Processes In Electric Power Systems Research Articles

Low-frequency oscillations analysis and big data

The increased observability of processes in electric power systems, provided by the widespread introduction of synchrophasor measurement technology, as well as the use of computational processing of measurement data arrays, has led to changes in the methodology for analyzing the power system operating modes. Along with the development of new approaches to modeling processes and received measurement signals, a class of data-based methods has emerged. In a number of recent studies, the analysis of synchrophasor measurement data at the large power system scale is considered as a big data problem. Despite the controversial nature of this point of view, the application of some big data methods in synchrophasor data analysis yields positive results. In the proposed report, an assessment of the volumes of initial and intermediate data in the analysis of forced low-frequency oscillations is performed. The effect of data explosion at intermediate stages of calculations is shown. The storage and transmission of these data can be replaced by their calculation in the presence of a storable and transmittable configuration of a generalized computational scheme. A method for compact visualization of an array of oscillation dynamic parameters is shown by the example of dissipating energy. In addition, an approach is presented for configuring streams of synthetic test data at the power system scale, which provides a desired result in the analysis of dissipative energy.

ANALYSIS OF ENERGY EXCHANGE PROCESSES WHEN BALANCING REGIMES ENERGY SUPPLY SYSTEMS WITH DISTRIBUTED GENERATION

It is shown that maintaining a balance between the production and consumption of electric energy is an important condition for the stable operation of modern energy supply systems. The active increase in the share of renewable energy sources forces the use of new algorithms for balancing demand and supply, in particular, at the expense of flexibility. This implies the need to implement new technological solutions and approaches to balancing the modes of generation and consumption (the ability to quickly respond to changes in demand and supply), which, in turn, requires a detailed analysis of energy exchange processes in electric power systems.
 It is recognized that there is a need for an in-depth analysis of the balance of energy components, and an assessment of electromagnetic compatibility in electric power systems, especially in the conditions of the growing influence of renewable energy sources on local electricity markets. Analysis of various factors influencing technological solutions and cooperation of different market parties are key components for developing effective management strategies and ensuring the stability of the electric power system.
 The peculiarities of the analysis of energy exchange processes in local electric power systems with the determination of exchange capacities, which are integral characteristics of the influence of various factors of the non-acidity of electricity on exchange processes, are considered. It is proposed to balance the components of electric energy on the basis of exchange processes in controlled intersections of local electric power systems using the components of instantaneous power at each energetically constant state. The exchange processes in local electric power systems are analyzed with the selection of different modes of their operation, in particular, when assessing the level of electromagnetic compatibility of the elements of the local electric power systems.
 The introduction of exchange capacities made it possible to develop indicators for assessing the level of electromagnetic compatibility of the elements of the local system. To estimate the share of consumers' contribution to the deterioration of the quality of electricity at the common connection point, an algorithm for evaluating the mutual influence of elements is proposed, with the allocation of the element's contribution to the distortion of electricity in the controlled intersection and the analysis of the magnitude of the influence of distorting factors on electromagnetic processes in the system element.
 An optimization model for achieving the specified levels of balancing (flexibility) in local electric power systems with energy accumulators has been developed.

On the Influence of Organizational and Technical Measures on the Cascade Evolvement of Accidents in Electric Power Systems with Heterogeneous Parameters

The aim of the study is to assess the effect of various organizational and technical measures on the evolvement of emergency cascade processes in electric power systems (EPS) with heterogeneous parameters and to determine the limits of the maximum permissible operation modes. The article presents the results of electrical operation mode calculations in the test configurations of 6, 35, 110, and 500 kV EPS containing 25, 36 and 40 nodes, which illustrate the influence of heterogeneity of the EPS parameters on the evolvement of cascade emergency processes. An approach to taking into account the heterogeneity of EPS parameters in planning and maintaining the EPS operation modes is presented. To enhance the EPS survivability and reduce the risk of cascade emergency processes to occur and evolve, distributed generation facilities of different capacities and FACTS devices were used in the EPS. In addition, power flows were redistributed by changing the loading of existing power plants with different electricity generation costs. The proposed approach was used to analyze the evolvement of a cascade-type system accident that occurred in the EPS of the Republic of Bashkortostan. By using the developed approach, the possibility of cascade emergency processes to occur and evolve can be evaluated in planning and maintaining the EPC operation modes, as well as to develop EPS configuration and operation mode adjustment measures aimed at preventing such emergencies from occurring.

