Search

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Faults can seriously damage high-voltage (HV) power systems, particularly if they occur on the long overhead transmission line (OHTL) that connects the nuclear power plant (NPP) to the electrical grid. Finding OHTL problems quickly and accurately is essential for the economy, safety, and dependability of the HV power systems. It is essential to pinpoint the problematic phase to avoid unneeded power outages. Thus, one of the most crucial research challenges is now how to identify, classify, and locate OHTL faults. In this study, transient current with high frequency oscillations that arise immediately after a defect at the sending end is investigated in a single-circuit, single-side fed Egyptian 500-kV HV long OHTL. Asymmetric and symmetric faults and locations are also represented in the Alternative Transients Program-Electro Magnetic Transients Program (ATP/EMTP) simulation model under varying fault resistance and inception angles. The proposed solution in this paper is an Optimized Support Vector Machine (OSVM), whose characteristics are optimized via a mutant particle swarm optimization (MPSO) method to detect 500 kV long OHTL faults. The localizer model is also built for practical applications, including power system noise contaminating fault signals. The findings prove that the suggested approach locates the fault in 0.012 seconds from the start of the event, with a 0.0098 percent average percentage error, and without being impacted by differences in fault distance, fault resistance, noise, or fault inception angle. Additionally, the optimised classifier reaches a 99.85% accuracy rate, enhancing line system dependability and advancing nuclear system development.

The paper presents the Fractional Fourier Transform-Singular Value Decomposition (FRFT-SVD) method for the localization of various power system faults in a 200 km long, 500 kV Egyptian transmission line using sent end-line current signals. Transient simulations are carried out using Alternating Transient Program/Electromagnetic Transient Program (ATP-EMTP), and the outcomes are then examined in MATLAB to carry out a sensitivity analysis against measurement noises, sampling frequency, and fault characteristics. The proposed work employs current fault signals of five distinct kinds at nineteen intermediate points throughout the length of the line. The approach utilized to construct the localizer model is FRFT-SVD. It is much more effortless, precise, and effective. The FRFT-SVD is utilized in this technique to calculate 19 sets of indices of the greatest S value throughout the length of the line. The FRFT-SVD localizer model is also designed to be realistic, with power system noise corrupting fault signals. To generate fault curves, the curve fitting technique is applied to these 19 sets of indices. Reduced chi-squared and modified R-squared criteria are used to choose the best-suited curve. The proposed work results in a very precise localization, with only a 0.0016% average percentage error for fault localization and a maximum percentage error of 0.002% for the 200 km Egyptian transmission line. Finally, this work can be employed as a proper link between the nuclear power plant and the grid. The proposed method is an efficient fault distance estimation method that might contribute to creating a dependable transient-based approach to power system protection. [ABSTRACT FROM AUTHOR]

In order to improve the operational safety and stability of power cables, it is necessary to conduct targeted research on different grounding modes. Firstly, the appropriate cable parameters were selected according to the specific use, and the model was established in ATP-EMTP according to the selected cable parameters. Then, the availability of three grounding modes models of grounding at one end, grounding at both ends and cross-connection grounding (cable core grounding, shielding layer grounding and armor layer grounding) were compared and verified by simulation. Finally, by setting the shielding layers of different thicknesses as a comparison, the impedance and current characteristics of the cables under three different grounding methods were analyzed. The result indicates that the impedance values of the three grounding methods are essentially the same. However, according to the current characteristics, when the shielding layer and the armored layer are cross-connected and grounded, their current is much smaller than that which is grounded by other grounding methods. Therefore, under the comprehensive consideration of economic benefits, this grounding is the best choice. This study provides guidance for the grounding mode of cable early laying and a reference for other cable related research.

