Search

This paper proposes a new event-based logic of the breaker failure protection to improve power system transient stability by shortening the total clearing time of extreme contingencies involving circuit breaker failures. Stability improvement is achieved by using dual-timer protection with shorter safety margin for multi-phase faults close to the power plant and longer safety margin for remote multi-phase faults and single-phase faults. The use of the output signal obtained for a short safety margin depends on how the substation is configured. In the breaker-and-a-half configuration, this output signal is used to speed up the opening of all adjacent circuit breakers. In substations with the dual (or triple) busbar configuration the output signal obtained with a short safety margin is used to speed up the busbar splitting. A case study was performed for a real large-scale power system. Simulation results confirmed the advantages of the proposed logic. Breaker failure protection with the proposed logic has been implemented in a substation of a large power plant.

Poland has had a total of 70 mines, but now more than half of them is out of operation. This mining closure raises with respect to the environment and unemployment. Innovative technology is needed to overcome the problems that arise and could simultaneously make use of abandoned mine infrastructure. The increased electricity generation coming from renewable energy, which produces fluctuating and intermittent energy for the electric power system, causes frequency problems such that energy storage technologies are needed. Abandoned mines can be used for the implementation of energy storage plants. This paper explores the possibility of using abandoned mines in Poland for electrical energy storage. Closed mines can be used to store clean and flexible energy. This idea has the potential to support sustainable economic development within the community following mine closure in Poland.

Series braking resistors (SeBR) offer an effective way to enhance transient stability for severe near-to-generator faults cleared with a delay. The SeBR is switched on for a short time, already during the fault. The SeBR should switch on as quickly as possible after identifying the risk of losing transient stability. Then, the SeBR is switched off, and it is the decision-making algorithm that chooses the switch-off time. This paper presents an algorithm to choose the moment the SeBR switches off. The algorithm identifies the direction of a rotor motion based on changes in the square of the current and real power of the synchronous machine. The proposed algorithm is characterized by its simplicity, and is easy to implement because it uses local measurements. To develop the control algorithm, the effect of the SeBR on power angle characteristics for a fault state and post-fault states were determined. In addition, the effect of the SeBR on transient stability is explained using the equal area method. The conducted simulation tests have confirmed that the proposed SeBR control algorithm leads to longer critical clearing times, and thus it contributes to enhanced transient stability.

This article proposes a state-variable stabilizing control algorithm for unified power flow controller in a multi-machine power system. This stabilizing control is activated in the transien...

For economic reasons, expansions of transmission networks are based on a compromise between capital cost and security of power system operation. At the same time, the power system must withstand typical highly likely contingencies. Various emergency state control systems, also called special protections, prevent emergencies following less likely contingencies. This paper describes overloads emergency state control (OLEC) used for the alleviation of overload in transmission networks near a power plant. Such control uses the functions of automated power reduction of generating units and has been implemented for a large steam power plant. The OLEC presented here uses different methods of generation curtailment for steam generation units. A case study illustrates the efficiency of the proposed control method.

This paper addresses comprehensive dimensioning of series braking resistors designed to improve transient stability of the power system. Since dynamic braking is one of the most cost-effective ways to improve transient stability, the applications of shunt and series braking resistors have recently expanded in the power industry. To find an effective algorithm for controlling series braking resistors appropriate resistor dimensioning should be performed first. This paper addresses the problem of dimensioning of series braking resistors. To solve that problem a mathematical model is employed for different operating states of the system equipped with a series braking resistor. This paper describes and discusses in detail the impact of series braking resistors on: power angle characteristics, intensity of dynamic braking in terms of transient stability improvement, voltage dynamic response during and after a fault, and turbo-generator shaft fatigue. Based on the analysis performed, criteria for the dimensioning of series braking resistors are formulated. Theoretical considerations are supported by simulation tests for nonlinear models of single-machine as well as multi-machine test systems.

