In this work we calculate the touch and step voltages in large ground mounted PV power plants either caused by earth faults in nearby high voltage power systems e.g. towers, substations or direct lightning strikes, respectively. Rammed steel profiles are often used instead of conventional concrete foundations to enable large ground mounted PV systems to be installed easily and quickly. These driven steel profiles act like natural earth electrodes and can therefore contribute to the earthing system. The aim of this work is to find out whether these natural earth electrodes together with equipotential bonding are already sufficient to ensure personal safety. Therefore we analyse the touch voltages of two main scenarios: First the interference in low frequency range for high voltage faults in nearby substations or line towers and secondly a lightning strike within a ground mounted PV power plant. Both scenarios have certain limits according to current standards.

The investigation of the dynamic characteristics of multi-converter systems is usually based on detailed modelling of the converters. This requires detailed control-related information about the converters, which is not suitable for grid operators and third-party research institutions to perform practical investigations of multi-converter grids. This paper proposes a validation and operation-oriented investigation approach to construct a system dynamics matrix of a multi-converter system with information on the grid topology, grid impedance and converter’s setpoints. In this paper, a three-converters system is modelled and the information of the stable equilibrium surfaces is investigated. According to the continuity of the stable equilibrium surfaces, the grid-forming converter has better robustness to the loss of synchronisation of the grid-following converter. On the other hand, the grid-following converter is not able to maintain stable operation in case of loss of synchronisation of the grid-forming converter.

This paper deals with the effects of an arc fault in the medium-voltage switchgear of a transformer substation (distribution substation), a common part of an electrical distribution grid. These transformer substations are widely used to step down medium voltage to low voltage and supply end-customers.The focus of the considerations is the pressure load caused on the inside of the electrical distribution substation building. For existing buildings made of masonry, hardly any literature is available taking the dynamic of the pressure load into account. However, available limit values for static pressure load might be exceeded. Due to the lack of accurate assessment methods for arc pressure loading by structural engineers, conservative approaches must be used. The costly consequence is that either great efforts must be made to limit the pressure or the distribution substation hast to be rebuilt. Therefore, an in-situ test was performed on a masonry transformer station to gain new insight into the pressure load capacity of masonry due to arcing events. The results show a higher load capacity of masonry than assumed.

The soil resistivity is an important value for the designing of earthing systems (ES). Therefore, sophisticated methods are needed to determine the soil model. In this work a simulated Earth Resistivity Tomography (ERT) is carried out over an ES. The survey line is placed partially above the ES in two different directions. The ERT provides enough data points to obtain the soil model including the isolation of the placed ES with the Geophysical Inversion Module pyGIMLI. Compared to traditional Wenner 4-point measurements (VES), which is a standard procedure, according to [1], [2], the ERT method provides more subsurface information within the same survey line length. Further, the synthetic soil model can be properly reconstructed with the inversion module.

Zusammenfassung Bei Erdschlüssen an Mittelspannungskabeln können in unmittelbarer Umgebung der Fehlerstelle durch den Eintritt von Strömen in das Erdreich Potentialanhebungen und somit Schritt- und Berührungsspannungen auftreten. Diese müssen hinsichtlich des Risikos einer Personengefährdung betrachtet werden. Eine besondere Situation entsteht dabei, wenn der Fehler im Nahbereich eines Swimmingpools auftritt, da sich hier Personen barfuß aufhalten können. Die dabei kleineren Übergangswiderstände zum Erdreich als bei Personen mit Schuhwerk führen zu größeren Körperströmen. Diese Situation wird unter Berücksichtigung der einschlägigen Normen auf ihr Gefährdungspotential beurteilt. Im Zentrum dieses Fachbeitrages steht die Frage, unter welchen Bedingungen es bei der Annäherung von Swimmingpool und erdverlegtem Kabel bei einem Erdschluss in kompensierten Mittelspannungsnetzen (20 kV und 30 kV) zu einer Personengefährdung kommen kann und welche Maßnahmen von den Betreibern dieser Kabel erforderlichenfalls zu treffen sind. Zwei unterschiedliche Fehlerszenarien werden im Detail analysiert: ein Kabelfehler in der Nähe eines Swimmingpools sowie ein Fehler im Bereich eines Kabelaufführungsmastes oder in einer Ortsnetzstation mit Potentialverschleppung über den Kabelbegleiterder. Die wesentlichen Einflussparameter werden hinsichtlich der Auswirkungen auf den Fehlerstrom sowie auf Schritt- und Berührungsspannungen untersucht. Aus den Untersuchungen geht hervor, dass bei den meisten betrachteten Fehlerszenarien keine Gefährdung für Personen hinsichtlich Schritt- und Berührungsspannungen zu erwarten ist. Einzig der Fehlerfall mit Potentialverschleppung über den Kabelbegleiterder in Gebieten mit spezifischen Bodenwiderständen von größer als 1000 Ωm muss im Anlassfall geprüft werden.

