High-voltage Electrical Network Research Articles

Application of non-Euclidean metric in the electric power industry for reduction of measurement uncertainty

The paper proposes the use of the non-Euclidean metric to reduce the uncertainty that occurs when measuring voltage for the tasks of ongoing continuous control of electric power consumption in large, branched high-voltage electric networks. The problem is that for continuous control of electric power consumption, it is necessary to install the active and reactive power measuring equipment in each node of the electric network (at each substation) and to ensure the transmission of measurement information to dispatching control centers. For countries with large electric networks, long distances between electric grid nodes and dispatch control centers, this requires huge capital costs. Therefore, it is advisable to place equipment for measuring electric power and voltage only in individual nodes of the electrical network, and then calculate the parameters of the remaining nodes based on Kirchhoff's laws. But at the same time, there is a significant measurement uncertainty, because the complex value of the voltage is usually not measured, only the modulus of the voltage values is used for the calculation. The use of non-Euclidean metrics provides the reduction of the input data uncertainty, which are necessary to control the consumption of electric power in each node of the electric network.

A Deep Learning Approach for the Automated Classification of Geomagnetically Induced Current Scalograms

During geomagnetic storms, which are a result of solar wind’s interaction with the Earth’s magnetosphere, geomagnetically induced currents (GICs) begin to flow in the long, high-voltage electrical networks on the Earth’s surface. It causes a number of negative phenomena that affect the normal operation of the entire electric power system. To investigate the nature of the phenomenon and its effects on transformers, a GIC monitoring system was created in 2011. The system consists of devices that are installed in the neutrals of autotransformers at five substations of the Kola–Karelian power transit in northwestern Russia. Considering the significant amount of data accumulated over 12 years of operating the GIC monitoring system, manual analysis becomes impractical. To analyze the constantly growing volume of recorded data effectively, a method for the automatic classification of GICs in autotransformer neutrals was proposed. The method is based on a continuous wavelet transform of the neutral current data combined with a convolutional neural network (CNN) to classify the obtained scalogram images. The classifier’s performance is evaluated using accuracy and binary cross-entropy loss metrics. As the result of comparing four CNN architectures, a model that showed high GIC classification performance on the validation set was chosen as the final model. The proposed CNN model, in addition to the main layers, includes pre-processing layers and a dropout layer.

Comparison of Intelligent Control Methods Performance in the UPFC Controllers Design for Power Flow Reference Tracking

The Unified Power Flow Controller (UPFC) is one of such emerging FACTS devices that can manage the power flow in Transportation System. Based on the control system associated with the management of UPFC, both the controllers of shunt and series converters of UPFC are controlled conventionally using PIs controllers. However, the PI system alone cannot control the UPFC in the presence of uncertainty of system parameters and disturbances. For this reason, the use of novel robust techniques based on artificial intelligence theory in the design control of UPFC is very efficient for improving its performances. In this regard, four approaches have been used in this study to replace the conventional PI controller and enhance the performance of the UPFC for power flow reference tracking. In the first approach, the fuzzy logic technique (Mamdani and Sugeno types) has been employed to provide dynamic control of series and shunt converters of UPFC, whereas in the second method, the controllers of UPFC are performed through the optimization techniques such as: PSO, PSO_SQP, and GA techniques. The proposed techniques based UPFC are tested in MATLAB/Simulink software by using UPFC with a 48-pulse voltage source converter (VSC) equipping a High Voltage (HV) electrical network. In terms of dynamic performance, the simulations’ results and the comparative analysis clearly show the superiority of the intelligent controllers regardless of the variation of powers that affecting the model plant. Compared to PI controller, they ensure good performance in terms of tracking and decoupling.

