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This paper intends to address the dynamic repair scheduling of electric power transmission systems based on look-ahead strategy approximation. The objective is to minimize system functionality loss during the restoration stage after disruptive events. A series of decisions regarding which damaged component to be repaired has to be made successively considering currently available information of repair time and its uncertainty in the future. To achieve this goal, the dynamic repair scheduling problem is represented as a stochastic Markovian decision process (MDP). To overcome the computational complexity of MDP derived from exponentially growing state space, the cost-to-go function is approximated by a look-ahead strategy based on repair importance ordering. Stage-dependent coefficients are used to balance the approximated functionality loss at different decision stages. The tradeoff between the efficiency and optimality can be achieved by adjusting the look-ahead depth and the updating policy of look-ahead strategy. The IEEE-14 and 118-bus systems were used for performance evaluation of the proposed method and comparison with various approaches. The results show that it can produce decisions close to the best-known solutions within small amount of time. [ABSTRACT FROM AUTHOR]

A novel traveling-wave-based fault-location algorithm for multiterminal transmission lines is introduced in this paper. Existing traveling-wave fault-location methods that based on the data measured at line terminals lack reliability and accuracy because time synchronization is needed, which brings error. To solve this problem, the complex structure of multiterminal power system is divided into several fault identification branches, current at the midpoint of each branched is measured, a novel fault-location algorithm is proposed, and the time synchronization error is eliminated. A line-based device is designed to measure the current at the midpoint of each branch. An accurate value of the traveling wave speed can be obtained by merely applying the data record in one measuring device. Thus, the fault-location accuracy is improved. The system model applied in this paper comprises one transmission line and two tapped lines, and the proposed method applies to networks with more terminals. Performance of this method is tested by different cases by PSCAD. The hardware platform has been tested in Sichuan Province, China. [ABSTRACT FROM AUTHOR]

DC ice melting is an effective technical method against ice disaster on transmission lines. To satisfy the demand for simultaneous de-icing and reactive power compensation for substations, this paper proposed a large-capacity low-cost DC deicer with reactive power compensation, which is mainly composed of rectifier transformer, Static Var Generator (SVG) and diode rectifier. In the proposed topology, SVG and diode rectifier share the rectifier transformer, but rectifier transformer capacity is not increased compared with a single deicer. This paper firstly presents the proposed topology and analyzes its advantages. Then, the rectifier transformer design is introduced, and the SVG control strategy is presented. Simulation results for the proposed device are presented, and an engineering devices with a capacity of 21.8 MVA developed for the 220 kV Fuchong substation is described. The simulation and application results indicate that the proposed devices work well. [ABSTRACT FROM AUTHOR]

Independent system operators (ISOs) are responsible for the secure and economic operation of the power systems. Accordingly, ISOs should solve an optimal power flow to minimize the operating cost of a system while meeting the system's security constraints. However, transmission congestion could drastically limit more economical generating units from being dispatched in the power system operation. In this paper, a decentralized transmission switching is introduced in the operation of multi-area power systems to manage the congestion both on regional transmission lines and tie lines while considering credible contingencies. Our proposed methodology relies on a decentralized optimization methodology. Thus, regional control centers in areas would be able to locally manage the congestion within their regional networks as well as tie lines connecting them to their neighboring areas. Several testing systems are studied in this paper to test the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

An improved hybrid unified power flow controller (IHUPFC) is developed in this paper to control the power flow and increase the utilization rate of the existing transmission lines. The IHUPFC is composed of an improved “Sen” transformer (IST) and a small capacity unified power flow controller (UPFC). After a detailed introduction of the structure and voltage regulation performance of the IST, this paper derives the capacity relationship between the IST and the UPFC. Then, this paper introduces the technology of the IHUPFC in power flow regulation and transmission capability improvement. Besides, the advantages of the IHUPFC in performance and structure are analyzed. The IST has simpler structure and larger power flow control area than a “Sen” transformer, and the IHUPFC provides a continuous active and reactive power flow control. Simulation and experiment studies are used to verify the practicability and superiority of the IHUPFC. [ABSTRACT FROM AUTHOR]

