needed to obtain accurate results of the consumption prediction, taking into account the numerous exogenous factors [...] Read more.

Short-term load forecasting (STLF) is fundamental for the proper operation of power systems, as it finds its use in various basic processes. Therefore, advanced calculation techniques are needed to obtain accurate results of the consumption prediction, taking into account the numerous exogenous factors that influence the results’ precision. The purpose of this study is to integrate, additionally to the conventional factors (weather, holidays, etc.), the current aspects regarding the global COVID-19 pandemic in solving the STLF problem, using a convolutional neural network (CNN)-based model. To evaluate and validate the impact of the new variables considered in the model, the simulations are conducted using publicly available data from the Romanian power system. A comparison study is further carried out to assess the performance of the proposed model, using the multiple linear regression method and load forecasting results provided by the Romanian Transmission System Operator (TSO). In this regard, the Mean Squared Error (MSE), the Mean Absolute Error (MAE), the Mean Absolute Percentage Error (MAPE), and the Root Mean Square Error (RMSE) are used as evaluation indexes. The proposed methodology shows great potential, as the results reveal better error values compared to the TSO results, despite the limited historical data. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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15 pages, 3852 KiB

Open AccessFeature PaperArticle

Identification of DC Thermal Steady-State Differential Inductance of Ferrite Power Inductors

by Salvatore Musumeci, Luigi Solimene and Carlo Stefano Ragusa

Energies 2021, 14(13), 3854; https://doi.org/10.3390/en14133854 - 26 Jun 2021

Cited by 14 | Viewed by 2254

Abstract

In this paper, we propose a method for the identification of the differential inductance of saturable ferrite inductors adopted in DC–DC converters, considering the influence of the operating temperature. The inductor temperature rise is caused mainly by its losses, neglecting the heating contribution [...] Read more.

In this paper, we propose a method for the identification of the differential inductance of saturable ferrite inductors adopted in DC–DC converters, considering the influence of the operating temperature. The inductor temperature rise is caused mainly by its losses, neglecting the heating contribution by the other components forming the converter layout. When the ohmic losses caused by the average current represent the principal portion of the inductor power losses, the steady-state temperature of the component can be related to the average current value. Under this assumption, usual for saturable inductors in DC–DC converters, the presented experimental setup and characterization method allow identifying a DC thermal steady-state differential inductance profile of a ferrite inductor. The curve is obtained from experimental measurements of the inductor voltage and current waveforms, at different average current values, that lead the component to operate from the linear region of the magnetization curve up to the saturation. The obtained inductance profile can be adopted to simulate the current waveform of a saturable inductor in a DC–DC converter, providing accurate results under a wide range of switching frequency, input voltage, duty cycle, and output current values. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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18 pages, 18223 KiB

Open AccessArticle

Comprehensive Model for Real Battery Simulation Responsive to Variable Load

by Gustavo Piske Fenner, Leonardo Weber Stringini, Camilo Alberto Sepulveda Rangel and Luciane Neves Canha

Energies 2021, 14(11), 3209; https://doi.org/10.3390/en14113209 - 31 May 2021

Cited by 5 | Viewed by 2976

Abstract

This paper proposes a battery voltage model that is suitable for variable operation. The model combines the features of the Kinetic Battery Model (KiBaM) and voltage model (VM), and it improves the accuracy and quality of the solution, addressing four characteristics of operation: [...] Read more.

This paper proposes a battery voltage model that is suitable for variable operation. The model combines the features of the Kinetic Battery Model (KiBaM) and voltage model (VM), and it improves the accuracy and quality of the solution, addressing four characteristics of operation: charging, discharging, rest after charge, and rest after discharge. This model will be known as 4-KiVM and shows low impact on computational burden. The proposed model can keep track of the voltage even when the load is inverted or turned off. To calibrate and validate the model, a NASA-provided dataset was used composed of a battery with variable charges and discharges, simulating real applications. A metaheuristic method based on tabu search is used to extract constants from this dataset and validate this hybrid model. In addition, a comparison of performance of the 4-KiVM against KiBaM, VM, and the electric circuit model (ECM) was made, showing its advantages. The results of the simulations showed a good prediction of the battery voltage response and SOC prediction in random (variable) use. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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17 pages, 6818 KiB

Open AccessArticle

Design of a Medium Voltage Generator with DC-Cascade for High Power Wind Energy Conversion Systems

by Jonas Steffen, Sebastian Lengsfeld, Marco Jung, Bernd Ponick, Mercedes Herranz Gracia, Aristide Spagnolo, Markus Klöpzig, Klaus Schleicher and Klaus Schäfer

Energies 2021, 14(11), 3106; https://doi.org/10.3390/en14113106 - 26 May 2021

Cited by 9 | Viewed by 3015

Abstract

This paper shows a new concept to generate medium voltage (MV) in wind power application to avoid an additional transformer. Therefore, the generator must be redesigned with additional constraints and a new topology for the power rectifier system by using multiple low voltage [...] Read more.