Novel method for setting up the relay protection of power systems containing renewable energy sources and hydrogen energy storage systems

Integration of renewable energy sources (RES) together with energy storage systems (ESS) changes processes in electric power systems (EPS) significantly. Specifically, rate of change and the lowest values of operating conditions during the emergencies are got influenced. Such changes can cause incorrect actions of relay protection (RP) as it was designed and adjusted with no regard for influence of RES and ESS. Detailed research on processes during the different normal and abnormal modes in both EPS and primary transducers and also in RP devices should be done to take preventive actions. To do this research mathematical modeling based on detailed and authentic models of all elements including RP should be used. HRTSim (which was developed by authors) software for simulating EPS provides the opportunity to create such models of EPS of any size without simplifications and limits. Using of this instrument together with detailed mathematical models of RP which were developed before provided the opportunity to investigate them rigorously in RES-integrated EPS. Settings providing adequate action of RP in certain conditions were performed as a result of this investigation. Fragments of these investigations are performed in this paper. Results of these investigations would be useful for designing new methods and tools of RP adjustment.

ИССЛЕДОВАНИЕ СОВМЕСТНОЙ РАБОТЫ АВТОНОМНОЙ ГАЗОТУРБИННОЙ ЭЛЕКТРОСТАНЦИИ И ГЕНЕРИРУЮЩЕГО УЗЛА С ВОЗОБНОВЛЯЕМЫМИ ИСТОЧНИКАМИ ЭЛЕКТРОЭНЕРГИИ

The relevance The installed capacity of renewable energy sources increases annually relative to the total installed capacity. Features of work inherent in renewable energy installations modify the nature of transient processes in electric power systems during emergency modes. A number of authors, when studying the operation of renewable sources as part of the energy system, consider the parallel operation of renewable sources with a powerful electric power system, and also do not take into account the drive motors of power plant generators. In this paper, the study of transient processes is carried out in an isolated electric power system with renewable energy sources, the power of which is comparable to the power of classical generators. This work is dedicated to the study of transient processes in an isolated electric power system with renewable energy sources, the power of which is comparable to the power of classical generators. The research takes into account the model of a synchronous generator drive motor and its control system, configured in accordance with applicable requirements and standards. Aim of research The main aim of the research is to assess the impact of renewable energy sources on the operating modes of an isolated gas turbine power plant during emergency disturbances. Research methods To achieve the main aim of the research the method of the simulation mathematical modeling in Matlab/Simulink was used. Results During the research, a number of curves were obtained that characterize the operating modes of an isolated power system during an emergency process. The analysis of these curves has showed that the stable operation of the power plant is possible with the installed capacity of renewable energy sources not exceeding 60 % of the power reserve of the power plant's lead generator.

Исследование математических подходов к определению частотно-зависимого внутреннего сопротивления провода воздушной линии электропередачи

Mathematical modeling of a power transmission line (PTL) is an important issue for a wide range of tasks in the electric power industry. Mathematical modeling is necessary when studying the transient processes in electric power systems. Analytical expressions that allow modeling power transmission lines in a wide frequency range, including low frequencies and direct current, make it possible to study the operation of relay protection and automation devices in various modes and improve the accuracy of devices of fault location. It is important not only to obtain analytical expressions to determine the frequency dependences of the resistance, but also to verify these expressions in comparison with more accurate methods based on the finite elements method (FEM). The study has been carried out using a mathematical tools based on cylindrical Bessel functions. To develop formulas, it is necessary to determine the constants of integration based on boundary conditions. To verify the obtained expressions, modeling has been performed in the COMSOL Multiphysics software package, which is based on the FEM. The article presents a study of the internal resistance of the wires of power transmission line using the example of AC 185/24 wire. An analytical expression has been obtained to determine the internal complex resistance of a bimetallic wire. The reliability of the obtained expressions is confirmed by the convergence of the simulation results in comparison with the results of simulation modeling in Comsol software and mathematical modeling using known analytical expressions. The proposed approach to determine the internal resistance of a wire makes it possible to get more accurate analytic definition of characteristics of an overhead power transmission line. And thus, to design more qualitative models to analyze transient processes in power transmission lines and investigate the operation of relay protection devices. The wire models developed in Comsol software can be considered as more accurate in a wide range of frequencies.