The ability to identify electric shock in the human body is a crucial consideration in the design of touch/leakage protective devices. In this paper, the $\alpha$ -dispersion characteristics of electrical impedance in the human body are investigated based on the Cole–Cole model. An improved electric shock identification method is proposed accordingly. The effects of various factors (e.g., transition resistance and feeder reactance) on the accuracy and reliability are analyzed. Feasibility and effectiveness of the method are verified via numerical simulation. The results indicate that 1) $\alpha$-dispersion is an effective feature for distinguishing living or nonliving organisms; 2) the proposed method is robust and unaffected by transition resistance; and 3) the computational cost is low to satisfy standard leakage current protective device requirements. This paper provides a solution to the dead-zone problem as well as a set of workable guidelines for protective device design. [ABSTRACT FROM AUTHOR]

This paper presents a decision tree based high-speed intelligent scheme for series-compensated transmission line protection using differential phase angle of superimposed current (DPASC). The conventional distance relaying scheme undergoes many shortcomings in transmission line protection in the presence of series compensation devices. The proposed scheme calculates the differential phase angle of current signals using full cycle discrete Fourier transform. The DPASC for each phase is used as an input to the data mining model known as decision tree (DT). The DT is used to generate thresholds to detect and classify the faults since determination of robust thresholds is an important challenge in protective relay engineering. The proposed method has been tested for different operating modes of transmission line in SIMIULINK/MATLAB software. Simulation results indicate that the proposed method is able to detect and classify the faults with acceptable accuracy, in less than half cycle. [ABSTRACT FROM AUTHOR]

To meet the growing power demand of the future, utilities and researchers have considered the addition of dc circuits in existing transmission corridors. The previous research has focused on analyzing the field environment, steady state induction and the negative effects of induction in the hybrid transmission lines. The overhead ground wires (OHGWs) have been used only for improving the lightning performance of overhead lines (OHL). In this paper, the spatial position of OHGWs has been studied with the objective of minimizing the steady state induction between power conductors as well as poorly grounded metallic objects like railroads and fences present near the ac-dc OHL. Candidate space for placement of OHGWs having shielding failure rate of less than four is identified using the conventional electro-geometric model. The steady state induction in the power conductors and nearby metallic objects is studied as a function of position of OHGWs using electro-magnetic transient simulation. The results indicate a strong correlation between the height of OHGWs and magnitude of induced voltage in power conductors, and metallic objects underneath the transmission line. The conscious effort in placement of OHGWs can reduce the magnitude of induced voltages while ensuring adequate lightning performance. [ABSTRACT FROM AUTHOR]

The paper demonstrates a power swing blocking and unblocking technique for a distance relay in a hybrid transmission line consisting of an overhead line and an underground cable using the Lissajous figure of the voltage and current signals. The tangents perpendicular to the axis of the current signal (denoted as TPI) on the Lissajous figure are found at exactly half cycle spacing during normal condition, while their spacings deviate from half cycle and are unequal during the power swing and a large number of TPIs are found within a small duration after fault initiation. This feature of the Lissajous figure is utilized to detect the power swing and the fault during the power swing. The proposed method is tested on a 5-machine 14-bus power system, simulated in electromagnetic transient program for symmetrical, asymmetrical, and nonideal faults, and found accurate. The faults during the power swing are detected within few milliseconds after fault initiation for different fault locations, fault resistances, load angles, fault inception times, and swing frequencies. The comparative analysis with two conventional and two novel methods shows the potential of the proposed method. [ABSTRACT FROM AUTHOR]

Lightning electromagnetic fields can couple to overhead power transmission and distribution lines, causing serious effects to the power system. Lightning electromagnetic fields that couple to overhead lines have a nonuniform distribution along the line conductors. Therefore, to ensure the accuracy of the numerical calculation results, a large number of discretization points are needed along the line, which might dramatically increase the computation time since the evaluation of lightning electromagnetic fields in the presence of a lossy soil involves, in general,Sommerfeldintegrals, or, even in the case of a perfectly conducting ground, numerical integration along the channel. This paper proposes a new approach to address this problem. The proposed approach is based on the Agrawalet al. coupling model, in which the horizontal lightning electric field along the line is represented by the complex exponential functions in the frequency domain using the matrix pencil method. The method is highly efficient in terms of computation time since the lightning-induced response of the line can be solved semi-analytically. The proposed approach is validated by two different validation examples. [ABSTRACT FROM AUTHOR]

