Power Cable Lines Research Articles

Multiplicity of overvoltages during arc single phase earth faults in 35 kV electrical grids

The arc overvoltages during the single phase to earth faults in electrical distribution grids of 6-35 kV are the object of the research in this paper. The development of 35 kV distribution electrical grids is accompanied by the construction of new overhead and cable power lines. It causes a change of the capacitive earth fault current in the grids and also affects the multiplicity of overvoltages in electrical distribution grids during the single phase to earth faults. The paper shows the research results of overvoltages during arc single phase to earth faults in 35 kV electrical grid with the different grounding modes of a grid neutral (an isolated neutral, a grounded neutral through an arc-quenching reactor, a grounded neutral through a resistor). The calculations were performed on the digital models of the investigation power grids. According to the research results, a mathematical model has been created, which allows obtaining the maximum expected multiplicity of overvoltages in 35 kV electrical grids during the single phase to earth faults. This allows making decisions about the optimal measures for the protection of an electrical equipment insulation taking into account expected values of overvoltages as early as at the stage of pre-design works for the development of such electrical grids.

ОЦЕНКА СОСТОЯНИЯ ВЫСОКОВОЛЬТНОГО ЭЛЕКТРООБОРУДОВАНИЯ МНОГОУРОВНЕВОЙ СИСТЕМЫ ЭЛЕКТРОСНАБЖЕНИЯ ЦЕХОВ ПРОИЗВОДСТВЕННОЙ МЕТАЛЛУРГИЧЕСКОЙ ЛИНИИ

В работе выполнен анализ повреждений по воздушным и кабельным линиям электропередач. Выполнен расчет основных показателей надежности для прогнозирования значения фактического ресурса основного высоковольтного электрооборудования для цехов производственной металлургической линии. Расчеты выполнены для существующей схемы с помощью программного комплекса[1]. Выполненный анализ полученных результатов разработанного алгоритма и методики расчета показателей надежности позволил оценить техническое состояния воздушных и кабельных линий подвержены интенсивному старению по уровню напряжения и оценить количество отключений по узловым подстанциям.

Modelling of diagnostics of the technical condition of cable lines and power supply systems

The article is devoted to research of state of modern cable lines and power lines used in the economy. The article describes the current state of problem diagnosis conductor cable lines and the factors affecting the reliability of lines. The developed mathematical model of conversion of value of operating voltage into the digital code allows to develop a method of measurement. The method based on the conversion of a harmonic signal into time intervals and a comparison of two adjacent ones according to expressions. The algorithm of the operation processed in the device for measuring the current voltage of the harmonic signal was shown.

Determining the mode of operation of the system section, taking into account the current topology and predictive analysis of the active-adaptive network of 6-10 kV

Technical solutions aimed at improving the reliability of power supply to consumers of the 6-10 kV network are proposed, a block diagram of a fundamentally new device for diagnosing and protecting cells of 6-10 kV power cable lines with a single algorithm of operation is shown, which allows simultaneously performing current protection of the controlled feeder and monitoring with a predictive assessment (residual resource) of the state of the cable insulation material. A possible scheme of interaction of elements of an active-adaptive power unit of 6-10 kV is shown on the example of a cell of a 6-10 kV cable line. he device will allow you to control leakage currents in distribution networks, taking into account the remaining cable life, reduce insulation losses during power transmission and increase the energy efficiency of the controlled network by reducing power interruptions to the consumer. The quantitative values of the device will be determined after its introduction into trial operation.

АНАЛІЗ МАТЕМАТИЧНИХ МОДЕЛЕЙ ЛІНІЙ ЕЛЕКТРОПЕРЕДАЧІ

This paper investigates a mathematical model of one elements of the power supply system - power transmission lines. The type of models depends on the initial simplifications, which in turn are determined by the complexity of the physics of processes. The task of improving the accuracy of modeling of emergency processes in the power system is due to the significant complexity of modern power systems and their equipment, high-speed relay protection, automation of emergency management and the introduction of higher-speed switching equipment. One of the reasons for a significant number of serious emergencies in the system is the lack of complete and reliable information for modeling modes in the design and operation of power systems. The development of a mathematical model of a three-phase power line, which provides adequate reflection of both normal and emergency processes, is relevant. The advanced mathematical model of power transmission lines allows to investigate various operational modes of electric networks. The improved mathematical model of the power transmission line reflects all the features of physical processes at state modes and transient process and provides sufficient accuracy of the results. The type of mathematical model of power transmission lines depends on the accepted simplifications, depending on the task of research. The purpose of this work is to analyze the mathematical model of the power transmission line to study the modes of operation of the power supply system, with the possibility of its application to take into account all the design features of overhead and cable power lines. The mathematical model of the power line for the study of the modes of operation of the power supply system is analyzed. It is used to take into account the design features of overhead and cable power lines, skin effect.

