Single-phase Short Circuit Research Articles

Harmonic Sequence Component Model-Based Small-Signal Stability Analysis in Synchronous Machines during Asymmetrical Faults

Power systems are complex and often subject to faults, requiring accurate mathematical models for a thorough analysis. Traditional time-domain models are employed to evaluate the dynamic response of power system elements during transmission system faults. However, only the positive sequence components are considered for unbalanced faults, so the small-signal stability analysis is no longer accurate when assuming balanced conditions for asymmetrical faults. The dynamic phasor approach extends traditional models by representing synchronous machines with harmonic sequence components, making it suitable for an unbalanced condition analysis and revealing dynamic couplings not evident in conventional methods. By modeling electrical and mechanical equations with harmonic sequence components, the study implements an eigenvalue sensitivity analysis and participation factor analysis to identify the variable with significant participation in the critical modes and consequently in the dynamic response of synchronous machines during asymmetric faults, thereby control strategies can be proposed to improve system stability. The article validates the dynamic phasor model through simulations of a single-phase short circuit, demonstrating its accuracy and effectiveness in representing the transient and dynamic behavior of synchronous machines, and correctly identifies the harmonic sequence component with significant participation in the critical modes identified by the eigenvalue sensitivity to the rotor angular velocity and rotor angle.

Online Full Range Copper Loss Minimization for Single-Phase Short-Circuit Fault Tolerant Control in Five-Phase PMSM

Online Full Range Copper Loss Minimization for Single-Phase Short-Circuit Fault Tolerant Control in Five-Phase PMSM

A Section Location Method of Single-Phase Short-Circuit Faults for Distribution Networks Containing Distributed Generators Based on Fusion Fault Confidence of Short-Circuit Current Vectors

A Section Location Method of Single-Phase Short-Circuit Faults for Distribution Networks Containing Distributed Generators Based on Fusion Fault Confidence of Short-Circuit Current Vectors

A method for determining the location and type of fault in transmission network using neural networks and power quality monitors

A new technique for identifying the location of a fault on a power line utilizing neural networks is presented in this paper. Specifically, the procedure involves four stages (three of which employ neural networks): gathering voltage input data via simulation, classifying the fault type, detecting the faulted line, and determining the fault position on the power line. This model was developed and tested for the IEEE 39 bus test system. Input voltages are obtained using DigSILENT PowerFactory software in which a set of three-phase and single-phase short circuits are simulated. Not voltages from all buses are used for the subsequent stages, only voltages from the optimally placed 12 buses in the IEEE 39 bus test system are used. In the second step, the first neural network is employed in order to classify the fault type – single-phase or three-phase. In the second stage, another neural network is used to determine the faulted line and in the third stage, the last neural network is developed to determine the fault position on the faulted line.

ДОСЛІДЖЕННЯ ПОДВІЙНИХ ЗАМКНЕНЬ НА ЗЕМЛЮ В МЕРЕЖАХ 10 КВ З ІЗОЛЬОВАНОЮ НЕЙТРАЛЛЮ

Reliability indicators of power supply systems as a whole are largely determined by the level of reliability of distribution electrical networks with a voltage of 6-35 kV. Emergency in networks with a voltage of 6-35 kV, operating in the mode with an isolated neutral, is often associated with internal overvoltages. Single-phase short-circuits occur in places of defects in the insulation of cable lines and substation equipment due to the aging of the insulation, non-compliance with the manufacturing technology of insulating structures at factories, non-compliance with the requirements of the instructions during the installation and operation of the equipment, as well as due to mechanical damage, which, sometimes at the time of their appearance, lead to only a partial decrease in electrical strength. Overloads lead to defects. Single-phase short-circuits in 10 kV networks that are not eliminated in time can lead to double earth faults. For protection in these networks, such protections as current cut-off, maximum current protection, current cut-off, zero-sequence current protection, current protections with blocking at minimum voltage are used. However, there are cases when there are cases of negative operation of such protections at a 10 kV substation during double earth faults. For example, a phase A short circuit occurred on the first line, which receives power from the buses of the investigated substation, and another short circuit (phase B) occurred on the second line. Instead of tripping the two damaged lines, the input circuit breaker tripped by mistake. This de-energized other (undamaged) lines that are fed from the same bus section as the damaged lines. Under such conditions, further studies of the currents in the lines during double circuits are required. For this, the use of the Matlab application program package is justified. This will significantly reduce the costs of physical modeling and verification of proposed proposals. The paper presents the results of studies of double earth faults in 10 kV networks with an isolated neutral in the "MATLAB" program package.

