ABSTRAC, PROTECTION ON TRANSMISSION OVERHEAD LINE

1. Jamali, S., Ghaffarzadeh, N., 2010. A wavelet packet based method for adaptive single-pole auto-reclosing. Journal of Zhejiang University-Science C-Computers & Electronics 11, 1016-1024.

Abstract: We present a new algorithm for adaptive single-pole auto-reclosing of power transmission lines using wavelet packet transform. The db8 wavelet packet decomposes the faulted phase voltage waveform to obtain the coefficients of the nodes 257, 259 to 262. An index is then defined from the sum of the energy coefficients of these nodes. By evaluating the index, transient and permanent faults, as well as the secondary arc extinction instant, can be identified. The significant advantage of the proposed algorithm is that it does not need a threshold level and therefore its performance is independent of fault location, line parameters, and operating conditions. Moreover, it can be used in transmission lines with reactor compensation. The proposed method has been successfully tested under a variety of fault conditions on a 400 kV overhead line of the Iranian National Grid using the Electro-Magnetic Transient Program (EMTP). The test results validated the algorithm's ability in distinguishing between transient arcing and permanent faults and determining the instant of secondary arc extinction

   2.   Moghadas, A.A., Shadaram, M., 2010. Fiber Bragg Grating Sensor for Fault Detection in Radial and Network Transmission Lines. Sensors 10, 9407-9423.

Abstract: In this paper, a fiber optic based sensor capable of fault detection in both radial and network overhead transmission power line systems is investigated. Bragg wavelength shift is used to measure the fault current and detect fault in power systems. Magnetic fields generated by currents in the overhead transmission lines cause a strain in magnetostrictive material which is then detected by Fiber Bragg Grating (FBG). The Fiber Bragg interrogator senses the reflected FBG signals, and the Bragg wavelength shift is calculated and the signals are processed. A broadband light source in the control room scans the shift in the reflected signal. Any surge in the magnetic field relates to an increased fault current at a certain location. Also, fault location can be precisely defined with an artificial neural network (ANN) algorithm. This algorithm can be easily coordinated with other protective devices. It is shown that the faults in the overhead transmission line cause a detectable wavelength shift on the reflected signal of FBG and can be used to detect and classify different kind of faults. The proposed method has been extensively tested by simulation and results confirm that the proposed scheme is able to detect different kinds of fault in both radial and network system

   3.   Carneiro, J.S.A., Ferrarini, L., 2010. Preventing Thermal Overloads in Transmission Circuits via Model Predictive Control. Ieee Transactions on Control Systems Technology 18, 1406-1412.

Abstract: A special protection scheme (SPS) based on model predictive control (MPC) is proposed to mitigate thermal overloads in advance, and so avoid cascade line tripping. The controller aims to keep the temperatures of conductors below their admissible limits before local relays intervene and trip out the lines. This objective is carried out by properly coordinating different control actions available in power systems, while minimizing a suitable cost function subject to explicit constraints on the conductor temperatures. The temperatures of transmission lines are predicted using a thermal model of bare overhead conductors. The electrical currents are obtained from the dc power-flow approximation of electric networks, whereas dynamic stochastic autoregressive integrated moving average models are used to describe the weather variables. Simulation results reveal that the proposed scheme might increase significantly the reliability of thermal control SPSs and reduce the overall efforts required to fulfill the control objectives

   4.   Karampelas, P., Ekonomou, L., Panetsos, S., Chatzarakis, G.E., 2011. LPAT: An interactive simulation tool for assessing the lightning performance of Hellenic high voltage transmission lines. Applied Soft Computing 11, 1380-1387.

Abstract: The paper presents the Lightning Performance Assessment Tool (LPAT), an interactive simulation tool which assesses the lightning performance of high voltage transmission lines. The LPAT design was based on a recently published methodology that has been developed in order to assess the lightning performance of the Hellenic high voltage transmission lines. This methodology has been adapted to enable tool's users to enter a large dataset required for the computations eliminating the possibility of mistakes. Moreover, LPAT, written in a high-level programming language and using the appropriate user interface models and programming architecture, enables electrical engineers to adapt the level of granularity in which they prefer to examine the lightning performance of a transmission line. This approach is proved to be ideal for electrical systems such as the Hellenic transmission system whose individual characteristics depend upon the meteorological and geographical characteristics of the Hellenic territory. This tool is also flexible to any modification and change in order to support different transmission systems. The presented simulation tool is valuable for designers of electric power systems intending in a more effective lightning protection. (C) 2010 Elsevier B.V. All rights reserved

   5.   Yahyaabadi, M., Vahidi, B., Tavakoli, M.R.B., 2010. Estimation of shielding failure number of different configurations of double-circuit transmission lines using leader progression analysis model. Electrical Engineering 92, 79-85.

Abstract: The protection of overhead transmission lines from lightning strokes is one of the most important tasks of safeguarding electric power systems. In order to do this job effectively, the lightning performance of the transmission lines has to be evaluated accurately. This paper presents the development of a method for estimating the shielding failure number of power transmission lines in different configurations by using the charge-simulation method. The effects of towers, sags of conductors, and a perfectly conducting ground are represented in a 3-D computation. In addition, the stepwise descending nature of a downward negative leader-streamer systems is taken into account by using an appropriate progression model. Upward leader inception and propagation is also modeled utilizing critical equivalent streamer-length criterion. The method is applied to compute the shielding failure of power transmission line for different configurations

   6.   Munukutla, K., Vittal, V., Heydt, G.T., Chipman, D., Keel, B., 2010. A Practical Evaluation of Surge Arrester Placement for Transmission Line Lightning Protection. Ieee Transactions on Power Delivery 25, 1742-1748.