Mechanism Configuration and Innovation Control System Design for Power Cable Line Mobile Maintenance Robot

SUMMARYHigh-voltage power cables are important channels for power transmission systems. Their special geographical environment and harsh natural environment can lead to many different faults. At present, such special operations in dangerous and harsh environments are performed manually, which not only has high labor intensity and low work efficiency but also has great personal safety risks. In order to solve such difficult problems, this paper studies the power maintenance robot for insulator string replacement, spacer replacement, damper and drainage plate maintenance; the basic configuration and the operation motion planning have been proposed; and the virtual prototype of the inspection maintenance robots has been developed, and then the mechanical structure of the robots has been optimized by the robot kinematics modeling and analyzed the working space based on the Monte Carlo method. The system platform, operation function, structural characteristics and related key technologies involved in the robot system development were systematically summarized; the deep integration point for the robot technology with big data, cloud computing, artificial intelligence, and ubiquitous power Internet-of-Things technologies was also discussed. Finally, the physical prototype of the insulator replacement, drainage plate tightening, and damper replacement operation robot has been developed; several experimental tests on a 220 V live line have been conducted so as to verify the robot engineering practicality; and the main development and future research direction have also been pointed out at last.

ЕКРАНУВАННЯ МАГНІТНОГО ПОЛЯ ПІДЗЕМНОЇ КАБЕЛЬНОЇ ЛІНІЇ ЗА ДОПОМОГОЮ Н-ПОДІБНОГО ЕКРАНА

In the article the magnetic field distributions, generated by underground extra-high voltage (330 kV) three-phase power cable line in the environment, in particular near the cables in the trench and on the ground, are analyzed for using of H-shaped shield made of different materials including aluminum, low carbon steel and non-oriented grain steel. As shown, the best shielding effectiveness is realized by aluminium shield. The H-shaped shield made of high-conducting non-magnetic materials is proposed to use in order to mitigate the magnetic field level on the ground down to regulated nonhazardous values. References 14, figures 7.

Проблемы обеспечения сейсмостойкости объектов электросетевого хозяйства при землетрясениях

The electric grid system is the basis for functioning of the Unified electric power system of Russia and technologically isolated electric power systems. One of the most serious problems in the electric power industry is the aging of the fixed assets of already built and operating power grid facilities. The second problem is to clarify the seismic hazard of the territories of the Russian Federation in the direction of its growth. As a result, the number of power grid facilities fall into the zones of increased seismic hazard. In the zone of 7 points or more, approximately 30 % of the entire length of electric networks and transformer capacities are located. Information is provided about the characteristics of seismic load and how the objects respond to an earthquake. The experience of earthquakes testifies to the high vulnerability of the overhead power lines, cable power lines, substations, power transformers, relay protection equipment and automation under intense seismic loads. Information is provided about massive damage to the power grid during earthquakes in the territory of Russia, Armenia, and other countries of the world. Frequently occurring short circuits during earthquakes in electrical networks, at transformer substations, in electrical equipment elements of power grid facilities lead to fires. It is determined that power grid facilities have less seismic resistance than electric power generation facilities, than buildings and structures where electrical equipment is located. The problem of insufficiency of the current regulatory framework for ensuring seismic resistance of electric power facilities was also identified. Possible measures to prevent accident rate and increase the resistance, reliability, and seismic stability of power grid facilities in case of earthquakes are considered. The development of normative regulation will allow to take measures to ensure the seismic stability of power grid facilities in operation, and to ensure that control and supervision activities are carried out at a higher level.