Main results of supplementary comparisons of high voltage and current measuring systems

High voltages of alternative current (AC) are important because they are needed for numerous applications in physics and engineering. High AC voltages are also used to test insulating materials for their dielectric properties. Calibrations of instruments for high-voltage measurements should provide metrological traceability to national standards. This applies to the requirements for both voltage measuring instruments and current measuring instruments. The transformer for high-voltage measurements is used to reduce the values of currents and voltages during measurements in high-voltage electrical networks.
 Voltage transformers (VTs) are used to accurately measure high AC voltages. Current transformers (CTs) are used to convert line currents in power systems to levels that are acceptable for other measuring instruments, which are necessary to trip protective devices. There are measuring installations that are well known for accurate measurements of the CT coefficient for large primary currents, and systems for determining the behaviour of the industrial current and VT under distorted waveforms, etc. The calibration of a high voltage measuring system must be traceable to national or international measurement standards. Mutual comparisons of calibration results of CT and VT standards are carried out with the participation of several national laboratories.
 The results of high voltage transformer measuring systems (GULFMET.EM-S6) and high current transformer measuring systems (GULFMET.EM-S7) supplementary comparisons are described. The comparisons were carried out between national laboratories from three Regional Metrology Organizations. In general, the participants of both comparisons have demonstrated a good agreement of the results in the ratio error and phase displacement for high voltage and current. The comparison results may be used to improve the participants’ existing calibration and measurement capabilities entries in the Key Comparison Database (KCDB) of the International Bureau of Weights and Measures (BIPM).

Application of the Wave Channels Method to Analyze the Switching Overvoltages in Energizing a High-voltage Cable Line

A study of cable line failures shows that a large number of faults occur in the connecting and terminal couplings of 110--500 kV power lines. Overvoltages caused by operational switching in the substation switchgear circuits contribute to the total number of failures. The switching overvoltage amplitude and frequency depend on the parameters of the source, switched circuits, and switching moment. The aim of the study is to identify the network and switched circuit parameters affecting the maximum overvoltage excited by energizing a 400 kV cable line and to determine the degree of their influence. The following factors are considered: switching phase, cable line length, source inductance, and line residual charge. The analysis was carried out by the wave channels method. To achieve this goal, an analysis model was developed in the EMTP-RV software environment, which made it possible to calculate the electromagnetic transients excited by cable line switching. The model has been verified with respect to the surge propagation velocity along a coaxial wave channel. Overvoltage calculations have shown that the switching phase and the line charge availability in the pre-switching operation mode have the most significant effect on the overvoltage value. The obtained study results apply to high-voltage electrical networks containing cable lines. The study results made it possible to quantify the degree to which the considered factors influence the overvoltages excited by switching 400 kV cable lines and to assess possible exceeding of the values permitted by the relevant standards, which will make it possible to have a preventive influence on the number of failures.

Application of GIS technologies to implement environmental monitoring of laboratory studies of soils under power transmission lines in the Southern foothills of Fergana region

Aim: The purpose of the study is to introduce GIS technologies and create digital maps of irrigated soils, databases for soil surveys and agrochemical properties of lands of protected zones of linear objects of the Fergana region, as well as to determine the influence of power lines on wheat yield. Methods: The article uses methods of spatial and system-structural analysis, cartographic, comparative-geographical, statistical, typological and natural-economic zoning. They are based on GIS technologies using modern technological software, such as ArcGIS 10.3(2), and SAS Planet 1.3. Mathematical statistical processing of research results was carried out based on the IRRISTAT program. Results: based on the new modernized method, irrigated soils of farms under power lines were evaluated, and digital attribute bonus maps were compiled. Scientifically-based recommendations aimed at improving soil properties and efficient use of land resources have been developed. Conclusion: Based on the results of research conducted based on GIS technologies, ArcGIS applications and the rules of direct genetic soil science, the influence of high-voltage electrical networks on the properties of the soil of electromagnetic fields and protection limits were determined. The definition of areas in the study area, the establishment of boundaries, the definition of zones of impact and protection of high-voltage electrical networks, the analysis of agrophysical, agrochemical and other soil properties, the ways of using attribute data from individual modern GIS technologists and ArcGIS applications have been improved and appropriate maps have been compiled.