Abstract: The use of metal-oxide varistor surge arresters (MOVs) in lightning protection of overhead transmission lines to improve reliability is of great interest to electric utilities. However due to economic reasons, it is not possible to completely equip an overhead transmission line with surge arresters at each transmission structure. In this paper, an evaluation of lightning protection design on a 115 kV transmission line using surge arresters, utilizing a model based on field data, is presented. The model developed is used for computer simulation using the Alternative Transients Program. Various design procedures aimed at maximizing the reliability of service on the transmission line using a minimal number of surge arresters are analyzed. Different designs considered for transmission line lightning protection using MOV arresters include: the use of a different number of surge arresters per tower, distance between towers with surge arresters and the dependence of these configurations on tower footing resistance. The lightning protection designs are analyzed using 'lightning flashover charts,' proposed in this paper. Also, an analytical model of two 115 kV transmission lines in Southwest U. S. has been developed and different surge arrester location strategies used on these transmission lines have been analyzed. Practical experiences and effectiveness of various lightning protection designs used on these transmission lines are discussed

   7.   Yang, S.J., Chen, S.D., Zhang, Y.J., Dong, W.S., Wang, J.G., Zhou, M., Wang, X.B., Yu, H., 2010. Characteristics Analysis of the Induced Overcurrent Generated by Close Triggered Lightning on the Overhead Transmission Power Line. Journal of Tropical Meteorology 16, 59-65.

Abstract: Techniques of artificially-triggered lightning have provided a significantly useful means to directly measure various physical parameters of lightning discharge and to conduct research on protection methods of lightning electromagnetic pulses. In this study, using capacitive and resistive dividers, current probes and optical fiber transmission devices, we measured and analyzed the induced overvoltage on the overhead transmission line and the overcurrent through Surge Protective Devices (SPD) when a lightning discharge was artificially triggered nearby on August 12, 2008 at Conghua Field Lightning Experiment Site. The triggered lightning discharge contained an initial current stage and eight return strokes whose peak currents ranged from 6.6kA to 26.4kA. We found that overcurrents through SPD were induced on the power line both during the initial continuous current stage and the return stroke processes. During the return strokes, the residual voltage and the current through the SPD lasted up to the ms (millisecond) range, and the overcurrents exhibited a mean waveform up to 22/69 mu s with a peak value of less than 2kA. Based on the observed data, simple calculations show that the corresponding single discharge energy was much greater than the values of the high voltage pulse generators commonly used in the experiments regulated for SPD. The SPD discharge current peak was not synchronous to that of the residual voltage with the former obviously lagging behind the latter. The SPD discharge current peak was well correlated with the triggered lightning current peak and the wave-front current gradient. The long duration of the SPD current is one of the major reasons why the SPD was damaged even with a big nominal discharge current

   8.   Lazaropoulos, A.G., Cottis, P.G., 2010. Capacity of Overhead Medium Voltage Power Line Communication Channels. Ieee Transactions on Power Delivery 25, 723-733.

Abstract: This paper considers broadband transmission via the overhead medium voltage (MV) grid. The MV broadband over power lines (MV/BPL) channels considered are three-phase overhead MV lines above lossy plane ground. To determine the end-to-end transfer function of any MV/BPL configuration the scattering matrix method is adopted. Various topologies of MV/BPL transmission channels have been studied with regard to their end-to-end signal attenuation and capacity. The analysis and relevant simulations reveal that broadband transmission via MV power lines depends drastically on the MV grid topology and the power constraints imposed to suppress electromagnetic interference to other services. A modification to the fixed spectrum allocation/all-protection model to regulate BPL emission is proposed employing power masks adaptive to locally existing wireless services

   9.   Christodoulou, C.A., Ekonomou, L., Fotis, G.P., Gonos, I.F., Stathopulos, I.A., 2010. Assessment of surge arrester failure rate and application studies in Hellenic high voltage transmission lines. Electric Power Systems Research 80, 176-183.

Abstract: The use of transmission line surge arresters to improve the lightning performance of transmission lines is becoming more common. Especially in areas with high soil resistivity and ground flash density, surge arresters constitute the most effective protection mean. In this paper a methodology for assessing the surge arrester failure rate based on the electrogeometrical model is presented. Critical currents that exceed arresters rated energy stress were estimated by the use of a simulation tool. The methodology is applied on operating Hellenic transmission lines of 150 kV. Several case studies are analyzed by installing Surge arresters on different intervals, in relation to the region's tower footing resistance and the ground flash density. The obtained results are compared with real records of outage rate showing the effectiveness of the surge arresters in the reduction of the recorded failure rate. The presented methodology can be proved valuable to the studies of electric power systems designers intending in a more effective lightning protection, reducing the operational costs and providing continuity of service. (C) 2009 Elsevier B.V. All rights reserved

10.   Nam, S.R., Park, J.Y., Kang, S.H., Kezunovic, M., 2009. Phasor Estimation in the Presence of DC Offset and CT Saturation. Ieee Transactions on Power Delivery 24, 1842-1849.

Abstract: A hybrid algorithm for phasor estimation is proposed that is immune to dc offset and current transformer (CT) saturation problems. The algorithm utilizes partial sum (PS)-based and multistage least-squares (MLS)-based methods before and after CT saturation is detected, respectively. The MLS-based method is initiated when the third difference of the secondary current detects the start point of the first saturation period. The determination of each saturation period is based on the sum of the secondary current from the start point of the first saturation period. A least-squares (LS) technique estimates the dc offset parameters from the single-cycle difference of the secondary current in the unsaturated periods. Removal of dc offset from the secondary current yields the sinusoidal waveform portion. Finally, the LS technique is used once again to estimate the phasor from the sinusoidal waveform portion. The performance of the algorithm was evaluated for a-g faults on a 345-kV 100-km overhead transmission line. The Electromagnetic Transient Program was used to generate fault current signals for different fault angles and remanent fluxes. The performance evaluation shows that the proposed algorithm accurately estimates the phasor of a current signal regardless of dc offset and CT saturation. The paper concludes by describing the hardware implementation of the algorithm on a prototype unit based on a digital signal processor

11.   Sadeh, J., Afradi, H., 2009. A new and accurate fault location algorithm for combined transmission lines using Adaptive Network-Based Fuzzy Inference System. Electric Power Systems Research 79, 1538-1545.

