Ing. Miroslav Müller, Ph.D.

Recently, there has been a gradual opening of the electricity flexibility market. Flexibility providers are now connected to very high and high voltage distribution networks in the Czech Republic. At the same time, steps are being taken to connect low-voltage flexibility providers as well. The behavior of flexibility providers at lower voltage levels may cause specific problems for the DSO, as distribution networks have not yet been built for this form of operation. Therefore, new operational and investment measures need to be put in place to continue to maintain the security and reliability of network operations. However, flexibility is also a tool that can bring benefits to the DSO if managed correctly. For this purpose, PREdistribuce and in cooperation with the CTU, Department of Electrical Power Engineering, have developed a software tool CFF (Capacity for Flexibility) that supports the network semaphore function. This tool determines the available capacities for flexibility transactions at individual distribution outlets, both for the current time and for the future. CFF works with a probabilistic model of load and generation. It uses metering data from both instantaneous and non-instantaneous meters. It also allows real-time dispatch processing as input to the calculation, if available at a given location in the distribution network. Using a probabilistic approach, the CFF tool thus facilitates the development of flexibility at the low-voltage level and allows the full use of the capacity of the existing infrastructure

Recently, there has been a gradual opening of the electricity flexibility market. Flexibility providers are now connected to the HV and MV distribution networks. At the same time, steps are being taken to connect also LV flexibility providers. The behavior of flexibility providers at lower voltage levels may cause specific problems for the DSO, as distribution networks have not yet been built for this form of operation. Therefore, new operational and investment measures need to be put in place to continue to maintain the security and reliability of network operations. However, flexibility is also a tool that can bring benefits to the DSO if managed correctly. To this end, PREdi has developed a software application that determines the available capacity for flexibility transactions at individual LV outlets.

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.

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 distribution system in Prague was, and still is, justifiably more demanding than the distribution network in other parts of our country. Any failure in the system and the associated currentlessness usually has a much greater impact here due to the concentration of the population and the importance of the services provided in the capital. For this reason, the distribution system operator in Prague, PREdistribuce joint-stock company, has been ensuring a high level of quality of its electrical grid for a long time, including a high level of supply reliability comparable to Western European capitals. However, the sensitivity of customers to power outages continues to increase, so PREdistribution is keen to further strengthen the current high level of reliability of electricity supply.

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.

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.

The contribution deals with probabilistic approach to distribution system analysis. This method is suitable for the development and planning of the system with decentralized renewables sources and electro mobility etc. The transition to a probabilistic approach can lead to higher quality of analysis and increase the predictive ability of power flow computation and provides reliable information for decision-making processes.

The paper deals with dynamic model of overhead line mechanics. Dynamical modelling are useful to study many different transient states and it is also possible used for determination of an effects of various influences. The analysis thus allows to detect potentially dangerous situations and can be prevented by performing the corrective actions. In contrast to the static model, dynamic model also allows to simulate the shock forces and determine the peak exceeding the allowable limits of safe state of operation of overhead lines. The mechanical model of the power line is based on modeling each elements and interaction of its neighbors. This method allows the description of complex structures. Each element has mass, length, rigidity and damping. Each model function is modelled as block with internal interaction. In case study is transient state with conductor ACSR 350/59 analyzed. Transient state is induced fall icy.

The paper describes a dynamic model of overhead line mechanics and its utilization for icing influence evaluation. The case study is performed for AlFe350/59 wire and for real overhead line. The case containing several connected fields is threated as conjunction spans using partially hinged insulator strings.

The paper deals with overhead line motion problems. The dynamic model is derived from string equation. The main contribution of the developed model is complex mechanics simulation in 3D. The result consist of a continuous description of the position of the wire along its length in both space and time domains. The model thus allows calculations of un-even effects of forces along overhead line length. The model is actually a combination of discrete and continuous calculations. The dynamic model is, according to its complexity, also useful to simulate various mechanical wave phenomena such as galloping. Each model function block is described in equation form. In the case study ACSR 350/59 wire is analyzed. In this part an auxiliary model of wind influence was integrated into the global model.

The paper deals with overhead line motion problems. The line model is based on dynamic description of catenary curve. Benefits of dynamic modeling in this field are decrypted and one of the used models is consequently explained. The dynamic model is derived from string equation. The main contribution of the developed model is complex mechanics simulation in 3D. The model of overhead line shaking is generally based on the superposition of harmonic components in particular spatial coordinates. Each individual harmonic component is solved separately in one step of calculation and than combined with other solutions. The results consist of a continuous description of the position of the wire along its length in both space and time domains. The model thus allows calculations of un-even effects of forces along overhead line length. The accuracy of the calculation is determined by the number of harmonics calculated and other parameters (e.g. step size, simulation time etc.). The model is actually a combination of discrete and continuous calculations. Each model function block is described in equation form. In the case study ACSR 350/59 wire is analyzed. In this part an auxiliary model of wind influence was integrated into the global model.