Visualization of electric power transmission systems centers on the one-line diagram, which is a simplified logical depiction of the circuit's connections and elements. Such a graph drawing is useful for supporting the study, analysis, and presentation of power system data. This paper proposes an automated way to generate one-line diagrams, given substation identifiers with geographic tags and the system bus-branch model. Two approaches to drawing the substations are given: a force-directed approach and a greedy approach, which in different ways modify the position and size of substations as drawn. For transmission line routing between substations, a Delaunay-based method is employed, which segments the transmission line drawings to avoid overlapping with substations and other lines. These methods show good visual properties in spacing, geographic context, relatively straight lines, and computational speed. The result is that large power systems, real and synthetic, can be easily and quickly visualized with a diagram that merges geographic context with logical clarity. [ABSTRACT FROM AUTHOR]

This paper presents the effectiveness of a microgrid (MG) in a distribution system. The combined heat and power (CHP) system is used to enhance the overall efficiency of the power system. Microturbines are used for CHP operation in this paper. The various methods of control of the MG are discussed. A simple low-cost model is proposed for MG based on frequency droop control for active power generation. The proposed model can be used in plug-and-play mode of operation of the MG. The model of MG is developed, and its performance is simulated in MATLAB platform. Performance of the model is studied under grid-connected and islanded conditions. [ABSTRACT FROM AUTHOR]

The number and locations of transmission lines that are likely to get simultaneously congested are useful information for analysis of power market. In this paper, we present a study that demonstrates the number of simultaneously congested transmission lines is very limited, as well as an algorithm for identifying a small set of transmission lines that may become simultaneously congested based on the current states of the system and market. To this end, we first investigate the maximum number of simultaneously congested lines. Then, a novel algorithm is developed to identify a smaller set using two scientific criteria – one is concerned with the absolute impact of generation dispatch decisions, and the other, the relative sensitivities of line flows with respect to the changes of generation outputs. The effectiveness of the proposed algorithm is demonstrated through two simulation studies, one based on IEEE 39-bus for illustration of concepts, and the other based on a large-scale, real-world power system for showing the practical application and significance of results. [ABSTRACT FROM AUTHOR]

Advanced communication technologies has allowed the power-line communication (PLC) channel to be a transmission medium that enables the transferring of high-speed digital data over the classical indoor electrical wires. The development of PLC systems for Internet, voice, and data services requires measurement-based models of the transfer characteristics of the power-line network suitable for performance analysis by simulation. In this paper, a statistical-based and deterministic PLC channel frequency model was proposed. This model has the advantage of using only one parameter: the channel class. Related software is also developed. In this paper, this model is further improved to represent the measured impulse responses, and related software is developed. First, a PLC channel classification is realized, and an average magnitude and phase channel model by class is proposed. Second, the multipath behaviour of the PLC channel is introduced: a statistical-based channel magnitude generator is built, and a refined phase model is suggested. Finally, the related software is briefly described. [ABSTRACT FROM AUTHOR]

In this paper, a new method is proposed for ampacity calculations of deeply installed cables. Two factors make these types of installations different from more common situations of cables located up to five meters underground. On the one hand, the time constant of the soil layer above the cable trench is very large, resulting in a very slow conductor temperature rise when the cable is first loaded, and, on the other hand, the weekly and yearly load-cycle variations can be taken into account to take the advantage of the greater laying depth. Both issues are explored in this paper. This paper introduces the concept of the equivalent laying depth which makes it possible to use the rating rules applicable to the steady-state conditions and avoid transient analysis. [ABSTRACT FROM AUTHOR]

This paper discusses numerical stability problems of a frequency-dependent transmission-line and cable modeling approach used for electromagnetic transient analysis. Time-domain numerical errors due to the discrete computation of convolution integrals can be estimated in terms of transfer function parameters for a given line or cable model. Based on this estimation, a methodology for the improvement of numerical stability is presented. The numerical advantages of the new method are supported by demonstrations and comparisons with existing models. The method presented in this paper is applicable to power cables and transmission lines. [ABSTRACT FROM AUTHOR]

This paper investigates the economical feasibility of four-phase (4P) overhead transmission lines, considered as a possible alternative to the traditional three-phase (3P) connections. The paper performs an economical comparison between innovative 4P transmission lines and traditional 3P lines, with the goal of evaluating the contests where a 4P connection could become convenient, accounting for different reliability, land occupation, visual impact, energy losses and investment costs. [ABSTRACT FROM AUTHOR]