Abstract: This paper presents a new and accurate algorithm for locating faults in a combined overhead transmission line with underground power cable using Adaptive Network-Based Fuzzy Inference System (ANFIS). The proposed method uses 10 ANFIS networks and consists of 3 stages, including fault type classification. faulty section detection and exact fault location. In the first part. an ANFIS is used to determine the fault type, applying four inputs, i.e., fundamental component of three phase currents and zero sequence current. Another ANFIS network is used to detect the faulty section, whether the fault is on the overhead line or on the underground cable. Other eight ANFIS networks are utilized to pinpoint the faults (two for each fault type). Four inputs, i.e., the dc component of the current, fundamental frequency of the voltage and current and the angle between them, are used to train the neuro-fuzzy inference systems in order to accurately locate the faults on each part of the combined line. The proposed method is evaluated under different fault conditions such as different fault locations, different fault inception angles and different fault resistances. Simulation results confirm that the proposed method can be used as an efficient means for accurate fault location on the combined transmission lines. (C) 2009 Elsevier B.V. All rights reserved

12.   Rakov, V.A., Rachidi, F., 2009. Overview of Recent Progress in Lightning Research and Lightning Protection. Ieee Transactions on Electromagnetic Compatibility 51, 428-442.

Abstract: This review paper, prepared for this second special issue on lightning of the IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY, summarizes major publications on lightning and lightning protection since the first special issue published in November 1998, i.e., during the last decade. The review is organized in the following five sections: lightning discharge-observations, lightning discharge-modeling, lightning occurrence characteristics/lightning locating systems, lightning electromagnetic pulse and lightning-induced effects, and protection against lightning-induced effects

13.   Paolone, M., Rachidi, F., Borghetti, A., Nucci, C.A., Rubinstein, M., Rakov, V.A., Uman, M.A., 2009. Lightning Electromagnetic Field Coupling to Overhead Lines: Theory, Numerical Simulations, and Experimental Validation. Ieee Transactions on Electromagnetic Compatibility 51, 532-547.

Abstract: The evaluation of electromagnetic transients in overhead power lines due to nearby lightning return strokes requires accurate models for the calculation of both the incident lightning electromagnetic pulse ( LEMP) and the effects of coupling of this field to the line conductors. Considering also the complexity of distribution networks in terms of their topology and the presence of power system components and protection devices, the implementation of the LEMP-to-transmission-line coupling models into software tools used to represent the transient behavior of the entire network is of crucial importance. This paper reviews the most significant results obtained by the authors concerning the calculation of lightning-induced voltages. First, the theoretical basis of advanced models for the calculation of LEMP-originated transients in overhead power lines is illustrated; then, the relevant experimental validation using: 1) reduced-scale setups with LEMP and nuclear electromagnetic pulse ( NEMP) simulators and 2) full-scale setups illuminated by artificially initiated lightning are reported. Finally, the paper presents comparisons between simulations and new experimental data consisting of measured natural lightning-induced voltages on a real distribution network in northern Italy, correlated with data from lightning location systems

14.   Matsubara, I., Sekioka, S., 2009. Analytical Formulas for Induced Surges on a Long Overhead Line Caused by Lightning With an Arbitrary Channel Inclination. Ieee Transactions on Electromagnetic Compatibility 51, 733-740.

Abstract: This paper presents analytical formulas for lightning-induced surges (voltage and current) on an infinite length of overhead line, which are generated by a nearby lightning stroke with arbitrary striking angle. The formulas are derived using the Rusck model, which is one of the electromagnetic coupling models based on a transmission-line approximation of a return stroke. The return-stroke current is approximated by piecewise linearly varying characteristics. The formulas are simple and convenient for lightning-induced effect analysis. The analytical formulas are validated by the comparison with a finite-difference method. The paper proposes approximate formulas of peak value and time to peak value of the lightning-induced voltages for a vertical lightning channel

15.   Zangl, H., Bretterklieber, T., Brasseur, G., 2009. A Feasibility Study on Autonomous Online Condition Monitoring of High-Voltage Overhead Power Lines. Ieee Transactions on Instrumentation and Measurement 58, 1789-1796.

     Abstract: For electric power transmission, high-voltage overhead power lines play an important role, as the costs for power transmission are comparatively low. However, the sag of the conductors (e.g., due to temperature variations, aging, or icing of conductors as a result of extreme weather conditions) may increase safety margins and limit the operability of these power lines. Furthermore, heavy loads due to icing or vibrations excited by wind streams increase the risk of line breakage. With online condition monitoring of power lines, critical states can be detected early, and appropriate countermeasures can be applied. In this paper, we investigate possibilities for monitoring devices that are directly mounted onto a conductor. The feasibility of powering the device from the electric field, protection of electronic circuitry from strong electric fields, and data transmission by means of a wireless link is demonstrated, as well as its operability during the presence of strong magnetic fields due to high currents and transient signals due to partial and spark discharge events

16.   Eissa, M.M., 2009. New principle for transmission line protection using phase portrait plane. Iet Generation Transmission & Distribution 3, 49-56.

Abstract: Phase portraits are a powerful mathematical model for describing oriented textures. An isotangent-based approach in a phase portrait is introduced to discriminate between internal and external faults. The scheme described is new and is a different approach to the problem of relaying ground faults on transmission lines. The geometrical theory of differential equations is used to drive a symbol set on the basis of the visual appearance of phase portraits. The 'phase portrait' of the instantaneous rate of change of current against voltage gives valuable information on the transient and stability characteristics of system configuration with high fault resistance and shunt susceptance of the transmission lines. Hundred percent of the protected zone is successfully discriminated rather than the external zone. An additional parameter that is considered, which is sometimes neglected in protection studies, is the shunt susceptance of the transmission lines

17.   Michishita, K., Ishii, M., Hongo, Y., 2009. Flashover Rate of Distribution Line Due to Indirect Negative Lightning Return Strokes. Ieee Transactions on Power Delivery 24, 472-479.