This paper shows a new concept to generate medium voltage (MV) in wind power application to avoid an additional transformer. Therefore, the generator must be redesigned with additional constraints and a new topology for the power rectifier system by using multiple low voltage (LV) power rectifiers connected in series and parallel to increase the DC output voltage. The combination of parallel and series connection of rectifiers is further introduced as DC-cascade. With the resulting DC-cascade, medium output voltage is achieved with low voltage rectifiers and without a bulky transformer. This approach to form a DC-cascade reduces the effort required to achieve medium DC voltage with a simple rectifier system. In this context, a suitable DC-cascade control was presented and verified with a laboratory test setup. A gearless synchronous generator, which is highly segmented so that each segment can be connected to its own power rectifier, is investigated. Due to the mixed AC and DC voltage given by the DC-cascade structure, it becomes more demanding to the design of the generator insulation, which influences the copper fill factor and the design of the cooling system. A design strategy for the overall generator design is carried out considering the new boundary conditions. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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34 pages, 1308 KiB

Open AccessArticle

Framework for Deterministic Assessment of Risk-Averse Participation in Local Flexibility Markets ^†

by Carlo Schmitt, Felix Gaumnitz, Andreas Blank, Olivier Rebenaque, Théo Dronne, Arnault Martin, Philippe Vassilopoulos, Albert Moser and Fabien Roques

Energies 2021, 14(11), 3012; https://doi.org/10.3390/en14113012 - 22 May 2021

Cited by 4 | Viewed by 2174

Abstract

Local flexibility markets (LFMs) are a market-based concept to integrate distributed energy resources into congestion management. However, the activation of flexibility for storage-based flexibility changes the respective state of charge. Compensation in later points of time is needed to regain the original flexibility [...] Read more.

Local flexibility markets (LFMs) are a market-based concept to integrate distributed energy resources into congestion management. However, the activation of flexibility for storage-based flexibility changes the respective state of charge. Compensation in later points of time is needed to regain the original flexibility potential. Therefore, we propose a LFM bid formulation including both flexibility and compensation. Furthermore, flexibility market participation might lead to inc-dec-gaming, i.e., congestion-increasing behavior to maximize profits. However, this inc-dec-gaming might lead to electricity market schedule deviations if LFM offers are not activated. We propose a risk-averse modeling formulation considering the potential non-activation of LFM bids to provide a framework for the assessment of LFM participation comparing different approaches. Our exemplary case studies demonstrate the proposed LFM bid formulation and show the impact of LFM participation modeling on inc-dec-gaming and congestion management costs. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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15 pages, 806 KiB

Open AccessArticle

Demand Response Alert Service Based on Appliance Modeling

by Ioanna-M. Chatzigeorgiou, Christos Diou, Kyriakos C. Chatzidimitriou and Georgios T. Andreou

Energies 2021, 14(10), 2953; https://doi.org/10.3390/en14102953 - 20 May 2021

Cited by 4 | Viewed by 1872

Abstract

Demand response has been widely developed during recent years to increase efficiency and decrease the cost in the electric power sector by shifting energy use, smoothening the load curve, and thus ensuring benefits for all participating parties. This paper introduces a Demand Response [...] Read more.

Demand response has been widely developed during recent years to increase efficiency and decrease the cost in the electric power sector by shifting energy use, smoothening the load curve, and thus ensuring benefits for all participating parties. This paper introduces a Demand Response Alert Service (DRAS) that can optimize the interaction between the energy industry parties and end users by sending the minimum number of relatable alerts to satisfy the transformation of the load curve. The service creates appliance models for certain deferrable appliances based on past-usage measurements and prioritizes households according to the probability of the use of their appliances. Several variations of the appliance model are examined with respect to the probabilistic association of appliance usage on different days. The service is evaluated for a peak-shaving scenario when either one or more appliances per household are involved. The results demonstrate a significant improvement compared to a random selection of end users, thus promising increased participation and engagement. Indicatively, in terms of the Area Under the Curve (AUC) index, the proposed method achieves, in all the studied scenarios, an improvement ranging between 41.33% and 64.64% compared to the baseline scenario. In terms of the

F_{1}

score index, the respective improvement reaches up to 221.05%. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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20 pages, 6028 KiB

Open AccessArticle

Machine Learning-Based Classification of Electrical Low Voltage Cable Degradation

by Egnonnumi Lorraine Codjo, Bashir Bakhshideh Zad, Jean-François Toubeau, Bruno François and François Vallée

Energies 2021, 14(10), 2852; https://doi.org/10.3390/en14102852 - 15 May 2021

Cited by 8 | Viewed by 3220

Abstract

Low voltage distribution networks have not been traditionally designed to accommodate the large-scale integration of decentralized photovoltaic (PV) generations. The bidirectional power flows in existing networks resulting from the load demand and PV generation changes as well as the influence of ambient temperature [...] Read more.

