kV Network Research Articles

Изменение режима работы системы электроснабжения сети 6 кВ при переходе от изолированной нейтрали к резистивно-заземленной

The existing system of the electric network 6 kV used in the greenhouse facilities “Ovoshchi Krasnodarskogo kraya” with the insulated neutral does not ensure its reliable operation. Short single-phase short circuits in the network lead to ferroresonance, multiple short circuits and failure of power line sections and electrical equipment of the network up to the complete halting of greenhouse production. To eliminate ferroresonance processes and overvoltages in the electrical network and increase the reliability of the electrical supply system of the greenhouse facilities “Ovoshchi Krasnodarskogo kraya”, the authors have analyzed the effi ciency of an electrical supply system of 6kV network at its transition from the isolated neutral to the resistive-earthed neutral. They have determined the values of the capacitive currents of the electric network sections of the greenhouse facilities to show the excess of their allowable values. Based on the results obtained, they have stated the need for the modernization of the neutral grounding system of the electric network of the greenhouse facilities by transition to the neutral grounding through the low resistors used in commercially available transformer neutral grounding cabinets with the resistors 100 ohm for the 6 kV networks. The change in operating mode of the high-voltage network of the greenhouse enterprise from the isolated neutral to the resistive-grounded neutral ensured its reliable operation without interruptions of power supply and disconnection of its consumers. The network modernization has increased the current at the point of a single-phase short circuit to ground and provided the possibility of an immediate shut down of the damaged lines, thereby avoiding repeated short circuits in power lines and damage of electric equipment caused by ferroresonance. It has also reduced the probability of intermittent short-circuits, overvoltage in the network and electric shock to personnel and bystanders.1

Upgrading Study of Kuwait High Voltage Network 275 KV

Kuwait transmission network (275 kV network) has a significant increase in short circuit level at some grid and power stations substations above the system limitations (80 % of the rupture capacity of the system 63 kA).This increase results from the growth of power demand and the increase of transmission network complexity. New power stations will be added in the next few years. This paper describes a solution to the problem by splitting the transmission network into three zones as well as constructing new high voltage transmission network (i.e. 400 kV) and connects it with the existing 275 kV network. All the new power stations must be connected to the new 400 kV network and the connection to the 275 kV network must be stopped

ОПРЕДЕЛЕНИЕ МЕСТА ПОВРЕЖДЕНИЯ В СЕТЯХ 6 КВ ПРИ ЗАМЫКАНИЯХ ЧЕРЕЗ ПЕРЕХОДНОЕ СОПРОТИВЛЕНИЕ

. During the operation of electrical networks, emergency modes often occur. It is necessary to determine the type and location of damage (LD) as soon as possible. Since a simple line leads to undersupply of electricity. 6 kV networks with isolated neutral are considered. In these networks, it is difficult to determine the location of the damage due to the isolated neutral. Short circuits can be metallic and through contact resistance. Metallic ones have been studied earlier, and through contact resistance are investigated in this article. In this case, it is more difficult to determine the LD. The LD was carried out using the empirical criteria developed in the work, depending on the phase voltages and currents. In this case, three options for placing measuring instruments at the beginning, at the end and simultaneously at the beginning and at the end of the line with measurement errors of ± 0.2 %, ± 2.5 % and ± 5 % were considered. The formula of each criterion contains increasing voltages and currents in the numerator, and decreasing in the denominator as the LD moves along the length of the line. Studies have shown that the smallest error is achieved with two-sided measurement (at the beginning and at the end of the line) and is: 0.27 % with a measurement error of ± 0.2 %; 5.22 % at ± 2.5 % and 10.42 % at ± 5 %. Such accuracy with transient resistance is sufficient.