When putting any unloaded transformer into service, a high-value current that can be very dangerous, called the inrush current, appears. The latter may cause problems and consequences in the electrical system. The challenges of visualizing the effects of transient regimes on the iron core's characteristics and the influence of the type of load on inrush current characteristics are covered in this study. The main purpose of this paper is to treat the influence of this transient phenomenon on the hysteresis loop of a single-phase transformer, in terms of its size, area, or position, and therefore, the influence of the load on the transient regime. A general study of the electromagnetic characteristics of the transformer iron core will be presented. Then, using the ATP-EMTP program, the purpose of the realized simulations is to visualize the relationship between the hysteresis loop and the magnetizing inrush current in the transient state. The results show the decrease of the hysteresis loop area and their shift with respect to the origin of the axes following the increase in the transient inrush current peak. As the second part of this article, there is a study of the influence of the load on the transient regime, i.e. inrush current. This is accomplished by adding a load with different configurations and various connections. The purpose is to find the effect of the load on the reduction of the transient inrush current phenomenon. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Test & Measurement Technology is the property of Publishing Center of North University of China and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

[Introduction] The safe and stable operation of UHV transmission lines is essential to the safety of power grids. When the new substation deconstructs the original long line in the power grid planning and construction, the following problems, such as the three-phase unbalanced current line does not meet the setting requirements, line high impedance over-compensation generates overvoltage, may occur. These problems may seriously threaten the safe and stable operation of the power grid and should be solved. [Method] In order to solve the above problems, the electromagnetic transient software ATP-EMTP was used to simulate the unbalanced current and overvoltage in 500 kV transmission lines on the same tower, so as to explore the influencing factors and change mechanism of these parameters, and then put forward countermeasures. [Results] The simulation results show that the main factors affecting the double circuit line's unbalanced current on the same tower include transposition and phase sequence arrangement. Increasing the number of transpositions can effectively reduce the unbalanced current level. By adopting a reverse phase sequence arrangement is also efficient. The main reason that affects the power frequency resonance over-voltage is whether the compensation degree is close to full compensation. During over-compensation, increasing the compensation degree can reduce the recovery voltage, but the potential supply current will increase relatively. [Conclusion] The above conclusions have guiding and reference significance for power grid planning, construction, and safe operation. Furthermore, it can effectively solve related problems in actual projects.

• Lightning attachment model effects on BFR of overhead lines are assessed. • Lightning peak current distribution effects on BFR of overhead lines are evaluated. • Typical 150 kV and 400 kV double-circuit overhead lines are studied. • Critical backflashover currents are obtained through EMT simulations. • Lightning peak current distributions yield more pronounced effects on BFR. The evaluation of the backflashover performance of overhead transmission lines requires the adoption of a lightning attachment model and a peak current distribution. These affect the estimated backflashover rate, BFR , of the lines. The present study aims to quantify the influence of lightning attachment model and peak current distribution on the BFR of double-circuit overhead lines. This is achieved by evaluating typical 150 kV and 400 kV lines. ATP-EMTP simulations are conducted to obtain the critical currents causing backflashover of line insulation. Then, the critical currents are used in lightning incidence computations to obtain BFR. The influencing parameters taken into account in this work are the low current and low frequency tower ground resistance, the location of lightning strike to the shield wire along the span, and the AC voltage phase angle, all affecting the critical backflashover current. Several lightning attachment models and peak current distributions are evaluated. Their influence on BFR is found to be considerable, especially for lower tower ground resistance values. The lightning peak current distributions yield more pronounced effects on BFR. The results of this study stress the need for computing BFR using a more accurate expression than the simplified one based on CIGRE TB 63. [ABSTRACT FROM AUTHOR]

Phasor-based differential protection is widely used as the main protection function of the power transformer due to its reliability and ability to discriminate internal from external faults and inrush currents. However, these methods present some delays due to phasor convergence during the fault occurrence and can fail during challenging situations, such as transformer energizations with low second-harmonic content and turn-to-turn and turn-to-ground internal faults. This paper proposes a novel time-domain power transformer differential protection based on Clarke and wavelet transforms with only one differential unit and with automatic setting to be used in any power transformer. Considering both actual and simulation data, the performance validation reveals that the proposed method is efficient, ultra-fast, simple, and independent of the fundamental and harmonic components of the differential current. The method was also implemented in a real-time digital simulator to demonstrate its practical feasibility. [ABSTRACT FROM AUTHOR]