The paper applies the well-known red-green-blue (RGB) coloring method to visualize traveling waves initiated by switching events or faults occurring in power systems. The three-phase voltage profile along a given transmission line is obtained first. This profile is then converted into a colored picture by assigning different colors to phase signals according to their intensity. An interesting outcome of repeating this process for each time step is the emergence of the Bewley diagram [1] which is commonly used to illustrate the behavior of traveling waves in space-time. The main contribution of the paper is to show that RGB coloring of phase signals reveals essentially the same profile as the one obtained by using the aerial mode of the signals transformed into the modal domain. Furthermore, it discusses how this result can possibly be useful in applications such as fault location. [ABSTRACT FROM AUTHOR]

Forward contracts play an important role for market power mitigation and risk hedging in electricity markets. In this paper, a two-settlement electricity market including a forward market and a spot market is formulated as a two-stage game. The linear supply function equilibrium (LSFE) model and Cournot model are used to model strategic bidding for the spot market, while the forward market is modeled by Cournot model. A co-evolutionary genetic algorithm (CGA) is employed to determine the market equilibrium. The paper then examines the question whether generation companies (GenCos) would voluntarily enter forward markets due to economic inspiration and studies theoretically and numerically the factors which can affect the bidding behaviors of GenCos. The effectiveness of CGA in determining the market equilibrium is investigated and demonstrated based on two test examples. The studies show that GenCos' decisions on the participation in forward markets depend significantly on the type of competition that they have in the spot market. Moreover, GenCos' bidding behaviors in the forward market can be affected by their cost parameters and the slope of system demand function significantly. [ABSTRACT FROM AUTHOR]

Due to the structure of underground cables, the frequency dependence of shunt admittances is more important to underground cables than to overhead lines. The main purpose of this paper is to establish a frequency-dependent underground cable model for advanced research and analysis regarding the influences of frequency-dependent shunt admittances on underground cable systems. The model will be more practical by adding the frequency dependence of shunt admittances into mathematical models and transferring them to the corresponding programming codes. In the cable Electromagnetic Transient Program (EMTP) models, the frequency dependence of shunt admittances could be represented by a set of equivalent circuits with constant parameters that can be determined by observing the characteristics of shunt admittances, then synthesizing them with a rational function approximation for discrete-time EMTP solutions. A number of simulation cases are presented in this paper to show that the frequency dependence of shunt admittances for underground cable systems leads to magnitude attenuation and strong traveling time reduction in a transient period of voltages. Also, the influences of frequency-dependent capacitances on cable systems are comparatively more impressive than those of frequency-dependent conductances. The conclusions are supported by numerical simulation results. [ABSTRACT FROM AUTHOR]

The influence of earth stratification on the conductor impedances is investigated in this paper. The generalized expressions for the self and mutual impedance of conductors in the multilayer earth case, which have been derived in a companion paper, are implemented on typical overhead power transmission lines and underground single-core power cable arrangements for discrete and exponential variations of earth resistivity. The accuracy of the results over a wide frequency range is justified by a proper finite-element method formulation. The differences in the impedances due to earth stratification are presented. The influence of the earth stratification on the actual transient responses of the conductor arrangements is also investigated. [ABSTRACT FROM AUTHOR]

Induced voltage and current in a deenergized transmission line caused by other lines nearby can be caused by electric-field and magnetic-field induction. These voltages and currents present a serious work hazard for line-crew personnel. Proper understanding of the phenomenon involved and identification of the associated hazards are necessary to safely perform deenergized line work. The purpose of this paper is to clarify some of the misconceptions that have been prevalent in the industry for many years as well as to expand on the test data available in literature. This paper discusses, in simple terms, the relevant parameters that affect the magnitude of the induced voltage and current as well as the work hazards they create. [ABSTRACT FROM AUTHOR]

This paper introduces a hybrid flow controller (HFC) as a new member of flexible ac transmission system (FACTS) controllers for steady-state and power-flow control of power transmission lines. HFC is a hybrid compensator (i.e., provides series and/or shunt compensation). Structurally, an HFC unit is composed of a mechanically switched phase-shifting transformer, a mechanically switched shunt capacitor, and multimodule, series-connected, thyristor-switched capacitors and inductors. This paper describes the steady-state operation, single-phase equivalent circuit, power-flow model, and V-I and P-Q characteristics of the HFC. This paper highlights the steady-state technical features of the HFC for power-flow control of a study system and also provides a quantitative comparison of the HFC, UPFC, and PST. [ABSTRACT FROM AUTHOR]