The paper focuses on the dynamic model of overhead lines and benefits associated with the dynamic modeling. The developed structure is described including component elements. The model contain coefficients, which are also described and explained briefly. Model elements integrates stiffness and damping components, which influence the resulting behavior of the model as a whole. The paper includes a case study that shows the use of the model described on typical example of icing fall from one field for different configurations of falling element. During the transient the position and motion of wire caused by falling ice is calculated.

The paper shows the possibilities of new approaches to the calculations for planning and management of the distribution grid. Increasing amount of less predictable phenomena (such as decentralized sources, electric mobility, etc.) reduces the explicitness of existing computational methods which require precise input data. The use of advanced methods of a manage ment theory allows obtaining a more accurate description of reality in terms of increased uncertainty.

An analysis of the distribution network structure and its influence on the power system functions is critical for the Smart Grid concept. It creates a base framework for the implementation of the Smart Grid concept into the distribution network environment including a compliance with all relevant links. The basic structure of the networks and facilities and transmission and distribution system are described in EC breakdown showing the interface between the transmission (TS) and distribution system (DS). This interface is one of the key points of the balance control system of the observed distribution network. Other nodal points create connection with all the resources within the analyzed part of the distribution network. Customer management functions are realized as the link between processes of Smart Grid and Smart Metering in the general concept. The paper analyses new trends and advances in the power system architecture.

Connection and system integration of large scale wind power into the network systems has rose a number of important issues that must be evaluated in order to continually keep the power systems operation secure. It is therefore very important in planning and operation phases of power systems to perform and investigate the impact of wind power on the transient and small-signal stability. This paper briefly explores critical clearing time as a transient stability margin to evaluate the tested power systems without and with doubly fed induction generator based wind turbines. Maximum amplitude of the power swing, its settling time and voltage recovery in the system are also studied as margins. Simulations for transient stability analysis in this paper are performed using the Power System Simulator for Engineering software tools.

The paper describes electromobility and its evelopment potential in the Czech Republic. The basic technology and necessary infrastructure for the successful operation of charging stations and charging electrical vehicles is given. The next section describes basic concepts of electromobility in relation to the power grid and future concepts like smart grids. At the end of the paper there is the simulation of growing shares of EV in urban network and possible impact on these grids.

The paper is based on CTU FEE study conclusions which focused on new trends impacts on the distribution system in Prague. The main topic is an increase of small PV sources on building roofs and electromobility development. Possible impacts are modelled by means of several different scenarios in the selected area. These impacts should require a change in DS operation conception. This is the only way how to ensure the required quality and reliability of electrical energy supply in a middle term period.

The paper presents modelling of overhead line dynamics. The model of overhead line (OHL) shaking is generally based on the superposition of harmonic components. Individual harmonic coordinate components are finally composed together. The accuracy of the calculation is determined by the number of harmonics calculated and other parameters. The model is actually a combination of continuous and discrete calculations. In the case study OHL ACSR 350/59 is analyzed.

The paper deals with the possibilities of FACTS devices installation and operation in the Middle European distribution systems. A voltage fluctuation that results in flicker is caused by Electrical Arc Furnace (EAF) power fluctuation. The UPQC can be an effective means to suppress voltage fluctuation connected with the function of the EAF. Hitherto, the flicker has been compensated for mainly by using Static Var Compensators (SVC), whose capability to eliminate voltage subharmonics is limited by the frequency up to 10 Hz at maximum. A model of a power system with an electric arc furnace was developed for a typical metallurgical plant. The paper would like to emphasize that FACTS devices should have their position not only in large transmission system but for specific tasks also in local distribution systems. This is all connected with technical-economical decision how to approach to solving all partial electrical systems operational issues.

As far as synchronized phasor measurement systems have emerged as a powerful tool to improve power systems performance and reliability and e.g. fault localization possibility, the need of precise, robust and fast method of phasor identification occurred. The authors present the SW and HW implementation of their original mathematical method of frequency and phase angle assessment. Statistical methods minimizing standard deviation of moving averages of the window lengths corresponding to possible frequency values for frequency assessment and numerical quadrature for phasor are used. The algorithm has been developed and tested using Mathematica SW. Microchip implementation using C language was realized and tested in laboratory conditions.