Peculiarities of transient recovering voltages at short circuit breaks in cable lines of high-voltage electric networks

Peculiarities of transient recovering voltages at short circuit breaks in cable lines of high-voltage electric networks

Transient Electromagnetic Processes Analysis in High Voltage Transmission Lines during Two-Phase Short Circuits

The mathematical model of a fragment of a high-voltage electric network is developed in this paper. The network consists of a long power line with distributed parameters and an equivalent three-phase active-inductive load. Neumann and Robin-Poincare boundary conditions were used to identify the boundary conditions for the long line equation. The parameter output voltage (voltage at the end of the line) is introduced into the paper for further universal use of the developed line model. On the basis of the developed mathematical model, the program code is written in the algorithmic language Visual Fortran. By means of it, oscillograms of transient electromagnetic processes of voltages and currents in the form of spatial, temporal and temporal-spatial distributions during remote two-phase short circuits in the transmission line of high voltage are obtained. Two transient electromagnetic processes are analyzed in the present work. The first one was analyzed during the switching on of the line to the normal mode of operation with the subsequent transition to the emergency mode. The second one was analyzed during the switching on the line in the mode of a remote two-phase short circuit to the ground. The results of transient electromagnetic process simulation in the form of analyzed figures are shown. All the results presented in this paper were obtained exclusively using numerical methods.

Calculation of the Voltage Unbalance Factor for High-Speed Railway Substations with V-Connection Scheme

In France, high-speed railway lines are powered by a 2 × 25 kV/50 Hz electrification system. The substations include two single-phase transformers connected to the high-voltage electrical transmission network on different pairs of phases according to a so-called “V-connection scheme”. In practice, due to the large variations in the power absorbed by the trains, this connection does not make it possible to satisfactorily limit the unbalance in the three-phase voltages. In order to correctly size a balancing system to be associated with the substation, it is necessary to calculate, with precision, the voltage unbalance factor as a function of the power drawn by the trains. In its first part, this paper presents modelling of the substation and proposes an algorithm which allows for the calculation of the upstream line voltage as a function of the power consumption at the secondary of the transformers. The voltage unbalance factor can then be determined over a long period of operation. In the second part of this paper, the same approach is applied with an unbalance-compensator based on Steinmetz circuits controlled by AC choppers. Finally, in both cases, the results of the calculations are validated by simulations performed with PLECS simulation software.

Modeling of the Coupling of the Lightning Shock Wave Flow Circuit in the High Voltage Electrical Network

This article focuses on the aggression of lightning overload on the equipment of the electrical network of sites where storm activity is very dense; and the electrocution of people located in the direct environment of the high-voltage substation during the flow of lightning current to the ground through the ground socket. The modeling of the flow circuit of the shock wave consisting of guard wire, lightning arrester and ground socket couple to the transformer of the high voltage substations, thanks to the approach of a servo block, led to the synthesis of a PID regulator (corrector) whose action is to reject the effects of the overvoltage on the network equipment and to significantly reduce or even cancel the effects of the step or touch voltage due to the distribution of the potential around the ground socket; and thus improve the quality of service of the high-voltage transmission and distribution electricity network, especially in stormy times.

Підвищення точності визначення місця виникнення короткого замикання в електричних мережах номінальною напругою 110-150 кВ

The article is devoted to the study of improving the efficiency of the electric network with a voltage of 110-150 kV through the use of a developed device FKZ, which uses a radio channel to transmit information. At the present stage of development of electric power industry the question of reliability of work of high-voltage electric networks plays an important role. During the operation of such electrical networks, emergencies inevitably occur, the most dangerous of which are short circuits. Determining the location of damage to the electrical network is the most complex, time-consuming and time-consuming technological operation with significant costs. Therefore, the task of improving the design of devices to determine the location of damage, the use of which will significantly reduce the level of operating costs for electrical networks, is relevant. One of the ways to solve the problem of improving the accuracy of determining the location of a short circuit in the electrical network is the use of special technical means - short circuit clamps. The scheme of the normal regime of the 150 kV electric network of PJSC Kirovogradoblenergo was used for the research. The analysis of the configuration of this network showed that it has a number of substations that receive power from transmission lines, which are deaf branches. Therefore, the installation of short-circuit latches on such lines is necessary. The authors of the article propose the introduction of a radio channel to transmit information about the state of the network and the place of damage to the next personnel of the substation. The most appropriate ways to organize a radio channel are: the use of GSM networks; use of unlicensed frequency transmitters. Approximate calculations have been carried out, which confirm the possibility of creating a radio channel for transmitting information from the short-circuit lock for a distance of up to 20 km, using transceivers of non-licensed frequencies.