АЛГОРИТМ ФУНКЦИОНИРОВАНИЯ ТИПОВОЙ ВЕТВИ АВТОМАТИЗИРОВАННОЙ ИНФОРМАЦИОННОЙ СИСТЕМЫ РЕГУЛИРОВАНИЯ

Relevance Improving the quality of control of dynamic processes in electric power systems involves the widespread introduction of optimal control methods implemented using computer and microprocessor technology. The efficiency of optimal control essentially depends on the class of the mathematical model that describes the processes in electric power systems. The use of power system models of a high accuracy class for choosing control laws does not allow real-time correction of system modes due to the large amount of calculation of the parameters of the optimal controller and insufficient convergence of computational processes. Having a Z-transfer function, it is not difficult to compose difference equations, the very record of which contains an algorithm that is easily programmable on a digital computer, which can ensure the accuracy of the solution for choosing optimal controllers. Aim of research The aim of the work is to apply the algorithm for the functioning of a typical branch of an automated information control system. Research methods For research, the VisSim software environment was used, which, unlike MATLAB, does not require expensive software. VisSim is freely available in the scientific community. To study the effects of frequency fluctuations on the rectified voltage of closed valve systems, the LAFC and LPFC methods were used in combination with the theory of random processes. Results From the point of view of the implementation of the signal processing algorithm, the numerical solutions of differential and difference equations are similar. But the representation and description of a link or fragment of the amplitude-pulse ACS in the form of difference equations allows using, along with models of physical ACS devices, also algorithmic blocks, the functions of which are performed by digital processors.

Accelerated algorithm for calculating Gramians of bilinear models of electric power systems

Bilinear models allow to characterize more precisely the behavior of physical processes in electric power systems and thereby improve the quality of their monitoring and control. However, the use of even medium size bilinear models usually requires a lot of computations. In order to improve the efficiency of bilinear analysis of power systems, this paper proposes an accelerated algorithm for calculating the Gramians of bilinear dynamical systems, which also takes into account the effects of sparse matrices. The conventional algorithms iterates the whole matrix. In contrast, in the proposed algorithm we continue iterate only large enough components of the solution matrix and exclude from iterations those components of the Gramian for which corrections become small. The algorithm was implemented and tested for four bilinear models.

Model of implicit pole electric machine based on mathematical formulation of magnetic field in air gap

When modeling transient processes in electric power systems, the issue of designing reliable models of electrical machines is of great interest. The most difficult task is to design the models of synchronous and asynchronous machines. The purpose of the project is to develop mathematical models of synchronous and asynchronous machines based on a generalized model of an implicit-pole machine that considers the change of rotor speed, geometric shapes, and the type of rotor and stator windings. Methods of mathematical modeling of electromagnetic fields in the air gap based on Maxwell equations and methods of the theory of electrical circuits are applied. A system of nonlinear differential equations is considered as a mathematical model of a generalized implicit-pole machine. The key assumption made is the high magnetic permeability of the stator and rotor cores. Technical data of real electric machines have been used for verification. Mathematical models of an implicit pole synchronous machine and an asynchronous machine with a phase rotor have been developed. These models can be used to analyze transient processes in the aggregate without dividing them into electromagnetic and electromechanical ones. The novelty of the models is the fact of non-sinusoidal distribution of the magnetic field in the air gap, various types of multiphase AC windings and rejecting the principle of constant rotation frequency at the time step of the simulation. The proposed mathematical models can be used to solve design problems, to analyze the modes of electric power systems, the operation of relay protection and automation of electric power facilities, and emergency automation. In the future, the equations that consider the influence of the damper circuits and the peculiarities of the windings will be added to the developed mathematical models. The purpose of further research is to develop models of salient-pole synchronous machines and asynchronous machines with a squirrel-cage rotor.

Novel approach for relays tuning using detailed mathematical model of electric power system

The correct operation of relay protection (RP) devices largely determines the security of electric power systems (EPS). The key point that in turn determines the behavior of protection in various emergency modes is a determination of their settings. The existing methodologies and tools often do not allow to provide RP settings adequate to the practical conditions of their functioning. This statement is confirmed by the statistics of faults in EPSs. The main reason for this issue is the inability to reliably reproduce transients in EPS via the software programs used in practice to calculate the RP settings. The Hybrid Real-Time Power System Simulator (HRTSim), developed by the authors, allows to reliably reproduce the entire range of normal and emergency modes and processes in EPS of any scale, topology and configuration by using detailed three-phase models of all power system components. Taking into account this possibility and features of the HRTSim, the task of detailed modeling of RP devices, including instrument current and voltage transformers, becomes relevant. The implemented special tools for RP modeling and the HRTSim in general allow to develop a new methodology for RP tuning. At the same time, the typical elements – relays – can be identified for each type of RP that determine their operation algorithm. This paper presents an analysis of the main relays of the most modern microprocessor-based RP devices and proposed principles of their tuning. The developed approach allows to adapt the RP settings to the practical conditions of their functioning in EPSs and to minimize the probability of RP maloperation.