The potential differences in the immediate vicinity of an earth fault location of 20 kV and 30 kV cables in earth fault current-limited grids (ohmic or resonant) are analyzed with regard to personal safety for general public, which might be barefoot. Not only occurring step voltages are assessed but also accessible touch voltages on the surface for persons in push-up-position. Two main fault scenarios are in the focus. The first scenario is a cable earth fault, where some part of the fault current flows through the damaged insulation into earth and causes a rise of surface potential in the vicinity, which can lead to step or touch voltages. In the second scenario the transferred potential via accompanying earth electrode in the case of earth faults in the nearby ring main unit (RMU) or cable termination tower is analyzed.Based on the investigations carried out, in the case of internal faults cables in medium voltage grids (resonant or current-limited) in practical cases, no danger to persons is to be expected with regard to impermissible body currents or potential differences (touch voltages, step voltages). Likewise, it can be assumed in the typical networks and situations, that there is no danger to persons due to transferred potential with the accompanying earth electrodes, especially if the earth potential rise (EPR) of the connected earthing system is less than four times the permissible touch voltage.

A large number of non-linear hardware and control units exists in power electronic system used in grid connected devices. The analytical transient stability analysis of grid-connected converters presents numerous difficulties. A common method to tackle this problem is the stability analysis using Lyapunov’s method. By applying this method, difficulties arise not only from finding a suitable Lyapunov function, but also from checking the constraint of Lyapunov stability. If the appropriate Lyapunov function is a high-order polynomial, it is very challenging to test if it meets the constraints of Lyapunov stability in certain regions. In this paper, the sum-of-squares programming method is used to obtain the estimation of a converter’s domain of attraction with a relatively small number of iterations compared to classically applied methods, such as the Monte Carlo method. The estimation of the domain of attraction are verified by time-domain simulations and StarSim’s controller hardware-in-the-loop tests in this paper.

In a power system with a high percentage of converter coupled generation, dynamic characteristics of the converter affects the stability of the whole power system. The interaction of the various control loops of the grid-side converter, e.g., the phase-locked loop and the DC link voltage control loop, dominates the various dynamic characteristics of the grid-side converter, including its low voltage ride-through ability. In this paper, the phase-locked loop is modeled and analyzed and a stability criterion for the converter, depending on the grid impedance, is obtained. According to this criterion, a common low voltage ride-through test device based on the shunt impedance voltage sag generator is analyzed. The results show that, and explain why, the test device cannot reproduce the characteristics of the practical grid, which is also verified by experiments using a controller-Hardware-in-the-loop system.

In this paper, an optimization-based algorithm for the detection of multi-branch outages is presented. The main advantage is its ability to detect an unknown number of tripped branches in meshed power systems solely based on node voltage angle information obtained with phasor measurement units (PMUs). The proposed algorithm uses a hybrid optimization approach combining particle swarm optimization with Newton’s method. The algorithm is tested on linearized load flow data as well as on a dynamic simulation of the Nordic-32-Bus system. In a sensitivity analysis the influence of the optimizer’s main parameters and the robustness against linearization errors and missing data is shown. The high ratio of correct detection results across the whole range of evaluated parameters identifies the proposed algorithm as a useful supportive tool for future decentralized SCADA applications.

The increasing cabling of medium voltage grids is also increasingly influencing the operation of electrical grid, which are often, due to historical origin, operated as compensated distribution grid. That is why the decentralized compensation has become a focus again, which, however, also has been raising many questions that must be resolved from the operator's point of view. These include additional thermal loads on equipment like cable shields or transformers and the proper continued functioning of existing systems such as the selective earth fault detection. In the paper, practical approaches and methods for determining these influences and limits are shown and the results are used, to answer the open questions, considering existing framework conditions.

As the share of inverters in the power system increases, the stability of inverters has an increasing impact on the reliable operation of power electronics dominated power systems. Since the synchronization mechanism plays a leading role in the dynamic performance of the inverter, its stability is one of the keys for the stable operation of the power system. The Grid Forming inverters have emerged in recent years, is completely different from the traditional Grid Following inverter in terms of synchronization mechanism. This paper will analyse and compare the differences in transient stability between the synchronization mechanisms of the two concepts of inverters through large-signal modelling and phase-portrait method. The analysis results show that the Grid Forming inverter is more robust in synchronization mechanism.

Well designed earthing systems are needed to ensure that occurring fault currents can be safely transported into the ground. Soil models are a key parameter for the dimensioning process of earthing systems. In previous research the soil is often assumed to be homogeneous or layered in its resistivity distribution. But the soil is arbitrary in its resistivity distribution. This work will give an input, which errors on the earth surface potential and step voltage will occur, if the soil model is not constructed accurately enough. Different standardized methods are used to interpret the measurement of soil resistivity to build a soil model. To get the measurement values, Wenners array is used within an earth resistivity tomography (ERT). For the interpretation, the method shown in IEEE Std. 80 will be used and compared with inversion theory. The impact of the different methods on the occurring earth surface potential and step voltages is analysed within a finite element method (FEM) simulation. It is expected, that the different methods for finding the soil model will influence the behaviour of the mentioned potentials. This analysis will help to use new methods to build up appropriate soil models for the designing process of earthing systems. The outcome can improve the efficiency of earthing systems and enhance personal safety.