The security of national energy systems as well as the transition to a low-carbon future are two hot topics of discussion in the international political arena. Research on the stability of centralized energy systems is currently focused on distributed generation. Developing a scalable microgrid model enabling its massive adoption is one of the safest and feasible ways to solve such problem. The paper aims to fill an existing gap regarding the operation model of microgrids that is a barrier for the large-scale integration of those in the conventional grid network. In the proposed approach the authors identified key processes to be considered when operating microgrids, in the conditions shown through an experimental (simulation) campaign. A three-phase research was performed: (1) systematic literature review to explore the management models of a stand-alone microgrid design and management; (2) a household experiment; and (3) a computer simulation of energy balance for a selected household. We identified eight key processes constituting a scalable microgrid: five core processes, two supporting processes, and one management process. Subsequently, we developed a map of these processes obtaining a microgrid process model for massive adoption. The model of processes can be considered as a repeatable pattern of conduct in the creation and maintenance of microgrids, which their future owners can follow. To support our literature findings, we performed an experiment and a computer simulation of three sub-processes of the (re)design of the infrastructure process: (1) wind turbine selection, (2) photovoltaic power plant selection, and (3) energy-storage selection. Results confirm conditional stability of the analyzed microgrid and the need for cyclical simulation exercises until unconditional stability is achieved. In terms of sustainability, to keep the microgrid permanently in a positive energy balance will require the implementation of all key processes.

The ability to forecast electricity generation for a small wind turbine is important both on a larger scale where there are many such turbines (because it creates problems for networks managed by distribution system operators) and for prosumers to allow current energy consumption planning. It is also important for owners of small energy systems in order to optimize the use of various energy sources and facilitate energy storage. The research presented here addresses an original, rarely predicted 48 h forecasting horizon for small wind turbines. This topic has been rather underrepresented in research, especially in comparison with forecasts for large wind farms. Wind speed forecasts with a 48 h horizon are also rarely used as input data. We have analyzed the available data to identify potentially useful explanatory variables for forecasting models. Eight sets with increasing data amounts were created to analyze the influence of the types and amounts of data on forecast quality. Hybrid, ensemble and single methods are used for predictions, including machine learning (ML) solutions like long short-term memory (LSTM), multi-layer perceptron (MLP), support vector regression (SVR) and K-nearest neighbours regression (KNNR). Original hybrid methods, developed for research of specific implementations and ensemble methods based on hybrid methods’ decreased errors of energy generation forecasts for small wind turbines in comparison with single methods. The “artificial neural network (ANN) type MLP as an integrator of ensemble based on hybrid methods” ensemble forecasting method incorporates an original combination of predictors. Predictions by this method have the lowest mean absolute error (MAE). In addition, this paper presents an original ensemble forecasting method, called “averaging ensemble based on hybrid methods without extreme forecasts”. Predictions by this method have the lowest root mean square error (RMSE) error among all tested methods. LSTM, a deep neural network, is the best single method, MLP is the second best one, while SVR, KNNR and, especially, linear regression (LR) perform less well. We prove that lagged values of forecasted time series slightly increase the accuracy of predictions. The same applies to seasonal and daily variability markers. Our studies have also demonstrated that using the full set of available input data and the best proposed hybrid and ensemble methods yield the lowest error. The proposed hybrid and ensemble methods are also applicable to other short-time generation forecasting in renewable energy sources (RES), e.g., in photovoltaic (PV) systems or hydropower.

