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This paper presents the interaction between the overhead transmission lines (OHTLs) and their towers. In this paper, the electric field around the tower of the overhead transmission lines is calculated. The charge simulation method, combined with the image method, is used to develop a model that consists of subconductors of the OHTLs and the tower. The charges on the surface of each subconductor of the overhead transmission lines are simulated by a set of infinite line charges, of various charge densities, along the length of the subconductor, and the induced charges on the surface of the tower are simulated by a set of finite line charges. [ABSTRACT FROM PUBLISHER]

This paper introduces a new noniterative fault-location algorithm for long transmission lines compensated by a series flexible ac transmission systems (FACTS) device. In the proposed algorithm, synchronous voltage and current samples from both ends of the transmission line are used and the distributed parameter line model in the time domain is applied. Due to the difficulties in the modeling of the series FACTS devices during a fault, the presented method does not use the model of the series devices. In this paper, the fault-location problem is converted to an optimization one in which the location and resistance of the fault are the decision variables. The proposed method includes three stages. Two fault locations are obtained, corresponding to the first two stages. In stage three, the obtained results from stages 1 and 2 are compared, and the correct fault location is selected. The proposed algorithm is a noniterative one and it is suitable for transmission lines compensated by any series FACTS device which could have the overvoltage protection and can be in any operating mode. The performance of the proposed algorithm is evaluated under different structural and fault conditions. The simulation results confirm the accuracy of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Transmission lines are vital components in power systems. Outages of transmission lines caused by overtemperature are a major threat to system reliability, so it is necessary to efficiently simulate line temperature under both normal operation conditions and foreseen fault conditions. Existing methods based on thermal-steady-state analyses cannot support the simulation of transient temperature evolution, and, thus, cannot provide timing information needed for taking remedial actions. Moreover, the conventional numerical method requires huge computational efforts and barricades system-wide analysis. In this regard, this paper derives an approximate analytical solution of transmission-line temperature evolution enabling efficient analysis on multiple operation states. Considering the uncertainties in environmental parameters, the region of overtemperature is constructed in the environmental parameter space to realize the overtemperature risk assessment in both the planning stage and real-time operations. A test on a typical conductor model verifies the accuracy of the approximate analytical solution. Based on the analytical solution and numerical weather prediction data, an efficient simulation method for temperature evolution of transmission systems under multiple operation states is proposed. As demonstrated on a Northeast Power Coordinating Council 140-bus system, it achieves over 1000 times of efficiency enhancement, verifying its potential in online risk assessment and decision support. [ABSTRACT FROM PUBLISHER]

This paper elaborates on the reasons for current unbalance in extremely high voltage/ultra-high voltage (UHV) double-circuit transmission-line systems based on analyses of a typical tower structure and feasible phase arrangements. In addition to the studies of the system under normal operation condition, the unbalanced currents of the double-circuit line under the condition of external faults are first investigated. The frequency-dependent model of UHV double-circuit lines is built using the ElectroMagnetic Transients Program including DC (EMTDC) software package. Simulation results and real data obtained from the power utility show that the circulating unbalanced currents in both cases of normal operation and external fault conditions cannot be ignored due to their high magnitude. The significant influence of the circulating unbalanced currents on pilot directional protection of double-circuit lines is proven and verified by various simulation tests and real field data. Consequently, an improved scheme is proposed to overcome the influence of circulating unbalanced current and significantly improve the reliability of pilot directional protection. [ABSTRACT FROM AUTHOR]

In this paper, a novel high-speed protection scheme, for transmission lines based on initial current traveling waves and employing mathematical morphology (MM) is proposed. This scheme, by comparing polarity and arrival time of initial current traveling wave from two terminals of the protected line, can discriminate the fault direction and internal faults from external faults rapidly. A new MM filter to extract transient components from fault-induced transient signals is designed. This MM filter can fast and accurately detect the arrival time and polarity of traveling waves in all conditions. Extensive simulation studies using EMTP and MATLAB have been carried out to evaluate the validity and reliability of the proposed scheme. The simulation results show that the proposed protection scheme can fast and reliably discriminate the fault direction and the internal faults from external faults in the most of conditions, especially in high impedance fault and low inception angle fault situation. The protection performance is immune to fault resistances, fault inception angles, fault types and fault location. [ABSTRACT FROM AUTHOR]