Abstract: The flashover rate of a distribution line associated with indirect lightning flashes is investigated based on numerical calculations and statistical analysis by taking account of the correlation between the peak value and the front duration of negative return-stroke current waveforms. When the grounding interval of an overhead ground wire and/or surge arresters is 200 in, surge arresters are more effective than an overhead ground wire in suppressing flashover of the power lines, and installation of both is very effective. The flashover rate decreases if there is correlation between the peak and the front duration of lightning current; and it significantly decreases with the increase of the ground conductivity. When the line is equipped with surge arresters only, the flashover rate associated with subsequent strokes is higher than that associated with first strokes; and calculation with the fixed front duration of 2 mu s for first stroke current does not always result in good estimates of flashover rate

18.   Tavakoli, M.R.B., Vahidi, B., Hosseinian, S.H., 2008. Discrete-event simulation of the shielding failure of the arrester protected overhead-lines to evaluate risk of flashover. International Journal of Electrical Power & Energy Systems 30, 614-623.

Abstract: Damages caused by lightning stroke in power system networks are severe for insulations and result in less reliable energy supply. Knowledge of protection schemes and better selection of these devices in power systems is a goal of designers to reduce the risk of flashover in any risky point. In this paper, a statistical procedure is presented to evaluate risk of failure in an overhead-line which is protected by arresters in most risky towers. Main aim of the work is to present the modeling aspects for considering random nature of stroke and its simulation procedure. The random nature of a lightning stroke composed of proper discrete-event simulation of a stroke via its peak current, front time and tail time and accurate mathematical representation of such lightning stroke in a transient analyzer. In addition, the maximum lightning current which causes shielding failure for a specified tower design and probabilistic specification of lightning for discrete-event simulation is taken into account. As a study case, random nature modeled lightning strokes are applied to a 230 kV overhead-line which is located in a hilly area and the risk of failure is calculated when arresters are located beside the stroke point. (C) 2008 Elsevier Ltd. All rights reserved

19.   Bhalja, B., Maheshwari, R.P., 2008. Wavelet-based fault classification scheme for a transmission line using a support vector machine. Electric Power Components and Systems 36, 1017-1030.

Abstract: This article presents a new approach for fault classification in a two-terminal overhead transmission line using a support vector machine classifier. Wavelet transform is used for the decomposition of measured signals and for extraction of the most significant features (feature extraction), which facilitates training of the SVM, particularly in terms of getting better classification performance (high accuracy). After extracting useful features from the measured signals, a decision of fault or no-fault on any phase or multiple phases of a transmission line is carried out using three SVM classifiers. The ground detection task is carried out by a proposed ground index. Two kernel functionspolynomial and Gaussian radial basis function (RBF)have been used, and performances of classifiers have been evaluated based on fault classification accuracy. In order to determine the optimal parametric settings of an SVM classifier (such as the type of kernel function, its associated parameter, and the regularization parameter C), five-fold cross-validation has been applied to the training set. It is observed that an SVM with an RBF kernel provides better fault classification accuracy than that of an SVM with polynomial kernel. One of the key points of this article is the development of an automatic fault data generation model using PSCAD and its application for training and testing of SVMs. To illustrate the effectiveness of the proposed scheme, extensive simulations have been carried out for different fault conditions with wide variations in the operating conditions and source impedances. It has been found that the proposed scheme is very fast and accurate, and it proved to be a robust classifier for digital distance protection

20.   Ekonomou, L., Gonos, I.F., Stathopulos, I.A., 2008. Lightning performance assessment of Hellenic high voltage transmission lines. Electric Power Systems Research 78, 703-712.

Abstract: A methodology for assessing the lightning performance of Hellenic high voltage transmission lines has been developed. Its main advantage is that the analysed transmission line is divided into regions and the analysis is conducted separately for each one region, taking into account the individual characteristics, which exist in each one of them. The developed approach intends to offer more accuracy in the assessment of lightning performance of Hellenic high voltage transmission lines and of similar lines, where they run at the same time through a plain region, a coastline and/or a mountainous region. The aims of the paper are to describe in detail the proposed methodology and to present results obtained by its application on operating Hellenic transmission lines of 150 and 400 kV. The computed results are compared with the results produced by another software tool published in the technical literature and with the real records of outage rate showing a good agreement. The presented methodology, which is coded in a comprehensive computer program, can be proved valuable to the studies of electric power systems designers intending in a more effective lightning protection. (C) 2007 Elsevier B.V. All rights reserved

21.   Kase, T., Kurosawa, Y., Amo, H., 2008. Charging current compensation for distance protection. Ieee Transactions on Power Delivery 23, 124-131.

Abstract: One difficulty of the application of line protections to long transmission lines is the influence of the large capacitance of the line. When a fault occurs on a long line, relatively large magnitude harmonic components of current and voltage are superimposed on the fundamental frequency component due to the large capacitance of the line. This harmonic component can cause oscillation of the distance measurement. It is difficult to remove the harmonic component completely because the order of the harmonic component varies with several conditions. Our research has shown that the degree of oscillation can be reduced significantly by compensating for the charging current in the impedance calculation. This proposed charging current compensation (CCC method provides an excellent result under all conditions. In this paper, the calculation method of CCC is introduced and good performance of CCC for the application to long overhead lines and to the long cable line is proven based on Alternative Transient Program simulations

22.   Calderaro, V., Galdi, V., Piccolo, A., Siano, P., 2007. Adaptive relays for overhead line protection. Electric Power Systems Research 77, 1552-1559.

Abstract: In the liberalized energy market scenario protective relays play an important role in assuring continuous service in the power system where a malfunctioning could lead to serious damages to a wide number of operators having access to the power system. Considering that power lines are operated many times below a rated load current, in this paper an adaptive procedure is presented in order to manage power distribution systems according to dependability or security requirements. In particular, a procedure to obtain an inverse time trip curve by means of a microprocessor, connected to a relay. is presented. The procedure adapts the trip characteristic depending on the conductor temperature, wind speed, emissivity and solar absorbity and is implemented on a microprocessor Rabbit 2200 considering a Drake conductor, 795 kcmil 26/7 ACSR. (C) 2006 Published by Elsevier B.V

23.   Xu, Z.Y., Du, Z.Q., Ran, L., Wu, Y.K., Yang, Q.X., He, J.L., 2007. A current differential relay for a 1000-kV UHV transmission line. Ieee Transactions on Power Delivery 22, 1392-1399.