Aerodynamic forces on iced cylinder for dry ice accretion – A numerical study

Within this paper the ISO 12494 assumption of standard of slowly rotating reference collector under ice accretion has been tested. This concept, introduced by (Makkonen, 1984), suggests that the power line cables, which are the basis of the “reference collector” in the ISO framework, are slowly rotating under ice load, due to limited torsional stiffness. For this purpose, several Computational Fluid Dynamics (CFD) simulations of the atmospheric ice accretion and transient airflow conditions over iced cylinder at different angles of attack were performed. In order to ascertain the similarity, several parameters were chosen, namely, drag, lift and moment coefficients, pressure and viscous force. The results suggest that the benchmark cases of rotating and uniced cylinder have “similar” aerodynamic loads when compared with the “averaged” results at different angles of attack (AoA), namely, the values of total pressure and viscous force. However, on individual and instantaneous basis the difference in the airflow regime between AoA cases and the benchmark cases can be noticeable. The results from the ice accretion simulation suggest that at long term the gravity force will be the dominating one, with rotating cylinder being a good approximation to the “averaged” angle of attack cases for the ice accretion.

Safety Issues Referred to Induced Sheath Voltages in High-Voltage Power Cables—Case Study

Load currents and short-circuit currents in high-voltage power cable lines are sources of the induced voltages in the power cables’ concentric metallic sheaths. When power cables operate with single-point bonding, which is the simplest bonding arrangement, these induced voltages may introduce an electric shock hazard or may lead to damage of the cables’ outer non-metallic sheaths at the unearthed end of the power cable line. To avoid these aforementioned hazards, both-ends bonding of metallic sheaths is implemented but, unfortunately, it leads to increased power losses in the power cable line, due to the currents circulating through the sheaths. A remedy for the circulating currents is cross bonding—the most advanced bonding solution. Each solution has advantages and disadvantages. In practice, the decision referred to its selection should be preceded by a wide analysis. This paper presents a case study of the induced sheath voltages in a specific 110 kV power cable line. This power cable line is a specific one, due to the relatively low level of transferred power, much lower than the one resulting from the current-carrying capacity of the cables. In such a line, the induced voltages in normal operating conditions are on a very low level. Thus, no electric shock hazard exists and for this reason, the simplest arrangement—single-point bonding—was initially recommended at the project stage. However, a more advanced computer-based investigation has shown that in the case of the short-circuit conditions, induced voltages for this arrangement are at an unacceptably high level and risk of the outer non-metallic sheaths damage occurs. Moreover, the induced voltages during short circuits are unacceptable in some sections of the cable line even for both-ends bonding and cross bonding. The computer simulations enable to propose a simple practical solution for limiting these voltages. Recommended configurations of this power cable line—from the point of view of the induced sheath voltages and power losses—are indicated.

A New Cross-Correlation Algorithm Based on Distance for Improving Localization Accuracy of Partial Discharge in Cables Lines

Locating the partial discharge (PD) source is one of the most effective means to locate local defects in power cable lines. The sampling rate and the frequency-dependent characteristic of phase velocity have an obvious influence on localization accuracy based on the times of arrival (TOA) evaluation algorithm. In this paper, we present a cross-correlation algorithm based on propagation distance to locate the PD source in cable lines. First, we introduce the basic principle of the cross-correlation function of propagation distance. Then we verify the proposed method through a computer simulation model and investigate the influences of propagation distance, sampling rate, and noise on localization accuracy. Finally, we perform PD location experiments on two 250 m 10 kV XLPE power cables using the oscillation wave test system. The simulation and experiment results indicate that compared with traditional TOA evaluation methods, the proposed method has superior locating precision.

Current State and Prospects of Development of Gas-Insulated Power-Transmission Lines and Busbars at 110–1100 kV

Issues related to the development and technical operation of gas-insulated lines are considered. A comparison of the technical parameters of lines with different types of insulation is performed. The throughput of and losses in power-transmission lines of different types are identified; the specific electric capacity and technical losses in the gas-insulated lines are determined, and their safety and environmental friendliness are evaluated. The assessment of gas-insulated line construction variants and dependence of their real dimensions on the nominal voltage is carried out. Options for using different gases in gas-insulated lines are considered. The comparison of the intensity of magnetic fields of overhead, cable, and gas-insulated power lines showing the efficiency of the gas-insulated line application is performed.

