Ing. Martin Čerňan, Ph.D.

The paper focuses on the problems associated with the supply of electricity to critical infrastructure in crisis situations. In the introductory passages, the paper focuses on the methodology of selecting critical infrastructure objects. Subsequently, attention is paid to selected aspects related to the operation of electricity generation in crisis situations. By using appropriate types of generating units (gas turbines), it is possible to gradually start islanding operations in the surrounding region, especially for critical infrastructure objects whose main task is the protection of the population. In the practical part, the article focuses on the issue of stability of the island mode of operation. The results of the case study show that for the switch-on plan, it is necessary to take into account the dynamic characteristics of islanded operation by gradually powering critical infrastructure objects in small power steps.

The paper focuses on critical infrastructure, more specifically on its resilience. The introductory parts of the paper define the concepts of critical infrastructure, critical infrastructure resilience and define the related legislative base. This is followed by a definition of typical critical conditions in the electricity sector. Attention is also given extensively to methods of critical infrastructure protection and strengthening critical infrastructure resilience. A survey of critical infrastructure options within the selected area has been carried out and evaluated. Based on the results, several recommended actions in sub-areas were identified and will be the focus of further research.

An emergency energy system is a backup power system used in critical situations with the aim of protecting lives and property from the consequences of energy loss, as is the case in hospitals (heart monitors, Ventilator,...etc), and also in sensitive facilities (military industries and government buildings). The emergency power system can contain batteries of all kinds, in addition to solar and wind energy equipment and other cheap types of energy. The concept of cyber security arose several decades after the invention of the computer. At first, there was no need for cyber security, as it was difficult for electronic attacks to occur, because access to computers was limited to specific numbers of users, as the devices were giant confined to a room with certain specifications and were not Linked to networks at the time, Energy sectors expose themselves to a range of cyber threats that can damage control systems. So management, engineering, and IT must adhere to a comprehensive approach that includes threat prevention, detection, and elimination. In this research we will try to mitigate the effects of the cyber attack on these systems by applying some algorithms in order to detect, identify and prevent such attacks, and we will see through the results we obtained that we have made remarkable progress in this field.

Ensuring a functioning critical infrastructure system is crucial for many industries, including energy. Due to the transformation of the energy sector, it is necessary to take into account the impact of the induced changes on critical infrastructure. The presented paper focuses on the assessment of the effects of small dispersed photovoltaic power plants (PV), which are gaining in popularity both in households and in other buildings. Specifically, it is an impact assessment within the emergence of island operation in the selected area with the aim of restoring power to the facilities included in the critical infrastructure system as soon as possible. The specificity of the considered small photovoltaic power plants is their autonomy and impossibility of control from the superior control system. The presented case study compares possible approaches to power recovery on the one hand and the impact of different levels of dispersed PV on the other. The results provide important conclusions for the expected development of the critical infrastructure system in connection with the increase in autonomous distributed electricity sources.

The paper focuses on the increasingly frequent issue of blackouts. The paper starts with a look at the methodologies for assessing incidents on electricity grids and statistics on incidents in Europe and North America. The core of the text consists of a description and analysis of two significant and distinct recent incidents. Based on the analysis, the paper concludes by outlining potential actions and expectations for future developments.

Effectiveness of using a parallel active power filter to compensate for the flicker of an electric arc furnace, and mitigate the reactive power consumption and terminal voltage variation in the grid is presented and evaluated in the contribution. The model of a power system with the electric arc furnace and parallel active power filter in the frequency domain has been developed. The selected results of simulation in the frequency domain using the data collected from the 60 t EAF are presented and evaluated.