Abstract: This paper describes the principle of a new current differential relay developed for a 1000-kV UHV transmission line that is being constructed in China. The distributed capacitive current along the relatively long overhead line will have a significant effect on the relay performance and should be taken into account in the relay principle. The study results in a new current differential relay based on the steady state transmission line equations, in which the distributed capacitive current is inherently represented. Analysis is carried out for different practical situations where shunt reactors or series capacitors are present in the system for compensation. Laboratory tests show that the relay principle developed in this study can be used as a main protection scheme for the 1000-kV UHV transmission line

24.   Theethayi, N., Thottappillil, R., Paolone, M., Nucci, C.A., Rachidi, F., 2007. External impedance and admittance of buried horizontal wires for transient studies using transmission line analysis. Ieee Transactions on Dielectrics and Electrical Insulation 14, 751-761.

Abstract: The paper investigates the applicability of some closed form expressions for the ground impedance and ground admittance of buried horizontal wires (bare and insulated) for lightning or switching transient analyses based on transmission line (TL) theory. In view of the frequency contents that typically characterize such transients, the behavior of the ground impedance and admittance is studied for a wide frequency range up to 10 MHz. Low frequency approximation of the ground impedance is not always appropriate for transient analysis. Sensitivity analyses show that, unlike overhead wires, the ground impedance for buried wires is little sensitive to the ground conductivity. On the other hand, the ground admittance varies strongly with the ground conductivity. The paper also discusses the results of transient analysis of buried cables performed by means of electromagnetic transient programs (EMTP) that neglect the ground admittance. The limits of such an approximation are discussed in order to evaluate the applicability of EMTP-like programs to the transient analysis of buried conductors. Transient pulse propagation in time domain based on finite difference time domain (FDTD) method of solution of TL equations is also discussed for a future inclusion of non-linear phenomena, like soil ionization and arcing/breakdown mechanisms, in the soil. The analysis presented could be useful in estimating surge propagation characteristics of buried wires for appropriate insulation coordination and transient protection

25.   Radojevic, Z., Terzija, V., 2007. Effective two-terminal numerical algorithm for overhead lines protection. Electrical Engineering 89, 425-432.

Abstract: In the paper an effective numerical algorithm for overhead lines protection, particularly fault location and adaptive autoreclosure, is presented. It is based on the two terminal line currents and voltages acquisition. For this purposes the synchronized sampling of all analogue input variables, i.e. the application of the Global Position System/Phasor Measurement Units, was assumed. The algorithm presented is derived in the spectral domain. By this the set of third harmonics variables and line parameters was also used. The prerequisite for successfully adaptive autoreclosure functionality realization was the suitable modelling of the electrical arc. Arc was considered as a source of higher harmonics, distorting by this other electrical variables. In the arc modelling, results of laboratory testing were used. Algorithm is tested for a typical network configuration, assuming by this that the line considered was short enough to neglect its capacitive nature. Based on the results obtained, it is very realistic that the algorithm presented could be implemented in praxis in modern Intelligent Electronic Devices (IEDs)

26.   Radojevic, Z., Terzija, V., 2007. Numerical algorithm for overhead lines protection and disturbance records analysis. Iet Generation Transmission & Distribution 1, 357-363.

Abstract: A new and very efficient numerical algorithm for overhead lines protection is presented. The algorithm particularly improves up-to-date solutions with regard to fault location, adaptive autoreclosure, detailed disturbance records analysis and fault data management. It is based on the two-terminal line currents and voltages acquisition. For this purpose, the synchronised sampling of all analogue input variables, that is, the application of the global positioning system/phasor measurement units, was assumed. The algorithm presented is derived in the spectral domain and based on the application of the discrete Fourier transform. The prerequisite for the successful adaptive autoreclosure functionality realisation was the suitable modelling of the electrical are. The electrical arc was considered as a source of higher harmonics. These are included in the complete fault model, which was the starting point for the development of this new algorithm. One of the algorithm's sophisticated features is its ability to determine both the arc and the fault resistance. For the purpose of arc modelling, the results of high current laboratory testing are used. The algorithm is tested through computer-based simulation of a line connected to two active networks. On the basis of the results obtained, it is very realistic that the algorithm presented could be implemented in praxis in modem intelligent electronic devices

27.   Nam, S.R., Sohn, J.M., Kang, S.H., Park, J.K., 2007. Modified notch filter-based instantaneous phasor estimation for high-speed distance protection. Electrical Engineering 89, 311-317.

Abstract: A novel method for estimating the instantaneous phasor of a fault current signal is proposed for high-speed distance protection immune to a DC-offset. The method uses a modified notch filter in order to eliminate the fundamental frequency component from the fault current signal. Since the output of the modified notch filter is the delayed DC-offset, delay compensation results in the same waveform as the original DC-offset. Subtracting the obtained DC-offset from the fault current signal yields a sinusoidal waveform, which becomes the real part of the instantaneous phasor. The imaginary part of the instantaneous phasor is based on the first difference of the fault current signal. Since a DC-offset also appears in the first difference, the DC-offset is removed from the first difference using the results of the delay compensation. The performance of the proposed method was evaluated for a-phase to ground faults on a 345 kV 100 km overhead transmission line. The Electromagnetic Transient Program was used to generate fault current signals for different fault locations and fault inception angles. The performance evaluation showed that the proposed method can estimate the instantaneous phasor of a fault current signal with high speed and high accuracy. The paper concludes by describing the hardware implementation of the proposed method on a prototype unit based on a digital signal processor

28.   Radojevic, Z.M., Shin, J.R., 2007. New digital algorithm for adaptive reclosing based on the calculation of the faulted phase voltage total harmonic distortion factor. Ieee Transactions on Power Delivery 22, 37-41.