ГРАФОАНАЛИТИЧЕСКОЕ ИССЛЕДОВАНИЕ РЕЖИМОВ ОДНОФАЗНОГО ЗАМЫКАНИЯ НА ЗЕМЛЮ

Relevance To determine the damaged phase in single-phase earth faults (SPEF), as well as for the purposes of relay protection and signaling of earth faults, it is important to know the phase voltages and the zero sequence voltage. Phase voltages are used to determine the damaged phase and determine the location of the damage. The zero sequence voltage is used to perform nonselective signaling of the SPEF and to determine the completeness coefficient of the fault in adaptive earth fault protections in networks with low earth fault currents. Single-phase short circuits in 6–35 kV networks occur as a rule through a fault resistance, the value of which can reach 5–7 kOhm or more. The fault resistance at the point of damage changes the values of both the zero sequence current and all phase voltages, and the zero sequence voltage. Therefore, the study of single-phase earth fault modes and the assessment of the effect of fault resistance on phase voltages and voltage. Aim of research The main aim of the research is to develop graphoanalytic methods for studying modes for SPEF through fault resistance in networks with an isolated neutral. Research methods Graphoanalytic methods are used to study the effect of fault resistance on phase voltages. The construction of phase voltage graphs directly in the fault resistance function may performe only for a specific electrical network. In the article, to perform the analysis in a generalized form, the equations of phase voltages are used as a function of intermediate variables, which depend on the value of the fault resistance, but do not depend on the parameters of the electrical network. As intermediate variables, the damage completeness coefficient, the relative fault resistance, as well as the angle by which the vector of zero sequence voltage, taken with the reverse sign, lags behind the vector of the pre-emergency voltage of the damaged phase. The main advantage of the phase voltage equations in the function of intermediate variables is that such equations have the same form for any electrical network. At the same time, voltage graphs and superimposed graphs of other parameters of the SPEF mode in relative units can be used as nomograms and allow us to study SPEF modes in a wide range of changes in fault resistances. Results Equations are obtained for the relative values of phase voltages and zero sequence voltages as a function of the damage completeness coefficient and the relative values of the fault resistance. Graphs of phase voltages and zero sequence voltages are constructed. Graphs of changes in the damage completeness coefficient and relative fault resistance are combined with voltage graphs. The obtained equations and constructed graphs are universal in nature, valid for any electrical network with an isolated neutral and can be used as nomograms for determining and analyzing all parameters of the SPEF mode in relative units. Formulas and examples of transition to named units are given.

Предложения по законодательному решению проблем гибели птиц на воздушных линиях электропередачи в Казахстане

Предложения по законодательному решению проблем гибели птиц на воздушных линиях электропередачи в Казахстане

Разработка способа селективного определения линии с однофазным замыканием на землю для промышленных сетей 6-35 кВ с изолированной нейтралью при преобладании несинусоидальной нагрузки

This paper presents a method for determining the outgoing line with a singlephase fault for 6–35 kV networks with a non-sinusoidal loads. The paper considers the relevance of applying the mathematical apparatus of the wavelet transform together with the traditional methods of fault location. The application of the wavelet is relevant in the problems of decomposition of non-sinusoidal current signal of outgoing lines. This is due to the loads of modern enterprises of the oil producing sector of Khanty-Mansiysk Autonomous Okrug–Yugra. It is proposed to modernize the existing algorithm for relative measurement of the level of higher harmonics. The proposed method makes it possible to determine the outgoing line by the total energy of the spectrum of higher harmonics for different network configurations.

Determining the location of damage in electrical networks 35-10-6 kV by an analytical method based on matrix equations of the 3rd degree with respect to voltages

The article investigates an analytical method for determining the fault location in 35 kV, 10 kV and 6 kV networks based on thirddegree matrix equations for voltages. The method is remote, with doublesided measurement, according to the emergency mode parameters, the mode parameters are voltages and currents at the beginning and at the end of the line. The case is considered when the errors in determining the location of the damage are calculated theoretical and, as shown by the calculations, are only 1% both for metal closures and for pair closures through the contact resistance. Actual errors will depend on the accuracy classes of current transformers, voltage transformers, voltmeters and ammeters, for example: 0.2 - 0.5 - 2.0 - 5.0. The case is considered with an error of ±5%. The annual economic effect per 1 feeder with a really possible error of 5% is 170 thousand rubles when replacing only the method and 230 thousand rubles when replacing both the method and the device. For 1000 feeders, the annual economic effect will be 170 million rubles and 230 million rubles, respectively. Thus, the considered analytical method for determining the location of damage is effective both from a technical and economic point of view.

Introduction of state-of-the-art low-voltage distribution network devices

Trends towards the development of distributed generation involve a number of problems related to maintaining the quality of electric energy in medium and, especially, low-voltage networks. The article examines the impact of monitoring the quality of electricity of low voltage classes on the reliability of the electrical network. MSZ EN 50160 and Hungarian Energy and Utilities Regulatory Office (MEKH) standards are considered. In accordance with MSZ EN 50160, the main indicators of the quality of electric energy are considered, such as: frequency, voltage fluctuations, rapid voltage changes, Flicker dose, voltage dips, short-term voltage interruptions, long voltage interruptions, temporary overvoltages of industrial frequency, transient overvoltages between current-carrying conductors and voltage ground , harmonic voltage fluctuations, interharmonic voltage fluctuations. SAIFI and SAIDI are calculated according to the Hungarian Energy and Utilities Regulatory Office. The devices for monitoring the quality of electricity of low-voltage networks are analyzed. The factors affecting the choice of the place of installation of monitoring devices are considered. It is presented how power quality monitoring systems can reduce the number of malfunctions in the 0.4 kV network, and the influence of monitoring systems on the quality of electric power in 6-35 kV networks is considered.