Two basic types of low voltage (LV) distribution exist in practice. The systems based on the European approach have long LV feeders whose sizing requires more careful design consideration than systems based on North American practice with shorter LV feeders. The most important criterion in conductor sizing is the correct estimation of the design loads. This paper describes the development and application of a probabilistic design method based on the Beta probability density function (pdf). The paper investigates an approximate approach for estimating load parameters in countries where a large load database is not available. This approach estimates the Beta parameters from the group after-diversity-maximum-demand (ADMD) for the customers. [ABSTRACT FROM AUTHOR]

In this paper, a new method called arbitrary-difference precise-integration (ADPI) algorithm is proposed to calculate the electromagnetic transients in single-phase nonuniform transmission line. The new method employs arbitrary difference in space domain and precise integration in time domain, respectively. It not only can create the difference equations arbitrarily according to the characteristics of the nonuniform transmission line but also can remove the Courant-Friedrich-Levy (CFL) stability condition restraint. The method presented in this paper is used to calculate the electromagnetic transients in a vertical conductor. The results show that compared with other methods such as finite-difference time-domain (FDTD) and electromagnetic transients program (EMTP) method, this new algorithm provides higher efficiency since the time step used in the simulation is no longer restricted by the stability condition. [ABSTRACT FROM AUTHOR]

In a previous paper [1], the voltage induced onto a 1-km above-ground pipeline by transmission line transients was shown to be significant in comparison to the induced voltage resulting from power system currents. This paper enhances the previous work in three distinct areas. First, both aerial and buried pipelines are considered. Above-ground pipelines are shown to be more at risk from transient-induced voltages. Second, parallelisms of up to 10km are simulated. The results show that increasing parallelisms do not result in higher induced voltages once a critical distance has been reached. Third, a backflashover from a tower in the vicinity to a pipeline is modeled. This allows conductive coupling to take place at the same time as inductive and capacitive coupling. Backflashovers are shown to be an important consideration in determining the maximum voltages observed on a nearby pipeline. [ABSTRACT FROM AUTHOR]

This paper analyzes the implementability of locational marginal price (LMP) and financial transmission right (FTR) mechanisms in the presence of high voltage dc (HVDC) lines in the regulated (i.e., under the control of system operator) network. The established framework of LMP-FTR mechanism assumes that the system under regulation is fully ac. Unregulated (or private) HVDC lines are taken into account within this framework through proxy-transaction bids from the line owners. However, as the flow over a regulated HVDC line has to be controlled by the system operator himself, the existing LMP-FTR framework becomes insufficient if the system contains or is expanded with regulated HVDC lines. The augmentation that should be made to the existing framework to include regulated HVDC lines is explained in this paper. It is shown that the flow over a regulated HVDC line can be modeled as a non-chargeable bilateral transaction without causing any threat of negative congestion surplus. For this power dispatch model, revenue adequacy of FTRs can be still ensured by means of the conventional simultaneous feasibility test (SFT) model. By utilizing the capacities of dc lines, a more general SFT model is further developed. The modified auction problem is discussed and tested for the non-negativity of net auction collection. The process of revenue adequate issuance of auction revenue rights is explained. Finally, the relative merit of a regulated HVDC line over a private HVDC line is discussed through a case study. [ABSTRACT FROM AUTHOR]

This paper provides an overview of the electric field (E-field) distribution on transmission line composite insulators applied in alternating current applications. Factors that affect the E-field distribution are discussed as well as the influence of the E-field distribution on the short and long term performance. Modeling and measurement methods are reported and examples of calculated E-field magnitudes determined are presented together with corona ring application information. This paper was developed by the IEEE Task Force on Electric Fields and Composite Insulators. [ABSTRACT FROM AUTHOR]

This paper discusses power-system instability and the importance of fast fault-clearing performance to aid in reliable production of power. An explanation regarding small-signal stability, high-impedance transmission lines, line loading, and high-gain fast-acting excitation systems is provided. Transient stability is discussed, including synchronizing and damping torques. The power-angle curve is used to illustrate how fault-clearing time and high initial response excitation systems can affect transient stability. The term "power-system stability" has become increasingly popular in generation and transmission. The sudden requirement for power-system stabilizers (PSSs) has created confusion about their applicability, purpose, and benefit to the system. This paper discusses the fundamentals of the PSS and its effectiveness. In today's paper industry, PSSs are being applied on larger machines in the northwest United States and Canada. [ABSTRACT FROM AUTHOR]

