Current earth fault distance measurement based on symmetrical components does not work very well in compensated systems because the steady-state currents through the fault location are significantly smaller than the load currents. It is not possible to distinguish between load current and fault current. It has also been assumed that the fault impedance, including the arc, is a linear impedance. However, this is not the case in the real world, especially for faults in the cable section of a line. The air gap creates an additional layer of insulation with increased and variable ignition voltage. This non-linearity affects the current waveform, voltage waveform, and frequency of the low-current arc. With the new modified method, it is now possible to distinguish between the fault current and the load current and to compensate for the effects of the nonlinearities of the fault impedances. The accuracy of the impedance measurement from the measuring point to the fault location is significantly improved. This paper presents the new method in detail for self-extinguishing and re-igniting earth faults in overhead and cable networks.

Hydrogen will play an important role as an energy storage in the future. For example, the National Hydrogen Strategy of the Federal Ministry of Economics and Climate Protection (BMWK) provides for the expansion of the installation capacity of electrolysis plants for the production of hydrogen from renewable energies in Germany from the current level of approx. 100 MW to 10 GW. With installation capacities of this magnitude, the availability of the electrolysis plants must be ensured by suitable protection concepts. Knowledge of the contribution of the electrolyser to the short circuit current in the event of a fault in an electrolysis plant is an important prerequisite for the design of protection systems for electrolysis plants. The paper presents the current findings on the short circuit current contribution of electrolysers (short-circuit current curve and parameters, relevant influencing variables) and the resulting research questions. The results are based on investigations carried out at the Institute of Energy Technologies (IET-4, Forschungszentrum Jülich) on a 50 kW PEM electrolyser. Furthermore, the test setup used for the experimental investigation of the short-circuit current of the electrolyser and the test specimens used are described.

With the proliferation of harmonic sources, network operators face significant challenges in identifying and interpreting sudden changes in harmonic emission behaviour due to the large volume of power quality data and the lack of automated analysis tools. This article introduces a novel algorithm that detects and characterises atypical harmonic emission patterns based on a comprehensive framework that includes data preparation, anomaly detection, and knowledge acquisition stages. By employing context-based features, the underlying data properties of both typical and atypical patterns are captured effectively. Sliding-window thresholds enable a flexible adaption of the algorithm to variations caused by seasonality and trends. In the knowledge acquisition stage, the significance and properties of atypical patterns are summarised using aggregated anomaly scores, significance categories, and a classification scheme. The algorithm's effectiveness is demonstrated through its application to over 5000 harmonic time series collected in the transmission system in Germany.

The integration of renewable energy sources into electricity grids increases the use of power electronic feeders. To ensure reliable grid integration, control methods are being developed to give these devices characteristics similar to synchronous machines, known as virtual synchronous machines (VSMs). However, VSMs cannot fully replicate synchronous machine behaviour, particularly during faults. Overcurrent capability is significantly reduced, and current limiting algorithms protect the power electronics, often distorting the current waveform. AtTU Dresden'sChair of Electrical Power Supply, a 220 kV physical network model enables short-circuit testing on a transmission line. This model includes three stations, a double-circuit transmission line, and various consumers and feeders. A VSM, connected via an isolating transformer, feeds into the grid. Short-circuit tests at various locations force the VSM into current limitation. Measurements of currents and voltages at the VSM terminals and transmission line were analysed to evaluate distance protection relay behaviour. The study highlights current behaviour during faults with conventional current limiting and assesses whether protection devices accurately detect and switch off faults. Hereby, we observed conventional current limiting in positive sequence systems caused distorted residual currents during asymmetrical faults, leading to relay misoperations and incorrect fault loop detection in some cases.

Due to the continuous integration of power-intensive consumers and producers into low-voltage networks, appropriate equipment models are increasingly important, especially for the calculation of the three-phase network state. Therefore, this paper proposes a generic modelling approach for three-phase two-winding transformers and transformer banks in phase-coordinates. Both asymmetrical and symmetrical transformers of both types can be represented. The different modelling options and the underlying data are comprehensively presented. A large variety of vector groups and neutral point treatments are supported. This paper not only presents the generic modelling approach but also introduces a new methodology for taking into account the asymmetry of three-phase transformers, which is characterised by a particularly low amount of data required. While many transformer models neglect the asymmetrical structure of transformers or require detailed construction data on core and winding geometry, the presented methodology uses only few core geometry ratios. If these data are not available, they can be estimated if necessary or suggested substitutes can be used. For all transformer types, the resulting 6x6, 7x7 or 8x8 matrix can be seamlessly incorporated into the network nodal admittance matrix. The model was validated by comparison with calculation results from established power system calculation programs and measurement results.