As an important part of substation, grounding grid is the main approach to release short-circuit current. Grounding grid is in the complex electromagnetic compund,and with increasely being operated, it is easily corroded for various reasons, resulting in short-circuit current not being discharged normally. It is difficult to detect the grounding grid without excavation, because it is generally buried underground. Therefore, it is very important to accurately detect the grounding grid without excavation. In this paper, a grounding grid detection method based on artificial intelligence hybrid algorithm is proposed. In order to verify the accuracy of the detection method, the grounding grid model is established by using electromagnetic transient simulation software ATP-EMTP. According to the ATP-EMTP simulation model, the node potential of each point of the grounding grid is detected as the reference object for verification. In order to remove the randomness of the simulation results, the average value of 20 tests was used as the corrosion diagnosis result. The results show that the missed diagnosis rate of the proposed in paper was 2.1%, which was reduced by 12.1%, 7.1% and 7.5% respectively compared with the other three algorithms. At the same time, the misdiagnosis is 2.1%, which is reduced by 10%, 6.2% and 12.9% respectively for the other three algorithms. In sum, the corrosion leakage diagnosis rate and misdiagnosis rate of the proposed artificial intelligence algorithm are lower than those of the other three optimization algorithms, and have higher accuracy and stability in corrosion diagnosis. [ABSTRACT FROM AUTHOR]

This paper discusses the step and touch voltages, based on body resistance, in a grounding grid after a lightning strike at a 434-/21-kV substation. To ensure grounding grid safety, the maximum step and touch voltage should not exceed the safety criteria defined by the IEEE Std. 80. In this paper, ATP-EMTP and a genetic algorithm are used to analyze and optimize the step and touch voltages in a power grid. The voltages are calculated under normal conditions of a lightning strike at a power system. Thevenin's theorem is applied to calculate the step and touch voltages. The genetic algorithm is applied in ATP-EMTP to obtain the minimum level of step and touch voltages in the grounding grid after lightning strikes the power system. The step and touch voltages at different positions of the grounding grid are explained in this paper using the ATP-EMTP and the genetic algorithm. The computer simulation shows that the proposed scheme is highly feasible and technically attractive.

Copyright of Technical Electrodynamics / Tekhnichna Elektrodynamika is the property of National Academy of Sciences of Ukraine, Institute of Electrodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In middle and low voltage distribution networks, single-phase grounding fault is most like to occur, so the mathematical model to accurately reflect the characteristics of grounding arc is the basis of network fault analysis. Based on arc-gap balance theory, this paper analyzes the characteristics of the classic Mayr model and Cassie model, establishes an arc model with reasonable combination of Mayr and Cassie, and further studies the influence of arc length parameters on arc characteristics, and reflects the physical characteristics of the grounding arc. Finally, the arc model is simulated in a 10 kV distribution network in the fault form of intermittent arc grounding. By comparing the results with the actual situation, the correctness of the arc model is verified, which lays a good foundation for the following fault analysis of distribution network. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Studying the insulator arc clearing effect upon OHTL systems. • Quantifying the effect of arc clearing by defining overvoltage's, and arc extinction time. • Discussing arc clearing impact on OHTL under Corona, arc distances, tower footing impedances, and inception angles. • Evaluate the performance of the overvoltage different mitigation methods. In high-voltage OHTL, Overvoltages and arc currents due to insulator transient arcs clearing severely affect the stability of power systems. In this paper, a 500 kV Egyptian OHTL was simulated using ATP-EMTP software package. The insulators transient arcs clearing of the system were tested under different impedances of tower footing, locations of insulator arc tower, angles at which the arc initiate. Additionally, the effects of the corona phenomenon were taken into account to achieve realistic study. Furthermore, these factors thoroughly were analyzed to determine worst-case scenarios. Also the paper evaluated the performance of the overvoltage mitigation methods based on the installation of neutral shunt reactors, MOSA (Metal Oxide Surge Arresters), or combinations of both. The results demonstrated that the combination of MOSA and neutral shunt reactors was the most effective mitigation technique, reducing overvoltages by approximately 57.4 %, arc currents by 80 %, and arc extinction time by 27.3 % Notably, the most severe overvoltages and peak arc currents occurred at an angle of θ = 180° and footing impedance 30Ω. Additionally, the corona phenomenon played a role in reducing the severity of overvoltages, arc currents, and arc extinction time by approximately 56 %, 56 %, and 1.8 %, respectively. Finally, These findings provide valuable recommendations for mitigating overvoltages, arc currents, and arc extinction time during insulator arc clearing events. [ABSTRACT FROM AUTHOR]