The current development of electric power industry in Poland, especially in the field of renewable energy sources, including wind power, brings about the need to introduce legislation on new work environment. The development of occupational safety and health (OSH) regulations that must be met by new workplaces, such as offshore substations becomes necessary in view of the construction of modern offshore wind power plants - offshore wind farms. Staying on offshore substation is associated with an increased exposure to harmful health factors: physical, chemical, biological and psychophysical. The main sources of health risks on offshore substations are: temperature, electromagnetic field, noise from operating wind turbines, direct and alternating current, chemicals, Legionella bacteria and social isolation of people. The aim of this article is to draw attention to the problem of offshore substation workers' exposure to harmful factors and to present methods of preventing and reducing the risk-related adverse health effects. In this paper, there are identified and described risks occurring on offshore substations (fire, explosion, lightning, accidents at work). Some examples of the means and the methods for reducing the negative impact of exposure on the human health are presented and discussed. The article also highlights the need to develop appropriate laws and health and safety regulations concerning the new working environment at the offshore substations. The review of researches and international standards shows that some of them can be introduced into the Polish labor market.Obecny rozwój elektroenergetyki w Polsce, szczególnie w zakresie odnawialnych źródeł energii (w tym farm wiatrowych), przynosi konieczność wprowadzenia uregulowań prawnych dotyczących nowych środowisk pracy. Opracowanie przepisów bezpieczeństwa i higieny pracy (BHP) dla pracowników elektroenergetycznych stacji morskich jest niezbędne w obliczu budowy nowych elektrowni wiatrowych na morzu – morskich farm wiatrowych. Przebywanie w morskich stacjach elektroenergetycznych wiąże się ze zwiększonym narażeniem zdrowotnym na szkodliwe czynniki fizyczne, chemiczne, biologiczne i psychofizyczne. Głównymi źródłami zagrożeń zdrowotnych są: temperatura, pole elektromagnetyczne, hałas pochodzący od pracujących turbin wiatrowych, stały i przemienny prąd elektryczny, substancje chemiczne, bakterie z rodzajuiLegionella/ioraz odizolowanie osób przebywających w stacji od życia na lądzie. Celem artykułu jest zwrócenie uwagi na problem narażenia pracowników elektroenergetycznych stacji morskich na czynniki szkodliwe oraz przedstawienie metod przeciwdziałania tym czynnikom, żeby ograniczyć ich negatywny wpływ na zdrowie. Wskazano i opisano także inne zagrożenia występujące w stacjach morskich (pożar, wybuch, wyładowania atmosferyczne, wypadki przy pracy). Omówiono również środki i sposoby zmniejszania wpływu czynników szkodliwych na organizm. W artykule zwrócono też uwagę na potrzebę opracowania regulacji w zakresie BHP dotyczących nowego środowiska pracy – elektroenergetycznej stacji morskiej. Przegląd standardów i opracowań zagranicznych pozwala uznać, że niektóre z nich mogą zostać zaadaptowane na polskim rynku pracy. Med. Pr. 2016;67(1):51–72.

In self-healing grid systems, high utility in the use of greedy algorithms is observed. One of the most popular solutions is based on Prim&rsquo, s algorithm. In the computation, the power grid is represented as a weighted graph. This paper presents a few possibilities of calculation of the numerical weight of a branch of the graph. The proposition of a modified edge weight calculation based on active power belongs to this group. The other solutions are novel subalgorithms bounded by real power, reactive power, and normalized factor. This factor is a mathematical combination of active and reactive power multiplied by influence coefficients. Requirements necessary for a power system are applied in the considered algorithms. Each of these proposed algorithms includes the power source limits, voltage level at busbars, and power system transmission features, such as transmission lines rated currents and power losses. All mentioned methods were compiled into separate algorithms, which can be used to compute graph model parameters. A simulation model based on Prim&rsquo, s algorithm was prepared to compare the suitability of presented concepts. All weights of the subalgorithms were compared to each other. That is why different power system restoration strategies may require various methods of calculating weights of the graph&rsquo, s branches.

Currently there is a high interest in offshore grids, especially can be mentioned the matter of increasing power generation from offshore wind farms, supplying offshore loads and cross-border connections. In this article typical elements incorporated within offshore grids will be mentioned: wind farms, high power loads, gas turbines and marine current farms. The aim of this article is to comment on means of modelling methods for angle stability analysis within offshore grids. Furthermore, this article dissertates about exemplary results of stability analysis of offshore grid test model.

Transmission network expansion planning involves various types of static and dynamic analyses. The complexity and increasingly difficult operating conditions of power systems raise the importance of dynamic analyses on the expansion planning stage. Primary studies in the field of dynamic analyses include rotor angle stability, voltage ride-through and frequency stability analyses. This paper presents four methods of rotor angle small signal stability assessment, which can be used in transmission network expansion planning. For each of these methods, the requirements for the calculation model and computational accuracy are discussed, among other aspects. Practical considerations related to the use of particular methods in planning analyses are presented. Theoretical considerations are illustrated with the results of stability assessment of a multi-machine test system.