It is well known that environmental loads, e.g., wind and ice, acting on power transmission lines are highly uncertain, as are the structural strengths of the towers supporting the lines. The design of such systems must take uncertainty into account in order to achieve acceptable reliability at a reasonable cost. The paper presents a simulation-based methodology for the optimal design of a transmission line which considers uncertainties in both environmental loads and structural resistance. The methodology is developed and illustrated for the simple problem of determining the optimal span length required for designing against tower failure. Wind, ice, and tower resistances are simulated over the extent of the transmission line and over the design life of the transmission system. Total expected system cost, along with the estimated probability of lifetime failure, are produced for a range of possible span lengths, allowing an informed decision regarding the optimum span length for the tower strength limit state. [ABSTRACT FROM AUTHOR]

This paper shows the application of a new insulation coordination procedure for phase-to-ground switching overvoltages, which is based on the variable behavior of the insulation strength according to the waveshape of the surges. It is the sequel to a paper which presented the methodology and calculation details of the procedure. After a series of transient simulations is run for two different transmission systems, both the traditional method and the new procedure are applied. Evaluation of the results focuses on the comparison between the two approaches considering the characteristics of the networks and the modeling of the low flashover probability region of the insulation strength curve. The new procedure is a refinement of insulation coordination studies and the results indicate the benefits that can arise from its application. [ABSTRACT FROM AUTHOR]

This contribution is the second part of a two-paper set concerning the effect of longitudinally varying soil conductivity on the propagation parameters of overhead lines. In this paper, an analysis is developed for the evaluation of the wave parameters characterizing the aerial modes of a three-phase overhead line running above an inhomogeneous soil whose conductivity varies along the line length. The global line section is broken down into a number of homogeneous uniform cells, the length and conductivity assigned to each cell, as well as the total number of cells, being randomly generated. Simulation experiments for low, mid, and high frequencies, clearly show that random conductivity fluctuations give rise to absolutely negligible variations of the wave-propagation parameters being analyzed-thus reinforcing the idea that the standard average-soil-conductivity-approach can be safely employed without significant errors incurred. Perturbation technique theoretical results are also derived for explaining the outcome of the simulation experiments. [ABSTRACT FROM AUTHOR]

Line differential protection provides the most selective protection scheme for transmission lines. It has an acceptable performance in situations which are challenging for the legacy distance protection. Following large disturbances, two or more areas of a power system may lose their synchronism and go out of step (OOS) which appears often as unstable power swings in some transmission lines. Existing OOS detection methods are based on the impedance trajectory seen by distance relays and conventional line differential protection cannot detect this condition. This paper introduces a new OOS detection method using the current phasors measured at both ends of a transmission line. Rigorous mathematical analyses and illustrated simulation study results are presented to substantiate the efficiency of the proposed method. The obtained results approve that the proposed method can be served as an efficient OOS detection method for line differential protection schemes. [ABSTRACT FROM AUTHOR]

An increasing number of extra-high-voltage (EHV) and ultra-high-voltage (UHV) transmission lines have motivated the need for ultra-high-speed line protection. Traveling-wave directional protection has the advantages of ultra-high-speed operation and high sensitivity, but its reliability is doubted due to its dependence on detecting the wave-heads of traveling waves and the limitation of the limited bandwidth of the coupling capacitive voltage transformer. Incremental-quantity directional protection is another ultra-high-speed alternative. Aiming at improving the reliability of a directional relay (namely the core of a directional protection) without compromising its ultra-high-speed operation, this paper proposes a novel ultra-high-speed directional relay based on correlation of incremental quantities. The incremental voltage and current within a specific window only consist of some specific fault-generated traveling waves. Therefore, the incremental voltage is in approximately direct proportion to the incremental current. The proportional coefficient is positive or negative in the case of a reverse fault or a forward fault, respectively. The correlation coefficient of the incremental voltage and current, processed by an averaging filter, is used to identify the fault direction. Extensive simulations verified that the proposed directional relay can serve as an ultra-high-speed and reliable directional relay for non-, shunt-, or series-compensated EHV/UHV transmission lines. [ABSTRACT FROM AUTHOR]