Low voltage distribution networks have not been traditionally designed to accommodate the large-scale integration of decentralized photovoltaic (PV) generations. The bidirectional power flows in existing networks resulting from the load demand and PV generation changes as well as the influence of ambient temperature led to voltage variations and increased the leakage current through the cable insulation. In this paper, a machine learning-based framework is implemented for the identification of cable degradation by using data from deployed smart meter (SM) measurements. Nodal voltage variations are supposed to be related to cable conditions (reduction of cable insulation thickness due to insulation wear) and to client net demand changes. Various machine learning techniques are applied for classification of nodal voltages according to the cable insulation conditions. Once trained according to the comprehensive generated datasets, the implemented techniques can classify new network operating points into a healthy or degraded cable condition with high accuracy in their predictions. The simulation results reveal that logistic regression and decision tree algorithms lead to a better prediction (with a 97.9% and 99.9% accuracy, respectively) result than the k-nearest neighbors (which reach only 76.7%). The proposed framework offers promising perspectives for the early identification of LV cable conditions by using SM measurements. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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17 pages, 7590 KiB

Open AccessArticle

Model-Based Identification of Alternative Bidding Zones: Applications of Clustering Algorithms with Topology Constraints

by Pietro Colella, Andrea Mazza, Ettore Bompard, Gianfranco Chicco, Angela Russo, Enrico Maria Carlini, Mauro Caprabianca, Federico Quaglia, Luca Luzi and Giuseppina Nuzzo

Energies 2021, 14(10), 2763; https://doi.org/10.3390/en14102763 - 12 May 2021

Cited by 8 | Viewed by 2463

Abstract

The definition of bidding zones is a relevant question for electricity markets. The bidding zones can be identified starting from information on the nodal prices and network topology, considering the operational conditions that may lead to congestion of the transmission lines. A well-designed [...] Read more.

The definition of bidding zones is a relevant question for electricity markets. The bidding zones can be identified starting from information on the nodal prices and network topology, considering the operational conditions that may lead to congestion of the transmission lines. A well-designed bidding zone configuration is a key milestone for an efficient market design and a secure power system operation, being the basis for capacity allocation and congestion management processes, as acknowledged in the relevant European regulation. Alternative bidding zone configurations can be identified in a process assisted by the application of clustering methods, which use a predefined set of features, objectives and constraints to determine the partitioning of the network nodes into groups. These groups are then analysed and validated to become candidate bidding zones. The content of the manuscript can be summarized as follows: (1) A novel probabilistic multi-scenario methodology was adopted. The approach needs the analysis of features that are computed considering a set of scenarios defined from solutions in normal operation and in planned maintenance cases. The weights of the scenarios are indicated by TSOs on the basis of the expected frequency of occurrence; (2) The relevant features considered are the Locational Marginal Prices (LMPs) and the Power Transfer Distribution Factors (PTDFs); (3) An innovative computation procedure based on clustering algorithms was developed to group nodes of the transmission electrical network into bidding zones considering topological constraints. Several settings and clustering algorithms were tested in order to evaluate the robustness of the identified solutions. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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19 pages, 1614 KiB

Open AccessArticle

Empirical Validation of a Biogas Plant Simulation Model and Analysis of Biogas Upgrading Potentials

by Jan Martin Zepter, Jan Engelhardt, Tatiana Gabderakhmanova and Mattia Marinelli

Energies 2021, 14(9), 2424; https://doi.org/10.3390/en14092424 - 24 Apr 2021

Cited by 17 | Viewed by 3620

Abstract

Biogas plants may support the transformation towards renewable-based and integrated energy systems by providing dispatchable co-generation as well as opportunities for biogas upgrading or power-to-X conversion. In this paper, a simulation model that comprises the main dynamics of the internal processes of a [...] Read more.

Biogas plants may support the transformation towards renewable-based and integrated energy systems by providing dispatchable co-generation as well as opportunities for biogas upgrading or power-to-X conversion. In this paper, a simulation model that comprises the main dynamics of the internal processes of a biogas plant is developed. Based on first-order kinetics of the anaerobic digestion process, the biogas production of an input feeding schedule of raw material can be estimated. The output of the plant in terms of electrical and thermal energy is validated against empirical data from a 3-MW biogas plant on the Danish island of Bornholm. The results show that the model provides an accurate representation of the processes within a biogas plant. The paper further provides insights on the functioning of the biogas plant on Bornholm as well as discusses upgrading potentials of biogas to biomethane at the plant from an energy perspective. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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19 pages, 4981 KiB

Open AccessArticle

Double-String Battery System with Reconfigurable Cell Topology Operated as a Fast Charging Station for Electric Vehicles

by Jan Engelhardt, Jan Martin Zepter, Tatiana Gabderakhmanova, Gunnar Rohde and Mattia Marinelli

Energies 2021, 14(9), 2414; https://doi.org/10.3390/en14092414 - 23 Apr 2021

Cited by 26 | Viewed by 3537

Abstract

This paper introduces a novel design of an electric vehicle (EV) fast charging station, consisting of a battery energy storage system (BESS) with reconfigurable cell topology. The BESS comprises two battery strings that decouple the power flow between EV and grid, to enable [...] Read more.