Assessment of the reliability of the mathematical model of the 0.4 kV rural electric network in Matlab Simulink on the example of a study of the steady-state mode of a single-phase short circuit

PURPOSE. Currently, modeling is one of the most reliable ways to study normal and emergency modes of operation of electrical networks. In this regard, a mathematical model of the 0.4 kV rural electric network was developed in the MATLAB Simulink program.PURPOSE. Evaluation of the accuracy of the parameters of the operating modes of the 0.4 kV rural electric network obtained by modeling in MATLAB Simulink by estimating the values of the steady-state single-phase short circuit current at different distances from the transformer substation.METHODS. The currents obtained using the 0.4 kV electrical network model developed in MATLAB Simulink were compared with the currents obtained using other calculation methods (according to GOST 28249-93, the simplified phase-zero loop method and the mathematical model «Project RZA»).RESULTS. It was revealed that the discrepancy in the results at individual points was 9-11%. When simulating a steady-state single-phase short circuit in MATLAB Simulink, it was found that the voltage of the damaged phase A decreases to 0 V, while the voltages on the two remaining intact phases increase by 1.4-1.5 times, i.e.E. by a factor of 2 to the values of 335-354 V when short-circuiting at the transformer terminals and to the values of 329-338 V when short-circuiting behind a section of a 0.4 kV power line.CONCLUSIONS. The resulting mathematical model of a 0.4 kV rural electric network in the MATLAB Simulink program can be used to study normal and emergency operating modes, study the modes of joint operation of renewable energy sources with a centralized network, and the processes of switching on backup generation sources.

PROTECTION COORDINATION OF PHOTOVOLTAIC POWER PLANT IN THE TIME DOMAIN

The safety of workers and equipment in the power grid requires the shutdown of power plants in case of maintenance or malfunction. The shutdown relies on protective devices that must be properly coordinated to isolate only the part of the grid affected by the malfunction. Using the DIgSILENT PowerFactory software, an analysis was conducted on a model of an accurate real grid integrating a photovoltaic power plant with a capacity of 390 kW. Protection coordination testing was carried out for three-phase, two-phase, and single-phase short circuit currents at arbitrarily selected locations at medium and low voltage levels. Protection in the time domain is coordinated on lines and busbars to determine the speed and selectivity of protective devices. The analysis results indicate that adequately adjusting the three-phase short circuit at the main transformer output 110/10 kV with an impedance of 0 Ω and an allowed protection operation time of up to two seconds can be correctly addressed within 36.7 ms.

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.

Results of a statistical study of types of single-phase faults in low-voltage ship electrical networks

The increase in the power supply of ships is manifested in growth of ship power plants' capacity, the total length of cable lines, and the number of electrified mechanisms. With the development of marine technology, the severity of the consequences of damage to ship electrical equipment and the costs of its maintenance and repair increase. The search for ways to improve the reliability and safety of electrical equipment should be based on design and technological solutions at the stages of its development and production, as well as an analysis of various factors that may appear during the operation of marine equipment and affect the condition of ship electrical systems. During studying these factors, it has been revealed that one of the common types of damage to electrical equipment of marine equipment is single-phase short circuits, the causes of which are varied. Preventing short circuits is labour intensive and in some cases impracticable. However, understanding the characteristics of this type of damage to low-voltage equipment is necessary to improve the reliability and safety of ship electrical systems. The conducted research is based on a survey of ship electrical mechanics. The results of the surveys have made it possible to analyze the frequency of occurrence of single-phase insulation faults, the duration of their existence, to identify the most likely places of occurrence of short circuits and equipment that is more susceptible to such damage compared to other elements of the electrical power system.

SOLUTION OF THE SYSTEM OF STATE EQUATIONS OF AN ELECTRICAL NETWORK WITH AN INSULATION DEFECT OR WITH A SINGLE-PHASE GROUND FAULT

A method for solving the system of equations of the state of an electric network with an isolated neutral is proposed, which is created based on the results of measuring the current vectors of the load connection phases and the phase voltages in relation to the ground, which allows to determine the occurrence of insulation defects, including single-phase short circuits to the ground, and also to determine distance to the single-phase ground fault location. In the well-known system of equations of the state of the electrical network, the parameters of the longitudinal resistance of the line phases are additionally taken into account, which consist of the resistance to the shorting point and the resistance beyond the point of shorting the phase to the ground. Due to simplification, the replacement circuit with additional line phase resistances turns into exactly the same circuit as the circuit without taking into account the line phase resistances, due to which the determination of the line resistance to the closing point is performed using a known algorithm. The accuracy of determining the distance to the closing point was evaluated on the mathematical model of the network node. It was established that the main factors affecting accuracy include the ratio of the capacitance values of the line and the network, the distance to the shorting point, as well as the resistance at the shorting point. When using automatic correction, the error in determining the distance to the shorting point with a resistance of 0.1 Ohm does not exceed 0.9% over almost the entire length of the line. Analytical expressions for determining insulation conductivity and the distance to a local insulation defect are proposed. The elements of the algorithm for determining the distance to the location of a local insulation defect and the results of the accuracy assessment of the method for the specific case of a phase-to-ground fault, in which the transient resistance at the fault location is not taken into account, are given. Automatic selection of circuits with low resistance at the point of the circuit is ensured by checking the value of the determined active resistance, as well as checking the voltage of the damaged phase in relation to the ground.