This paper presents the test results of the method "faulted phase earthing" (FPE) in isolated and compensated MV-networks. The task of the project is to create similar advantages for cable networks and mixed networks as the earth fault compensation for the overhead line network. First, the main advantages of earth fault compensation for overhead lines compared to low-resistance and solid earthing are listed. Subsequently, standardization for the operation of compensated networks as overhead line networks has been adapted over the past decades. The main advantage of self-extinguishing of the arc without intervention of the protection or the operating personal is no longer given for cable networks. The proportion of cable is steadily increasing in the existing networks, and the overhead line part is being partially reduced. As a result, earth fault compensation is increasingly coming into question, and networks are often converted to low-resistance earthing. New findings regarding the arc suppression behaviour of the earth fault compensation in future networks are presented and a solution combining ‘Faulted Phase Earthing’ is shown. The paper uses real earth fault measurements to describe and discuss the function of the FPE and the positive effects of the FPE on a compensated or isolated system in detail.

The growing penetration of inverter-based generation in modern power grids poses significant challenges to grid stability and the reliability of conventional protection systems. When encountering grid faults, power converters behave significantly differently from synchronous generators. As a result, studying the interaction between conventional grid protection technologies and power electronic converters is of great interest. However, comprehensive laboratory setups that allow for detailed experimental studies remain scarce. This study introduces a unique experimental setup designed to comprehensively investigate the behavior of converter-dominated power systems under fault conditions. The setup integrates freely configurable laboratory converters into a power grid model, which includes scaled replicas of overhead transmission lines and commercially available protection and control devices. This integrated approach enables the simultaneous examination of converter control, transmission line physics, and protection device behavior in a controlled laboratory environment. Experimental results highlight challenges in fault detection and fault current behavior. However, they also demonstrate that selective fault clearing remains possible with conventional protection schemes, provided that grid-forming converters maintain grid connection and effectively limit fault current.

This paper investigates the frequency response of a one-bus test system incorporating converter-based generation, with a focus on the role of grid-forming (GFM) converters in stabilizing future power systems. An RMS simulation is conducted on a test system composed of aggregated generation and load blocks, grouped according to their inertia and frequency support characteristics. The results highlight the critical contribution of GFM converters in maintaining frequency stability in low-inertia grids - a scenario anticipated in the near future due to the ongoing energy transition and the gradual phase-out of conventional synchronous generation. Using DIgSILENT PowerFactory (PF) templates for GFM converters, simulations examine different scenarios involving load increases and the disconnection of synchronous machine (SM) block under varying GFM penetration levels. The findings show that while higher GFM integration may result in lower frequency nadir, the outcome depends strongly on the control system parameters. Nevertheless, GFM converters contribute to frequency stabilization by injecting active power in a manner that emulates the dynamic response of SMs. This one-bus system serves as a conceptual prototype for modelling individual nodes in the SysZell project, where inertial response in cellular energy system should be investigated for the first time. In future work, this model will be extended to reflect dispatched power at each node, based on market simulation and time-series for renewable-energy (RE) based resources for years 2037 and 2045, while taking into account for both economic factors and technical constraints on grid side.

The transient behavior of grid-forming converters changes significantly when the maximum current limit is reached. Conventional control methods based on the positive-sequence component can lead to non-sinusoidal current waveforms under unbalanced conditions and faults. This poses challenges for numerical protection relays, which are designed for generator-based systems. Consequently, protection technology must adapt to future grid structures with increased integration of decentralized power systems. In the short term, aligning grid-forming converter behavior with the operating principles of existing protection relays is essential. This article analyzes the dynamic performance of differential protection relays in relation to the current-limiting methods used by converters. Conventional control methods will lead to sinusoidal deviations when non-symmetrical faults are present. It is shown that current limiting methods can affect the performance of the differential protection. Distorted short-circuit currents can block the fault trip of the differential protection by overfluxing detection. A novel control method is compared with a conventional approach for an unbalanced grid fault. Results show that the proposed method enables differential protection performance comparable to generator-based systems, ensuring fast and selective fault handling critical for grid reliability.