The high accuracy of fault location in transmission lines reduces outage time and increases system reliability. Most of the time needed for fixing the fault is consumed in determining the location of the fault. Many fault location methods are usable for single-fault events. This paper presents an advanced fault location algorithm to detect, discriminate, and locate single and simultaneous shunt faults. A combination of single- and double-end techniques and travelling wave fault signature is used to accurately determine the fault location. Comprehensive simulation results are investigated to make sure that the introduced algorithm is capable of detecting and identifying the fault locations accurately, whether there is a time shift between occurring the two faults or not. ATP-EMTP package and MATLAB wavelet transform toolbox are used to simulate a 500-kV transmission system and analyze the transient signals generated after the fault occurrence. [ABSTRACT FROM AUTHOR]

This paper uses ATP/EMTP to simulate different fault types as single line to ground fault, three phases to ground fault, double line fault, direct lightning strokes, and flashover for Egyptian Bassous-Cairo West 500 kV transmission line single circuit. By using 3D Biot-Savart Law technique, the measured current at sending end using substation optic fiber CT utilized for calculating transient magnetic field, and then certain comparing of selected features of the calculated transient magnetic field under different phases are used for fault detection and classification. The results show that the calculated transient magnetic field at sending end have unique shape for each abnormal condition, so it is very effective to extract the transient components from the fault signals, then detection and classification of faults can be done accurately. The fault location scheme is based on divide line length into sections each section contain only one sensor, then the comparison between measured transient magnetic field from installed non contact, 3-axis Magnetoresistance, magnetic field sensors at tower section sensors and calculated measured transient magnetic field from substation optic fiber CT. It was discovered that this method is able to offer high accuracy fault location. [ABSTRACT FROM AUTHOR]

Modeling of lightning return-stroke channel affects significantly the estimation of fast-front overvoltages arising across overhead line insulators, thus, also the lightning performance of power lines. This paper introduces a simplified method for estimating the minimum lightning currents causing shielding failure flashover and backflashover of overhead transmission line insulation, as affected by lightning channel equivalent impedance. The validity of the proposed methodology is demonstrated through ATP-EMTP simulations of typical 66 up to 765-kV overhead transmission lines with variable tower ground resistance. An assessment is made of the effects of lightning channel equivalent impedance on the lightning performance of overhead lines, that is, shielding failure flashover and backflashover rates. Lightning channel equivalent impedance values of 1000 and 400 Ω are suggested, respectively, for shielding failure and backflashover studies, based on the results obtained in this paper together with a discussion on the literature data regarding channel impedance. [ABSTRACT FROM AUTHOR]

Highlights • The dual port model is used for ground conductor calculations and the EMF ground grid standard model is used for comparative analysis. The relationship between the various induced voltages of the grounding grid and the lightning current injection point is studied by using the dual port model. • A comparative study of auxiliary annular grounding grid and square grounding grid is discussed. • The characteristics of the first grounding discharge with the auxiliary grounding grid instead of the main grounding grid is discussed. Abstract In this paper, a new approach for designing groudging grid is proposed. The design is based on constracting an auxiliary annular grounding grid and transforming the lingtning rod's grounding poing from main grounding grid to auxiliary grounding grid. Modal analysis and softwave simulataes is employed to obtain the transformed lightning current (and the voltage) and the reduced ressitance. The dual port model is used to calculate the impedance value of the grounding grid. The calculation results of the model are compared with the standard grounding body model EMF. At the same time, the relationship between the induced voltage of each point of the grounding grid and the distance of the lightning current injection point is studied by using the dual port model. The reduced resistance is simulated by building annular grounging grid model and square grounging grid model and making a comparison in performance betwen them. Farther, when there is a lingtning event, instead of providing a low impedance path by the main grounding grid, the design provide anther path by the auxilary grounding grid, which can transfer the lightning current into the auxilary grounding grid. All the model analysis and simulation results are presented and discussed in the paper. [ABSTRACT FROM AUTHOR]