This paper presents a new method for online symmetrical components and phase-angle extraction from high-voltage transmission-line faults. This method is based on the Adaline neural networks and the instantaneous power theory, also known as the p-q method. A new current decomposition is proposed in order to derive the direct, inverse, and homopolar current components. The average and oscillating terms of powers in the \alpha \beta frame are separated by using four Adaline neural networks. The Adalines use a cosine and sine as inputs in order to learn the linear combination of the powers. The resulting symmetrical components are used by three other Adalines for phase-angle estimation between direct and inverse current components. These phase angles permit classifying the fault types. The neural networks use an online learning process-based Widrow–Hoff algorithm and can adapt their weight parameters to the power-supply evolution. Simulation results show the performance and the robustness of this method and provide a perspective for protection relay improvement. [ABSTRACT FROM AUTHOR]

By utilizing multiline voltage-source (VSC)-based flexible ac transmission system (FACTS) controllers, independent controllability over each compensated line of a multiline system can be achieved. While VSC-based multiline FACTS controllers emerged as a new opportunity to control two independent ac systems, the main constraints and limitations that are presented to the conventional transmission-line protection systems need to be investigated. In this paper, the impacts of VSC-based FACTS controllers on distance relays while controlling the power flow of compensated lines are evaluated analytically and by detailed simulations for different fault types and locations. [ABSTRACT FROM PUBLISHER]

Increasing shares of fluctuating renewable energy sources induce higher and higher power flow variability at the transmission level. The question arises as to what extent existing networks can absorb additional fluctuating power injection without exceeding thermal limits. At the same time, the resulting power flow characteristics call for revisiting classical approaches to line temperature prediction. This paper presents a probabilistic modeling and simulation methodology for estimating the occurrence of critical line temperatures in the presence of fluctuating power flows. Cumbersome integration of the dynamic thermal equations at each Monte Carlo simulation trial is sped up by a specific algorithm that makes use of a variance reduction technique adapted from the telecommunications field. The substantial reduction in computational time allows estimations closer to real time, relevant to short-term operational assessments. A case study performed on a single line model provides fundamental insights into the probability of hitting critical line temperatures under given power flow fluctuations. A transmission system application shows how the proposed method can be used for a fast, yet accurate operational assessment. [ABSTRACT FROM AUTHOR]

In this paper, by creating a 3-D model of power-line equipment and lightning leader progression models, an alternate procedure for calculating the shielding failure rate (SFR) of transmission lines is presented. The stepping nature of lightning downward leader is modeled according to field observations with the use of discrete line charges approaching the earth. A simplified self-consistent model for an upward connecting leader is also adopted to find the position of lightning incidence to the transmission line. The required electric field in an environment is computed by using the charge simulation method. A comparison has been made between the SFR calculated by proposed method and the values calculated by conventional electrogeometrical model. In addition, different previously proposed incidence criteria are implemented and compared. Some comparisons are also made between the calculated SFR and available field data for selected overhead lines. [ABSTRACT FROM AUTHOR]

This paper presents a new two-terminal impedance-based fault-location algorithm, which takes into account the distributed parameter line model. The algorithm utilizes unsynchronized measurements of voltages and currents from two ends of a line and is formulated in terms of the fundamental frequency phasors of symmetrical components of the measured signals. First, an analytical synchronization of the unsynchronized measurements is performed with use of the determined synchronization operator. Then, the distance to fault is calculated as for the synchronized measurements. Simultaneous usage of two kinds of symmetrical components for determining the synchronization operator makes that the calculations are simple, noniterative, and at the same time highly accurate. The developed fault-location algorithm has been thoroughly tested using signals of Alternate Transients Program-Electromagnetic Transients Program versatile simulations of faults on a transmission line. The presented evaluation shows the validity of the developed fault-location algorithm and its high accuracy. [ABSTRACT FROM AUTHOR]