The work focuses on the possibilities of improving the Static Var Compensator (SVC) control system for more effective reduction of the flicker effect. The studied SVC control system consists of an open control loop, which provides a fast response to dynamic changes in Electric Arc Furnace (EAF) power, and a closed control loop, which provides precise control to ensure the required value of the power factor in the Point of Common Coupling (PCC). The improvement consists in the use of alternative techniques for signal processing of input control variables. The first alternative technique is the use of Second Order Generalized Integrator (SOGI), which is also used in other related applications. The second alternative technique is to use the flicker weighting function, which corresponds to the function used to measure the flicker effect using a standardized flicker meter. Experimental laboratory equipment and theoretical model in frequency domain was used to verify the properties of the proposed techniques. To simulate the dynamic behavior of EAF, data measured from real operation were used, which were implemented into an experiment using VSC. Analysis of measured data and data obtained from laboratory apparatus shows high similarity. The experiments were carried out in several variants to reflect the differences in the various stages of the production process in the EAF. For all variants, the resulting flicker effect was evaluated and the individual techniques were compared with each other and with the results of other works.

The paper focuses on critical infrastructure and its resilience. The introductory parts of the paper define the concepts of critical infrastructure and resilience of critical infrastructure and further define its legislative basis. Then follows the definition of typical critical states in the field of power engineering. To a large extent, attention is also focused on methods for critical infrastructure protection and methods for strengthening critical infrastructure resilience. Within the selected area, a survey of the possibilities of critical infrastructure was carried out, which was evaluated. Based on the results, several recommended steps were identified in the sub-areas to which further research will be devoted.

The paper focuses on the lifetime of the 90 MVAr SVC system in the steel plant with 60 ton UHP EAF + 60 ton LF. The system is powered from the 110 kV primary distribution system, which is powered from transmission system substation 400/110 kV (220 kV in the past). The system was commissioned in 1994. During the operation of the facility, several major changes occurred. The first major change was the intensification of the steel production. This change of the SVC operation was not significantly influenced by the sizing of the equipment. Another major change was the gradual change of short-circuit conditions at the PCC point (reconstruction of the transmission system node from the 220 kV system to the 400 kV system). There was a need to monitor the 110 kV system voltage to avoid damaging the higher harmonic filter capacitors. One major accident occurred during operation due to failure of the thyristor block cooling system. The crash was eliminated by a complete replacement of thyristor blocks and protection extensions that identify similar types of faults in time. Periodic inspections of the equipment also resulted in replacement of higher harmonic filter capacitors (vessel leakage, deteriorated tg δ, capacity drop).

The paper focuses on the issues associated with the supply of electricity to critical infrastructure in crisis situations. In the introductory passages, the paper focuses on the methodology of selecting objects of critical infrastructure. Subsequently, attention is paid to selected aspects associated with the operation of electricity generation during a crisis situations. By using suitable types of production units (gas turbines), it is possible to gradually start island operation in the surrounding region, primarily for critical infrastructure facilities, whose main task is to protect the population. In the practical part, the paper focuses on the issues of stability of the island operation mode. The results of the case study show that for the switch-on plan it is necessary to take into account the dynamic characteristics of island operation by feeding the objects of critical infrastructure gradually after small electrical power steps.

Efficiency of electricity systems is currently a high priority for the society. Our article focuses on the area of low voltage distribution system, where we focus more deeply on the possibilities of reducing technical losses. To achieve this goal, many traditional methods are known which require modification and intervention in the distribution system. Our concept is based on the possibility of reducing active losses using small photovoltaic systems installed at low voltage customers. For this purpose, a low voltage feeder model of the corresponding structure was created in this work. Using this model, a case study based on real data (solar irradiation data and typical daily diagrams of low voltage customers) was performed. The results of the simulations show considerable potential for reducing technical losses using the described concept.

A model based predictive direct power control with finite set of control variables for the three phase four-switch-based converter B4 connected to an unbalanced grid is introduced. The instantaneous active and non-active powers are outputs of the controlled system. The alternative instantaneous non-active power theory is used that preserves harmonic free grid currents not only for a symmetrical but also unsymmetrical voltage system. Simulation results for the L grid filter are presented and analyzed.

A model of the three-phase voltage converter for simulation of its modes of operation in standard as well as fault states is presented The presented model can be used to simulate steady-states and also transients at dc and ac side of the grid-connected converter. Based on simulation, an algorithm was designed to identify and localize a fault in some phase of the three-phase converter. The algorithm was experimentally verified.