Single-Phase Short-Circuit Fault Tolerant Control for Five-Phase Permanent Magnet Machines With Copper Loss Reduction

Single-Phase Short-Circuit Fault Tolerant Control for Five-Phase Permanent Magnet Machines With Copper Loss Reduction

Influence of overvoltage waves on the development of partial discharges

A theoretical study of the development dynamics of partial discharges in defects in cable insulation of medium voltage networks in the presence of an overvoltage wave has been carried out. Simulation modeling of the development of partial discharges was performed on the basis of a model with three capacitors, supplemented by a model for the appearance of a seed electron. A single-phase short circuit to earth with several breaks in the electric arc was the source of the overvoltage wave. Simulation modeling showed that the number and power of partial discharges significantly increased over the period of the fundamental harmonic. The amplitude of the periodic component of the transient process was already enough to recharge the defect for large insulation defect and it is the highest harmonic that becomes decisive in the formation of partial discharges. This fact may be one of the explanations for a possible trend in medium voltage cable networks, where a failure on one cable is followed by a group of subsequent failures in nearby cable lines within a few days.

Analysis of the Influence of Load on the Value of Zero-Voltage Asymmetry in Medium-Voltage Networks Operating with Renewable Energy Sources

The phenomenon of voltage asymmetry is common in electricity networks and is the cause of many unfavourable phenomena occurring, such as an increase in power and energy losses, as well as the abnormal operation of certain loads. Voltage asymmetry can be caused by several different factors, which include the design of the transmission line (e.g., routing of conductors in relation to each other and the earth), the parameters of consumer circuits (e.g., unequal loading of individual phases), or the design of network equipment (e.g., generators or transformers). An asymmetrical condition also occurs during system disturbances such as single-phase short circuits or lightning. One of the many factors impinging on voltage asymmetry in the electrical network is also the effect of load, but in the case of medium voltage power networks, this effect is neglected in the literature. This paper presents and evaluates the influence of the power consumed by consumers on the values of zero-voltage asymmetry factor indices in medium voltage compensated power networks with the neutral point earthed by an inductance (Petersen coil) operating with wind and photovoltaic power plants.

Использование модулей фазных напряжений для выбора поврежденной фазы при замыканиях на землю

In case of short circuits, the selection of damaged phases always precedes the determination of the damage location. To select the damaged phase, filter selector of the damaged phase are widely used, using symmetrical components of phase currents. In networks with an isolated neutral, the phase currents during a ground fault are determined mainly by load currents and in most cases the phase current of the damaged phase differs little from the currents in the undamaged phases. Therefore, phase currents and their symmetrical components are not used to select the damaged phase in single-phase short circuits. To select the damaged phase in networks with an isolated neutral, the properties of the phase voltage modules and the neutral offset voltage are used. Single-phase earth faults occur, as a rule, through fault resistances, the values of which can reach several thousand ohms. Therefore, the study of devices for selecting the damaged phase using voltage modules with single-phase earth faults through significant fault resistances is an urgent task. The purpose of the article is to investigate the properties and consider the directions of improvement of damaged phase sensors using phase voltage modules, to determine the areas of their selective action depending on the magnitude of the fault resistance at the point of damage. Describe algorithms in which the voter will act selectively both with metal damages and with damages through fault resistance.

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.

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

АЛГОРИТМ ВЫЧИСЛЕНИЯ ЕМКОСТНЫХ ТОКОВ ПРИ ОДНОФАЗНОМ ЗАМЫКАНИИ НА ЗЕМЛЮ, ИСПОЛЬЗУЮЩИЙ ПАРАМЕТРЫ АВАРИЙНОГО И ДОАВАРИЙНОГО РЕЖИМОВ

Relevance Single-phase earth faults are the most common type of damage in networks with an isolated neutral. At the same time, there are no universal solutions for localization and search of single-phase circuits. The availability of information on the capacitive currents of a damaged line can become the basis for the development of new relay protection and automation algorithms for the localization and elimination of single-phase short circuits in networks with an isolated neutral. The current trend in 6–35 kV distribution networks is the development and implementation of intelligent power grid technologies that allow for high-precision measurements and data transmission. The article presents, developed by the authors, an algorithm for calculating capacitive currents in single-phase earth faults using technologies of intelligent electrical networks. Aim of research Development of an algorithm for calculating capacitive line currents in single-phase earth fault using the parameters of emergency and preemergency modes. Creation of a simulation model of a device implementing the developed algorithm, and subsequent evaluation of the algorithm based on the results of simulation modeling. Research methods The study of the developed method was performed in the Matlab Simulink software package. Results An algorithm for calculating capacitive currents in a single-phase earth fault using the parameters of emergency and pre-emergency modes is presented and described in detail. The conducted studies of the developed algorithm using simulation modeling have shown high accuracy in calculating capacitive currents in the single-phase earth fault mode.