This paper introduces a novel design of an electric vehicle (EV) fast charging station, consisting of a battery energy storage system (BESS) with reconfigurable cell topology. The BESS comprises two battery strings that decouple the power flow between EV and grid, to enable charging powers above the grid capacity. The reconfigurable design is achieved by equipping the battery cells with semiconductor switches and serves two main purposes. First, it aims at solving cell unbalance issues to increase safety, reliability, and lifetime of the battery. Second, it enables the BESS to actively control the EV charging process by changing its cell configuration in a real-time fashion, making a DC-DC converter redundant. The paper presents a modelling approach that captures the reconfigurable design including the controlling algorithm used for cell engagement. The simulation results show that the BESS is able to fulfil the EV request with sufficient accuracy for most of the fast charging process. However, the switching of cells leads to variations in the charging current that can potentially exceed the tolerance band defined in IEC61851-23. Therefore, complementary measures are suggested to achieve a suitable current control during all phases of the charging process. The estimated BESS efficiency during the EV fast charging process is

93.3

%. The losses caused by the reconfigurable design amount to

1.2

% of the provided energy. It is demonstrated that the proposed design has a competitive efficiency compared to a battery buffered fast charging station with DC-DC converter. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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15 pages, 5524 KiB

Open AccessArticle

Mutual Coupling Compensation Techniques Used for Distance Protection of Parallel Lines

by Michael O Donovan, Noel Barry, Joe Connell and Eoin Cowhey

Energies 2021, 14(7), 1982; https://doi.org/10.3390/en14071982 - 2 Apr 2021

Cited by 5 | Viewed by 6464

Abstract

When a distance relay protects a transmission line located on a dual circuit tower, a coupling effect will occur between the two circuits. Transposition of the circuits can reduce the mutual impedances, but this does not cater to the zero-sequence mutual coupling impedance [...] Read more.

When a distance relay protects a transmission line located on a dual circuit tower, a coupling effect will occur between the two circuits. Transposition of the circuits can reduce the mutual impedances, but this does not cater to the zero-sequence mutual coupling impedance during earth faults. As a result, the impedance measured by a distance relay under phase-to-earth fault conditions in these circumstances will not represent the correct impedance to the fault point unless these effects are taken into account. On multi-circuit lines, primarily if they operate in parallel, a zero-sequence mutual coupling should be considered when calculating settings for distance protection function. A 220 kV parallel line sharing the same tower was analysed using DigSilent Power Factory in the simulations. Phase-to-earth faults in different configurations were analysed on this system, and the reach of the protection relay was then estimated for operation. The results confirm how a protection relay can overreach and underreach in a distance protection scheme due to the influence of mutual coupling. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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16 pages, 3813 KiB

Open AccessArticle

A Hybrid Hilbert-Huang Method for Monitoring Distorted Time-Varying Waveforms

by Radu Plamanescu, Ana-Maria Dumitrescu, Mihaela Albu and Siddharth Suryanarayanan

Energies 2021, 14(7), 1864; https://doi.org/10.3390/en14071864 - 27 Mar 2021

Cited by 4 | Viewed by 2684

Abstract

The electric power systems together with the entire energy sector are rapidly evolving towards a low-carbon, secure, and competitive economy facing revolutionary transformations from technical structure to economic value chain. Pathways to achieve sustainability led to the development of new technologies, accommodation of [...] Read more.

The electric power systems together with the entire energy sector are rapidly evolving towards a low-carbon, secure, and competitive economy facing revolutionary transformations from technical structure to economic value chain. Pathways to achieve sustainability led to the development of new technologies, accommodation of larger shares of unpredictable and stochastic electricity transfer from sources to end-users without loss of reliability, new business models and services, data management, and so on. The new technologies and incentives for local energy communities along with large development of microgrids are main forces driving the evolution of the low voltage energy sector changing the context and paradigm of rigid contractual binding between utilities and end-user customers (now progressing to flexible prosumers with generation and storage capabilities). The flexibility and operation of a prosumer can be enhanced by a non-intrusive time-frequency analysis of distorted power quality waveforms for both generation and demand at the point of common connection. Therefore, it becomes of importance to discriminate among successive quasi-steady-state operation of a given local system using only the aggregated waveforms information available in the PCC. This paper focuses on the Hilbert–Huang method with modifications such as empirical mode decomposition improved with masking signals based on the Fast Fourier Transform, Hilbert spectral analysis, and a post-processing method for separating components and their amplitudes and frequencies within distorted power signals for a low-voltage prosumer operation. The method is used for a time-frequency-magnitude representation with promising localization capabilities enabling efficient operation for prosumers. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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10 pages, 2395 KiB

Open AccessArticle

Fault Simulations in a Multiterminal High Voltage DC Network with Modular Multilevel Converters Using Full-Bridge Submodules

by Ioan-Cătălin Damian, Mircea Eremia and Lucian Toma

Energies 2021, 14(6), 1653; https://doi.org/10.3390/en14061653 - 16 Mar 2021

Cited by 3 | Viewed by 1536

Abstract

The concept of high-voltage DC transmission using a multiterminal configuration is presently a central topic of research and investment due to rekindled interest in renewable energy resource integration. Moreover, great attention is given to fault analysis, which leads to the necessity of developing [...] Read more.

