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The traditional fault control strategy of converter-interfaced renewable energy sources (CIRESs) may bring about a lower sensitivity level or misoperation of fault component-based directional elements. To overcome this problem, a new control scheme is proposed to adjust sequence impedance angles of CIRESs by computing suitable current references of the CIRES controller. Meanwhile, these current references are maximized by an iterative algorithm to make full use of the short-circuit capacity of CIRESs. The proposed control scheme is applicable to various faulty conditions such as different fault types, power factors, weak grids, and larger fault resistances. Compared with the new directional elements that need to update protection algorithms, the proposed control strategies can make CIRESs compatible with the existing directional elements whilst the necessary fault ride-through (FRT) requirements can still be satisfied. Furthermore, all the controller parameters are not required to be revised based on the detected fault type, even with only local measured data collected. The associated PSCAD simulations, real-time digital simulator (RTDS) testing and the downscale hardware experiment verify the proposed method., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Intelligent Electrical Power Grids

To promote the integration of renewable energy resources into modern energy systems, high-voltage dc (HVdc) and circuit breaker (CB) technologies have become critical to achieving secure and efficient energy transmission. This article reviews the technical development of the related areas, compares diverse breaker concepts and topologies, investigates possible coordination and testing solutions, and points out the remaining challenges as well as future needs. The time-domain simulation and comparative analysis are adopted in this article to analyze and compare the performances of different HVdc CBs. By making use of different selectivity levels of multiterminal HVdc (MTdc) grids, the suitable planning and placement of HVdc CBs can be conducted. Furthermore, by providing insights into the performance of HVdc CBs, the work presented in this article can serve as a useful asset for the upcoming standardization and industrial application process of HVdc grid and CB design and testing., Intelligent Electrical Power Grids, Electrical Engineering Education

This paper puts forward a new algorithm based on Kullback Leibler divergence (KLD) for discriminating inrush and internal fault currents in power transformers. Specifically, the main idea of this algorithm is to utilize the current signal discrepancy of the distribution with ideal fault current waveforms. To such an aim, the proposed index reproduces the differential current signal. Utilizing fast modified least squares technique (MLSE), the differential current signal is generated. Applying the reconstructed differential current and ideal sinusoidal waveforms to the KLD indicator, the distribution discrepancy of the current signal from ideal sinusoidal waveform discriminates inrush and internal fault currents. Also the internal/external identification (IEI) index is introduced that utilizes the phase content of the signals from CTs on both sides to distinguish internal and external faults, especially the faults accompanied with CT saturation. As a result, the proposed method can distinguish inrush currents, internal and external fault currents with/without current transformer (CT) saturation and internal fault currents during transformer energization. The performance of the proposed index is evaluated using practically recorded data and is further compared with the state-of-the-art.

Differential protection, as the key protection element in the power transformers, has always been threatened with sending false trips subjected to external transient disturbances. As a result, differential protection needs an additional block to distinguish between internal faults and external transient disturbances. The protection system should i) be able to perform based on raw data, ii) be able to learn fully temporal features and sudden changes in the transient signals, and iii) impose no assumption on noise. To address these challenges, a fast recurrent neural network, namely fast gated recurrent neural network (FGRNN). By removing the reset gate in the gated recurrent unit (GRU), the proposed network is capable of learning abrupt changes in addition to significantly reducing the computational time. Furthermore, a loss function based on an information theory concept is formulated in this paper to enhance the learning ability as well as robustness against non-Gaussian/Gaussian noises. A generalized form of mutual information is also adopted to form a noise model-free loss function, then incorporated with the designed deep network. Simulated and experimental examinations engaging various external factors, in addition to a comparison between the proposed fast GRNN, GRU, and seven firmly-established methods indicates the faster and more reliable performance of the proposed algorithm.

Modular multilevel converters (MMCs) have emerged as a viable choice in future DC grid architectures due to their scalability to meet voltage level requirements. However, MMC-based DC distribution systems are at risk of short-term outages during the faults in either the DC or AC networks feeding the MMC, so it remains a challenge to accomplish AC and DC fault ride-through (FRT) capability in such applications. To ensure stable operations of the DC terminals, FRT strategies are required for the faults on both the AC and DC sides of the converter. This paper proposes a FRT strategy for the AC and DC side of the converter to ensure stable and economically viable operation of the DC distribution network. The asymmetrical faults in the upstream AC grids are managed by using the integrated energy of the MMC. Whereas, the DC FRT capability of the MMC is accomplished by changing the redundant submodules of the MMC to full-bridge submodules (FBSMs), thus allowing a DC FRT to be achieved by using DC circuit breakers that are low cost and reduced in size. Applying the proposed DC FRT strategy, which makes possible the use of low-cost and reduced in size DC circuit breakers in DC distribution, results in a reduction in the overall initial investments., Peer Reviewed, Postprint (published version)