Phase-to-ground faults are the most common type of fault on overhead lines and require accurate detection and selective isolation by distance protection systems to ensure reliable energy transmission. Conventional distance protection relays analyse the impedance of the phase-ground loop of the affected phase, utilizing line impedances to configure protective settings specific to each line. Accurate setting parameters are among the most critical components in a distance protection relay, as they are essential for determining the correct fault location. Improper configuration of these settings can significantly reduce the efficiency of the entire protection system. These settings include the symmetrical components of positive-sequence and zero-sequence impedances, along with the resulting ground impedance compensation factor, so-calledkE-factor. Building on a previously developed line model that realistically simulates overhead lines —including finite length of ground wires and tower propagation resistances—this paper explores the sensitivity of the zero-sequence impedance and the ground impedance compensation factor in distance protection relays by analysing the impact of variations in influencing variables. A case study illustrates discrepancies between calculated and measured impedances in real overhead lines. Further, potential errors in impedance determination, such as inaccuracies from oversimplified mathematical models, are also addressed, highlighting the influencing variables that affect zero-sequence impedance andkE-factor.

Fully electric cars will be increasingly used in the near future in many countries.They are commonly known as electric vehicles (EVs) and use power electronic-based rectifiers for charging their batteries, which may significantly impact power quality in LV and MV distribution grids.Of particular importance are harmonic emissions of EV chargers, which are strongly influenced by the distortion of the supply voltage.This paper presents the results of testing and analyzing harmonic current emission of eight different single-phase EV chargers, with respect to supply voltage distortion.The analysis is based on extensive measurements performed at a test stand, capable of accurately reproducing supply voltage waveforms with desired distortion.The harmonic model consists of a constant part and a part that depends on the level of harmonics in the supply voltage.In order to characterize each EV charger in a general model, some characteristic indices are introduced, which quantify the sensitivity and linearity of harmonic currents of EV chargers to harmonics present in the supply voltage.The paper presents and discusses results for each individual EV charger, as well as a comparison of them.

The growth of renewables in public energy networks requires suitable strategies to assess the stable operation of the respective power electronic devices, e.g., inverters. Different assessment methods can be performed with regard to the available knowledge and the assessment objective, e.g., a specific frequency range or the input signal characteristics that are typically classified into small-signal and large-signal disturbances. This paper addresses the limits of the measurement-based small-signal stability analysis in the harmonic frequency range of commercially available single-phase inverters for photovoltaic applications. The harmonic stability is analyzed, and the results for a sinusoidal background voltage and distorted background voltages are assessed based on measurements. The measurements prove that even in the harmonic frequency range, the harmonic stability analysis can only provide a sufficient but not a necessary condition in terms of the statement towards an instable operation.

This paper presents a framework to assess the grid compatibility of single-phase inverters connected to public low voltage network, which is characterized by a stable operation at reasonable emission. The assessment is based on considering emission, immunity and stability. The state of the art for commercially available devices relies only on the classical, impedance-based stability analysis based on the Nyquist criterion. However, experiences have shown that this is not sufficient for a statement towards the stable operation of an inverter, since the stable operation can also be affected by other factors than the network impedance, e.g. a background voltage distortion. Exemplary laboratory measurements of two commercially available single-phase PV inverters are presented to validate the statement by showing that despite the impedance-based stability criterion is met, inverters can still trip in presence of a high background voltage distortion. The paper concludes that the immunity of the inverter with regard to the voltage distortion at the point of connection (PoC) is additionally of importance for its stable operation.

Conventional distance protection relays face the challenge of accurately calculating fault distances for unbalanced or non-transposed lines. The unbalance of the lines results in significant deviations during distance calculation. Previous studies have presented methods that compensate these deviations, for example by compensating for coupling effects. Often, these methods require complex relay configurations or need information from multiple measurement points. This paper, in contrast, introduces a new algorithm that calculates the measurement deviations for all fault loops in a conductor-selective way without the use of additional measurements. This method is universally applicable to different line and tower constructions, including non-transposed and special-transposed lines. The method works in the natural system and includes capacitive coupling effects, allowing for accurate correction of distance calculation results after short circuit tripping. Experimental results have validated that the proposed method reduces the deviations significantly and increases the accuracy of fault localization.