The concept of high-voltage DC transmission using a multiterminal configuration is presently a central topic of research and investment due to rekindled interest in renewable energy resource integration. Moreover, great attention is given to fault analysis, which leads to the necessity of developing proper tools that enable proficient dynamic simulations. This paper leverages models and control system design techniques and demonstrates their appropriateness for scenarios in which faults are applied. Furthermore, this paper relies on full-bridge submodule topologies in order to underline the increase in resilience that such a configuration brings to the multiterminal DC network, after an unexpected disturbance. Therefore, strong focus is given to fault response, considering that converters use a full-bridge topology and that overhead power lines connect the terminals. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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34 pages, 938 KiB

Open AccessArticle

An Optimal Power Flow Algorithm for the Simulation of Energy Storage Systems in Unbalanced Three-Phase Distribution Grids

by Lukas Held, Felicitas Mueller, Sina Steinle, Mohammed Barakat, Michael R. Suriyah and Thomas Leibfried

Energies 2021, 14(6), 1623; https://doi.org/10.3390/en14061623 - 15 Mar 2021

Cited by 15 | Viewed by 2769

Abstract

An optimal power flow algorithm for unbalanced three-phase distribution grids is presented in this paper as a new tool for grid planning on low voltage level. As additional equipment like electric vehicles, heat pumps or solar power systems can sometimes cause unbalanced power [...] Read more.

An optimal power flow algorithm for unbalanced three-phase distribution grids is presented in this paper as a new tool for grid planning on low voltage level. As additional equipment like electric vehicles, heat pumps or solar power systems can sometimes cause unbalanced power flows, existing algorithms have to be adapted. In comparison to algorithms considering balanced power flows, the presented algorithm uses a complete model of a three-phase four-wire low voltage grid. Additionally, a constraint for the voltage unbalance in the grid is introduced. The algorithm can be used to optimize the operation of energy storage systems in unbalanced systems. The used grid model, constraints, objective function and solver are explained in detail. A validation of the algorithm using a commercial tool is done. Additionally, three exemplary optimizations are performed to show possible applications for this tool. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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18 pages, 7555 KiB

Open AccessArticle

Empirical Analysis of High Voltage Battery Pack Cells for Electric Racing Vehicles

by Khaled Sehil, Basem Alamri, Mohammed Alqarni, Abdulhafid Sallama and Mohamed Darwish

Energies 2021, 14(6), 1556; https://doi.org/10.3390/en14061556 - 11 Mar 2021

Cited by 12 | Viewed by 3041

Abstract

This paper examines the specifications of lithium battery cells, which are considered one of the most vital sources for electrical energy storage units. The specifications have been covered to associate battery performance with its usage for electrically powered motor vehicles. With the motivation [...] Read more.

This paper examines the specifications of lithium battery cells, which are considered one of the most vital sources for electrical energy storage units. The specifications have been covered to associate battery performance with its usage for electrically powered motor vehicles. With the motivation of rapid deployment of electric vehicles (EVs) around the world, the key contribution of this study is to provide a comparative investigation of well-known commercially available Li-ion battery cells used as a pack for electric race car. Five lithium cells from different manufacturers were analyzed for start voltage, end voltage, current, and the use of active cooling under different test conditions. Thermal imaging was used to provide more comprehensive analysis of tested battery packs. The outcomes of this experimental investigation are described in the sections below in the order in which the analyses were conducted. The key findings of this study are presented in the conclusion section. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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14 pages, 4785 KiB

Open AccessArticle

Economic Feasibility of Photovoltaic Micro-Installations Connected to the Brazilian Distribution Grid in Light of Proposed Changes to Regulations

by Gabriel Nasser Doyle de Doile, Paulo Rotella Junior, Priscila França Gonzaga Carneiro, Rogério Santana Peruchi, Luiz Célio Souza Rocha, Karel Janda and Giancarlo Aquila

Energies 2021, 14(6), 1529; https://doi.org/10.3390/en14061529 - 10 Mar 2021

Cited by 14 | Viewed by 2441

Abstract

Brazil is currently undergoing changes to regulations on distributed generation (DG), specifically for solar energy micro-generation. The changes proposed by the Brazilian Regulatory Agency suggest that only the cost of energy be compensated to investors. The service costs and other charges related to [...] Read more.

Brazil is currently undergoing changes to regulations on distributed generation (DG), specifically for solar energy micro-generation. The changes proposed by the Brazilian Regulatory Agency suggest that only the cost of energy be compensated to investors. The service costs and other charges related to energy tariffs must be divided among consumers. Investors with existing installations and class entities have contested these proposals, calling them “sun-fees”. To date, no scientific papers have been published discussing these changes. The new regulations propose an end to cross subsidies, where all consumers (even those who do not have DG) pay for the transmission and distribution systems. This study compares the economic feasibility of micro-generation before and after implementing the new standards proposed by the regulatory agency. We used data on average electrical energy demand, energy price, and solar radiation in different regions. The national averages were used as a base comparison with other scenarios. The results show that projects are viable for all analyzed scenarios, however, after implementing the proposed changes, the discounted payback time is extended. This, however, does not make projects unfeasible. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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17 pages, 1563 KiB

Open AccessArticle

Open Source Modelling and Simulation of the Nordic Hydro Power System

by Iasonas Kouveliotis-Lysikatos, Angelica Waernlund, Manuel Marin, Mikael Amelin and Lennart Söder

Energies 2021, 14(5), 1425; https://doi.org/10.3390/en14051425 - 5 Mar 2021

Cited by 4 | Viewed by 3761

Abstract

In this paper, we present the results from the development and the simulation of a hydro power model for Sweden and Norway, using SpineOpt software and openly available data. We employ (i) hydrological and market data from the Nordic region and (ii) the [...] Read more.