Transmission expansion planning requires static and dynamic analyses. Planning criteria include the selection of contingencies consisting of faults and their clearing, performance standards, transmission system adjustments, and corrective action plan. Performance standards relating to power system dynamics mainly concern the voltage ride through and transient angle stability i.e. retaining synchronism after the occurrence of the contingencies mentioned. The selection of planning contingencies, for which performance standards must be complied with, is important in terms of capital expenditures in transmission network expansion and secure power system operation. This paper discusses planning contingencies accepted by various transmission network operators worldwide and describes a set of planning contingencies proposed by the authors.

SUMMARY The article shows that for many problems appearing in power system planning and operation the shortcircuit power becomes an important and useful factor. Checking up the short-circuit power can limit a number of time consuming detailed analyses. The paper concerns mainly the power system angle and voltage stability. Detailed stability analyses of power systems are performed at short-term and mid-term planning of transmission network development. Increased load demands and market economics are pushing transmission networks closer and closer to their operational limits. Therefore it is necessary to perform even a simplified power system stability assessment also at long-term planning. The article shows that very simple criteria of angle and voltage stability based on short-circuit power can be used as screening filters for fast contingency selection. The suggested criteria have been verified for a real large-scale system. Copyright © 2014 John Wiley & Sons, Ltd.

Cierpienie pozostaje wielką tajemnicą, nieogarniętą przez ludzki rozum. Żaden postęp, żadna technika czy medycyna wyposażone nawet w najnowocześniejsze zdobycze nie są w stanie wyeliminować ze świata cierpienia oraz nieszczęścia. Towarzyszą one człowiekowi niemal od zarania dziejów i towarzyszyć będą aż po kres. Jednych cierpienie dotyka w mniejszym, drugich w większym wymiarze. W życiu św. Siostry Faustyny Kowalskiej należącej do największych znanych na światową skalę współczesnych Świętych dokonało się misterium cierpienia, które zmieniło jej życie i objawiło bliskość Chrystusa. Ta skromna kobieta wybrana została do głoszenia całej ludzkości Bożego Miłosierdzia. Istotną rolę w życiu cierpiącej zakonnicy odgrywały cnoty teologalne (wiara, nadzieja oraz miłość) w połączeniu z sakramentami świętymi, które ją w cierpieniu umacniały, pozwalając jej cieszyć się przy tym pokojem duszy i owocami ufności w Bogu złożonej. Dzienniczek Siostry Faustyny jest przejmującym zapisem duchowych wzlotów oraz ciemności, stanowiąc świadectwo wiary trudnej i niezłomnej. Przede wszystkim jest jednak dowodem ostatecznego zawierzenia największemu przymiotowi Boskiemu – Jego niepojętemu i nieskończonemu Miłosierdziu.

A Static Var Compensator (SVC) installed in a power transmission network can be effectively used to enhance the damping of electromechanical oscillations [Schweickardt, H. E., Romegialli, G., & Reichert, K. (1978). Closed loop control of static VAR sources (SVS) on EHV transmission lines. IEEE Pes winter power meeting, (paper no A78, pp. 135–136), New York, Jan. 29–Feb. 3]. An adequately designed robust controller, which takes into account variations in the operating conditions, can help to achieve the desired damping control. The proposed approach described in this paper is aimed to achieve damping of electromechanical oscillations by considering a systematic approach, based on interval systems theory and Kharitonov's Theorem. The method presented allows for the design of a fixed-parameter, low-order controller, given a supposed stability degree of the system. The synthesis of a robust SVC controller is divided into two tasks. The first is the determination of the region of stability in the controller parameter plane by plotting the stability boundary locus. The second task is the optimization of the selected controller parameters from the obtained solutions to the first task. Examples of eigenvalue analysis and time simulation demonstrate the effectiveness and robustness of the designed controller.

This paper presents a selection method for phase shift transformer PST controller input signal. Simple conditions of input signal selection are obtained using frequency response analysis. The proposed method requires a suitable modeling of power system including PST device. The two types of power system models described in this paper are the nonlinear equations system model and the linearized model. The linearized model is represented as a block diagram transfer function model and as a state space representation model. The block diagram model presented in this paper has been used for the PST feedback input signal selection. Five locally available measurements at the switching node of the PST are considered. The results of frequency domain tests have confirmed that the block diagram transfer function model is a useful tool for power system analysis. The LQR method is used to achieve the final verification and the choice of input control signal.