Highlights • Automatic adaptive setting of overcurrent relays. • Fuzzy logic based method for time-current-voltage based relays. • Short-circuit analysis of distribution system with distributed generation. • Comprehensive tests with different fault impedances, transformer energization and motor start. • Good performance for realistic system verified with time domain analysis. Abstract In this paper an adaptive protection system based on the Fuzzy Logic for the adjustment of the overcurrent relay's pick-up currents with instantaneous and current-voltage based inverse-time units is proposed. In the methodology two variables are taken into consideration: the pre-fault current and the variation of current, which define various classes of the pick-up currents. This characteristic gives an adaptive behavior in the sense of accepting modified actuation curves. The framework for modeling and simulation was the Alternative Transients Program - The Electromagnetic Transients Program (ATP-EMTP). Due to the flexibility provided by the method, which allows the incorporation of new logic or changes on decision making, it resulted in an adaptive method that presented good performance by automatically following changes on the system operation condition and increased the sensitivity of the overcurrent protection. Tests with different short-circuit impedance in a distribution system with Distributed Generator (DG) have been carried out. [ABSTRACT FROM AUTHOR]

The JMarti model is used worldwide for electromagnetic transient simulations of transmission lines. This paper proposes increasing the accuracy of the model by using only real poles through vector fitting. The JMarti model uses a rational approximation process that ends in models that include only real poles and zeros. By using vector fitting to synthesize the functions of the JMarti model, one can have complex and real poles. In this work, a process in which complex poles are replaced by real ones, based on the non-dominance of complex poles for smooth functions, is implemented. The improvement in the accuracy is demonstrated through the ATP-EMTP (alternative transient program) program by modeling two cases: a single-phase transmission line configuration and an asymmetrical overhead line configuration. Additionally, the solutions of the test cases with the numerical Laplace transform are taken as references. The results show that, through the proposed methodology, not only an increase in accuracy possible but also the proposed methodology also can be used to improve the computational efficiency of the JMarti model. The presented methodology can easily be applied to any application in which the frequency response data present a smooth behavior. Finally, the presented methodology can be easily applied in an iterative way. [ABSTRACT FROM AUTHOR]

This paper deals with an analysis of impedance-differential protection algorithm applied to locate faults on a double-circuit transmission line. In particular, the study of fault location accuracy for the case of using the relation between currents for negative-sequence not for zero-sequence, as it was presented so far, is provided. It results from the well-known fact that zero-sequence impedances are in practice considered as quite unreliable data. Therefore, one has to limit usage of zero-sequence impedance parameters as much as possible. Such approach was applied in this paper and therefore the use of the additional relation of currents for negative-sequence is under investigation. The fault signals from ATP-EMTP simulation on the sample double-circuit transmission line was applied for evaluating the fault location accuracy. References 8, figures 4, table 1.

One of the major references to deal with electromagnetic transients is the ATP-EMTP program whose associated tools, ATPDraw (a graphical interface) and MODELS (a programmable language), have pushed its use to other electrical system analysis. In this context, this article aims to show the development of a computational block to represent the photovoltaic generator in ATP, with its respective mask and configuration in ATPDraw. Starting from the classical mathematical foundation, a photovoltaic module is developed from data available in manufacturers' manuals. The ideality equations are then modified to attend different purposes: applying new values of temperature and irradiation, choosing series and/or parallel association of modules, including different values of series and parallel resistances. The final multipurpose photovoltaic generator is validated by comparison of its results with those found in the related technical literature. [ABSTRACT FROM AUTHOR]

Copyright of Technical Electrodynamics / Tekhnichna Elektrodynamika is the property of National Academy of Sciences of Ukraine, Institute of Electrodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Results of field measurement of trapped charges on a 275 kV cable will be presented. The instrumentation and calibration method used in the measurement will be discussed. It will be shown that if the cable is not force-discharged by means of earth switches, the trapped charges will decay very slowly. The atmospheric parameters such as humidity and temperature affect the discharge time, which also depends on how much of the circuit is exposed to open air. The measurement results are used in EMTP-ATP simulation to confirm that trapped charges may be sufficient to cause sheath voltage limiters (SVL) of the cable to fail. The number of SVL breakdown depends on the mode of SVL failure, i.e. whether it attains low impedance (short circuit) or open circuit when the energy absorbed exceeds the rating. [ABSTRACT FROM AUTHOR]

