Three-phase Electrical Network Research Articles

Study of the State Primary Measurement Standard of the Unit of Phase Shift Angle Between Two Voltages

Phase measurements are necessary for determining main parameters of the oscillatory process in complex electrical networks. Most often, it is precisely the phase shift angle (PSA) between two oscillatory processes of the same frequency that is measured. An essential indicator of the quality of electrical energy is the coefficient of asymmetry in a three-phase electrical network, which depends on the load of consumers in this network. This indicator is affected by a short circuit between two phase voltages. Phase measurement standards, phase meters, and phase converters are included in the measuring equipment for phase measurements. They are widely used in such fields as radiolocation, radio navigation, non-destructive testing, radio engineering, telecommunications, acoustics, metallurgy, machine and aircraft industry, space industry, as well as in scientific research and defence. The State Measurement Standard of Ukraine of the PSA unit between two voltages in the frequency range from 0.01 Hz to 10 MHz is maintained at the State Enterprise “UKRMETRTESTSTANDARD”, Kyiv. It provides metrological traceability of phases measured in the country. The main components of the standard were calibrated at the PTB, the National Metrology Institute of Germany. In Ukraine, numerous measurement standards and measurement instruments for phase measurements (more than 500.000 units) are used, in particular, phase calibrators, phase meters, phase shifters, synchronoscopes etc. Regular study of metrological characteristics of the DETU 09-07-11 measurement standard is conducted both in the main (from 5 Hz to 200 kHz) and in the extended (from 0.01 Hz to 10 MHz) frequency range. The PSA values obtained as a result of the research in the main frequency range do not exceed 0.001° (which is maximum according to measurements at all calibration points 0.00015°), and in the extended frequency range – 0.01° (which is maximum according to measurements at all calibration points 0.0053°). To eliminate the systematic measurement uncertainty component of the phase measurement standard, a special calibration is regularly performed using a set of resistive and capacitive phase bridges.

Error Analysis of Common Power Meter Installation Faults on Three-Phase Networks

The article is concerned with the operation of electric power quality meters and analyzers when incorrectly installed on a three-phase electrical network. An analytical study of the meter’s errors under the conditions of faulty installation was carried out. All possible types of installation errors are considered according to the proposed classification, as well as possible combinations of a pair of installation faults simultaneously. Classification of installation faults is also proposed. Matrix expressions are derived that allow modeling of any type of installation faults to quantify power and symmetry measurement errors. The proposed method allows to obtain quantitative signs that can identify a specific installation fault. The results of this study can help the development of an algorithm for the automatic detection of installation faults and their correction. The analytical results were confirmed by simulation studies on a three-phase network model in the MATLAB/SIMULINK environment. Experimental results, obtained from a commercial power quality analyzer operated under controlled laboratory conditions, are also reported.

Power Losses Reduction in Three-Phase Unbalanced Distribution Networks Using a Convex Optimization Model in the Complex Domain

This article presents a solution methodology to minimize power losses in three-phase unbalanced distribution networks. This approach involved an efficient complex-domain model that is categorized under mixed-integer convex optimization. The methodology employed consisted of efficient load rotation at each constant power node via a three-phase rotation matrix that allows defining each load connection to minimize the expected power imbalance at the terminals of the substation, as well as the total grid power losses, and improve voltage profile performance at each system phase. The load imbalance, expressed as a percentage, can be defined as a function of the active, reactive, or apparent power. In addition, considering the complex-domain representation of three-phase electrical networks under steady-state conditions, a mixed-integer convex model was formulated to reduce the power imbalances. With the purpose of determining the initial and final power losses of these distribution systems, the successive approximations method was employed to address the three-phase power flow problem. As a result, numerical validations in the IEEE 25-bus system and a 35-node three-phase feeder showed that the final active power losses vary depending on the objective function analyzed. Therefore, for the test feeders studied, it is necessary to evaluate each objective function, with the aim of finding the one that yields the best numerical results. Power losses reductions of about 3.8056 % and 6.8652 % were obtained for both test feeders via the proposed optimization methodology. All numerical validations were performed in the Julia programming environment, using the JuMP optimization tool and the HiGHS solver.