SELECTION OF THE TECHNIQUE OF ARRANGEMENT OF EQUIPMENT SERVICE AREA TO PROVIDE THE PERMISSIBLE TOUCH VOLTAGE

Ensuring the permissible value of the touch voltage in operating electrical installations is a necessary condition for the electrical safety of personnel and third parties. In the study, based on literature data, it is analyzed in which cases it is impossible to achieve the permissible values of the touch voltage only with the help of the design of the grounding system. It is shown that ensuring the permissible value of the touch voltage is performed by arranging in a special way both the place of operational maintenance of the equipment and the territory of the opendoor switchgear. It is study the selection a technique of arrangement of the service place to ensure the permissible value of the touch voltage on the equipment of the opendoor switchgear during a single-phase short circuit to the ground. When performing the work, statistical methods of analysis, the ammeter-voltmeter method for experimental determination of the resistance of the base according to the method of Research&Design institute "Molniya" NTU "KhPI" were used. For the first time, on the basis of statistical data, the necessity of arrangement of equipment service area to ensure an acceptable value of touch voltage at operating substations of class 110 (150) kV and 330 (220) kV was analyzed. The spread of base resistance (ground resistance of human foot) values was determined experimentally. The most common ways of arrangement of equipment service area were analyzed: technological (natural), namely: a reinforced concrete pool with a layer of crushed stone, a cable channel or tray, asphalt paths and specially created (artificial) ones, namely: a metal structure , a layer of crushed stone, reinforced concrete slabs, concrete slabs without scaffolding, paving slabs, concrete slabs (paving slabs) with gravel admixtures, polymer sand slabs. The base resistance was measured for the listed techniques at operating substations. The advantages and disadvantages of various arrangement of equipment service area are determined, and recommendations for their use are provided.

Neutral Voltage Modeling and Its Remediation for Five-Phase PMSMs Under Single-Phase Short-Circuit Fault Tolerant Control

Field-oriented control (FOC) still serves as an advanced way to control ac motors for industrial applications, as such, this technique is being expanded to the postfault operation of five-phase permanent magnet synchronous motors ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\Phi $ </tex-math></inline-formula> -PMSMs) under phase fault conditions. Previous articles have proved that the motor’s neutral voltage (NV) oscillates over the dc-bus midpoint under a single-phase open-circuit fault (OCF), and NV remediation is needed for the successful fault-tolerant FOC. However, regarding the short-circuit faults (SCFs), neither the NV model nor its remediation is elaborated. The NV oscillates severely under SCFs, and it deserves an in-depth understanding for better making use of this faulty drive. To this end, this work establishes an NV model for a general <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\Phi $ </tex-math></inline-formula> -PMSM under the single-phase SCFs, including interturn and ground SCFs, and an NV remedial rule is, therefore, provided to rectify the phase voltage modulation that forms the basis of an inverter-driven system. In addition, the presented rule requires little knowledge of the motor parameters, and it can also be very easy to implement. Finally, the experimental and simulation results confirm the validity of the presented NV model as well as its remedial method.

Rotor Loss and Temperature Field of Synchronous Condenser Under Single-Phase Short-Circuit Fault Affected by Different Materials of Rotor Slot Wedge

A synchronous condenser (SC) can provide the dynamic reactive power for the ultra-high-voltage direct current converter station during the system voltage drop caused by the single-phase short-circuit fault, which is one of the prevalent faults. However, the single-phase short-circuit fault can also result in the increase of the rotor loss and temperature and thus restrict the transient operating ability of the SC. A key factor that affects the rotor loss and temperature rise is the material of the rotor slot wedges. For a 300-MVar SC with the rotor slot wedges made of the aluminum, beryllium bronze, and stainless steel, the rotor loss and temperature distribution under the single-phase short-circuit are calculated by coupling the electromagnetic and temperature field models of the SC with the models of the power grid. The variations of the rotor losses along with the rotor slot wedge conductivity are revealed. The rotor regions, where the highest temperature rise appears, are obtained. According to the maximum permissible temperature of the rotor material, the transient operating ability of the SC withstanding the single-phase short-circuit fault is obtained. This article can provide the theoretic basis for improving the transient operating ability of the SC.