In this paper, we present the results from the development and the simulation of a hydro power model for Sweden and Norway, using SpineOpt software and openly available data. We employ (i) hydrological and market data from the Nordic region and (ii) the abstract representation of the multi-vector modelling and simulation engine SpineOpt, to compile an open-source model of a large portion of the hydro power plants of the Nordic region, for conducting realistic hydro power generation studies. We place the hydro power system operation within the structuring of the Nordic electricity market and study the effect that different objectives have on the operational results. By employing the SpineOpt functionalities for automating the transformation of the temporal resolution of the model, we explore the trade-of between its computational burden and accuracy. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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27 pages, 8882 KiB

Open AccessArticle

Combined Framework with Heuristic Programming and Rule-Based Strategies for Scheduling and Real Time Operation in Electric Vehicle Charging Stations

by Héricles Eduardo Oliveira Farias, Camilo Alberto Sepulveda Rangel, Leonardo Weber Stringini, Luciane Neves Canha, Daniel Pegoraro Bertineti, Wagner da Silva Brignol and Zeno Iensen Nadal

Energies 2021, 14(5), 1370; https://doi.org/10.3390/en14051370 - 3 Mar 2021

Cited by 11 | Viewed by 2772

Abstract

This paper proposes a flexible framework for scheduling and real time operation of electric vehicle charging stations (EVCS). The methodology applies a multi-objective evolutionary particle swarm optimization algorithm (EPSO) for electric vehicles (EVs) scheduling based on a day-ahead scenario. Then, real time operation [...] Read more.

This paper proposes a flexible framework for scheduling and real time operation of electric vehicle charging stations (EVCS). The methodology applies a multi-objective evolutionary particle swarm optimization algorithm (EPSO) for electric vehicles (EVs) scheduling based on a day-ahead scenario. Then, real time operation is managed based on a rule-based (RB) approach. Two types of consumer were considered: EV owners with a day-ahead request for charging (scheduled consumers, SCh) and non-scheduling users (NSCh). EPSO has two main objectives: cost reduction and reduce overloading for high demand in grid. The EVCS has support by photovoltaic generation (PV), battery energy storage systems (BESS), and the distribution grid. The method allows the selection between three types of charging, distributing it according to EV demand. The model estimates SC remaining state of charge (SoC) for arriving to EVCS and then adjusts the actual difference by the RB. The results showed a profit for EVCS by the proposed technique. The proposed EPSO and RB have a fast solution to the problem that allows practical implementation. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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26 pages, 12603 KiB

Open AccessArticle

Design Space Optimization of a Three-Phase LCL Filter for Electric Vehicle Ultra-Fast Battery Charging

by Davide Cittanti, Fabio Mandrile, Matteo Gregorio and Radu Bojoi

Energies 2021, 14(5), 1303; https://doi.org/10.3390/en14051303 - 27 Feb 2021

Cited by 17 | Viewed by 4310

Abstract

State-of-the-art ultra-fast battery chargers for electric vehicles simultaneously require high efficiency and high power density, leading to a challenging power converter design. In particular, the grid-side filter, which ensures sinusoidal current absorption with low pulse-width modulation (PWM) harmonic content, can be a major [...] Read more.

State-of-the-art ultra-fast battery chargers for electric vehicles simultaneously require high efficiency and high power density, leading to a challenging power converter design. In particular, the grid-side filter, which ensures sinusoidal current absorption with low pulse-width modulation (PWM) harmonic content, can be a major contributor to the overall converter size and losses. Therefore, this paper proposes a complete analysis, design and optimization procedure of a three-phase LCL filter for a modular DC fast charger. First, an overview of the basic LCL filter modeling is provided and the most significant system transfer functions are identified. Then, the optimal ratio between grid-side and converter-side inductance is discussed, aiming for the maximum filtering performance. A novel design methodology, based on a graphical representation of the filter design space, is thus proposed. Specifically, several constraints on the LCL filtering elements are enforced, such that all feasible design parameter combinations are identified. Therefore, since in low-voltage high-power applications the inductive components typically dominate the overall filter volume, loss and cost, the viable LCL filter design that minimizes the total required inductance is selected. The proposed design procedure is applied to a 30 kW, 20 kHz 3-level unidirectional rectifier, employed in a modular DC fast charger. The performance of the selected optimal design, featuring equal grid-side and converter-side 175 μ