CALCULATION METHOD FOR THE CONTRIBUTION OF HVDC STATIONS WITH LINE-COMMUTATED CONVERTES (LCC) TO THE AC SHORT-CIRCUIT CURRENT

Short-circuit currents are a key measure for the planning of AC high voltage electrical networks. In this paper, the short-circuit current contribution of a HVDC system with line-commutated converters (LCC) to the short-circuit current in the AC system is investigated. Based on simulations in PSCAD/EMTDC the influence of different factors on the short-circuit current contribution is studied. These factors include the rating of the HVDC system, its operating point, different DC links such as back-to-back links, cables and overhead lines with varying DC line lengths and the type of short circuit and its distance from the HVDC converters. Based on the findings relevant factors are identified. On the basis of the simulation results a simplified analytical approximation for the short-circuit current contribution is derived, which takes into account the identified relevant factors.

ОЦІНКА ПАДІННЯ НАПРУГИ В ІНДУКТИВНОМУ ОПОРІ З'ЄДНУВАЛЬНИХ ПРОВОДІВ НЕЛІНІЙНИХ ОБМЕЖУВАЧІВ ПЕРЕНАПРУГ

Purpose. The results of studying the voltage drop in the inductive ractance of the connecting wires of surge arresters installed in open switchgear are presented. Methodology. Free software for circuit simulation was used to solve electri- cal circuits with nonlinear parameters. To take into account the differences between the negative and positive lightning current impulses, the oscillograms of real lightning currents were digitized using free specialized software. Results. The duration of the impulse front (as well as the total impulse duration) of the positive lightning significantly exceeds the corresponding parameters of the negative lightning current, so the charge carried by the positive lightning significantly exceeds the charge carried by the negative lightning. For these reasons, positive lightning, although less common than ЕЛЕКТРОЕНЕРГЕТИКА, ЕЛЕКТРОТЕХНІКА ТА ЕЛЕКТРОМЕХАНІКА Вісник КрНУ імені Михайла Остроградського. Випуск 4/2021 (129) 162 negative lightning, is more dangerous. It is found that due to the slower front of the impulse, the voltage drop in induc- tive reactance of connecting wires of the surge arresters in the case of positive lightning in 8-11 times less than in the case of negative lightning. Analytical formulas for calculating the inductance of the connecting wires, which take into account the geometric dimensions of the wires, provide more accurate results than the average inductance value of 1.3 μH/m given in the literature. Originality. The approach takes into account the differences between impulses of light- ning currents of negative and positive polarity, which cannot be achieved with use of the approximation of lightning currents by simplified mathematical expressions. Practical value. It is found that voltage drops in the inductive reac- tance will be more dangerous in case of long wire lengths and negative lightning current impulses with a steep front. Conclusions. Further development of the proposed approach is seen in its use for the analysis of circuits for protection of electrical equipment of high-voltage electrical networks from lightning overvoltages using surge arresters. Refer- ences 15, figures 10.

ВПЛИВ СТРУМІВ БЛИСКАВКИ НЕГАТИВНОЇ ТА ПОЗИТИВНОЇ ПОЛЯРНОСТІ НА ПАРАЛЕЛЬНЕ З'ЄДНАННЯ НЕЛІНІЙНИХ ОБМЕЖУВАЧІВ ПЕРЕНАПРУГ

Purpose. Studying the effect of non-identical protective characteristics of surge arresters on the efficiency of several arresters in parallel connection. Methodology. Free software for circuit simulation was used to solve electrical circuits with nonlinear parameters. To simulate the effect closest to real conditions, oscillograms of real lightning currents, digitized using free specialized software, were used. Results. The study of the parallel connection of two typical surge arresters designed for high-voltage networks of voltage class 110 kV was performed. To analyze the effect of non- identical protective characteristics, the residual voltage of one of the arrester was varied as a percentage of the residual voltage of the other one. It was found that when the difference between the residual voltages of the surge arresters ex- ceeds 6%, the current distribution through the surge arresters can reach a ratio of 1:4. Deliberate parallel connection of surge arresters is an effective solution to increase energy handling capability, provided that the residual voltages of the surge arresters are as close as possible. It was shown that a small difference in residual voltages is more dangerous in the case of positive lightning, which is characterized by a longer current impulse duration than negative lightning. It was shown that at the same amplitude of lightning currents, at struck by a positive lightning the surge arrester should absorb energy 10 times more, than at struck by a negative lightning. Originality. The approach takes into account the differences between impulses of lightning currents of negative and positive polarity, which cannot be achieved when using the approximation of lightning currents by simplified mathematical expressions. Practical value. The use of the proposed approach allows a more in-depth analyzing the various schemes of protection of electrical networks against overvoltages, because it takes into account the actual features of the lightning current curve. Conclusions. Further development of the proposed approach is seen in its use both in the selection of surge arresters to protect electrical equip- ment of high-voltage electrical networks, and in the educational process.