Software and Hardware Decision Support System for Operators of Electrical Power Systems

The transience and unpredictability of processes in electric power systems (EPS) determine complexity of its control. This problem is especially relevant for EPS with renewable energy sources and flexible alternating current transmission systems technologies. Automatic control systems simplify the solution of this problem. Despite this, many issues related to EPS state control are solved by power system operators. Decision support systems (DSS) are applying to increase efficiency of operators work. However, existing algorithms in practice are inoperable in some cases: unrealizable decisions are formed, or decision cannot be found at all, etc. Another important problem is impossibility to preliminarily verify the proposed solution. In this regard, operators can additionally use EPS simulators, which are usually limited either by the size of simulated scheme or by the details of equipment mathematical models. The limitations are a consequence of numerical methods using, which are badly applicable for large-scale power systems simulation. In this article, a novel DSS has been developed based on a hybrid approach to EPS modeling combining properties and capabilities of several simulation techniques: analog, physical and digital. The implicit integration of differential equations in analog way makes possible modeling faster than real time. Such opportunity allows operator to verify more decisions and select the most effective ones. The algorithm for DSS application has been developed and described in the article. The properties and capabilities of the developed DSS are confirmed by experimental studies and tests in a real EPS.

MODES EVALUATION FEATURES IN LOCAL POWER SYSTEMS WITH DISTRIBUTED GENERATION AND STORAGE

The structure of local electric power systems with sources of Dispersed Generation is considered. The main models of these systems are presented. A detailed classification of the generation unit of local power systems with sources of scattered generation is presented, which contains the main characteristics of generators. Different types of means of electricity storage and features of their application are analyzed. The main types of storage devices that contain devices for storing electricity using capacitors and supercapacitors, devices for mechanical energy storage, devices for storing chemical energy, storage devices for thermal energy are identified. Energy processes in electric power systems with distributed generation sources and electric energy storage devices are carefully analyzed by estimating the values and signs of exchange capacities in the intersections of these systems. Among the above processes: non-sinusoidal modes in the intersections of local power systems and frequency deviations in sinusoidal and non-sinusoidal modes of operation. To optimize energy processes in these systems, a method of visual display of technical and economic indicators is proposed, which allows a comprehensive assessment of systems with distributed generation sources and different types of electrical energy storage and processes in them. Taking into account the peculiarities of the structure and functioning of systems with sources of dispersed generation, such criteria as the economic component of the cost of system elements, its availability in the specified region, environmental friendliness and service life are selected. To combine technical and economic criteria, it is proposed to use their graphical representation.

Evaluating the Effect of Geoinduced Currents on the Startup Modes of Power Transformers1

Results are presented from a study of the influence on the startup modes of transformers of sign-constant currents in the windings of power transformers that may be related to geomagnetic perturbations in the earth’s magnetosphere and ionosphere and to electromagnetic processes in electric power systems. Magnetization processes in power transformers produced by geoinduced currents (GIC) with hysteresis taken into account are analyzed. Acomputational study is based on a model of a segment of the 500 kV grid using the EMTP-RV program (PowerSys, France) which can be used for calculations of transient processes in nonlinear electrical circuits with hysteresis taken into account. It is argued that GIC must be taken into account in calculations of the thermal and electrodynamic stability of transformers when choosing the settings for relay protections.

Оценка воздействия геоиндуцированных токов на пусковые режимы силовых трансформаторов

This paper describes the researching results of sign-constant currents impact appears in power transformer windings on inrush modes, the origin of which can be associated with geomagnetic disturbances in the Earth's magnetosphere and ionosphere and with electromagnetic processes in electric power system. The magnetization processes of power transformers caused by geo-magnetically induced currents (GIC) are analyzed, with taking into account the hysteresis phenomenon. The calculation study was carried out on a 500 kV network section model using the EMTP-RV software (PowerSys, France), which allows performing calculations of transient processes in non-linear electrical circuits with taking into account hysteresis phenomenon. The need of taking GIC into account in the calculations of transformers thermal and electro dynamic withstand during setting of protective relays is substantiated.