SIMULATION AND RESEARCH OF SINGLE-PHASE SHORT CIRCUITS IN THE ELECTRICAL NETWORK

The purpose of this work is to model single-phase short circuits in a three-phase electrical network and identify their type by analyzing the angular frequency of the spatial vector. Recently, the saturation of electric networks with powerful non-linear loads, the introduction of conversion equipment and renewable energy sources lead to the need for systematic analysis and research of the quality of electric energy (QEE). One of the factors that significantly affect the operation of electrical equipment is short circuits. In the article, based on the developed model of the formation of QEE distortions, a single-phase short circuit in a three-phase electrical network is investigated by switching it to a single-phase system with two α-β projections and a zero-sequence voltage vector.
 Studies of the influence of the location of the short-circuit point on the voltage in the electrical network have shown that the difference in the distance from the point of damage to the load, type of short-circuit leads to varying degrees of voltage change. Conducted studies have shown that different types of malfunctions and parameters of the electrical network at the point of short circuit cause different disturbances in the electrical voltage in the power supply system. The presence of a short circuit of the same type at different locations leads to different voltage drops and overvoltages. Short-term changes in voltage are the most common distortions of the quality of electrical voltage in electrical networks. The simulation results based on the developed model are consistent with the theory and reliably simulate the change in voltage in the electrical network.
 In the future, the presented model can help in creating a basis for the identification and subsequent control measures of voltage change violations.

Study of electricity transmission of a solar power plant into a three-phase electrical network

The development and research of the energy indicators of a solar power plant based on a block of solar panels of the Era-370W-24V-Mono type with a capacity of 110 kW and a solar hybrid inverter based on power transistors CM1200DC-34S, which transmits power to a three-phase electrical network, is presented. The control system of a hybrid inverter that transmits electric energy from solar panels with a power factor close to unity and a content of higher current harmonics less than 4 % has been developed. For Era-370W-24V-Mono solar panels, a polynomial approximation of the energy characteristics was carried out, namely the dependence of the selected power on the consumed current, which allows to improve the mode of maximum power selection from solar panels. A study of power losses in a hybrid inverter of a solar power plant was conducted, the dependence of total power losses on the switching frequency of power transistors in the mode of maximum power selection was obtained. It was determined that the efficiency of the hybrid inverter of the solar power plant ranges from 98.4 % at a PWM frequency of 1 kHz to 92.7 % at a PWM frequency of 6 kHz

IDENTIFICATION AND CLASSIFICATION OF SINGLE-PHASE VOLTAGE DIPS USING THE METHODOLOGY OF THE SPATIAL VECTOR OF ANGULAR FREQUENCY

A new method of identification and classification of voltage dips in a three-phase electric network is presented. The method is based on the representation of voltages of the electrical network by one complex variable - a spatial vector of the angular frequency. The main characteristics of the spatial vector, which are used to identify and classify dips, are the major and minor semi-axes, the angle of rotation of the formed ellipse. For balanced dips, the space vector goes in a circle in the complex plane with a radius equal to the voltage. For unbalanced dips, the spatial vector is an ellipse with parameters that depend on the phase of the voltage drop, the magnitude of the dip, and the phase angle shift.
 This method introduces a new level of accuracy and reliability in the analysis and classification of voltage dips, making it a tool for improving the quality of power supply and increasing the stability of electrical systems. The use of this method can help reduce the impact of unplanned interruptions in the supply of electricity to the enterprise and home, which is becoming a key task in the modern electricity sector.

Study of the energy parameters of the system “solar panels – solar inverter – electric network”

The article presents the results of research into the process of transferring electrical energy from solar panels through a hybrid solar inverter to a three-phase electrical network. An automatic regulation system is presented, which provides power regulation and operation in the mode of maximum power selection from solar panels. The results of the study of the energy efficiency of the system, the parameters of electromagnetic compatibility and the emission of higher harmonic currents are presented.

