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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.

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.

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.

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.

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.

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.