Using the Stiffness Indicators of 110 and 220 kV Electric Network Nodes to Estimate Short-Circuit Currents

The topical problem of evaluation, analysis and limitation of short-circuit currents in electrical networks by simple and accessible methods without resorting to rather complex conventional calculations is addressed. The article suggests a new procedure for estimating short-circuit currents at network nodes based on their stiffness degree determined by the values of electric power system (EPS) configuration generalized parameters. The node balance admittance defined as the difference between the nodal admittance matrix diagonal and non-diagonal elements is used as the node stiffness indicator. The problem solution adequacy is confirmed by examples of constructing stochastic models for estimating short-circuit currents at the 110 kV networks nodes in the regional EPS and 220 kV nodes in the Moscow power system. The obtained stochastic models feature high values of correlation coefficients. This opens the possibility to determine (predict) average and interval values of short-circuit currents at network nodes, as well as the probability of their going beyond the established boundaries, which is important for short-circuit current limitation measures, including enhancement of the EPS configuration reliability.

Condition Assessment of Gas Insulated Switchgear Using Health Index and Conditional Factor Method

This paper proposes a comprehensive procedure to assess the condition of gas insulated switchgear (GIS) equipment by using the conventional weight and score method and introducing a conditional factor to improve the accuracy of the health index evaluation. Generally, the inspection and testing of GIS components are conducted according to manufacturer recommendations and guidelines in the international standards. However, this raw data has not been simplified and systematically processed for condition assessment. The score and weight technique are applied to transform the physical condition according to visible and measurable aging to numerical values in terms of component and bay health index values. The accuracy of the obtained health index has been improved by a conditional factor, which considers invisible aging factors, such as age, number of switching operations, degree of satisfactory operation, obsolescence, and adequacy of the interrupting rating. Here, a condition evaluation procedure has been developed and compared with the fuzzy logic method and the health index dominant score technique with satisfactory results. Subsequently, the proposed procedure has been developed as web application software to evaluate 175 bays of GIS in both 115 and 230 kV networks of an independent power producer supplying electricity of 3094 MW to a large industrial estate in Thailand. Eight GIS bays showed moderate or poor condition and the proper actions were assigned to prevent their failure. The software is in use in practice as a decision support tool to effectively manage the maintenance tasks and to improve supply reliability.

Intelligent Relay Protection System for Overhead Lines in Electrical Networks with Low Earth Fault Currents

Nuclear power plants (NPP) are one of the main sources of electricity. The distribution of electricity generated by nuclear power plants, or backup power supply to individual consumers of the power plant's own needs, can be carried out via a 6-35 kV network. These networks operate with an isolated or compensated neutral. This causes the fact that the currents of single-phase ground faults (SPGF) in case of accidents on overhead power lines (OL) are quite small and SPGF are difficult to identify. The article deals with the issues of identifying the SPGF and the corresponding selective response of the overhead line protection system. The limitation of the functioning of relay protection against SPGF, built on the classical principle of operation "if-then", is proved. The error of the traditional protection system is explained by the lack of a mechanism for updating the setpoints in accordance with changes in environmental conditions that affect the capacitive component of the conductivity of overhead lines. As an example of similar an influence, the effect of icing of wires, as well as the triboelectric effect in the form of accumulation of a space charge in the air gap around the line, is described. In this regard, a method is described for correcting the protection setpoints due to periodic measurements of the capacitance of the lines by means of their location probing. Thus, it is proposed to improve the traditional current protection against SPGF by giving the system the ability to adapt, but within the framework of its response as an agent with a simple behavior. The construction of a more advanced system of protection against SPGF in the form of an intelligent agent of the electrical network is also considered. The essence of this system is to use an artificial neural network as a subagent processing information. The advantage of a neurocomputer system for protection against SPGF is proved, which forms an integral assessment of the state of power transmission lines and learns to detect SPGF on a digital shadow following the electrical network. It indicates the possibility of classifying the proposed system of protection against SPGF as an intelligent agent due to the ability to adapt, learn and develop.