NEURAL NETWORK MODELING OF RELAY PROTECTION WITH A TIME DELAY

Modern electric power facilities – stations and high-voltage substations – have become digital objects with the active use of high-speed local networks directly involved in the technological process. Management, analysis and control of information exchange in the digital substation of the power system require the development of new means and approaches. For these purposes, machine learning methods can be used, in particular the apparatus of artificial neural networks (ANN). The paper shows the possibilities of using direct propagation ANNs (multilayer perceptrons) for modeling and identifying anomalies in the operation modes of relay protection with a time delay. The results of training and testing of the ANN are presented on the example of analyzing the operation of the over current protection in the “sliding time window” mode in a three-phase electrical network. The proposed neuroalgorithm and configuration of the ANN can be used to control the modes and accuracy of relay and cybernetic defenses.

Control of line voltage unbalance factor in three-phase distribution grids caused by single-phase photovoltaic systems

This study investigates the use of photovoltaic systems to regulate the voltage amplitude of electric power networks and to analyze their impact on the stability of Line Voltage Unbalance Factor (LVUF). It will be shown that instability of the LVUF can occur when single-phase domestic photovoltaic systems equipped with a voltage controller are connected to the three-phase low voltage network. The degradation of the LVUF is one of the problems to be avoided in three-phase electrical networks. To address this problem, this paper presents a complementary algorithm to be applied on the existing controller of the photovoltaics system. This algorithm calculates the optimum reference voltage for the controller, to keep the voltage amplitude within the permitted range, and at the same time prevent the degradation of the LVUF.

Monitoring dan Kendali Tegangan Jaringan Listrik Fase-tiga melalui Smartphone

This paper describes the creation of a minimum system for monitoring and controlling the voltage on a three-phase electrical network. Making a minimum system based on the result of previous research that has been implemented in the forms of device assembly, programming, and performance measurement. The research objectives are (i) assembling the hardware and programming based on Arduino software version 1.8.10 and (ii) measuring the minimum system performance. The research method for achieving the objective of assembling a minimum system is carried out through integrated wiring as an effort to get the hardware achievement, while for programming is an effort to get the software achievement. The implementation of the research method for measuring the performance as an effort to get the achievements of hardware and software is carried out by giving the orders to activate the paths of each phase. The result of the assembly is the integration of the Arduino UNO R3 module, Ethernet Shield type of W5100, MikroTik RouterBoard, relay modules, and Android smartphone, while the results of the programming are compiling and uploading the syntax to the Arduino module and making applications in the .apk format for a smartphone. Performance measurements are carried out by activating conditions for the three phases of phase-R, phase-S, and/or phase-T. The conclusion can be obtained, that the manufacture of a minimum system is appropriate for the fulfillment with respect to the presence of an electronic device for monitoring and controlling the voltage on a three-phase electrical network.

A high gain observer design for the three-phase shunt active power filter interfacing a photovoltaic source

In this article, a nonlinear observer is designed for a system consisting of a PVS photovoltaic source associated with a shunt active power filter (SAPF) and connected to a three-phase electrical network. In addition to improving the quality of energy in the distribution network (unity power factor), the use of SAPF also allows the injection of photovoltaic energy into the network. Since the system model is nonlinear and some variables are unknown (inaccessible to measurement), a high-gain observer is constructed. The advantage of this solution lies in the estimation of the unmeasured state variables (variables of the photovoltaic source). It is shown using theoretical analysis, under certain conditions of persistent excitation, that all estimation errors disappear exponentially. The effectiveness of the solution is verified by numerical simulation under Matlab/Simulink.