Research, Development and Application of Hybrid Model of Back-to-Back HVDC Link

Recent hybrid simulators (or co-simulators) of the electric power system are focused on scientific and research features to propose and develop novel and more accurate simulators. The present paper demonstrates one more hybrid modelling approach based on application and combination of three modeling approaches all together: physical, analog and digital. The primary focus of the proposed approach is to develop the simulation tool ensuring such vital characteristics as three-phase simulation and modeling of a single spectrum of processes in electric power system, without separation of the electromagnetic and electromechanical transient stages. Moreover, unlimited scalability of the electric power system model and real-time simulation to ensure the opportunity of data exchange with external devices have been considered. The description of the development of the hybrid model of back-to-back HVDC link based on the proposed approach is discussed and analyzed. To confirm properties of the mentioned hybrid simulation approach and hybrid model of back-to-back HVDC link, the simulation results of the interconnection of non-synchronously operating parts of the electric power system; power flow regulation; dynamic response to external fault and damping of power oscillation in electric power system are presented and examined. Moreover, to confirm the adequacy of the obtained results, the comparison with a detailed voltage source converter HVDC model (Simulink Matlab) and Eurostag software are introduced.

Increase of Transient Stability Level of Gas Turbine Power Plant Using FACTS

The article is devoted to the development of the mathematical models of modern devices of flexible alternating current transmission systems (FACTS) when calculating the modes and stability of power systems and to the analysis of influence of the specified devices on transient stability of the generators. The considered scheme contains the generators with the gas turbine drive that have electromechanical parameters providing lower level of transient stability compared to units of higher power rating, which in some cases requires implementation of measures for transient stability enhancement. As examples of FACTS the following devices have been considered: compensating device based on voltage- sourced converter (STATCOM), static synchronous series compensator (SSSC) and the unified power flow controller (UPFC). The known examples of mathematical models of FACTS devices vary in complexity. For a preliminary assessment of the effectiveness of the FACTS devices, it is proposed to use simplified models that adequately reflect their impact on transients. The use of models made it possible to establish a positive impact of the devices on transient stability of generating equipment in case of short circuits in the electric network. The important conclusion here is that the use of the UPFC device based on two converters (with a corresponding increase in cost) compared to one converter device (STATCOM or SSSC) slightly increases the level of transient stability and the limit time of short circuit disconnection. The proposed method of simulating the FACTS devices is suitable for numerical calculations of transient processes in electric power systems, in particular, to estimate the impact on the transient stability level of the parallel operation of power plants in case of disturbances.

Approach in the modeling of wind turbines for power system stability studies and evaluation of their impact on electric power systems

Wind power - one the fastest evolving in renewable energy industry. From year to year the share of wind energy in power systems are increasing as well as increasing the size of wind farms. A large-scale wind farms that produce hundreds of megawatts of electricity have a serious impact on the power grid. This paper discusses proposed approaches to modeling wind farms using the Hybrid Real-Time Power System Simulator (HRTSim), to study stability and transient processes in electric power systems.

Synthesis of a hybrid model of the VSC FACTS devices and HVDC technologies

The motivation of the presented research is based on the need for development of new methods and tools for adequate simulation of FACTS devices and HVDC systems as part of real electric power systems (EPS). The Research object: An alternative hybrid approach for synthesizing VSC-FACTS and -HVDC hybrid model is proposed. The results: the VSC- FACTS and -HVDC hybrid model is designed in accordance with the presented concepts of hybrid simulation. The developed model allows us to carry out adequate simulation in real time of all the processes in HVDC, FACTS devices and EPS as a whole without any decomposition and limitation on their duration, and also use the developed tool for effective solution of a design, operational and research tasks of EPS containing such devices.

The Impact of the Bologna Agreement on Electric Power Engineering Education in Latvia

The fast transmission to a market form of economics in Latvia caused many complex problems, not least for electric power engineering education. As a result, there was a perceived need for reorganisation of the structure of the educational process, forms of teaching and the contents of courses. This reorganisation, and the transformation of courses and degree programmes, was applied across all educational levels to avoid too narrow a specialisation. The task was carried out with the active participation of some universities from within the European Community and with the participation of electric utilities in financing practically oriented projects. An especially successful aspect of this cooperation was participation in local research activity, which led to the development of new devices for monitoring and control of processes in electric power systems, as well as participation in a large European research project.