• Electromagnetic transient model for varistor-based surge protective devices. • Resistive, inductive, and capacitive behavior of varistor-based SPDs. • Residual voltage of SPDs depends significantly on their base configuration. • Excellent simulation results for a wide range of very fast-front impulse currents. • The model can be used for insulation coordination studies and dimensioning of SPDs. This work provides a simplified transient model for low-voltage DIN rail surge protective devices (SPDs), accounting for their resistive, inductive, and capacitive behavior. The time-domain modeling approach is based on impulse current and sinusoidal voltage experiments. The lumped-circuit model is implemented in the ATP-EMTP environment and yields results in satisfactory agreement with the experimentally derived residual voltage and energy absorption of commercially available DIN rail SPDs for single- and three-phase installations. The proposed model can be used for evaluating the protection level and maximum residual voltage of SPDs under standard and non-standard surge currents and can be an effective tool employed in insulation coordination studies of power systems. [ABSTRACT FROM AUTHOR]

• Stochastic shielding failure flashover rate approach for horizontal overhead lines. • Fractal-based model for lightning incidence estimation to a 66 kV overhead line. • Stochastic modeling considering the AC power frequency voltage and conductors' sag. • ATP-EMTP model for critical flashover current estimation for a 66 kV overhead line. • Basis for a generalized lightning performance assessment methodology for HVAC lines. A methodology is proposed for estimating the shielding failure flashover rate (SFFOR) of single-circuit overhead lines with horizontal phase configuration. An application to a 66 kV overhead line is presented. A stochastic lightning attachment model is employed, based on the concept of fractal structures, to compute the probability of shielding failure to the line. Results of stochastic modeling are combined with those of an ATP-EMTP model for estimating the critical lightning currents causing flashover of the line insulation. Shielding failure results of the proposed methodology are compared and discussed with results obtained employing the methodology of the IEEE Std 1243. Innovation of this work lies in estimating the SFFOR of overhead lines by considering the stochastic nature of lightning attachment, physical criteria associated with leader discharges' inception and propagation, as well as electromagnetic transient simulations to predict lightning-related flashover to overhead lines accurately. [ABSTRACT FROM AUTHOR]

Lightning caused interruptions by shielding failures or by back-flashover. Lightning over voltages cannot be avoided but their influence can be limited by appropriate over voltage protection. In this paper, Characteristics and hazards of lightning overvoltage in the Egyptian Bassous-Cairo West 500-kV transmission line single circuit are analyzed and discussed. Some effective factors, which affecting generated lightning back-flashover across the insulator of a transmission system are analyzed. These factors are included magnitude of lightning stroke, front and tail times of lightning stroke impulse, and chopped current. The influence of connecting Substations Surge Arrester SSA and Line Surge Arrester LSA are investigated. This paper also provides a procedure to limit lightning flashover and back-flashover. ATPEMTP simulation program is applied to analyze the lightning over-voltage of power line. The result show that there is a 100% probability of an insulator flashover in case high peak, short front time, and any tail time of lightning strokes without any installed arrester. LSA prevent insulator flashover than back flash over. [ABSTRACT FROM AUTHOR]

This paper presents the performance and protection of medium-voltage (MV) aerial cables against lightning faults by means of laboratory experiment and digital modeling. With the series of laboratory tests, practical examination of lightning hazard to shielded and unshielded aerial cables is conducted, and the need for shield wire protection is established. For the purpose of simulation studies, digital models are developed by using Alternative Transient Program-Electromagnetic Transient Program (ATP-EMTP) and its transient analysis of control system features. The performance of lightning flashover overvoltage on shielded and unshielded aerial cable is evaluated with the developed digital models. The evaluation is made by considering a direct lightning strike on wooden poles, messenger wires, and nearby trees. Based on the experimental and simulation results, practical recommendations are proposed for improvement in lightning performance of aerial cables. This study offers possible solutions for the protection of aerial cables against lightning flashover, induced overvoltage, and direct lightning strike, which may improve electricity reliability and availability to customers. [ABSTRACT FROM AUTHOR]

Transformer inrush current can be efficiently mitigated by controlled switching. For energization of three-phase transformers, several strategies have been developed that depend on whether the residual flux can be measured and whether independent-pole-operated or three-pole-operated circuit-breakers are used. In this paper, a comparative analysis of these strategies has been carried out. Residual flux uncertainty and dispersion of the characteristics of the circuit-breaker can significantly affect the performance of the controlled switching. These issues have been taken into account in the analysis of each strategy since they can influence the performance in different ways. The study has resulted in the selection of the most appropriate strategy for each case. [ABSTRACT FROM AUTHOR]