АНАЛІЗ РЕЖИМУ РОБОТИ ЕЛЕКТРИЧНОЇ МЕРЕЖІ ПРИ ОДНОФАЗНИХ КЗ НАПРУГОЮ 6-35 КВ

In three-phase electrical networks during the operation of power supply systems, damage to electrical equipment and difficult modes of operation are possible. Damage associated with insulation failure, rupture of wires and cables of power lines, personnel errors when switching, lead to a short circuit between the phases or on the ground. At a short circuit in a closed circuit there is a big current, voltage drop on elements of the equipment increases that leads to the general decrease in voltage in all points of a network and disturbance of work of consumers. Complex modes of operation of electrical networks occur, as a rule, as a result of accidents or after emergency shutdowns of equipment, with subsequent overloads and voltage deviations from the nominal values. And although these modes have been considered acceptable for some time, they create the preconditions for various types of damage and disorders in the operation of power grids. To ensure normal operation of electrical networks and prevent the development of accidents, it is necessary to respond quickly to changes in the mode of operation of the electrical network, immediately separate damaged equipment from serviceable and, if necessary, turn on a backup power supply. These functions are performed by relay protection and automation devices. Principles of operation of relay protection devices. 1. Current protection. Short circuits are accompanied by a sharp increase in current that exceeds the value predetermined by the calculation, which will perform simple relay protection devices that can control the value of currents. Separate the maximum current protection, which acts to disconnect the damaged network element with a time delay and current cut-offs, which operate without a time delay. The difference between them is in the choice of how to ensure selectivity. The currents controlled by the relay protection device can be measured in phases (through current transformers), or individual components of phase currents can be measured (currents of direct, reverse and zero sequences. This method is based on the method of symmetrical components). Current types of protection are divided with control of power direction (directional) and without control (non-directional). Current protection works on the principle of operation not only in case of damage to one of the network elements, but also to adjacent ones. Therefore, current protection is referred to as protection with relative selectivity. 2. Differential protection. The basis of the principle of differential protection is the comparison of homogeneous, instantaneous values at the ends of the protected element of the network (transformer, busbar section, generator, overhead line). Usually compare currents in magnitude and phase. Differential protection by its principle works only in case of damage to the protected element of the network, so it is performed without time delay and differential protection is called protection with absolute selectivity. 3. Remote protection. In the event of short circuits in the electrical network is not only a sudden increase in current, but also a sharp decrease in voltage, ie a decrease in resistance. The advantage of relay protection devices based on this principle is that the resistance to the fault does not depend on the current and voltage, but only on their ratio. This allows protection at short-circuit currents less than the nominal for electrical equipment. Single-phase earth faults account for about 70% of all damage to electrical equipment. According to the Rules of technical operation in the event of a single-phase short circuit to "ground" in 6-35 kV electrical networks, relay protection devices must act either to turn off the equipment or to "signal". At the enterprises with special working conditions and the increased risk of damage of the equipment and defeat of people by action of an electric current protection against single-phase short circuits on the earth operates on shutdown with the minimum endurance of time. Thus, after the analysis of the modes of operation of power supply systems, the importance of using switching devices of relay protection to ensure normal operating conditions of electrical networks and prevent accidents is confirmed. Also, the use of relay protection devices must be justified for each individual electrical equipment according to the principles of operation and characteristics of the proper functioning of the switching apparatus. In case of emergencies, namely single-phase earth faults, 6-35 kV electrical network operation modes and operation of single-phase earth fault protection are performed according to various technical parameters, depending on the type and connection scheme of the neutral of this power system.

PI CONTROLLER FOR CONTROLLING A THREE-PHASE INVERTER OF A PV SYSTEM CONNECTED TO THE ELECTRICAL NETWORK

In order to improve the efficiency of photovoltaic panels it is necessary to introduce the technique of Maximum Power Point (the technique of the MPPT). In the literature, several strategies are mentioned, among which the perturbation and observation (P&O) algorithm. The aim of this work is to a simulation study in MATLAB of a photovoltaic panel connected to the network using DC-DC and DC-AC converters. DC Boost converter is checked by the MPPT command to adjust the output voltage of the photovoltaic panel and maximize the power produced by the photovoltaic panel. The PI controller is used to control the inverter three-phase to make the connection of the photovoltaic panel to a three-phase electrical network.

Учёт несинусоидального/несимметричного режима работы электрической сети коммунально-бытового назначения при расчете уровня тока нулевого проводника

During the operation of 0.4 kV electric networks, asymmetry of currents and voltages is unavoidable. As is known, unbalanced operation of 0.4 kV networks is stemming from nonuniform distribution of loads between the phases. This results in that a fundamental frequency zero-sequence current will flow through the neutral conductor in a four-wire three-phase electric network. On the other hand, during balanced operation of a four-wire electric network containing loads with a nonlinear volt-ampere characteristic, higher harmonic currents multiple to three are summed in the neutral conductor. Therefore, it is of relevance to analyze unbalanced operating conditions of a four-wire electric network containing loads with a nonlinear volt-ampere characteristic. The article presents the characteristics of a municipal load for analyzing unbalanced/nonsinusoidal conditions of its operation. For carrying out full-valued assessment of unbalanced operating conditions of a four-wire electric network, a simulation model of a 0.4 kV network section containing a nonsinusoidal load is developed. It is shown that during unbalanced operation of an electric network containing electric loads with a nonlinear volt-ampere characteristic it is recommended to take into account zero-sequence current higher harmonic components that are not multiple to three. An algorithm for calculating the neutral conductor current harmonic component for determining the cable temperature rating is developed.