Hardware solutions for connecting static capacitor banks in high voltage electrical networks

This work is dedicated to finding effective hardware solutions for implementing the power part of reactive power compensation units for high voltage electric networks. It shows the possibility of cooperative usage of thyristor and electromechanical key elements for switching static capacitor batteries in high-voltage networks. Based on the suggested hardware solutions main technical and cost characteristics of thyristor capacitor units are determined. The rationality of their use in industrial high-voltage electrical networks of 6-10 kV is concluded. It is shown that the usage of hybrid thyristor capacitor units allows one to reduce the expenses, to provide the required range of accuracy of reactive power regulation, to cut power losses in the network, to guarantee normalized voltage level in the load nodes and to increase the reliability and duration of power equipment life cycle.

Первое в энергосистеме России токоограничивающее устройство на основе высокотемпературной сверхпроводимости

Superconducting fault current limiter (SFCL) is an innovative method for reducing the level of short-circuit currents in high-voltage electrical networks. This reduces the number of points of separation of the electrical network in conditions of short-circuit current limitation and thereby increases the network capacity and reliability of power supply to consumers. At the same time, the development of such devices poses new challenges for power engineers related to the integration of this equipment into the existing power system. The article discusses the process of implementation and pilot operation of the SFCT 220 kV pilot project (produced by CJSC “SuperOx”) at the 220/20 kV “Mnevniki” high-voltage substation in Moscow. The project required an extensive set of scientific studies and tests to confirm the characteristics of new devices and the possibility of their use in Russian power systems, the use of digital modeling technologies to test the operability of relay protection devices, as well as the development of new methodological documents for calculating the short-circuit current and relay protection parameters. As a result of the work, SFCT was switched on at the 220/20 kV “Mnevniki” substation at the end of 2019. The subsequent operation of the SFCT in 2019-2020 fully confirmed the declared characteristics of the device and the correctness of the selected technical solutions. The article is devoted to the features of the process of integrating a new device into the existing power system, the main technical solutions, the results of testing and operation of the device, as well as possible prospects for the development of SFCT technology.

The influence of changing resistance on the determination accuracy of short circuits in power lines

In high-voltage electrical networks, the occurrence of short circuits leads to forced interruptions in the power supply of large consumers and disruptions in intersystem communications. More than 65% of all types of occurring short circuits are single-phase short circuits [1]. In a single-phase short circuits (SPSC), a change in the zero sequence resistance (ZSR) especially significantly affects the inaccuracy in detection of damage sites (DDS). When choosing DDS methods, preference is given to remote methods according to the parameters of the emergency conditions (PEC), which are recorded by special instruments or determined from the oscillograms of emergency conditions. The use of modern microprocessor-based relay protection and automation devices (RPA) [26] or emergency event recorders allow viewing the oscillograms of emergency events. In a branched 110 kV network with a complex configuration, the DDS accuracy is influenced by a change in the ZSR. Averaging of specific parameters often leads to erroneous results. The choice of one value from the oscillograms puts the maintenance personnel in difficulty. In the scientific work, the influence of changes in the ZSR on the accuracy of the DDS is considered. The changes in the ZSR are influenced by the position of the on-load voltage regulator (OLTC) switches of transformers with a grounded neutral. In the work, for a more accurate record of the specific parameters of the network, a calculation program has been compiled, which allows making changes in the calculated specific parameters of the network. To determine the short-circuit current from the oscillograms, it is proposed to determine the stable state of accidents in which the current value will be approximately the same. The analysis of the oscillograms of SPSC in 110-220 kV networks in the southern part of the electric power system of Turkmenistan has been carried out.