μ

H inductors and 15 μ

μ

F capacitors, is verified experimentally on an active front-end prototype, both in terms of harmonic attenuation capability and current control dynamics. A current total harmonic distortion (THD) of 1.2% is achieved at full load and all generated current harmonics comply with the applicable harmonic standard. Moreover, separate tests are performed with different values of grid inner impedance, verifying the converter control stability in various operating conditions and supporting the general validity of the proposed design methodology. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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26 pages, 11312 KiB

Open AccessArticle

Initial Results of an Extensive, Long-Term Study of the Forecasting of Voltage Sags

by Michele De Santis, Leonardo Di Stasio, Christian Noce, Paola Verde and Pietro Varilone

Energies 2021, 14(5), 1264; https://doi.org/10.3390/en14051264 - 25 Feb 2021

Cited by 16 | Viewed by 1845

Abstract

This paper presents the preliminary results of our research activity aimed at forecasting the number of voltage sags in distribution networks. The final goal of the research is to develop proper algorithms that the network operators could use to forecast how many voltage [...] Read more.

This paper presents the preliminary results of our research activity aimed at forecasting the number of voltage sags in distribution networks. The final goal of the research is to develop proper algorithms that the network operators could use to forecast how many voltage sags will occur at a given site. The availability of four years of measurements at Italian Medium Voltage (MV) networks allowed the statistical analyses of the sample voltage sags without performing model-based simulations of the electric systems in short-circuit conditions. The challenge we faced was to overcome the barrier of the extremely long measurement times that are considered mandatory to obtain a forecast with adequate confidence. The method we have presented uses the random variable time to next event to characterize the statistics of the voltage sags instead of the variable number of sags, which usually is expressed on an annual basis. The choice of this variable allows the use of a large data set, even if only a few years of measurements are available. The statistical characterization of the measured voltage sags by the variable time to next event requires preliminary data-conditioning steps, since the voltage sags that are measured can be divided in two main categories, i.e., rare voltage sags and clusters of voltage sags. Only the rare voltage sags meet the conditions of a Poisson process, and they can be used to forecast the performance that can be expected in the future. However, the clusters do not have the characteristics of memoryless events because they are sequential, time-dependent phenomena the occurrences of which are due to exogenic factors, such as rain, lightning strikes, wind, and other adverse weather conditions. In this paper, we show that filtering the clusters out from all the measured sags is crucial for making successful forecast. In addition, we show that a filter, equal for all of the nodes of the system, represents the origin of the most important critical aspects in the successive steps of the forecasting method. In the paper, we also provide a means of tracking the main problems that are encountered. The initial results encouraged the future development of new efficient techniques of filtering on a site-by-site basis to eliminate the clusters. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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14 pages, 7863 KiB

Open AccessArticle

Research and Solutions to Minimize Frontal Area Overheating of Hydro Generator Stator with Vertical Axis

by Victorita Radulescu

Energies 2021, 14(5), 1243; https://doi.org/10.3390/en14051243 - 24 Feb 2021

Cited by 1 | Viewed by 1975

Abstract

About ten hydroelectric power plants realized from 1970 to 1990 in Romania are confronted with stator overheating. The developed mathematical model analyzes the voltage stability based on modal analysis of the Jacobian matrix, identifying the hazardous modes of variation between voltage and flow [...] Read more.

About ten hydroelectric power plants realized from 1970 to 1990 in Romania are confronted with stator overheating. The developed mathematical model analyzes the voltage stability based on modal analysis of the Jacobian matrix, identifying the hazardous modes of variation between voltage and flow rate, correlated with the characteristics of the analyzed generators and their response to these variations. Vulnerable elements in the system for inductive and capacitive modes of operation are identified. In these conditions, hydro generators cannot attend the secondary voltage control, not even for a frequency power dependency control. The elaborated mathematical model was tested at the hydroelectric power plants Gilceag, Mariselu, and Susag with similar functioning conditions. The necessary conditions for stator ventilation and variation of flow hydrodynamic parameters during the operation were established. The theoretical model was tested with an experimental method applied separately for the thermal and ventilation conditions. Some results obtained during the measurements are illustrated and correlated with the theoretical results. The model was tested to prevent the onset instability of voltage drops and accelerated overheating. Finally, some solutions to minimize the stators overheating based on local conditions are recommended. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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15 pages, 4486 KiB

Open AccessArticle

Coordinated Speed Control Strategy for Minimizing Energy Consumption of a Shearer in Fully Mechanized Mining

by Zheng Zheng, Dilei Chen, Tao Huang and Guopeng Zhang

Energies 2021, 14(5), 1224; https://doi.org/10.3390/en14051224 - 24 Feb 2021

Cited by 5 | Viewed by 1791

Abstract

As one of the major pieces of equipment in fully mechanized coal mining, the drum shearer plays a critical role in improving the efficiency and energy utilization in the coal mining production process. In this paper, an energy consumption model of a shearer, [...] Read more.