Bei Freileitungen wird der Einfluss von Erdseilen häufig unter der Annahme einer ideal leitenden Verbindung zur Modellerde im Leitungsmodell berücksichtigt. Darüber hinaus werden zur Berechnung der induktiven Verkopplung konventionell unendlich lange Leiter Erde-Schleifen betrachtet. Der Ansatz geht dabei von einem in Leitungsrichtung homogenen Feldbild aus. Abweichungen von diesem Ansatz treten zum Beispiel am Leitungsanfang und -ende sowie in der Nähe von Verdrillungsmasten auf, da in diesen Bereichen kein homogenes Feld zu erwarten ist. Ebenfalls können Erdseile und Lichtwellenleiter-Erdseile nicht als uns endlich lang angenommen werden, da durch die spannfeldweise Erdung Ausgleichsströme in jedem Spannfeld auftreten, sodass auch hier der Ansatz eines homogenen Feldbildes nicht erfüllt ist. Mit dem Hertz’schen Dipolansatz wird ein komplexer Integralausdruck zur Berechnung der Impedanz von Leitern beliebiger Länge erarbeitet. Dieser lässt sich bei endlicher Leiterlänge nicht in einer geschlossenen Form darstellen, weshalb numerische Methoden zum Einsatz kommen. Um den numerischen Rechenaufwand zu reduzieren, wird der Integralausdruck mithilfe der Image-Theorie approximiert, was die Berechnung für praxisnahe Anordnungen ermöglicht. Mit den Ergebnissen wird ein Leitungsmodell aufgebaut und in MATLAB implementiert, welches es möglich macht, die Leitungsparameter und speziell die Nullimpedanz unter Berücksichtigung verschiedener Einflussparameter zu berechnen. Das Modell wurde sowohl mit einer fiktiven als auch mit einer realen Leitung validiert. Anhand des entwickelten Modells werden Parameterstudien durchgeführt, um signifikante Einflussfaktoren auf die Nullimpedanz zu identifizieren.

Demand Side Management is a key concept within the Smart Grid vision to promote energy efficiency, load flexibility and interaction between the consumers and other power grid stakeholders.Disaggregated information requires an advanced load monitoring system of individual appliance consumption.A smart house is envisioned to include a Nonintrusive Load Monitoring (NILM) system to support demand side management and motivate the users to adopt energy saving practices.NILM systems use input electrical measurements taken at the energy meter point of a house and estimate the individual appliance operation and consumption through mathematical algorithms.Each appliance can be distinguished from others through a set of particular attributes namely load signatures that can be computed from transient signals, steady state signals or both.This paper aims to characterize current switching transients, for NILM applications and to discuss how they are affected by variation of factors such as point on wave of switching, network impedance, supply voltage distortion and sampling frequency of the meter.For that purpose, measurements of residential appliances of several categories are acquired and processed.The conclusion of this work is the assessment of suitability, robustness and efficiency of appliance identification based on current transients.

The shift towards more renewable generation, the decline of thermal power plants and increased demand from electric vehicles and heat pumps challenges the electricity system operation. TheSysZellproject focuses on ancillary services for frequency stabilization in an altered institutional setup. It builds on the Cellular Energy System concept proposed in the projectZellNetz2050which co-optimizes power scheduling and transmission in a decentralized manner. This setup mitigates grid overloading and minimizes short-term interventions. However, ancillary service provision has not been addressed so far. In expectation on how network frequency stabilization will change in the future, this projects assesses how the previous works can be extended. This contribution highlights the research project’s content, notably analyses of alternatives for procurement of frequency stability services, application of simulations, and designing decision-support tools.

In overhead power line analysis, the influence of ground wires is often considered assuming an ideally conducting connection to the model earth. Additionally, for calculating the inductive coupling, conventionally infinitely long conductor-earth loops are examined, assuming a homogenous field along the conductor direction. Deviations from this approach occur, for example, at the beginning and end of the line as well as near transposition towers where a homogenous field can not be expected. Moreover, ground wires and optical ground wires can also not be assumed to be infinitely long as equalizing currents occur in each span due to the span-by-span earthing so that the approach of a homogeneous field is not fulfilled here either. Utilizing the Hertzian dipole approach, a complex integral expression for calculating the impedance of conductors of arbitrary length is derived. Since this expression cannot be represented in closed form for finite conductor lengths, numerical methods are employed. To reduce computational complexity, the integral expression is approximated using image theory, facilitating computations for practical uses. Subsequently, a MATLAB-based model is developed and validated with both a fictitious and a real tranmission line, enabling the calculation of line parameters, particularly the zero-sequence impedance, while considering various influencing factors. The developed model is utilized for parameter studies to identify significant factors affecting the zero-sequence impedance.