Dynamics of Farmland Birds in Traditional Agroecosystems: The Value of Countryside Elements in Avian Conservation

In India, urbanization and growth of cities have fragmented farmlands and the area under cultivation is dwindling. This study examined the ecological characteristics of rice fields, the inherent value of countryside elements and the relative occurrence of four species of farmland birds Dicrurus macrocercus, Turdoides affinis, Pavo cristatus, and Psittacula krameri along the Cauvery delta region, widely known as the granary of Tamil Nadu. The abundance and distribution of birds were analyzed at 30 sampling points for a year using the unlimited-radius point-counts. Among the four species recorded, D. macrocercus utilized more heterogeneous farmlands, while P. krameri was recorded in more intensively cultivated regions of the farmland. Pre-harvested rice fields predominantly supported species abundance and richness and exhibited a greater value for farmland birds than plowed, flooded or post-harvested fields. The abundance and richness of birds in agroecosystems increased with native vegetation cover and woody shelterbelts. D. macrocercus displayed greater tolerance towards monoculture plantations and elements within the mosaics like cable poles and power lines. Bird abundance in farmlands also correlated positively with decreasing distance from the mainland for D. macrocercus and T. affinis and showed a negative correlation for P. cristatus and P. krameri. D. macrocercus also displayed specialized resource utilization foraging techniques coinciding with cultivation activities resulting in bird-farmer mutualism. Cross-validation of the AIC models also showed that rice fields margined by greater amounts of vegetation cover and retention of species-specific modified elements supported the greatest abundance of farmland birds.

АНАЛИЗ И ВЫБОР МЕТОДИКИ В РЕШЕНИИ ЗАДАЧ ИНТЕЛЛЕКТУАЛИЗАЦИИ СИСТЕМ ПРОГНОЗИРОВАНИЯ ТЕРМОФЛУКТУАЦИОННЫХ ПРОЦЕССОВ В КАБЕЛЬНЫХ СЕТЯХ

The article is devoted to research on the creation of diagnostics and prediction ofthermofluctuation processes of insulating materials of power cable lines (PCL) of electric powersystems based on such methods of artificial intelligence as neural networks and fuzzy logic. Thenecessity of developing a better methodology for the analysis of thermal conditions in PCL isshown. The urgency of the task of creating neural networks (NS) for assessing the throughput,calculating and predicting the temperature of PCL conductors in real time based on the data ofthe temperature monitoring system, taking into account changes in the current load of the line andthe external conditions of the heat sink, is substantiated. Based on the main criteria, traditionaland neural network algorithms for forecasting are compared, and the advantage of NS methods isshown. The classification of NS methods and models for predicting the temperature conditions ofcosmic rays has been carried out. To solve the problem of forecasting the PCL resource, a networkwas selected with direct data distribution and back propagation of the error, because networks of this type, together with an activation function in the form of a hyperbolic tangent, are tosome extent a universal structure for many problems of approximation, approximation, and forecasting.A neural network has been developed to determine the temperature regime of a currentcarryingcore of a power cable. A comparative analysis of the experimental and calculated characteristicsof the temperature distributions was carried out, while various load modes and thefunctions of changing the cable current were investigated. When analyzing the data, it was determinedthat the maximum deviation of the data received from the neural network from the data ofthe training sample was less than 2.5 %, which is an acceptable result. To increase the accuracy, alarge amount of input and output data was used when training the network, as well as some refinementof its structure. The model allows you to evaluate the current state of isolation and predictthe residual life of PCL. The model can be used in devices and systems for continuous diagnosisof power cables by temperature conditions.

Design of Power Cable Lines Partially Exposed to Direct Solar Radiation—Special Aspects

Power cable lines are usually buried in the ground. However, in some cases, their ending sections are mounted along the supports of overhead lines. This leads to a situation where the cables are exposed to direct solar radiation and, consequentially, overheat. The paper presents the advanced computer modelling of power cables’ heating, considering their insolation as well as the effect of wind. The temperature and current-carrying capacity of power cables—during exposure to direct solar radiation—are evaluated. An effective method of limiting the unfavourable impact of the sun is discussed. In the presence of solar radiation, the proposed method enables a significant increase in the power cables current-carrying capacity.