As one of the major pieces of equipment in fully mechanized coal mining, the drum shearer plays a critical role in improving the efficiency and energy utilization in the coal mining production process. In this paper, an energy consumption model of a shearer, derived from the analysis of the cutting and traction resistances on the shearer during different processes within a working cycle, is established. Based on the derived model, control and coordination strategies between the two speeds are proposed to minimize the shearer’s energy consumption in unidirectional mining. The case study of a real coal mine shows that the proposed models are valid, and the optimal control of shearer speeds can effectively reduce the energy consumption by 5.16% in a working cycle. To gain further insights into the impact of traction speed and drum rotational speed on the shearer’s energy consumption, several speed coordination cases are employed to further compare with the optimized one. Our study results show that the energy consumption of a shearer can be decreased with the increase of traction speed while decreasing drum rotational speed in coordination. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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28 pages, 5906 KiB

Open AccessArticle

The Innovative FlexPlan Grid-Planning Methodology: How Storage and Flexible Resources Could Help in De-Bottlenecking the European System

by Gianluigi Migliavacca, Marco Rossi, Dario Siface, Matteo Marzoli, Hakan Ergun, Raúl Rodríguez-Sánchez, Maxime Hanot, Guillaume Leclerq, Nuno Amaro, Aleksandr Egorov, Jawana Gabrielski, Björn Matthes and Andrei Morch

Energies 2021, 14(4), 1194; https://doi.org/10.3390/en14041194 - 23 Feb 2021

Cited by 21 | Viewed by 4695

Abstract

The FlexPlan Horizon2020 project aims at establishing a new grid-planning methodology which considers the opportunity to introduce new storage and flexibility resources in electricity transmission and distribution grids as an alternative to building new grid elements, in accordance with the intentions of the [...] Read more.

The FlexPlan Horizon2020 project aims at establishing a new grid-planning methodology which considers the opportunity to introduce new storage and flexibility resources in electricity transmission and distribution grids as an alternative to building new grid elements, in accordance with the intentions of the Clean Energy for all Europeans regulatory package of the European Commission. FlexPlan creates a new innovative grid-planning tool whose ambition is to go beyond the state of the art of planning methodologies by including the following innovative features: assessment of the best planning strategy by analysing in one shot a high number of candidate expansion options provided by a pre-processor tool, simultaneous mid- and long-term planning assessment over three grid years (2030, 2040, 2050), incorporation of a full range of cost–benefit analysis criteria into the target function, integrated transmission distribution planning, embedded environmental analysis (air quality, carbon footprint, landscape constraints), probabilistic contingency methodologies in replacement of the traditional N-1 criterion, application of numerical decomposition techniques to reduce calculation efforts and analysis of variability of yearly renewable energy sources (RES) and load time series through a Monte Carlo process. Six regional cases covering nearly the whole European continent are developed in order to cast a view on grid planning in Europe till 2050. FlexPlan will end up formulating guidelines for regulators and planning offices of system operators by indicating to what extent system flexibility can contribute to reducing overall system costs (operational + investment) yet maintaining current system security levels and which regulatory provisions could foster such process. This paper provides a complete description of the modelling features of the planning tool and pre-processor and provides the first results of their application in small-scale scenarios. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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Review

Jump to: Editorial, Research

23 pages, 693 KiB

Open AccessReview

Concepts and Methods to Assess the Dynamic Thermal Rating of Underground Power Cables

by Diana Enescu, Pietro Colella, Angela Russo, Radu Florin Porumb and George Calin Seritan

Energies 2021, 14(9), 2591; https://doi.org/10.3390/en14092591 - 1 May 2021

Cited by 10 | Viewed by 4224

Abstract

With the increase in the electrical load and the progressive introduction of power generation from intermittent renewable energy sources, the power line operating conditions are approaching the thermal limits. The definition of thermal limits variable in time has been addressed under the concept [...] Read more.

With the increase in the electrical load and the progressive introduction of power generation from intermittent renewable energy sources, the power line operating conditions are approaching the thermal limits. The definition of thermal limits variable in time has been addressed under the concept of dynamic thermal rating (DTR), with which it is possible to provide a more detailed assessment of the line rating and exploit the electrical system more flexibly. Most of the literature on DTR has addressed overhead lines exposed to different weather conditions. The interest in the dynamic thermal rating of power cables is increasing, considering the evolution of computational methods and advanced systems for cable monitoring. This paper contains an overview of the concepts and methods referring to dynamic cable rating (DCR). Starting from the analytical formulations developed many years ago for determining the power cable rating in steady-state conditions, also reported in International Standards, this paper considers the improvements of these formulations proposed during the years. These improvements are leading to include more specific details in the models used for DCR analysis and the computational methods used to assess the power cable’s thermal conditions buried in soil. This paper is focused on highlighting the path from the initial theories and models to the latest literature contributions. Attention is paid to thermal modelling with different levels of detail, applications of 2D and 3D solvers and simplified models, and their validation based on experimental measurements. A salient point of the overview is considering the DCR impact on reliability aspects, risk estimation, real-time calculations, forecasting, and planning with different time horizons. Full article

(This article belongs to the Special Issue Verifying the Targets—Selected Papers from the 55th International Universities Power Engineering Conference (UPEC 2020))

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