The paper deals with modelling of the overhead line dynamics using catenary description. Introductory part describes key benefits of dynamic modelling in this field and consequently explains one of the models used. The dynamic model is derived from string equation. The main contribution of the developed model is complex simulation in 3D. The model of overhead line (OHL) shaking is generally based on the superposition of harmonic components of particular spatial coordinates. Individual harmonic coordinate components are finally composed together. The results consist of a continuous description of the position of the wire along its length in both space and time domains. The model thus allows calculations of un-even effects of forces along OHL length (eg. different thickness of icing). The accuracy of the calculation is determined by the number of harmonics calculated and other parameters (eg. step size, simulation time, solver method etc.). The model is actually a combination of continuous and discrete calculations. All model function blocks are described in equation form.

The paper deals with overhead line motion problems. The line model is based on dynamic description of catenary curve. Benefits of dynamic modeling in this field are decrypted and one of the used models is consequently explained. The main contribution of the developed model is complex mechanics simulation in 3D. The model of overhead line shaking is generally based on the superposition of harmonic components in particular spatial coordinates. Each individual harmonic component is solved separately in one step of calculation and than combined with other solutions. The results consist of a continuous description of the position of the wire along its length in both space and time domains. The model thus allows calculations of un-even effects of forces along overhead line length. The accuracy of the calculation is determined by the number of harmonics calculated and other parameters (eg. step size, simulation time etc.).

This paper deals with problems of overhead line motion. The line model is based on a dynamic description of a catenary curve. The benefits of dynamic modeling in this field are decrypted, and there is an explanation of one of the models that is used. The dynamic model is derived from a string equation. The main contribution of the model is in 3D simulation of complex mechanics. The model of an overhead line shaking is generally based on the superposition of harmonic components, in particular the spatial coordinates. Each individual harmonic component is solved separately in one step of calculation, and is then combined with the other solutions. The result is a continuous description of the position of the wire along its length in both the space domain and the time domain. The model thus allows calculationsof uneven effects of forces along the length of an overhead line. The accuracy of the calculation is determined by the number of harmonics and other parameters.

The paper focuses on the issues of advanced methods to achieve security and reliability of electrical power systems, mainly focusing on transmission systems. Advanced principles and techniques in monitoring systems are discussed. The key part of the paper deals with application possibilities of PMUs (Phasor Measurement Unit) and their integration into WAMPaC systems (Wide Area Monitoring, Protection and Control). Assessment criteria are explained in a mathematical form and demonstrated in terms of case studies. Significant power system states were analyzed in the case studies. PMUs usage for voltage phase monitoring is demonstrated for three cases - usual system state, high-load state and islanding. In this context the attention is paid to the possibilities of power system observability improvement using measuring chain error elimination.

This paper deals with dynamical model of overhead line. The main reason to study these problems is to create power line overloading model. The dynamic catenary based model is also useful for modelling of dynamics states caused by weather (such as temperature changes, snow etc). There is shown how this model has been created; its properties are clarified and compared. Equations describing the dynamic behaviour of the component are shown. The important part of study is simulation on three related spans. Between spans can wire move and wire tension is depending on excitation forces. Multi-span model are used for many different simulations where thick of ice and falling ice part are changed. Dynamics model is also validated in steady state and simulated data are compared with real spans. Case studies focus on difference between minimal and maximal sag during transient for each span.

Large power system disturbances and their consequences represent a challenging problem for power system operation, its security and reliability. This fact has reinforced interest in the new generation of monitoring systems. Synchronized Phasor Measurement System has emerged as a powerful tool to improve power systems performance and reliability and e.g. fault localization possibility. Data measured by PMU (Phasor measurement unit) are source of progressive research and can be used for network state modeling including lot of variable parameters. The paper describes a PMU hardware solution developed at CTU in Prague and mainly an effective method of detecting synchronous phasors of voltages and currents for differently disturbed electrical quantities time behaviours.

. This paper concentrates on dynamical model of overhead line. The main reason to study these problems is to create power line overloading model. The dynamic catenary based model is also useful for modeling of dynamics states caused by weather (such as temperature changes, snow, ice fall, and wind surges etc).There is shown how these models have been created; its properties are clarified and compared. Equations describing the dynamic behavior of the component are shown. The important part of study is model comparison with the cantilever beam model on which the model is validated before it will be tested with a real wire. Comparison between models has been done in many cases. The model is continuously checked and verified to accept requirements of modeling lines. Great emphasis is placed on the analysis of the length element discretization and parameters dependence.