Evaluation and Analysis of Harmonic Distortion on 330kV Network Case Study Selected Sub-Region Nigerian Power System for Improve Power Quality

This paper presented fundamental characteristics of harmonic studies and its related work. The total harmonic distortion (THD) of the transmission line were computed using harmonics contents parameters of the waveform (harmonic voltage and impedance magnitude values). Results of THD for the 330kV transmission line are presented using harmonic load flow analysis in ETAP—domain on the view to measure the level of distortion in the network. Figure 2 shows the section of the harmonic load flow simulation in order to check for degree of harmonic distortion in the system under investigation. The provision of the harmonic frequency with greater magnitude exceeding THD and IHD limits are violated in accordance to IEC 61000-3-6:2008 (European Standards) are used as benchmark for measurement. That is the distortion for current and voltage (THDi% and THD%) are 0.5 and 1.5 respectively particularly harmonic order (h) ≤ 13. Consequently, the harmonic frequency violations with greater magnitude of 5th, 7th, 11th, and 13th order in the network are mitigated with 3-unit of single tuned filter to the affected buses for improved power quality.

A Novel Robust Strategy for the Concurrent Control of Frequency and Voltage in the Synchronous Generator With Real Structured Uncertainties

In this article, a novel robust strategy is proposed for concurrent control of the synchronous generator's voltage and frequency in a single machine infinite bus plant. The methodology is based on infinity norm and Mu analysis and synthesis to prepare the robust function of the power system stabilizer, automatic voltage regulator, and load frequency control systems. Ten real structured uncertainties have been considered for the K 1, K 2 and K 4 to K 6 coefficients of the Heffron–Phillips generator model, inertia constant, damping coefficient, the governor speed regulation coefficient, and the amplifier and exciter gains. Each uncertain parameter has a nominal value in the generator operating point with 25% tolerance excepts to amplifier and exciter gains where their tolerances are 12.5%. The proposed strategy efficiency lies in the strict converting of all ten real parametric uncertainties into the generalized structure of µ synthesis and the formation of efficient weighting functions. Based on the proposed strategy and H ∞ norm optimization, µ-synthesis D-K iteration procedure and loop-shaping manner, three controllers have been obtained whose robust performances (RPs) are guaranteed. The supremacy of the offered controllers is shown by comparing their functions in four scenarios and three patterns. The simulation results reveal the good RP of the designed controllers. Also, for a benchmark problem as a single machine connected to a 230 kV network, the capabilities of the designed robust controllers have been shown.

Computation of the zero-wire current under an asymmetric nonlinear load in a distribution network

Recently the electrical receivers with a nonlinear volt–ampere characteristic have increased significantly in utility electrical networks. The authors suggest applying a detailed account of their characteristics to analyze asymmetric/non-sinusoidal operating mode on an external electrical network. This paper is devoted to the problem of calculating the current level in a zero wire with an asymmetric operating mode of utility electrical networks containing such electrical receivers. A simulation model of the 0.4 kV network section of the urban electrical networks of Dushanbe has been developed. It is shown that a consideration of the higher harmonic components of the zero-sequence current is required, which is not a multiple of three. An algorithm for calculating the harmonic component of the zero-wire current has been also developed to determine the heating temperature of a cable. The obtained results make it possible to correctly select the cross-section of the zero wire of the cable line in the 0.4 kV distribution network for feeding a non-sinusoidal/asymmetric load.

A METHOD FOR CALCULATING THE RIPPLE CONTROL SIGNAL IN A 110 KV NETWORK

In the article, a method is presented for the calculation of the propagation of the ripple control signal in a 110 kV network. A frequency dependent network model is described for the calculation of the propagation of the ripple control signal. A comparison of the results of the calculation of the propagation of the ripple control signal and the results of corresponding measurements in a 110 kV network are presented.

Arc plasma energy evolvement in 60 kV network circuit breakers

Wydawnictwo SIGMA-NOT wydaje czasopisma fachowe informujące swoich czytelników o najnowszych osiągnięciach naukowych i nowoczesnych rozwiązaniach technicznych w Polsce i na świecie, popularyzuje problemy techniczne oraz poszerza wiedzę i kulturę techniczną.

CONSIDERATION OF THE CRITERION OF THE INFLUENCE OF ASYMMETRIC LOAD ON VOLTAGE DISTORTION IN A 10 kV NETWORK FOR RECOMMENDATIONS FOR REDUCING VOLTAGE ASYMMETRY