This paper presents a novel technique for computing dangerous voltages due to direct lightning strike into the communication tower and associated earthing system, which is based on the use of the well-known ATP-EMTP software package. The earthing grid and the communication tower structure are approximated by the circular cross section conductors. In numerical model, conductors are subdivided into segments (1D finite elements) and Clark's model with distributed constant parameters is then applied. Because of the limitations of ATP-EMTP software package, the leakage resistance of buried segments is modelled as additional lumped parameter. Analytical expressions for distributed and lumped segment parameters are derived using the average potential method. Mutual electromagnetic coupling between segments is neglected due to the limitations imposed by the ATP-EMTP software package, which is based on transmission line approach. Separate computer program is developed for obtaining the earth surface transient potential distribution, from which step and touch voltages are then computed.

Evaluation of the dielectric strength of transmission line insulation subjected to fast-front overvoltages is of major importance for the insulation coordination of overhead lines and connected substations. Among models proposed in literature for the prediction of the dielectric behavior of long air gaps and insulators under lightning overvoltages, leader development models (also called leader progression models) have a greater physical significance. These models consider the predischarge current flowing in the gap during the leader propagation phase preceding breakdown. However, this current is often disregarded for simplicity in fast-front overvoltage simulations. In this study the effects of simulating predischarge current on voltage–time characteristics of long air gaps and insulators, critical currents of overhead transmission lines as well as fast-front overvoltages arising at substations are investigated with the aid of ATP–EMTP. Including predischarge current in simulations, affecting the flashover characteristics of air gaps and insulators, results in slightly higher estimates of the minimum backflashover current of overhead transmission lines. However, it does not affect the estimated minimum shielding failure flashover current of overhead lines. In addition, simulating predischarge current may affect the overvoltages arising at substations due to shielding failure of the connected overhead lines depending on withstand or flashover of line insulation. In the case of backflashover the wavefront steepness and amplitude of the overvoltages are lower. Thus, predischarge current effects should be considered in insulation coordination of overhead transmission lines and substations. [ABSTRACT FROM AUTHOR]

The paper deals with the impact of subsequent strokes on the backflashover rate (BFR) of HV overhead transmission lines (OHLs), assessed by means of an ATP-EMTP Monte Carlo procedure. The application to a typical 150 kV Italian OHL is discussed, simulating several tower grounding system arrangements. Subsequent strokes parameters are added to the statistical simulation variables: peak current, front time, time-to-half value, lightning polarity, line insulation withstand, lightning location and phase angle of the power frequency voltage. The input data are fed to an ATP-EMTP complete circuit model of the OHL, including line insulation, lightning representation and tower grounding system, the latter simulated by a pi-circuit model able to simulate the effects due to propagation and soil ionization, at modest computational costs. Numerical results evidence a non-negligible BFR increase (in relative terms) due to subsequent strokes: for spatially concentrated grounding systems the BFR increase approximatively vary in inverse proportion with the low frequency grounding resistance, whereas for spatially extended grounding systems the BFR increase depends on the grounding system behavior at high frequencies. [ABSTRACT FROM AUTHOR]

• The application of line surge arresters to 150 kV overhead lines is investigated. • The required energy absorption capability of line surge arresters is determined. • Non-gapped line arresters and externally gapped line arresters are compared. • Surge arrester installation configurations are evaluated for critical lines. • Lightning performance improvement of a critical 150 kV overhead line is quantified. This paper investigates the application of Line Surge Arresters (LSAs) to 150 kV double-circuit overhead lines through ATP-EMTP simulations. The 150 kV lines under study are the backbone of the autonomous electrical system of Rhodes island in southeastern Aegean Sea, Greece. Hence, lightning-related insulation flashovers causing outages of these lines may lead to a blackout of this isolated system. In this work, both Non-Gapped Line Arresters (NGLAs) and Externally Gapped Line Arresters (EGLAs) are evaluated. Two installation configurations with 3 and 6 LSAs per tower are considered protecting one circuit and both circuits of the line, respectively. Simulations were performed for both lightning strikes to phase conductors and tower; these may cause shielding failure flashover and backflashover, respectively. The conducted current through the LSAs and the voltage at their terminals are computed, enabling the estimation of the energy stressing the LSAs. The effects of the lightning current time to half value, the phase angle of the operating voltage, and the power frequency ground resistance of towers are assessed. The required LSA energy absorption capability is determined. The lightning performance of a critical overhead line of the Rhodes 150 kV system is estimated and its improvement due to LSA installation is quantified. [ABSTRACT FROM AUTHOR]