Differential protection, as the key protection element in the power transformers, has always been threatened with sending false trips subjected to external transient disturbances. As a result, differential protection needs an additional block to distinguish between internal faults and external transient disturbances. The protection system should i) be able to perform based on raw data, ii) be able to learn fully temporal features and sudden changes in the transient signals, and iii) impose no assumption on noise. To address these challenges, a fast recurrent neural network, namely fast gated recurrent neural network (FGRNN). By removing the reset gate in the gated recurrent unit (GRU), the proposed network is capable of learning abrupt changes in addition to significantly reducing the computational time. Furthermore, a loss function based on an information theory concept is formulated in this paper to enhance the learning ability as well as robustness against non-Gaussian/Gaussian noises. A generalized form of mutual information is also adopted to form a noise model-free loss function, then incorporated with the designed deep network. Simulated and experimental examinations engaging various external factors, in addition to a comparison between the proposed fast GRNN, GRU, and seven firmly-established methods indicates the faster and more reliable performance of the proposed algorithm.

With the continuously increasing penetration of networked microgrids (MGs) on the local utility grid (UG), MGs face the challenge to avoid increasing system fault currents during low-voltage ride-through (LVRT). To solve this challenge, an active fault current limitation (AFCL) method is proposed with three parts: 1) a novel phase angle adjustment (PAA) strategy is conducted to relieve the impact of MGs output fault current on system fault current; 2) the current injection (CI) strategy for LVRT is formulated to fit the function of PAA; 3) a novel converter current generation (CCG) strategy is developed to achieve a better voltage support ability by considering network impedance characteristics. The proposed AFCL method is applied to the back-to-back converter, as a connection interface between MGs and UG. Extensive tests and pertinent results have verified the improvements of proposed AFCL method with better LVRT performance, while the networked MGs output fault current does not increase the amplitude of system fault current.

To promote the integration of renewable energy resources into modern energy systems, high-voltage dc (HVdc) and circuit breaker (CB) technologies have become critical to achieving secure and efficient energy transmission. This article reviews the technical development of the related areas, compares diverse breaker concepts and topologies, investigates possible coordination and testing solutions, and points out the remaining challenges as well as future needs. The time-domain simulation and comparative analysis are adopted in this article to analyze and compare the performances of different HVdc CBs. By making use of different selectivity levels of multiterminal HVdc (MTdc) grids, the suitable planning and placement of HVdc CBs can be conducted. Furthermore, by providing insights into the performance of HVdc CBs, the work presented in this article can serve as a useful asset for the upcoming standardization and industrial application process of HVdc grid and CB design and testing., Intelligent Electrical Power Grids, Electrical Engineering Education

Актуальність теми. До недавнього часу електроенергетичні системи характеризувалися централізованим виробництвом електричної енергії, мережами високої на середньої напруги для передачі електричної енергії та мережами низької напруги для її розподілу. Традиційно до розподільної мережі не було підключено жодних джерел розосередженої генерації, однак це змінюється починаючи з минулого десятиліття. В даний час до розподільної мережі підключені різні типи джерел малої генерації, більш відомих як розподілена генерація. Завдяки цілям скорочення CO2 багато дрібних джерел, інтегрованих у розподільну мережу, є відновлюваними джерелами енергії, наприклад, вітрогенератори, невеликі гідростанції та фотоелектричні панелі, також високоефективні не поновлювані джерела енергії, такі як газотурбінні установки. Підключення джерел розподіленої генерації не тільки змінює напрямок перетоків навантаження в розподільній мережі, але й може вплинути на струм короткого замикання. Більшість захисних приладів розподільної мережі налаштовані на спрацювання при виявленні струму короткого замикання або струму, який перевищує номінальний робочий струм мережі. Саме через те що джерела розосередженої генерації впливають на внесок мережі до струму короткого замикання, комутаційно-захисне обладнання мережі може працювати некоректно. В багатьох статтях ця проблема розглянута досить поверхово. Представлений огляд усіх можливих проблем захисту та їх класифікація. Мета та завдання дослідження. Основною метою роботи є розробка моделей та методів техніко-економічної оцінки впливу джерел розосередженої генерації на надійність повітряних розподільних мереж 6-20 кВ. Відповідно до мети поставлені наступні завдання: - аналіз світової практики оцінки надійності електропостачання; - аналіз сучасних технічних засобів розосередженої генерації як складової частини Smart Grid технології; - розробка моделей та методів техніко-економічної оцінки впливу джерел розосередженої генерації на надійність повітряних розподільних, Actuality of theme. Until recently, power systems were characterized by centralized power generation, high to medium voltage grids for electricity transmission, and low voltage grids for its distribution. Traditionally, no distributed generation sources have been connected to the distribution network, but this has changed since the last decade. Currently, different types of small generation sources, better known as distributed generation, are connected to the distribution network. Thanks to CO2 reduction targets, many small sources integrated into the distribution network are renewable energy sources, such as wind turbines, small hydropower plants and photovoltaic panels, as well as highly efficient non-renewable energy sources such as gas turbine plants. Connecting distributed generation sources not only changes the direction of load flows in the distribution network, but can also affect the short-circuit current. Most switchgear protection devices are set to fire when a short circuit or current that exceeds the rated operating current of the network is detected. Due to the fact that the sources of distributed generation affect the contribution of the network to the short-circuit current, the switchgear and protection equipment of the network may not work properly. In many articles, this problem has been addressed rather superficially. An overview of all possible security issues and their classification is provided. The purpose and tasks of the study. The main purpose of the work is the development of models and methods of technical and economic assessment of the influence of sources of dispersed generation on the reliability of air distribution networks 6-20 kV. According to the purpose the following tasks are set: - analysis of the world practice of assessing the reliability of electricity supply; - analysis of modern dispersed generation equipment as an integral part of Smart Grid technology; - development of models and methods of technical and economic assessme