Abstract: This paper presents a new numerical algorithm suitable for determining adaptive dead time, and blocking automatic reclosing during permanent faults on overhead lines. It is based on terminal voltage input data processing. The decision if it is safe or not to reclose is determined by the voltage signal of faulted and tripped line phase using the total harmonic distortion factor calculated by discrete Fourier transform. The algorithm was successfully tested using signals recorded on the real power system. The tests demonstrate the ability of the presented algorithm to determine the secondary arc extinction time and to block unsuccessful automatic reclosing of high-voltage lines with permanent fault

29.   Benato, R., Caldon, R., 2007. Distribution line carrier: Analysis procedure and applications to DG. Ieee Transactions on Power Delivery 22, 575-583.

Abstract: This paper deals with the analysis of carrier signal transmission in medium-voltage (MV) distribution networks. A multiconductor matrix procedure based on the bus admittance matrix, which accounts for the earth return currents, enables predicting the high-frequency behavior of the distribution networks and, hence, the effectiveness of transmitted signals. To this aim, suitable models have been implemented based on the Carson's theory for overhead lines with ground return and Wedepohl's theory for cable lines. A comparison with the modal analysis demonstrates the advantages of the multiconductor matrix algorithm with respect to the modal analysis. In order to validate the theoretical results, two measurement campaigns have been carried out on real MV networks. A good agreement between measured and computed values has been verified. Since distribution networks are generally unlike each other, the procedure becomes a valuable tool, which makes it easy to assess the feasibility of distribution line carrier (DLC) applications in any system. In particular, a protection system to prevent the islanding of dispersed generators is proposed. In addition, in a foreseeable hypothesis of allowed islanding operation of portions of distribution networks (microgrids), DLCs are proposed as communication control of the interface device at the point of common coupling

30.   Radojevic, Z.M., 2006. Numerical algorithm for adaptive single pole autoreclosure based on determining the secondary arc extinction time. Electric Power Components and Systems 34, 739-745.

Abstract: This article presents a new numerical algorithm suitable for defining recloser reclaim time and blocking automatic reclosing during permanent faults on overhead lines. It is based on terminal voltage input data processing. The decision if it is safe or not to reclose is determined from the voltage signal of faulted and tripped line phase using fundamental and third harmonic calculated by discrete Fourier transform. The algorithm was successfully tested using signals recorded on the real power system. The tests demonstrate the ability of presented algorithm to determine the secondary arc extinction time and to block unsuccessful automatic reclosing of HV lines with permanent fault

31.   Ekonomou, L., Iracleous, D.P., Gonos, I.F., Stathopulos, I.A., 2006. An optimal design method for improving the lightning performance of overhead high voltage transmission lines. Electric Power Systems Research 76, 493-499.

Abstract: This paper presents a method for the optimal design of high voltage transmission lines taking into consideration shielding and backflashover failure rates. The minimization of suitably defined performance indices, which relate the failures caused by lightning in a transmission line to both line insulation level and tower footing resistance, is aimed. Optimum values for both line insulation level and tower footing resistance are calculated. The method is applied on several operating Hellenic transmission lines of 150 and 400 kV, respectively, carefully selected among others, due to their high failure rates during lightning thunderstorms. Special attention has been paid on open loop lines, where a possible failure could bring the system out of service causing significant problems. The obtained design parameters, which reduce the failure rates caused by lightning, are compared with the existing design parameters of the transmission lines leading up to useful conclusions. The proposed optimization method can be proved a valuable tool to the studies of electric power systems designers, intending to reduce the failure rates caused by lightning. (c) 2005 Elsevier B.V. All rights reserved

32.   Kim, K.S., Gutierrez, D., An, F.T., Kazovsky, L.G., 2005. Design and performance analysis of scheduling algorithms for WDM-PON under SUCCESS-HPON architecture. Journal of Lightwave Technology 23, 3716-3731.

Abstract: Results of the design and performance analysis of two new algorithms for efficient and fair scheduling of variable-length frames in a wavelength division multiplexing (WDM)passive optical network (PON) under the Stanford University aCCESS-Hybrid PON (SUCCESS-HPON) architecture are reported. The WDM-PON under the SUCCESS-HPON architecture has unique features that have direct impacts on the design of scheduling algorithms. First, an optical line terminal (OLT) uses tunable transmitters and receivers that are shared by all the optical network units (ONUs) served by the OLT to reduce the number of expensive dense WDM (DWDM) transceivers. Second, also for cost reduction, ONUs have no local DWDM light sources but use optical modulators to modulate optical continuous wave (CW) bursts provided by the OLT for upstream transmissions. Therefore, the tunable transmitters at the OLT are used for both upstream and downstream transmissions. To provide efficient bidirectional communications between the OLT and the ONUs and guarantee fairness between upstream and downstream traffic, two scheduling algorithms have been designed: 1) batching earliest departure first (BEDF); and 2) sequential scheduling with schedule-time framing ((SF)-F-3). The BEDF is based on the batch scheduling mode where frames arriving at the OLT during a batch period are stored in virtual output queues (VOQs) and scheduled at the end of the batch period. It improves transmission efficiency by selecting the frame with the earliest departure time from a batch of multiple frames, which optimizes the usage of tunable transmitters in scheduling. Considering the high complexity of the optimization process in BEDF, the (SF)-F-3 based on the sequential scheduling mode has also been designed as in the original sequential scheduling algorithm proposed earlier. In (SF)-F-3, the authors use VOQs to provide memory space protection among traffic flows and a granting scheme together with schedule-time framing for both upstream and downstream traffic to reduce framing and guard band overhead. Through extensive simulations under various configurations of the tunable transmitters and receivers, it has been demonstrated that both the BEDF and (SF)-F-3 substantially improve the throughput and delay performances over the original sequential scheduling algorithm, while guaranteeing better fairness between upstream and downstream traffic

33.   Nguyen, T.T., Holt, R., 2003. Lightning protection of transmission lines: optimal shielding design procedure. Iee Proceedings-Generation Transmission and Distribution 150, 659-667.