A new insulation coordination procedure for switching overvoltages is presented. Based on the results of experiments, it considers the effect of the waveshape of impulses on the air gap strength, especially the impact of the time to crest and existing bumps above the continuous leader inception level. Signal-processing tools are applied to simulated overvoltage waveforms in order to extract their parameters which influence the insulation strength; the risk of failure of the transmission system is then derived. The procedure contributes to the refinement of insulation coordination studies and transmission-line projects. Application and results are provided in the companion paper. [ABSTRACT FROM AUTHOR]

The modern power system and complex interconnected smart grid have many parallel transmission lines to increase reliability and security. The current complexity of the large-scale power system configuration has led to cause difficult situations for the relay engineers for system coordination and operating time of the distance relays. A new centralized wide-area monitoring system is used for parallel and single lines protection. A new wide-area main protection system based on phasor measurement units “PMUs” is deployed on a real interconnected large-scale power grid. The main concept of the idea is based on describing by ${\text{differential}}\;{\text{equations}}$ the dynamic operation of the transmission lines during the fault. The differential equations can be solved through paths movement in a ${\text{phase}}\;{\text{diagram}}$. The time is added as a third axis to the ${\text{phase}}\;{\text{diagram}}$ to enhance the performance in three-dimensional (3D)–Phase Surface. The solution curves corresponding to paths are represented graphically in $3{\text{D}} - {\text{Phase}}\;{\text{Surface}}$. The ${\text{solution}}\;{\text{curves}}$ can move closely or widely separate from the ${\text{equilibrium}}\;{\text{point}}$ indicating the case of the transmission lines as being faulted or not. The fault on the lines can be precisely recognized using this concept. The simulation of the interconnected system network using ${\text{MATLAB}}/{\text{SIMULINK}}$ is used. The relay showed for the first time a solution for the parallel transmission-lines problems in a wide area. [ABSTRACT FROM AUTHOR]

This paper presents the assumptions and formulation of a hybrid electromagnetic model, developed for general application in numerical solutions of lightning current-related problems. Results provided by this model show very good agreement with experimental data for the transient response of a transmission-line tower to impulsive currents. [ABSTRACT FROM PUBLISHER]

A differential protection scheme, based on real-time analysis of a time–frequency based technique, is proposed for a transmission line with a midpoint-connected static synchronous compensator (STATCOM). The first intrinsic mode function obtained from the decomposition of current signals from both ends of the transmission system, processed through an ensemble empirical mode decomposition technique, is used to estimate the discrete Teager energy (DTE) through online Hilbert–Huang transformation. The differential DTE from both ends of the line is used to detect the exact faulty phase. For analysis, a midpoint STATCOM compensated transmission line model is considered and simulated using EMTDC/PSCAD. Test cases, such as high fault resistance, fault inception angle, reverse power flow, current transformer saturation, and variation in source impedance, are generated for different operating modes of the STATCOM. The method is also tested for a cross-country fault in a double-circuit transmission system. Comparative assessment reports with other conventional approaches verify the reliability, speed, and feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

Hardware designed for use on high-voltage transmission lines must be designed to be free of corona. Historically, design adequacy has been verified by testing in the laboratory. However, this is problematic because laboratory testing is done using a single-phase system and the electric fields on the surface of the hardware (the driver of corona) are different between laboratory and field environments. Using three-dimensional simulations, it is shown that this difference is significant. Hence, the use of single voltage testing is problematic. In addition, the use of a corona sphere to match laboratory conductor electric fields to those in the field does not improve the process. Furthermore, it appears feasible to replace (at least some) testing with simulation. [ABSTRACT FROM PUBLISHER]