DEVELOPMENT OF A MATHEMATICAL MODEL OF TRANSITIONAL PROCESSES IN THE ELECTRICAL NETWORK IN PHASE COORDINATES

Distribution electrical networks of great length are characterized by a high order of the system of equations of electromagnetic transients. To improve the efficiency of modelling such networks, it is necessary to develop formalized procedures that provide automation of both the solution and the formation of systems of equations using modern computer technology. To simplify the development of mathematical models, transformations are used to move from a real three-phase network to other coordinate systems, but this is achieved at the expense of additional restrictions. To solve the problems of choosing and increasing the efficiency of means for limiting currents and overvoltages during transient processes in electrical networks, it is necessary to have a model reflecting a number of features, both of the networks themselves, and of the transient processes occurring in them. This is implemented in a model based on the representation of network elements not by single-phase equivalents, but by equations in phase coordinates. These equations contain the parameters of the network elements (active resistances, own and mutual inductances and capacitances) and the parameters of its mode (currents, voltages, phase powers), corresponding to the real physical parameters of electrical systems. A mathematical model of electromagnetic transient processes in an electrical network in phase coordinates has been developed. Calculation of the transient process when using the implicit method and representing the three-phase elements at the integration step by discrete models makes it possible to reduce the solution of a system of differential equations to multiple formation and solution of a system of equations. The diakoptic method for studying complex systems was developed, which was used to develop a mathematical model of electromagnetic transient processes in a three-phase electrical network. The proposed form of representation of discrete models of three-phase multipoles allows one to formalize both the solution procedure and the procedure for drawing up equations of transient processes for three-phase circuits of electrical networks of arbitrary configuration. Prospects for further research are computational experiments to study electromagnetic transient processes during ground faults in electrical networks of arbitrary configuration with various neutral modes and means of limiting currents and overvoltages.

Laboratory bench for the study of the causes and means of combating unacceptable deviations of the supply voltage in domestic premises

Introduction. One of the ways to improve the level of professional training of electrical engineers studying in higher educational institutions of Ukraine is to use in the educational process modern innovative switching equipment, protection, measurement and signaling equipment, etc. This gives students the opportunity to acquire a high level of training, which will allow them to improve their professional competence, contribute to their professional development, and allow them to become qualified specialists in later life. This direction of development of training requires a significant financial investment, which cannot be realized at the expense of public funds. At the Department of Electrical Apparatus of NTU «KhPI» it was possible to find alternative sources of funding – at the expense of an international grant and sponsorship from a number of electrical companies in Ukraine. The continuation of the selected vector of development is the development of laboratory work to study the causes of the occurrence of unacceptable deviations in the supply voltage in household premises and modern means of combating this dangerous phenomenon. Relevance. The need for students to study the problem of protecting household consumers from unacceptable voltage deviations in the power supply network is due to the fact that this is required by the current situation, which has developed with the technical condition of in-house distribution networks, which in most cases is extremely unsatisfactory. Unacceptable voltage deviations in the household network, depending on their level, can lead to a reduction in the service life of expensive electrical equipment, their failure, as well as a possible fire. Therefore, acquainting students in practice with the reasons for the occurrence of unacceptable voltage deviations in the household network, teaching them how to combat this phenomenon is an urgent task. Purpose. Design and manufacture of a laboratory stand for researching the causes of occurrence and means of dealing with unacceptable deviations in the supply voltage in domestic premises. Results. The developed laboratory stand allows students to study in detail the processes occurring in general in a three-phase electrical network after the break of the neutral N conductor, and to quantitatively analyze the level of voltage dips and overvoltages under asymmetrical load. Modern relays for the protection of household consumers ZUBR D32 and ADECS ADC-0110-32, used in the developed laboratory bench, allow students to familiarize themselves with the features of their installation, configuration, operation and functioning. Discussion. A laboratory stand developed at the Department of Electrical Apparatuses of NTU «KhPI» to study the causes of occurrence and means of combating unacceptable deviations of the supply voltage in household premises will increase the professional competence of students, contribute to their professional development, and will allow them to become qualified specialists in later life.