Industries that produce flicker are often placed close to each other and connected to the same power grid system. This implies that the measured flicker level at the point of common coupling (PCC) is a result of contribution from a number of different flicker sources. In a mitigation process it is essential to know which one of the flicker sources is the dominant one. Therefore this paper proposes a method to determine the flicker propagations and trace the flicker sources by using flicker power measurements. Flicker power is considered as a quantity containing both sign and magnitude. The sign determines if a flicker source is placed downstream or upstream with respect to a given monitoring point and the magnitude is used to determine the propagation of flicker power throughout the power network and to trace the dominant flicker source. This paper covers the theoretical background of flicker power and describes a novel method for calculation of flicker power that can be implemented in a power network analyzer. Also a conducted field test based on the proposed method is described in the paper. [ABSTRACT FROM AUTHOR]

A method is proposed for estimating interharmonic frequencies in power system voltage and current signals. The method is based on a spectrum-estimation method known as "estimation of signal parameters via rotational invariance techniques" (ESPRIT). To allow for a more reliable spectral estimation and to cover nonstationarity in the signal, a sliding-window version of ESPRIT is introduced. This paper describes the basic ESPRIT method as well as sliding-window ESPRIT. The paper discusses the application of the method to one synthetic signal and three measurement signals. It is shown that the method allows for very accurate frequency estimation of interharmonic components. The limitations of the methods, such as line splitting and spurious components, can be overcome by using the coherent information obtained from the sliding-window method. A number of remaining issues are also discussed in this paper. [ABSTRACT FROM AUTHOR]

In this paper, a short-circuit transmission line method is proposed for passive intermodulation (PIM) evaluation of metallic materials. The method is introduced as a current-based PIM evaluation method that is effective for characterization of metallic materials and electrical contacts. The impedance matching condition is not required for a device under test. Therefore, its shape can be advantageously chosen arbitrarily. The proposed method realizes quantitative characterization of metallic materials, and demonstrates that characterizing the materials in terms of applied current density is effective to provide a fair assessment for material choice. Using the proposed method, copper foils with arbitrary width and thickness were evaluated without any effects on characteristic impedance. The proposed method is applicable to actual microwave components such as SMA connectors. The paper presents that the PIM level obtained using the proposed method is 18 dB higher than that in the conventional impedance-matched line method. As a result, a clear interpretation from the proposed method to the matched line method is also presented. [ABSTRACT FROM AUTHOR]

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-hike 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. [ABSTRACT FROM AUTHOR]

This paper presents the operational supervision of corona losses in the load dispatching system of Svenska Kraftnät, the Swedish National Transmission System Operator. The aim of this supervision is to decrease the total active losses in the 220–400 kV national grid during the winter period, when the corona losses can be high. These losses are calculated from measured quantities on the inservice transmission lines and the voltage dependence of these losses are also taken into account during voltage optimization, when operational mitigation is planned against corona losses. The calculation method used has been verified by a year-long field measurement during 2003–2004. The evaluation of the measured data contains very interesting relations between the weather parameters and the corona losses. Both this measurement and the conclusions are also described in this paper. [ABSTRACT FROM AUTHOR]

Long extra high voltage (EHV) ac lines cannot be loaded to their thermal Limits in order to keep sufficient margin against transient instability. With the scheme proposed in this paper, it is possible to load these lines very close to their thermal limits. The conductors are allowed to carry usual ac along with dc superimposed on it. The added dc power flow does not cause any transient instability. This paper presents the feasibility of converting a double circuit ac line into composite ac-dc power transmission line to get the ad- vantages of parallel ac-dc transmission to improve stability and damping out oscillations. Simulation and experimental studies are carried out for the coordinated control as well as independent control of ac and dc power transmissions. No alterations of conductors, insulator strings, and towers of the original line are needed. Substantial gain in the loadability of the line is obtained. Master current controller senses ac current and regulates the dc current orders for converters online such that conductor current never exceeds its thermal limit. [ABSTRACT FROM AUTHOR]