Self-blocking modular multilevel converter (SB-MMC) is able to block dc fault current with relatively lower number of power semiconductors and lower valve power loss compared to other dc fault tolerant MMC topologies. Operating principle, design, reliability, and redundancy analysis of SB-MMC have been studied while the equivalent modeling and application of SB-MMC at overhead VSC-HVDC have not been fully investigated. Since operating principle of SB-MMC is different from half-bridge MMC, the existing equivalent modeling method of half-bridge MMC cannot be directly applied to modeling of SB-MMC. As dc fault at overhead VSC-HVDC are typically temporary, how to securely and quickly restart a VSC-HVDC after isolating dc fault also needs detailed studies. To solve the above two challenges, an equivalent model (EM) and a fast recovery control of overhead VSC-HVDC based on SB-MMC are proposed. Accuracy of the proposed model is verified by extensive simulations in PSCAD/EMTDC. The proposed fast recovery control further exploits the control capability of SB-MMC and enables fast and secure recovery of overhead VSC-HVDC based on SB-MMC. The proposed model and controllers also provide guidance for the modeling and application of other MMC topologies that are able to block dc fault current. [ABSTRACT FROM PUBLISHER]

This study presents a new accelerated single-pole trip scheme for distance relays zone-2 single-phase-to-ground faults. A novel nonpilot scheme for detecting the remote-end circuit breaker (CB) operation based on measured signals of unfaulted phases is presented. The proposed method is founded on mutual coupling characteristics of different fault stages between faulted and unfaulted phases. Single-pole tripping of the remote-end CB causes variation of induced voltage on unfaulted phases. The current signals due to this variation are utilized as indicators to issue the accelerated single-pole trip command. The algorithm proficiency in various conditions is tested and impacts of different elements, such as fault resistance, fault location, tower configuration, etc., on its performance are analyzed. Implementation of the new accelerated trip method results in dependability improvement, while it has no adverse effect on the protection security. Extensive simulation results confirm that the proposed method is well capable of protecting internal faults and provides a fast, accurate, and reliable protection technique. [ABSTRACT FROM PUBLISHER]

Line-commutated converter-based-high-voltage direct-current (LCC-HVDC) transmission technology has been developing very rapidly. However, the sensitivity and reliability of HVDC line protection require further improvement. An analysis of different line fault types is conducted to show that the normalized voltage change rate without the influence of wave propagation can more effectively distinguish between internal and external faults with high fault resistances. Owing to the difficulty of obtaining an accurate solution for a traveling wave, a novel traveling-wave propagation calculation method is developed by making use of the step response of a transmission line with consideration for its frequency-dependent characteristics. A novel traveling-wave protection (TWP) scheme for two-terminal LCC-HVDC transmission lines is then proposed based on the developed traveling-wave propagation calculation method and fault analysis results. The proposed protection scheme is tested based on fault simulation data using an EMTDC/PSCAD simulation platform and the fault-recorded data from an actual undesired tripping event of conventional TWP. The results demonstrate that the proposed TWP scheme, compared with conventional TWP, can more reliably and correctly detect faults with high transition resistances under different operation modes. [ABSTRACT FROM AUTHOR]

How to control overvoltages in ultra-high voltage (UHV) systems is critical to ensure their safe operations, and the switching overvoltage level is an essential aspect of insulation coordination. The deep suppression of switching overvoltage is thus a key issue of current ultra-high voltage (UHV) systems. Presently, the low residual voltage surge arresters and the arresters with controllable residual voltage are being developed. These new arresters could be an effective way to provide deep suppression of switching overvoltages in UHV systems. Simulations show that the low residual voltage arresters will dramatically reduce overvoltage levels of various types of switching overvoltages. Much lower overvoltage levels can be obtained by distributing arresters along the line. As a result of using these low residual voltage arresters, present overvoltage protection methodologies and insulation coordination rules will be changed; overvoltage withstand requirements for UHV power apparatus will be greatly reduced, and the closing resistors for breakers can be eliminated. [ABSTRACT FROM AUTHOR]

This letter presents the extension of a previously proposed frequency-domain (FD) approach for the analysis of electromagnetic transients (EMTs), primarily due to a set of discrete switching events, in an electric power network. The method is based on dividing the analysis time window into a set of subwindows with equal or unequal time lengths and solving each in the FD. The sampling time step is also independently selected for each subwindow. The extended method, formerly proposed for a single transmission line, can readily use the concept of network equivalents, achieving efficient EMT solutions of large systems, and can simultaneously accommodate slow and fast dynamics. [ABSTRACT FROM PUBLISHER]