Decentralized earth fault compensation coils (EFCC) in resonantly grounded medium voltage networks are becoming increasingly popular. Their installation imposes several requirements on the earthing system in terms of equipment and personnel safety as well as the functionality of the ground-fault protection devices. Based on two practical examples of networks (urban and rural), the challenges and their possible solutions are presented and verified by on-site measurements. Due to the impressed current of the distributed EFCC, the earth potential rise (EPR), the touch voltage, the transmitted voltages to neighboring stations and to the low voltage installation (PEN conductors) have to be analyzed. The role of cable shields in relation to earthing and the influences on the distribution of the zero sequence currents discussed. In addition, this work investigates the currents flowing on the interconnecting cables between two different network areas under fault conditions with different distributions of compensation. The cable shields grounded at both ends are loaded by flowing zero sequence currents. This leads to additional heating of the cables. It is analyzed which zero-sequence currents are permanently permissible in order to avoid a maximum insulation temperature and to prevent additional aging of the cables

This article describes the method for magnetic field evaluation according to Directive 2013/35/EU and the Austrian implementation (VEMF). It focuses on a method using a harmonic factor in order to consider harmonics when evaluating multifrequency fields of energy power systems. The differences in the evaluation, and the use of different methods of consideration of the multi-frequency fields is discussed in detail with an example. The main goal is to find a simple method to prove, that the requirements of Directive 2013/35/EU are fulfilled.

This paper proposes an advanced emergency control strategy for embedded VSC-HVDC links after AC disturbances, such as line tripping and generation loss. The control goals are to minimize the impact of the disturbance on the AC-network, which includes improving the long-term voltage stability with utilizing possible unloading capacity of parallel AC elements. The proposed algorithm is evaluated against other control strategies for embedded VSC-HVDC links by applying it to a simple demonstration network. The test system includes all necessary VSC converter dynamics, the VSC-HVDC link current and voltage limits and simple load recovery characteristics for an evaluation of the long term voltage stability. The simulation results are explained and the advantages of the proposed emergency control strategy are discussed.

The proportion of grid-connected power electronic equipment is already large enough to influence the dynamic characteristics of the modern power system. Ensuring the stability of grid-connected power electronic equipment in all relevant situations is one of the foundations for reliable power system operation. In contrast to conventional rotating machines, the stability of power electronic devices mostly depends on the applied control strategy, and a large diversity of different complex control strategies are in practical use. Also, the investigation of stability of such systems needs to take into account the non-linear behaviour of the power electronic equipment. These are the main reasons why the system behavior of grid-connected power electronic equipment cannot be reproduced satisfactorily when aplying a single method of stability analysis, evaluation and testing method. During the last years, faults which led to tripping of converters due to stability problems occurred frequently even though standardized fault compliance tests were performed on these converters. In this paper these stability issues are analyzed. Also, a three-dimensional stability analysis method is suggested in order to comprehensively cover system behavior. The three dimensions are the time/scale dimension, the equipment number dimension and the local or global range of the stability analysis dimension. Based on this three-dimensional framework, this paper proposes a stability evaluation as well as a test process applying a hardware-in-the-loop test concept. Through the verification and testing of the stability of the actual grid-connected power electronic equipment, the method proposed in this paper is verified for up-to-date equipment.

This paper shows the influence of the soil model simplification on the prospective touch voltage of a simple earthing system, consisting of two half spherical shaped earthing electrodes. The apparent soil resistivity is measured using Wenner’s electrodes array configuration. This data is used to build an approximated soil model with finite cubes by solving this inverse problem. Simplifications of the soil model will be applied to compare the prospective touch voltage of the different models. The results are found by using the means of Finite Element Method (FEM) modelling. It can be seen that, in this case, the best approximation is found by taking the average soil resistivity of each horizontal layer of the reference model to build a layered model.

Electrical earthing (grounding) is necessary for the proper operation of electrical systems, machines and electronic equipment in the event of a fault, for protection against lightning and personal injury, and for reasons of electromagnetic compatibility. Earthing is understood as ”making an electrical connection between a given point in a system or in an installation or in equipment and a local earth“. Electrical grounding systems are designed according to national and international standards, with some of these standards occupying a significant place in the legal hierarchy in Austria and being binding. Simple structures are designed using approximate formulas given in the literature and standards; more complex arrangements use programs with analytical or numerical models for the calculation and design of grounding systems. Underground infrastructure projects require additional considerations. Starting with the technical and legal requirements, the typical process steps for the design of electrical grounding systems are shown.