New Arc Stability Index for Industrial AC Three-Phase Electric Arc Furnaces Based on Acoustic Signals.

This research proposes a new index to evaluate the stability of the melting process, in three-phase electric arc furnaces (EAFs), based on the acoustic signals generated during the different stages of the casting. The proposed stability index is obtained by characterizing the time and frequency domain of the acoustic signals. During EAF monitoring, acoustic signals were acquired using a microphone coupled to an NI USB-9234 acquisition system. To validate the results, the voltage and current signals were measured with the aid of a Circutor AR6 power analyzer for three-phase electrical networks. The results showed that the acoustic signal energy in the frequency range of 1 to 12 kHz can be used as an indicator of the process stability in the EAF. Finally, the validity of the proposed stability index is evaluated from the process characterization using the harmonic distortion analysis methods and the dynamic U-I characteristics of the arc voltage and current signals. The results obtained demonstrated the effectiveness of the proposal and constitute a starting point for advances in the automatic control of the process in the EAF, from the acoustic signals.

Research, design, manufacture leakage current protection device for 660V/1140V underground mine electrical networks

This paper presents the results of researching, designing and manufacturing leakage current protection device for 660 V/1140 V ungrounded three-phase electrical networks. The outstanding features of the device are: ability to create wide deformation characteristic; automatically detect and grounded the leakage phase. Device test results show that relay operation time ​​for symmetrical and asymmetric leak resistors are 30 kΩ/60 kΩ per phase and 20 kΩ /50 kΩ for 660 V/1.140 V networks respectively. The total operating time of the device when single phase leaking through a 1 kΩ resistor not exceed 105 ms. The circuit automatically detects and accurately grounded the leakage phase through 100 Ω resistance, the total detection and grounded the leakage phase time does not exceed 110 ms. This research result can be applied in the design and manufacture of high-quality and reliable leakage current protection devices used in underground mines, replacing imported products.

Control of an Active Filter by Duty Cycle Modulation (DCM) for the Harmonic Decontamination of a Three-Phase Electrical Network

This paper presents the control of the active filter by Duty Cycle Modulation (DCM) for the harmonic pollution control of a three-phase electrical system. Several research works have preceded this work, but most of them deal with the control by pulse-width modulation and the differences lie around the THD reduction performance, the quality of the wave obtained, the simplicity of the scheme and the cost of the control. For this purpose, we propose a very innovative approach to active filter control which aims at reducing the current THD at a lower rate than pulse-width modulation techniques improving at the same time the wave quality with a more simplified control scheme. First we present the schematic diagram of the active filter, then we present the design of the control of this active filter based on the real and imaginary instantaneous power method which uses the algebraic “Clark” transformation. The Duty Cycle Modulation controller is used to obtain the required control commands to be injected to the inverter. We then developed a simulink model of the active filter to validate this study. The simulations were performed in the Matlab/Simulink environment. The results obtained show a significant improvement on the harmonic current control techniques for the THD of 1.02% which was 26.25%, the elimination of noise in the signal and the simplicity of the control with an easier implementation than the pulse width modulation (PWM) make the Duty Cycle Modulation (DCM) control a very promising tool.

Experimental Studies of the Developed Method for Determining the Insulation Parameters in an Asymmetric Network by a Voltage up to 1000 V at Mining Enterprises

In the work experimental studies of the developed method for determining the insulation parameters in an asymmetric electrical network by a voltage up to 1000 V at mining enterprises were carried out. It is based on measuring the module values of line voltage, angle of phase shift between vectors of damaged phase voltage relative to the ground and line voltage at two other phases, as well on measuring the module value of damaged phase voltage relative to the ground before and after connecting additional capacitive conductivity between the network’s phases and the ground. The results of experiment showed that the developed method for determining the insulation parameters has satisfactory accuracy and safety when operating three-phase electrical networks by voltage up to 1000 V at mining enterprises.