Ing. Zbyněk Brettschneider, 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

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.

This paper shows some opportunities offered by new approaches to processing planning and distribution network management data. The increasing amount of phenomena that are difficult to predict (e.g. decentralized sources, electromobility etc.) decreases the informative value of currently used calculation methods. These methods also require accurate input data. Using methods from the probability theory allows us to describe the reality more accurately in the conditions with increased amounts of uncertainty.

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.

The chapter explains the basics of excitation systems of generators, main types of exciters its principles and realizations of each type of exciter. Also the problems with replacing of old types for the new ones are mentioned. The power systems stabilizer with construction and main principle are mentioned at the end of chapter.

This paper deals with the analysis of these transient phenomena demonstrated on the example of connection of 2×26 MW PVPP into 110 kV distribution system through AC medium voltage cables 17 km and 24 km long. The simulation calculations analyze features during the switching on of the cables and they discuss several possibilities of the distribution of the shunt reactor. Further, the problems considering the voltage regulation of the 110 kV level are described. The paper is concerned with the usage of a device of the FACT (STATCOM) type.

The chapter explains how power plants with synchronous generators supply active and reactive power to the electrical grid. There are described the system and ancillary services utilized in large power plants. Mainly principles of active power - frequency control and voltage control are explained for the most important services applied in transmission systems.

The chapter describes main control systems and key technological processes. The main communication systems and protocols like RS232, Modbus, CAN, TCP/IP are mentioned. Also the division of main process and control structures in power plants are given.

Power System Stabilizers (PSS) are designed to enhance damping of power system oscillations in order to extend power transfer limits of the system and maintain reliable operation of the grid. The basic reasons for tuning PSS parameters are to compensate for the phase lag due to the power system, generator, and excitation system, and to provide electrical torque in phase with speed via the excitation system and generator. This paper deals with results from tuning and testing of PSS3B with the 235MVA TG ETUII in the CEPS transmission system. The tuning method was based on the simulation model in the frequency and time domain. A Bode plot was drawn to tune the PSS's time constants to compensate for phase lag. In addition, eigenvalue analysis was used to determine a reliable PSS gain, Ks, and a time-domain transient program was used to verify operation of the PSS in the presence of predictable disturbances, such as the AVR (Automatic Voltage Regulator) step test and generator unloadi

The paper deals with a model of the electrical part of whole supply system of the experimental reactor COMPASS-D. On this model of the electrical supply system, the new ideas and the solution were verified.

The autonomous Load Shedding System LSS reacts to impending network instabilities, resulting from unexpected outages of outside supplies, by shedding low-priority loads. And this is being done in a record-breaking within 200 milliseconds. The paper deals the instance of application LSS in the large factory and use simulation in design. LSS measures the energy input provided by two lines and actual power consumption of shedded load. Continually checks the balance of energy input and load. In case of frequency drifting, LSS disconnects the energy input provided by two lines, all turbogenerators are switched to speed regulation and actual balance of the energy input and load is levelled by shedding of load by given priorities.

The dependence of current effective values on applied harmonic voltage of unloaded transformer cannot be used for time domain analysis. Because of the unavailability of the time domain measured values authors has developed method to obtain the nonlinear transformer model with hysteresis with the reasonable accuracy. The paper describes step by step the assessment of time domain characteristics based on measured effective values.

Extending of the UCTE and increasing active power transmissions (bearing on a common European electricity market) increase risk of interarea oscillations. Liability to these oscillations is escalated by geographically longitudinal interconnection of power systems, by occurrence of network congestions and transmissions of large amount of power on long distances. So that transmission system operators have to pay attention to these phenomena, prepare and implement arrangements to prevent rising and spreading oscillations. One of the common used possibilities is installation of power system stabilizers (PSS) into excitation system of synchronous s generators. The paper deals with theoretical and practical evaluation of abilities of power units equipped by PSS to damp interarea oscillations.

The 3rd harmonic and its odd multiples result in phase voltages and currents curve deformation, especially at one phase circuits. The 3rd harmonic and its multiples are influenced by the sources connection type and consumers character. The supplying voltage disturbance by the 3rd harmonic occurs quite often and that is why its filtration is needed. The 3rd harmonic filtration is carried out by different instruments than at classical voltage and current higher harmonics when passive or active filters are used. The paper introduces the possibility of using passive transformer filter with the winding with a very low zero impedance. This passive filter construction and model function verification is described further.

This paper is focused on comparison between MATLAB and ATP-EMTP simulation of power supply for experimental thermonuclear reactor COMPASS-D which will be moved from Culham Laboratory to the Czech Republic. Proposed power supply system consists of two synchronous machine 50 MVA, three phase transformers and controlled 24 and 12 - pulse rectifiers. The controlled rectifiers are used to feed a system of reactor coils by varying DC current of special shape. Some important parts of the system was verified by simulations in MATLAB and consequently in ATP-EMTP. The results and experiences from both simulating programs were summarized.

This paper describes mathematic model of current measurement transformer (CMT) for fast response protection device. The model takes into account real magnetic core properties, that means nonlinear function B=f(H). Undistorted transfer through CMT is very important for working of response protection device. We analyzed output current of CMT dependent on different value of load. Than we inquire into current silence.

The article deals about possibilities of the hydrogen production with respect to the environment, its storage and transport. Hereafter deals with possibilities of the hydrogen utilization with a view to the fuel element and its more effectively utilization in future. Last but not least it makes a reference to the current fuel element projects placed on the Department of Power Engineering CVUT- FEL.

Three-phase transformer is a very expensive and important part of the electrical transmission and distribution systems and in many cases the properties of the transformer are essential for phenomena that can occur, i.e. short connection current form, overvoltages, ferroresonant processes etc. Classical methods fail if the non-linearity and hysteresis cannot be neglected. The paper deals with the time-domain mathematical model of the three-limb construction nonlinear transformer and its implementation in the POWER SYSTEM BLOCKSETŽ.

Three-phase transformer is a very expensive and important part of the electrical transmission and distribution systems and in many cases the properties of the transformer are essential for phenomena that can occur, i.e. short connection current form, overvoltages, ferroresonant processes etc. Classical methods fail if the non-linearity and hysteresis cannot be neglected. The paper deals with the time-domain mathematical model of the three-limb construction nonlinear transformer and its implementation in the POWER SYSTEM BLOCKSETŽ.