The low-voltage distribution grid is an essential link for the integration of distributed renewable sources. It is expected to experience stronger loading and load variation in the near future. At the same time, part of the low-voltage network is an aging infrastructure. Distribution system operators are therefore becoming increasingly interested in being able to diagnose their low-voltage assets. This paper describes corrosion phenomena that are observed in aluminum conductors after a damage is inflicted to a cable section. Such a damage is suspected to initiate long-Term degradation. Short-duration intermittent current peaks are observed in laboratory experiments and similar peaks are now also recorded in the field. The perspectives for online monitoring, by registering these events, are investigated by having a large number of measurement devices installed on connections in service. The research is directed to gain a better understanding of the relation between the current peaks and cable circuit failures as well as the underlying degradation mechanisms.

The low-voltage distribution grid is an essential link for the integration of distributed renewable sources. It is expected to experience stronger loading and load variation in the near future. At the same time, part of the low-voltage network is an aging infrastructure. Distribution system operators are therefore becoming increasingly interested in being able to diagnose their low-voltage assets. This paper describes corrosion phenomena that are observed in aluminum conductors after a damage is inflicted to a cable section. Such a damage is suspected to initiate long-Term degradation. Short-duration intermittent current peaks are observed in laboratory experiments and similar peaks are now also recorded in the field. The perspectives for online monitoring, by registering these events, are investigated by having a large number of measurement devices installed on connections in service. The research is directed to gain a better understanding of the relation between the current peaks and cable circuit failures as well as the underlying degradation mechanisms.

Direct Drive high-temperature superconducting (HTS) wind turbine generators have been proposed to tackle challenges for ever increasing wind turbine ratings. Due to smaller reactances in HTS generators, higher fault currents and larger transient torques could occur if sudden short circuits take place at generator terminals. In this paper, a finite element model that couples magnetic fields and the generator's equivalent circuits is developed to simulate short-circuit faults. Afterward, the model is used to study the transient performance of a 10-MW HTS wind turbine generator under four different short circuits, i.e., three-phase, phase–phase clear of earth, phase-phase-earth, and phase-earth. The stator current, fault torque, and field current under each short circuit scenario are examined. Also included are the forces experienced by the HTS field winding under short circuits. The results show that the short circuits pose great challenges to the generator, and careful consideration should be given to protect the generator. The findings presented in this paper would be beneficial to the design, operation and protection of an HTS wind turbine generator.

Single Wire Earth Return (SWER) system is an inexpensive method for extending power to remote areas in scantly populated countries such as Australia. SWER network introduces several challenges to the conventional methods for protection relays. This paper focuses on the protection aspect of the SWER network and investigates the effectiveness of the existing conventional protection mechanism in detecting and suppressing common fault conditions including High Impedance faults (HIFs). While the existing SWER distribution network protection system can detect HIFs, it may be often taken as a normal step load increase due to the low fault current levels. The persistence of the HIFs compromises safety of people within the vicinity of the fault and also increase risk of fire, therefore, a new protection strategy for the detection and identification of HIFs to mitigate the risks is necessary. This paper presents a new algorithm based on mathematical morphology, called the Decomposed Open-Close Alternating Sequence, (DOCAS) for the detection and identification of any power system disturbances in SWER systems. The effectiveness of the proposed method in the detection and identification of the High Impedance Fault and differentiate with other conditions such as Single line-to-ground (SLG) fault and step load increase is demonstrated. The simulation results show that the HIFs can be clearly distinguished from the other conditions by analysing the transients generated by the HIFs.