To date, there is a fairly large number of electrical equipment that is a source of asymmetric modes of operation in medium and low voltage electrical networks. This electrical equipment can create conductive low-frequency electromagnetic interference in electrical networks by the coefficient of voltage asymmetry in the reverse sequence. Studying the methodological basis of research on the theory of conductive low-frequency interference, it was found that when switching from one adjacent electrical network to another (for example, from a 0.4 kV network to a 10 kV network and vice versa) potential for conductive low-frequency interference decreases, i.e. the interference is partially suppressed by a certain amount. This amount is called the criterion determining the changes of the voltage asymmetry coefficient values in the reverse sequence in the transition of conductive low-frequency electromagnetic interference to the adjacent network. The purpose of this article is to develop a mathematical model for the study of network parameters affecting voltage asymmetry in the reverse sequence, which is reduced to a method for determining the value of the criterion for the effect of an asymmetric load on voltage distortion in a 10 kV network for recommendations for reducing voltage asymmetry. The article describes in detail the method of calculating this value and how it can be used to form recommendations for reducing voltage asymmetry. Scientific novelty of the study consists in the fact that an empirical mathematical model has been obtained that determines the criterion for the influence of an asymmetric load in a low-voltage network, the impact on which makes it possible to improve the electromagnetic situation in a 10 kV electrical network. This parameter can be taken into account when designing elements of electrical networks to determine the electromagnetic environment.

Модель совместной работы системы тягового и внешнего электроснабжения

Purpose: To improve record accuracy of external power supply network influence on the operation of traction power supply systems of industrial frequency AC. The article shows that existing mathematical models of traction and external power supply joint operation have sounding limitations. These limitations almost exclude the possibility of their practical use. At the same time, when projecting a new electrification, it is required to choose the most efficient external power supply scheme. At the exploitation of existing electrified sections, the necessity arises to assess equalizing current value during repairs in external power supply networks and to adopt a decision on changing power supply and sectioning schemes. Corresponding model is required to solve these tasks. Methods: Analysis of existing mathematical models and computer programs for joint calculation for traction and external power supply networks. Development of three-phase PU-generator models on the basis of EMF source behind an inductive resistance, development of three-phase and single-phase load models. Results: The article presents a description of a mathematical model implied to study the joint operation of 25 kV AC traction power supply systems and 110-750 kV power supply systems. The principles of building the model of three-phase and single-phase PU-generators on EMF source basis behind inductive resistance as well as the models of three-phase and single-phase loads are considered. Based on the given mathematical expressions, a computer model has been developed that allows analyzing the joint operation of three-phase external power supply networks and single-phase traction ones. The model is implemented in MATLAB-Simulink software package. Using this computer model, the influence of power flows through 110–330 kV network of Karelenergo and “FSK EAS” Public Companies on equalizing currents in the traction network of Knyazhaya — Idel section of Oktyabrskaya railway was analyzed. Practical importance: The reliability raise for traction power supply system operation at the expense of precise calculation of equalizing currents. Energy loss reduction in a traction network in account of traction network optimal power supply scheme choice.

Evaluating Performance of Medium High Electricity Distribution through FMECA Method

Major electricity distribution falls in medium-high power with 20 kV networks. They serve major industries and residential areas that serve entire customers. Due to its importance, however, these networks dealing with many potential unknown problems; and deliver severe impacts to company revenues. Operating and maintaining mediumhigh power system are not easy tasks since they involve with unknown and unpredictable disturbances. Any potential distribution may bring down entire networks. So it is important for every utility company to ensure the medium-high power networks properly managed and anticipated to any potential disturbances. The article applies FMECA method to identify and analyse any potential problems that may disturb the power networks. FMECA method has advantages to provide recommendation and systematic preventive steps for network operation and maintenance team. The outcome of the article is expected to be used as a reference for technicians to anticipate the potential problems far before it happens.

An Optimized Solution for Fault Detection and Location in Underground Cables Based on Traveling Waves

Faults in the power system affect the reliability, safety, and stability. Power-distribution systems are familiar with the different faults that can damage the overall performance of the entire system, from which they need to be effectively cleared. Underground power systems are more complex and require extra accuracy in fault detection and location for optimum fault management. Slow processing and the unavailability of a protection zone for relay coordination are concerns in fault detection and location, as these reduce the performance of power-protection systems. In this regard, this article proposes an optimized solution for a fault detection and location framework for underground cables based on a discrete wavelet transform (DWT). The proposed model supports area detection, the identification of faulty sections, and fault location. To overcome the abovementioned facts, we optimize the relay coordination for the overcurrent and timing relays. The proposed protection zone has two sequential stages for the current and time at which it optimizes the current and time settings of the connected relays through Newton–Raphson analysis (NRA). Moreover, the traveling times for the DWT are modeled, which relate to the protection zone provided by the relay coordination, and the faulty line that is identified as the relay protection is not overlapped. The model was tested for 132 kV/11 kV and 16-node networks for underground cables, and the obtained results show that the proposed model can detect and locate the cable’s faults speedily, as it detects the fault in 0.01 s, and at the accurate location. MATLAB/Simulink (DigSILENT Toolbox) is used to establish the underground network for fault location and detection.