Ryzyko uszkodzenia cieplnego izolacji kabli elektroenergetycznych z powodu oddziaływania promieniowania słonecznego

Low-voltage, as well as high-voltage power cable lines, are usually buried in the ground. The ampacity of the power cables in the ground mainly depends on the thermal resistivity of the soil, which may vary in a wide range. A common practice in power cable systems performance is to supply them from a pole of an overhead line. If so, a section of the line is located in free air and can be directly exposed to solar radiation. In some cases, the ampacity of power cables placed in free air is lower than in the ground. Differences in ampacities can be very high if thermal resistivity of the soil is very low, and simultaneously solar irradiation of cables in air occurs. This paper presents the risk of power cables overheating and in consequence the risk of their failure, when part of the underground power cable line is placed in free air. Temperature distribution of cables in the air (with and without solar radiation) for various load currents is presented. Thermal endurance of power cables insulation, operating with the overheating, is estimated.

Active Power Losses in Three-Phase Cable Power Lines

Active Power Losses in Three-Phase Cable Power Lines

Аппроксимация переходных резонансных напряжений и токов в обмотках силовых трансформаторов для определения собственных частот колебаний и коэффициентов затухани

Transient interaction between power transformers and power cable lines may give rise to resonance overvoltages in the transformer primary windings. To develop protection measures against resonance overvoltages and to design transformers resistant to resonance overvoltages, it is necessary to know the natural frequencies of the transformer windings. Recent years have seen very rapid development of transformer windings high-frequency models. However, the mathematical models used in practice, which came from calculations of impulse overvoltages in transformer windings, reproduce the frequency dependences of losses and damping at natural frequencies with insufficient accuracy. To verify and improve the mathematical models used for analyzing high-frequency processes in transformer windings, it is necessary to have sufficient experimental data on the values of natural frequencies and damping factors. Methods for experimentally determining the natural frequencies and damping factors of power transformer windings are considered. Theoretical principles and analytical expressions for transient voltages and currents obtained for simplified equivalent circuits of windings with lumped parameters are given. An approach is proposed, according to which the transient voltages and currents in the winding are represented as the sum of steady-state and free components. The free component is then approximated using the theoretical expressions obtained for the equivalent circuits of the windings. The results of applying the approach to approximating the transient voltage at the midpoint and the current in the neutral of a dry-type transformer’s high-voltage winding are presented.

Математическое моделирование срока службы полимерной изоляции кабелей

The studies of the service life and residual life of various insulating materials are described. The known mathematical models of insulation aging applicable to AC power cable lines are considered. Based on the models and the previously proposed approach, the service life and residual life of cables with XLPE, EPR and PVC insulation are estimated. The assessment is carried out using the data from monitoring the voltage and current of a 6 kV cable transmission line laid at one of the electric power enterprises. Air temperature obtained from open sources. The results showed the applicability of all models for estimating the residual life due to the small difference in the predicted life. In real conditions, the service life of the listed types of insulation can be different due to their dielectric and design features

Analysis application possibilities of high-temperature superconductors in electric networks

In the article the technical analysis of existing constructive decisions concerning use of high-temperature superconducting cables is carried out. The features of the use of superconductors in electrical distribution networks are analyzed. The advantages of using high-temperature superconductors in comparison with low-temperature superconductors are established. It is determined that the use of high-temperature superconductors, due to the increased critical parameters, provides an increase in the power of transmission lines and energy saving. From the analysis it follows that high-temperature superconductor wires of 2G generation have better operational characteristics, respectively, their use is more efficient compared to wires of 1G generation. A scheme of a three-phase high-temperature superconducting power transmission network with a neutral wire is considered. The working conditions of a three-phase power network with high-temperature superconducting cables are analyzed. It is determined that the use of two cores of a high-temperature superconducting cable of a distributed power transmission system provides an increase in the throughput of electric power in distribution electric networks. Accordingly, the efficiency of electric power transmission is increased, as well as the loss of AC power and operating costs are reduced. It is shown that the use of the reactor reduces the requirements for protection devices, facilitates the operation of electrical installations, including generators of power plants, and also reduces the cost of distribution networks equipment. It is indicated that the smallest power loss in a three-phase distributed power transmission system using high-temperature superconducting cables can be achieved with a symmetrical load operation mode. The results of technical analysis can be used to develop recommendations for improving the characteristics of cable power lines.