Abstract: The paper first derives a set of shielding constraints which must be satisfied for achieving effective shielding against lightning for all of the phase conductors of an overhead transmission line in relation to earth-wire placement. The shielding constraints are obtained from the analysis related to the rigorous proof of the premise that, once the earth-wire position has been determined to achieve effective shielding for a nominated critical lightning stroke current, then shielding of the phase conductors is still maintained for stroke currents greater than the critical value. An optimal shielding design procedure is then developed in which the cost function relating to earth-wire position(s) is minimised subject to shielding constraints and specified clearance constraints. Results of lightning protection designs using the procedure, to achieve effective shielding for a range of transmission-fine configurations, are presented

34.   Hammons, T.J., 2003. Power cables in the twenty-first century. Electric Power Components and Systems 31, 967-994.

Abstract: This paper presents a variety of Viewpoints from engineers within the power cable industry as to how current trends in the cable industry will influence future cable designs, particularly With polymeric insulation, lapped dielectrics, and improved diagnostic techniques. The use of high-temperature superconductors and designer polymers as well as the possible availability of conducting polymeric materials is also considered. The paper first reviews how the design of distribution cables has differed historically around the world, the major differences being allied to the systems. Designs largely have been divided into two main categories: those countries following U.K. and European practices, and those having adopted the U.S. system design. However, these differences, such as the use of three-phase cables in the U.K. as opposed to single-phase cables in the U.S., are not so obvious nowadays. Installation practices are becoming rather more standardized, such as the use of ducts, directional drilling, etc. The predominant primary insulation is cross-linked polyethylene (including tree-retardant XLPE), which is used all around the world. Some constructional differences such as the "dry" and "wet" designs persist. The paper then discusses cables from the mid-twentieth century projected into the twenty-first century. Highlighted are the opportunities that will present themselves in the twenty-first century: fluid-filled cables, XLPE cables, intelligent cables, and designer polymers that optimize performance and economic advantages of buried cables. It then focuses on economic trends, power generation trends, lower-cost underground systems, overhead line/underground cables, and materials and environmental trends including use of high-temperature conductors to up-rate overhead circuits. The trend will be toward greater security and utilization using on-line diagnostics, greater circuit diversity due to distributed generation and lower cost cable systems, and extensive use of polymeric materials having low environmental impact. A futuristic view of energy cables in the year 2050 is presented. Discussed are the elements of the "info-energy cable, " the advantages of the cable technology, and the advantages for the network configuration. A realistic view of tendencies in cable systems technology over the next decade is outlined. Also discussed is choice of cable for subsea power links: choice of cable design that exists for subsea power links, the merits of the various designs, installation of submarine cables, protection of submarine cables, new challenges in HVdc submarine cable systems, and future developments. The manufacture and installation of long continuous lengths of subsea power cable is discussed with reference to some key installations. The paper goes on to examine the Kontex HVdc link between Denmark and Germany. The cable link has been in commercial operation since 1996, and with a total length of 172 km and a transmission capacity of 600 MW at 400 kV is still unique worldwide. Details of the link together with its installation and commissioning are explained. Gas-insulated transmission lines are also discussed together with whether they are ready for real-world transmission systems

35.   Gonzalez, S., Gil, M.A., Hernandez, J.O., Fox, V., Souto, R.M., 2001. Resistance to corrosion of galvanized steel covered with an epoxy-polyamide primer coating. Progress in Organic Coatings 41, 167-170.

Abstract: The resistance to corrosion provided by an epoxy-polyamide primer attached to a galvanized steel panel was assessed by electrochemical impedance spectroscopy. Three different coating thicknesses were tested in this work, namely 100, 200 and 500 mum, which were applied on panel sections cut-off from overhead electrical transmission-line towers. Corrosion tests were performed by exposing the painted coupons to a 3.08 NaCl aqueous solution in a horizontal flat-cell. Changes in the impedance characteristics of the systems were found to occur as a function of the exposure time in all the three cases, though their evolution with time showed marked differences which derived directly from the different thicknesses of the coatings. With the thinnest coating considered, the primer film could not provide an effective protection for the metal that underwent corrosion asa result of the delamination process. On the contrary, when the coating film was sufficiently thick, effective protection of the metallic substrate was provided by the epoxy-polyamide film. (C) 2001 Elsevier Science B.V. All rights reserved

36.   Volcker, O., Koch, H., 2001. Insulation co-ordination for gas-insulated transmission lines (GIL). Ieee Transactions on Power Delivery 16, 122-130.

Abstract: In this paper focus is given to the insulation co-ordination of a closed system with integrated surge arresters. The calculations of transient overvoltages are made with typical applications of the integration of GIL in the 400 kV net of overhead lines. The overvoltages in the system are calculated and discussed for system lengths of 1 km and 10 km. Recommendations for such applications for the insulation levels are given. The GIL design configuration, the lightning overvoltages of overhead lines, and the overvoltages in the GIL are discussed under respect of overvoltage protection measures. Together with the use of surge arresters the insulation levels due to overvoltages are discussed. The insulation co-ordination is a very important measure for system optimization. Calculated values found for the insulation level of the GIL were proven with type tests and long duration test set-ups. Some test results are also explained in this paper

37.   Bekut, D.D., Svenda, G.S., Strezoski, V.C., 2000. Dead zone phenomenon in distance relaying of overhead transmission lines. Electric Power Systems Research 56, 1-8.

Abstract: This paper refers to the distance protection of overhead transmission line. The phenomenon of 'dead zones' in distance relay operation is established. This phenomenon consists of a segment of an overhead line, inside the distance relay reach, where the relay can not detect a fault. The nature of the dead zone phenomenon is the most complex when the distance protection of mutually coupled lines is considered. Thus, clarifying the nature and proposing measures for elimination of dead zones from distance protection are main objectives of this paper. A simple example is considered to get a qualitative insight into the dead zone appearance. Presented considerations ate illustrated by example belonging to the actual power system of Yugoslavia. (C) 2000 Elsevier Science S.A. All rights reserved

38.   Larionov, V.P., Korolev, A.V., 1998. Interruptions of the power supply in 1150 kV overhead power lines during thunderstorms. Electrical Technology Russia 78-83.