[EN] This work proposes a new method for fault diagnosis in electric power systems based on neural modules. With this method the diagnosis is performed by assigning a generic neural module for each type of element within the electric power system, whether it is a transmission line, bus or transformer. A total of three generic neural modules are designed, one for each type of element. The neural modules for buses and transformers comprise two diagnostic levels that take into consideration the logic states of switches and relays, both internal and back up; the neural module for transmission lines, however, also has a third diagnostic level which takes into account waveforms of fault voltages and currents, as well as the frequency spectrums of these waveforms in order to verify if the line had in fact been subjected to a fault, and at the same time to determine which type of fault (L-g, LL-g, LL, LLL, LLL-g),by means of a neural structure. This third diagnostic level can be carried out given the fact that every transportation line subjected to a fault will present fault currents and voltages before the fault is eliminated from the system by the intervention of its protection systems., [ES] En este trabajo se propone un nuevo método para el diagnóstico de fallas en sistemas eléctricos de potencia basado en módulos neuronales. El método realiza el diagnóstico mediante la asignación de un módulo neuronal genérico para cada tipo de componente que conforma al sistema eléctrico de potencia, ya sea línea de transporte, bus o transformador. En total se diseñan tres módulos neuronales genéricos, uno para cada tipo de componente. Los módulos neuronales para buses y transformadores se componen de dos niveles de diagnóstico tomando en cuenta los estados lógicos de interruptores y relevadores tanto propios como de respaldo, a excepción del módulo neuronal para líneas de transporte, que además de los dos niveles de diagnóstico con los que cuentan los módulos neuronales para buses y transformadores, cuenta con un tercer nivel de diagnóstico que toma en consideración los oscilogramas de voltajes y corrientes de falla, así como los espectros de frecuencia de estos oscilogramas, para verificar si la línea de transporte realmente estuvo sujeta a una falla y a la vez determinar el tipo de ésta (L-g, LL-g, LL, LLL, LLL-g), esto a través de una estructura neuronal. Este tercer nivel de diagnóstico, es posible llevarlo a cabo ya que toda línea de transporte que es sometida a una falla presentará corrientes y voltajes de falla, antes de que ésta sea liberada del sistema por la acción de sus esquemas de protección

Protection of a distribution network in the presence of distributed generators (DGs) using overcurrent relays is a challenging task due to the changes in fault current levels and reverse power flow. Specifically, in the presence of current limited converter interfaced DGs, overcurrent relays may fail to isolate the faulted section either in grid connected or islanded mode of operation. In this paper, a new inverse type relay is presented to protect a distribution network, which may have several DG connections. The new relay characteristic is designed based on the measured admittance of the protected line. The relay is capable of detecting faults under changing fault current levels. The relay performance is evaluated using PSCAD simulation and laboratory experiments.

[Resumen] Para diseñar una toma de tierra es preciso calcular su resistencia equivalente y la distribución de potencial en la superficie del terreno durante una derivación de corriente [1, 2, 3]. Para elllo las normas sólo proponen fórmulas aproximadas para los casos más sencillos. Desde los años 70 se han desarrollado métodos matriciales (Computer Methods) como el APM, en los que los electrodos se subdividen en segmentos cuyo comportamiento se modela a partir de ideas intuitivas (superposición de fuentes de corriente puntuales, promediado del error, etc.) [1, 3, 4, 5, 6]. Sin embargo, la aplicación de estos métodos da lugar a anomalías desconcertantes al aumentar la segmentación de los conductores, con la consiguiente incertidumbre en su margen de error [2, 5]. Los autores han desarrollado una formulación de elementos de contorno en las que se enmarcan los citados métodos matriciales. De esta forma, los metodos matriciales admiten finalmente una fundamentación rigurosa, y es posible explicar su comportamiento asintóticamente anómalo, así como identificar las fuentes de error y valorar la fiabilidad de los resultados de su aplicación.

[Abstract] Grounding systems are designed to guarantee personal security, protection of equipments and continuity of power supply. Hence, engineers must compute the equivalent resistance of the system and the potential distribution on the earth surface when a fault condition occurs [1], [2], [3]. While very crude approximations were available until the 70’s, several computer methods have been more recently proposed on the basis of practice, semi-empirical works and intuitive ideas such as superposition of punctual current sources and error averaging [1], [3], [4], [5], [6]. Although these techniques are widely used, several problems have been reported. Namely: large computational requirements, unrealistic results when segmentation of conductors is increased, and uncertainty in the margin of error [2], [5]. A Boundary Element formulation for grounding analysis is presented in this paper. Existing computer methods such as APM are identified as particular cases within this theoretical framework. While linear and quadratic leakage current elements allow to increase accuracy, computing time is reduced by means of new analytical integration techniques. Former intuitive ideas can now be explained as suitable assumptions introduced in the BEM formulation to reduce computational cost. Thus, the anomalous asymptotic behaviour of this kind of methods is mathematically explained, and sources of error are rigorously identified.