The chapter shows the mathematical description of chain saw shape of a conductor hanging in the gravity field. There are described horizontal and inclined span, mainly for calculating the conductor sag and span length. Also the conductor stress and state equation are shown for calculating forces and mechanical shapes. The unbalanced and dynamic states are mentioned too.

The chapter describes the most important types of stranded conductors used for overhead lines. There are mentioned the most often ACSR conductors and their material or shape modifications as well as some specialized conductors enabling to withstand higher temperatures without increasing their sag too much. This can increase the lines transmission capacities.

This paper concentrates on electromagnetic field solutions in surface induction heating. The modern version of the finite element method with adaptation mesh is used. Problems related to common mesh use in surface heating tasks are element diameter and solution accuracy. High calculation complexity leads to very long calculation times using common methods. The task is solved with HP adaptation mesh. Calculation is extremely fast and has exponential convergence through suitable adaptive combination element diameter and polynomial degree. Results are shown on the case study. Electromagnetic field is solved for widely extended train rail UIC 60.

The paper is concerned with transformation of dynamic behaviour of the meshed power system to the cooperation dynamic of two regulated generators working to the equivalent connection. The transformation preserves dominant dynamic features of the original system and the resulting layout enables monitoring of faults representation to the value of its equivalent connection and their impact to the function of regulations and protection equipments. The paper show possible solution to the problem of connecting distributed generations to the existing electrical system. In this paper we have processed advanced model and tools consisted in formulation of the equivalent system in order to study the dynamic behaviour of the system. The results from steady state conditions and short-circuit calculations are the basic information for the formation of the simplified dynamic equivalent.

A new experimental procedure for heat transfer coefficient assessment. The principle of the method is based on nonlinear regression applied on measured temperature and time data during unsteady heating process. A simple formula for total heat transfer coefficient has been proposed.

In this paper, we present the new approach to the thermal fields and Ampacity of underground cables in steady state using the adaptive Higher-Order Finite Element Method (hp-FEM). Where, the Delaunay algorithm based on the distance function is used for creating the adaptive mesh in the domain surrounding cables. In particular, for increasing the accuracy of solution, the higher-order elements (up to 7th order) are applied in our procedure. The advantages of the coupled Delaunay mesh and higher-order elements are to obtain the higher accurate solution and can decrease the CPU time. The proposed method has tested to two practical models of single- and double-circuit buried cables in the homogenous soil. The numerical results of this work were compared to the ones that obtained by Boundary Element (BEM), Finite Difference Methods (FDM) and the data of cable manufacturer.

Large power system disturbances and their consequences represent a challenging problem for the power industry and especially for system operators who are responsible for the network operation, its security and reliability. This fact has reinforced interest in the new generation of monitoring systems with the aim to gain a precise and maximum knowledge about those disturbances and their impact. Most of these severe events with impact on the entire system typically occur in or near the transmission system (TS) and are therefore best monitored at TS level. This puts great demands on the equipments and in general restricts the use of the data since it becomes property of the TSO. Synchronized Phasor Measurement System has emerged as a powerful tool to improve power systems performance and reliability and fault localization possibility. An example of fault event that occurred in TS and was registered by Phasor Measurement Units installed in the distribution system will be shown.

Common methods for fault localization require for proper function a lot of specialized instruments. These special instruments should be permanently installed or moved to required distribution area. New fault location method needs only a few synchronously measured voltage and current phasors in the fault time for its proper function. The OHL parameters are used for more accurate calculation. The fault is located very quickly using relatively small amount of explained input data and a very special methods. This method can be performed on-line without the line to be switched off. The solving algorithm is based on matrix multiplication with discrete optimization. This is due to the fact that each line segment can be described as the matrix with OHL parameters. During the calculation the immediate fault rate is traced. The evaluation time strongly depends on the computer calculation capabilities and required accuracy.

This paper deals with Transformer Core Optimization. For number of tested core steps maximal surface area is solved with diameter restrictions. Firstly the algorithm solves the initial number of sheets. Solved real number of sheets is transformed and then used as initiative point for integer programming. The solving algorithm uses methods for numerical search of local minimum (maximum). Target function is the surface area of the resultant shape inscribed into a unit circle. Result is integer number of sheets for each section. For optimization is used new library implemented into a professional computer algebra system of Mathematica. In the case study optimization method results are shown.

The paper deals with methods of optimization of transformer core cross-section. A new library solving the task in a professional computer algebra system of Mathematica was written by authors. The results are shown on an illustrative example.