This paper describes theoretical and practical applications of FACTS devices such as STATCOM for voltage control and active power losses optimization. The idea and development with applying STATCOM for the optimization is presented. STATCOM provides an improvement in power quality and active power consumption stabilization. This effect could be used in applications where a variable load voltage should be compensated. It would result in a power stability improvement and decrease a risk of critical events caused by those sources. Using STATCOM, we are able to control the voltage at the node to which this device is connected and at the same time it is possible to reduce active power losses. The shown simulation provides information for STATCOM design and placement in power grids. Applying Particle Swarm Optimization showed the potentials to use this method in power grids to improve their operation and selected criteria.

Electricity supply is a fundamental need of a modern society. A crucial property of electricity supply reliability, is achieved by keeping a power system in a secure state most of the time. A secure state means that the risk of a disturbance to spread further and endanger the system integrity, resulting into supply interruption, is minimal. Large wind power integration can also lead to problems on the voltage control and power quality at large. Voltage control when wind turbines are used can usually be achieved by changing the amount of reactive power compensation (by shunt capacitors installation). The lack of control on the active and reactive powers can disturb the voltage on the Point of Common Coupling (PCC).

This paper aims on analysis of automation equipment benefits in medium voltage distribution networks. As measures for reliability improvement, the reclosers, remotely controlled pole-top smart switches and FPIs (Fault passage Indicators) were considered. SAIFI, SAIDI and supply interruptions were selected as main indicators of evaluation. Gains of each element were analyzed on simplified networks in two cases. Difference between variants is the presence of backup supply. Required inputs are the average number of annual permanent faults, number of branches longer than 1 km, overall number of customers, average annual number of interruptions and non-delivered energy, localization and fault clearance times for each feeder. In conclusion the different solutions for different types of MV feeder are provided.

The paper deals with the analysis of the formation of ferroresonance in MV systems. The analysis is focused on ferroresonance caused by instrument voltage transformer (IVT) connected to the outlet of the tertiary winding 10,5 kV autotransformer 400/110 kV. A non-linear element in this case is the magnetic circuit of IVT Ferro-resonance, in this case exhibits similar to the imperfect ground connection. The two phases may arise overvoltages in two phases and undervoltage in one phase. The rate of these adverse events is given by the initial conditions and load of switched circuits when circuit is switched on. Similarly, other exhibit nonlinear chaotic circuits. The main adverse effects include overvoltage that can damage the power system components well as a significant harmonic distortion. For prevent this problem the authors conducted the case study resonant circuit as a whole. In this case it is magnetic circuit of the IVT, in which saturate a hysteresis the magnetic flux depending on the winding currents. In the article before are described two approaches to determine hysteresis curves. The first approach is based on laboratory measurements of the properties of IVT, the second approach, developed by the authors is based on the measurement of nonlinear resonant circuit as a whole. The developed method additionally incorporates speech hysteresis. A non-linear circuit is described by the set of differential equations. Based on the knowledge of the basic parameters of the individual elements of the system is possible to analyze the resulting ferroresonance by solution system of differential equations in software Wolfram Mathematica. The analysis shows that the circuit can be for certain parameters even behave chaotically. It is, however, only certain ranges of the parameters. The simulation also confirms that ferroresonance is manifested like ground failure. To limit the exposure of ferroresonance is based on the analysis carried out several possible actions.

This paper deals with the solution of the issue of exceeding the permissible levels for long-term flicker effect Plt in industrial distribution systems. Flicker effect in distribution systems is often exceeded as a result of the connection of electric arc furnaces, which exhibits high variable electrical power in-take. The article shows the benefits of measures on the steel plants, the distribution system operator and the transmission system operator. The main benefits were the installation SVC device and reconstruction of substation 220/110 kV to substation 400/110 kV. Measurements have shown that the flicker has a major impact and configuration system 110 kV. In some cases, exceeded values flicker effect, and therefore the final part of the article deals with the possibility of deployment of active filters low power.