Considerations concerning the damping of power swings using a FACTS device like TCPS are presented in this paper. The case of a generator-infinite bus test system is taken into consideration. Phenomena have been analysed both by performing computer simulations of the mathematical model and experimental analysis in laboratory conditions. A short description is given of the laboratory set up equipped with a TCPS device used for the experimental analysis.

Submarine (offshore) HVAC and HVDC cable power grids will play bigger and bigger role in the nearest future. In particular it will be connected with development of offshore wind farms and establishment of submarine transmission interconnections between the various national power systems. It results in necessity to elaborate proper procedures of designing of cable links (lines) which are part of HVAC and HVDC submarine power grids. Concept of offshore cable power grids in the context of introducing (injecting) of power generated in offshore wind farms to on-shore power grids and intersystem power exchange have been described in the paper. Submarine cable link as an element of submarine power grid have been described. Examples of existing submarine cable links and the ones that are being designed, as well as examples of offshore power grids have been given. Then technical characteristic of HVAC and HVDC submarine power cables have been presented. In the further part of the paper general power system requirements concerning cooperation of submarine cable link and on-shore power grid have been formulated. The main part of the paper concerns designing process of HVAC and HVDC submarine cable links. General and detailed rules of designing of both types of submarine cable links, considering difficulties well known from practice, have been described. At the end of the paper summary and final conclusions have been presented.

Detailed stability analyses of a power system are performed at short-term and mid-term planning of transmission network development. At long-term planning, due to the uncertainty of power system data, the stability analyses are either omitted or performed in a simplified method. Currently, due to the economical and ecological reasons, the power system operators are interested to use the transmission network as close as possible to the thermal and stability limits. Therefore it is necessary to perform even a simplified power system stability assessment also at long-term planning. The paper shows that very simple criteria of angle and voltage stability based on short-circuit power can be used for the sake of long-term planning. The suggested criteria were verified for a real large-scale power system.

Summary form only given, as follows. This paper describes new structures for stability-enhancing excitation controllers designed using a nonlinear multi-machine system model and Lyapunov's direct method. Two control structures are presented: a hierarchical structure in which the AVR is the master controller and the PSS the slave controller and a traditional structure in which the PSS constitutes a supplementary loop to the main AVR. Both controllers are shown to be robust, as the damping they introduce into the system is insensitive to changes in both the system topology/parameters and the pattern of network flows. Each individual controller contributes positively to the overall system damping with no undesirable interaction between controllers. These features should allow a decentralized approach to the design of the AVR+PSS. Such a design approach is compatible with the new competitive market structures and should result in savings on commissioning costs. Simulation results for a multi-machine power system are presented that confirm the above and show that the two control structures are very effective in damping both local and inter-area power swings.

In perspective, by 2030, a change of the fuel/ technology structure of capacity power will take place during the next dozen or so years in many countries of the European Union. Such changes are also planned in the Polish Power System (NPS) structure of capacity power which, in addition to the economic and environmental is also reflected under the angle of frequency control and tie-line power in interconnected power systems. The submitted paper discusses the proposed changes in the structure of capacity power on the example of the NPS. Moreover, some results of system frequency and tie-line power control (load and frequency control) in a heterogeneous generation power system are presented.

Stability analyses of a power system are performed at short-term and mid-term planning of transmission network development. Increased load demands and market economics are pushing transmission networks closer and closer to their operational limits. Therefore it is necessary to perform even a simplified power system stability assessment also at long-term planning. The article shows that very simple criteria of angle stability and voltage stability based on short-circuit power can be used as screening filters for fast contingency selection. The suggested criteria have been verified for a real large-scale system.

Internal interactions between control paths are a pivotal issue in multifunction FACTS controller design. One of the main stages of controller synthesis is an appropriate interaction analysis. This paper presents an analysis of interactions of Unified Power Flow Controller (UPFC). It is shown that multifunction operation of UPFC controller could be a source of interactions. The test system analysis has been performed on the basis of linear system control theory.