Simulation of the insulation monitoring system of the high-voltage electrical network of a vehicle with a hybrid power plant

The paper presents the results of mathematical and simulation modeling, as well as calculated and experimental dependencies, which make it possible to evaluate the operation of the insulation resistance monitoring system of the high-voltage power grid of a hybrid vehicle. The work also provides circuits for measuring insulation resistance, a mathematical model in the MATLAB Simulink environment, and the peculiarities of the operation of the software and hardware simulation complex. The aim of the work is to obtain the most reliable mathematical and physical model of insulation resistance, to determine the architecture of a high voltage battery with the IRM system included in it, to identify the key functions and characteristics of the IRM system, to test the simulation system. The introduction justifies the importance of the IRM system and provides references to standards that govern the requirements for measuring and identifying utility faults. The block diagram of the high voltage battery control system is presented. The composition of its main elements is described. The functions and key characteristics of the IRM system are considered, typical characteristics of insulation monitoring systems are given. A schematic diagram of determining the insulation resistance of conductors and an electric circuit is clearly considered. An equivalent circuit of a differential DC amplifier with a unipolar power supply is presented, which is used to amplify small differential voltages on a shunt when changing large common-mode voltages, which is part of the measuring circuit. Mathematical and simulation modeling was carried out to evaluate the method for calculating the insulation resistance according to the well-known scheme, which is used when measuring using the three-voltmeter method. There was considered the mode of checking the the insulation control system, when several test procedures performed containing simulation of the fault and operating condition of the insulation by connecting and measuring the test resistance. The results of physical simulation of the IRM system and measurement of insulation resistance, voltage between each of the high voltage supply wires and the high voltage battery case, voltage between the wires, battery voltage were obtained. The actual insulation resistance was calculated. The conclusions explain the effectiveness of physical and simulation modeling, obtaining a reliable mathematical model and low error in modeling the insulation characteristics.

Faulty Feeder Identification Based on Data Analysis and Similarity Comparison for Flexible Grounding System in Electric Distribution Networks.

Reliability and safety are the most important indicators in the electric system. When a ground fault occurs, the electrical equipment and personnel will be greatly threatened. Due to the zero-sequence voltage/current sensor networks applied in the system, the fault identification and diagnosis technology are developing rapidly, including the application of ground fault suppression. A flexible grounding system (FGS) is a new technology applied to arc extinguishing in medium and high voltage electric distribution networks. Its characteristic is that when the single-phase ground fault occurs, the power-electronic-based device is put into the electric system to compensate and suppress the ground point current to be close to zero in a very short time. In order to implement the above process, the corresponding faulty feeder identification method needs to meet the requirements of rapidity and accuracy. In this article, based on the real-time sampled data from the zero-sequence current/voltage sensors, an improved faulty feeder identification method combining wavelet packet transform (WPT) and grey T-type correlation degree is proposed, which features both accuracy and rapidity. The former is used to reconstruct the transient characteristic signal, and the latter is responsible for calculating and comparing the similarity of relative variation trend. Simulation results verify the rationality and effectiveness of the proposed method and analysis.

Schlieren Images of Negative Streamer and Leader Formations in CO2 and a CF3I-CO2 Electronegative Gas Mixture

In electrical networks, SF6 gas is currently used to insulate high-voltage equipment, however, due to its high environmental impact, new alternatives such as CO2 and electronegative gas mixtures such as CF3I-CO2 are being trialled to replace SF6 and create a sustainable energy system. A high-voltage lightning impulse (1.2 μs/50 μs) was used to approximate the disturbance in a high-voltage electrical network caused by a lightning strike and helped to identify the likely streamer and leader formations in different gases insulating a piece of gas insulated switchgear. In this paper, the theoretical and practical aspects of electrical streamer and leader formations in pure CO2 and an electronegative gas mixture of CF3I-CO2 are examined using schlieren videography in small length rod-plane gas gaps between 20 and 50 mm in length. Schlieren allows the examination of gas density in streamer formations and for the differences in weakly attaching gases, such as CO2, and electronegative gas mixtures, such as CF3I-CO2, to be studied. The gas pressure is varied in order to examine the differences in streamer and leader formation as the gas density is varied and hence the probability of electron collision is varied.