This paper deals with the simulation of industrial distribution system with electric arc furnace - non-linear load of variable active and reactive power. The simulation is considered with all key features such as passive harmonic filters, Thyristor Controlled Reactor (TCR), Electric Arc Furnace (EAF) modeled by Cassie Mayer-model of the arc, transformers and other equipment. Management TCR is based on measuring and managing susceptance in the Point of Common Coupling (PCC). Results of the simulations is that the device Static Var Compensator (SVC) controlled manner described limit flicker effect and allow to crucially increase the performance of the furnace. The benefit is the ability developed simulation analysis of interactions SVC with modern supplement FACTS devices such as active filters.

The paper deals with the problems of harmonic voltages in systems where there is the undesirable parallel resonance between the inductive system HV and capacitive cable networks for large customers. In the introductory part of the paper are shown characteristic impedance seen from the point PCC for different conditions in the system. Next, in the text explaining the problems of harmonic voltages in this type of system. As a solution will be described two possible designs compensation filtration equipment which will subsequently be evaluated in terms of the quality requirements of electricity.

This paper is focused on description of complex mathematic model of Electric Arc Furnace (EAF). The mathematical model is designed to develop and test various configurations and propose means to improve the quality of electricity in the industrial network. The advantage of the developed mathematical model is the use of not simplified circuit, which usually lead to not completely correct description of the system. The model consists of two parts. The first sub-section describes the mathematical model linking the arc Cassie model for large currents and the arc Mayer model for small currents. The second is the electrical part that specifies the involvement of EAF furnace transformers and mutual inductance impact of short current paths. Of profits description EAF through a set of differential equations with variable lengths excitation curves. The article then demonstrated results system solutions that show real impact on the quality of electricity.

The paper deals with characteristics of air reactors with resistance de-Qing rings. The rings are located in the plane of the inductor, thus the system acts as an air transformer to the secondary winding connected to a short circuit. This configuration air reactors are typically used in passive resonant harmonic filters for easy adjustment and fine-tuning the filters frequency response of the filter. Appropriately adjusting filter characteristics can limit the generation of parallel resonance between the filter and the primacy of the power system. Benefit is effectively suppress interference on load with a continuous frequency spectrum of received current.

The paper describes a mathematical model of the electric arc furnace in the time domain, which is designed to develop measures to improve the power quality. The model is based on a combination of Cassie and Mayer model of the arc, where Cassie model is applicable for large currents and Mayer model applies to small currents. Variable arc lengths act as excitation parameters in the model. The second part of the model focuses on the description of the furnace transformer secondary winding connected in delta and the furnace circuit. The whole system is described as a system of differential equations which solution is obtained values indicating the power quality. The model clearly states problems with higher harmonics of voltage and flicker effect. This model can be useful for designing of control algorithms of FACTS devices, where the device activity and dynamics could be simulated. As an example, the kit for improving power quality in industrial distribution network with electric arc furnace was developed. For power factor correction, elimination of harmonics and voltage unbalance SVC with passive harmonic filters can be used and flicker effect can be mitigated using low power active filters with appropriate control strategy.

The paper presents the principles and the utilization of regression methods for measurement using electrical quantities samples. Direct electrical devices parameters measurement in operation can be sometimes a hard or even impossible task. The presumption of electrical circuits linearity and harmonic signal component orthogonality allows us to determine the circuit parameters using the sampled data and the least-square regression method. Examples of the developed method utilization are given in the paper. The first example is devoted to harmonic filters equivalent circuit data assessment. The second one deals with the measurement of active losses in highly reactive devices e.g. arc-suppression coils.

The paper analyses the solution possibilities of tuning, diagnostics and incorrect function discovering for higher harmonics filters in industrial applications. The paper principle topic is the possibility analysis of filters RLC elements parameters calculation during standard device operation. The method verification is carried out with a mathematical model as well as with a measurement in terms of a case study. The case study results from filters voltage and current measurement in a tube rolling mill in a metallurgical company.