Abstract: The main cause of power interruptions in 1150 kV overhead power lines during thunderstorms are lightning strikes on the earth wire in the middle part of a span followed by breakdown of the <<earth wire-phase conductor>> gap. The use of negative protective angles of the earth wire does not eliminate the possibility of such breakdowns. An increase in the protection efficiency can be achieved by minimizing the probability of a breakdown of the air gap between the earth wire and the conductor during lightning discharges on the earth wire in the middle part of a span

39.   Dudurych, I., Rosolowski, E., 2000. Analysis of overvoltages in overhead ground wires of extra high voltage (EHV) power transmission line under single-phase-to-ground faults. Electric Power Systems Research 53, 105-111.

Abstract: Overhead ground wires (GW) of extra high voltage (EHV) power transmission lines, apart from lightning-induced overvoltage protection are frequently used for carrier-current communication. In this case the ground wires are suspended on insulators, the dielectric strength of which should be sufficient for the line operational conditions. The insulation level is defined from the condition of the single-line-to-ground (SLG) fault, thus insulator protecting spark gaps should not be flashed-over during such conditions - in order to maintain continuity of the communication channel along the line. Overvoltages during such faults depend on many parameters such as fault place, fault angle, pre-fault load etc. Therefore, designers should investigate the problem for determination of the worst-case scenario. In this paper, dependence of the overvoltages on 750 kV power transmission line ground wires upon the SLG fault place and pre-fault load of the line in transient and steady states is investigated. The analysis was performed by using dynamic are model incorporated into the EMTP program. The provided simulations show that adequately introduced primary and secondary are models are decisive factors for an accurate simulation of the electromagnetic phenomena in the EHV transmission lines during an are crossing-over there the primary are plays an important role) and during so called dead-time, when the secondary are takes place. This paper gives some recommendations for the insulator strings coordination in the 750 kV earth wires on the basis of computer simulation results. (C) 2000 Elsevier Science S.A. All rights reserved

40.   Decat, G., Van Tongerloo, J., 1998. Monitoring the magnetic field in houses under 50 Hz high-voltage overhead transmission lines. International Journal of Environment and Pollution 9, 341-351.

Abstract: This paper deals with a one-week monitoring of the 50 Hz magnetic field on the ground floor and the first floor of houses under 150, 220 and 380 kV high-voltage overhead three-phase AC transmission lines. The field strength varied with the current intensity, the conductor height, and the storey of the house. Because current intensity varies with time the magnetic field depended on the time of day and the day of the week. The recorded magnetic field ranged from 0.1 mu T to 4.5 mu T.. The maximum value was at least 20 times weaker than the 100 mu T exposure level recommended by the guidelines of the International Radiation Protection Association (IRPA) and about 140 times smaller than the 640 mu T of the European Prestandard (CENELEC). The B-field was, for 99.9% of the measuring time, larger than the 0.2 mu T cut-off point used to define categories of exposed and unexposed subjects in EMF epidemiological studies and, for 99.3% of the time, was greater than the 0.3 mu T level used by US private engineering companies as the 'prudent avoidance' exposure limit. The weakest average magnetic field was at least 40 times larger than the 0.02 mu T background value

41.   Radojevic, Z.M., Terzija, V.V., Djuric, M.B., 1998. Numerical algorithm for blocking autoreclosure during permanent faults on overhead lines. Electric Power Systems Research 46, 51-58.

Abstract: This paper presents a new numerical algorithm for blocking autoreclosure during permanent faults on overhead lines. It is based on one terminal input data processing and it is derived in time domain. The fault nature (arcing or arcless fault) is determined from the are voltage amplitude estimated using the least squares error technique. The faulted phase voltage is modeled as a serial connection of fault resistance and are voltage. The new approach does not require the line zero sequence parameters as input data and the algorithm is derived for the case of the most frequent single-phase to ground unsymmetrical fault. The results of algorithm testing through computer simulation and under laboratory conditions are given. The influence of remote infeed, fault resistance, network topology and other factors are investigated and systematically presented. (C) 1998 Elsevier Science S.A. All rights reserved

42.   Koch, H., Schuette, A., 1998. Gas insulated transmission lines for high power transmission over long distances. Electric Power Systems Research 44, 69-74.

Abstract: The gas insulated transmission line (GIL) is a technology developed for the needs of the 21st century, where huge metropolitan areas need an electrical supply for the public and industry. Natural resources of energy are often far away from metropolitan areas. The GIL, as an alternative to overhead lines and synthetic cables, will help to solve local energy supply needs. The technology developed is based on over 20 years of experience, with gas insulated systems that are in synergy with pipeline technic. (C) 1998 Elsevier Science S.A

43.   Carpenter, R.B., Auer, R.L., 1995. Lightning and Surge Protection of Substations. Ieee Transactions on Industry Applications 31, 162-170.

Abstract: Lightning and switching transients along with ground faults create significant voltage anomalies on transmission and some distribution circuits. Not only direct strikes, but nearby strikes, create significant voltage anomalies and subsequent line outages. Recent developments have made it possible to provide a solution to lightning and surge problems, and also reduce the overall cost of substation designs. It is now possible to prevent lightning strikes to any substation component (including the protection system), and to limit incoming transient voltages to as little as 10% over their normal sine wave peaks. This paper defines the problem confronting protection systems engineers, reviews the protection systems conventionally used and defines two new. protective systems: the Dissipation Array(R) System (DAS(R)) and the series hybrid forms of surge protection. The DAS(R) has been in use for over twenty Sears as a strike preventor. The series hybrid protection concept is new to substation applications, but has been in use at secondary levels of up to 2500 V for approximately sixteen years. As a result, lightning or other forms of transient phenomena does not need to be a threat to substations or drive up the overall costs. An earlier paper illustrates how strikes and ''flashovers'' involving the phase conductors and overhead ground wires (neutral) can also be eliminated. (See [4])