Controlled switching technology with independent-pole-operated circuit breakers is an effective way to eliminate transient transformer inrush currents. This technique cannot usually be applied at lower voltage levels where three-pole-operated circuit breakers are more frequent. In this paper, the optimal instant for a simultaneous closing is obtained as a solution of a min–max problem. The proposed strategy has been evaluated in a test system using EMTP/ATP and has presented highly satisfactory results, even when actual characteristics of circuit breakers are taken into account. [ABSTRACT FROM AUTHOR]

The ATP-EMTP has become a reference program for electromagnetic transients computer simulations. Due to the contributions of its officer's users groups spread around the world, several improvements were made and additional resources have been developed to facilitate and expand its application. Tools, like ATPDraw, PlotXY, TACS, DBM and MODELS, can drive and enable excelent research studies which may result in internationally renowned scientific papers in the field of Electrical Systems. It is then presented in this paper an additional user guide for these tools with procedures tested in practice and often not covered by official manuals, combined with an analysis of the use of TACS/DBM and MODELS through the computational implementation of a speed governor. The purpose is to identify the potentiality as well as the advantages and disadvantages of TACS/DBM and MODELS. Thus, any user interested in the correct and effective use of these tools may determine the one most suitable to accomplish the computer simulation. [ABSTRACT FROM PUBLISHER]

This paper presents a technical/economic comparison between remedial measures aimed at improving the lightning performance of an existing Italian three-phase 150-kV overhead line. The line is characterized by a very high back-flashover rate (BFOR), due to large grounding resistance values. Two countermeasures are proposed: grounding system improvement with additional vertical rods and line metal oxide surge arrester (MOSA) installation on one or all phases. A Monte Carlo ATP-EMTP procedure developed by the authors, which takes into account both the tower grounding nonlinear transient response due to soil ionization and MOSA nonlinear response, has been applied to evaluate and compare the effectiveness of the proposed countermeasures. The installation of MOSA on all phases is technically the best option, but it is relatively expensive. Tower grounding improvement and MOSA installation on the lower phase yield very similar BFORs: the economic comparison strongly depends on tower's accessibility and soil nature. [ABSTRACT FROM AUTHOR]

This paper presents the detailed engineering study conducted to design a high-impedance restricted earth fault (REF) scheme for four 11/0.415-kV, Dyn11, and 2500-kVA power transformers in an industrial power system. Analytical calculations carried out to specify the components constituting the REF scheme and to determine the appropriate relay settings are provided. The proposed REF scheme is evaluated using reliable Alternative Transients Program–Electromagnetic Transients Program simulations. The obtained results validate the adequacy of the design and highlight the advantages of using such a protection, such as fast and reliable operation even under severe current transformer saturation conditions. [ABSTRACT FROM PUBLISHER]

An accurate algorithm for locating faults on two‐terminal transmission lines is presented in this study. The presented method does not require values of line parameters to locate the fault; therefore variation of line parameter values does not affect its accuracy. The method utilises synchronous post‐fault measurements of currents and voltages in both terminals and is based on the distributed time‐domain representation of transmission lines. Unlike conventional methods, fault location is converted to an optimisation problem. Then, this problem is solved by genetic algorithm to find the accurate location of fault. Furthermore, modifying the problem to be solved by the Newton optimisation method is discussed in this study. Simulation results performed by ATP/EMTP verify high accuracy of the presented method, and reveal that it is not significantly affected by fault resistance, fault type, fault inception angle and source impedance. Moreover, effect of measurement errors and synchronisation errors on the accuracy of presented method have been analysed which verify the efficiency of the algorithm in these conditions. [ABSTRACT FROM AUTHOR]

In this paper, a new method for inrush current mitigation of three-phase transformers with isolated neutral is presented. The method uses controlled switching and requires independent-pole-operated circuit breakers. Two switching operations are proposed at time instants that achieve optimal mitigation of inrush current. [ABSTRACT FROM AUTHOR]