The fractional frequency transmission system (FFTS) is a very promising long-distance transmission approach, which uses lower frequency (50/3 Hz) to reduce the electrical length of the ac power line, and thus, its transmission capacity can be increased several fold. This paper introduces the experimental installation of FFTS and primary experiment results. The experiment uses the phase-controlled cycloconverter as the frequency changer, stepping up 50/3 Hz electricity to 50 Hz electricity and supplying it to the utility grid. Thus, a new flexible ac transmission system device is successfully established in this experiment. The synchronizing process of 50/3 Hz transmission system with 50 Hz utility system is introduced in this paper. The experiment results show that a 1200 km/500 kV transmission line can transmit more than 2000 MW electric power when employing the FFTS. The experiment also illustrates that there is no essential difficulty to realize FFTS in engineering practice. [ABSTRACT FROM AUTHOR]

This paper proposes a method for choosing the best transmission system expansion plan considering a probabilistic reliability criterion (RLOLE). The method minimizes the investment budget for constructing new transmission lines subject to probabilistic reliability criteria, which consider the uncertainties of transmission system elements. Two probabilistic reliability criteria are used as constraints. One is a transmission system reliability criterion (RLOLETS) constraint, and the other is a bus/nodal reliability criterion (RLOLBus) constraint. The proposed method models the transmission system expansion problem as an integer programming problem. It solves for the optimal strategy using a probabilistic branch and bound method that utilizes a network flow approach and the maximum flow-minimum cut set theorem. Test results on an existing 21-bus system are included in the paper. They demonstrate the suitability of the proposed method for solving the transmission system expansion planning problem subject to practical future uncertainties. [ABSTRACT FROM AUTHOR]

This paper presents a new method for estimating avoided transmission and distribution costs associated with small load reductions, named the one-year deferral method. It is established on the basis of the system planner's actual response to a small reduction in the forecast annual peak load. This paper has also explored the noninteger deferral time (i.e., a fraction of a year) in the present worth method, which is seemingly inconsistent with the system planning practice. In addition, as allowed by the new method, the effect of the size and type (shape) of a load reduction stream (i.e., a series of reductions in the forecast annual peak loads) on avoided costs is studied, which is important for determining generic avoided cost values intended for various applications. [ABSTRACT FROM AUTHOR]

Economic transmission switching has been proposed as a new control paradigm to improve the economics of electric power systems. In practice, the transmission switching operation itself is a disruptive action to the system. Frequently switching lines into or out of service can create undesirable effects on the security and reliability of power systems and may require new investments in the automation and control systems. In this paper, we formulate an economic seasonal transmission switching model where transmission switching occurs once at the beginning of a time period (season) and then the transmission topology remains unchanged during that period. The proposed seasonal transmission switching model is a large-scale mixed integer programming problem. The objective of the optimization model is to minimize the total energy generation cost over the season subject to loads and N-1 reliability requirements. We develop a novel decomposition method that decomposes the seasonal problem into one-hour problems which are then solved efficiently. We demonstrate our model and the decomposition approach on the 14-bus, 39-bus, and 118-bus power systems and show potential cost savings in each case. [ABSTRACT FROM PUBLISHER]

Owing to wind power inherent characteristics and technical constraints of power systems operation, a considerable amount of wind energy cannot be delivered to load centers and gets curtailed. Transmission congestion together with temporal mismatch between load and available wind power can be accounted as the main reasons for this unpleasant event. This paper aims to concentrate on the wind energy curtailment for which it provides a combinatorial planning model to maximize wind power utilization. Jointly operating the wind power generation system with pumped hydro energy storage (PHES), the planning procedure tries to reach schemes with the minimum level of wind energy curtailment as well as low imposed cost of transmission network reinforcement. In this regard, a well-organized posterior multi-objective (MO) optimization framework is proposed aimed to properly deal with wind energy curtailment cost, total social cost, and also storage units' revenue as some unavoidable factors in planning studies of power systems. The presented method is conducted on the modified IEEE Reliability Test System (IEEE-RTS) and the obtained results introduce its applicability and efficiency in planning procedure of the renewable-based power systems. [ABSTRACT FROM PUBLISHER]

This paper proposes a hybrid firefly algorithm (HFA) to assist in decision-making for reactor arrangement in underground cable transmission systems. The HFA method is proposed based on the analysis of phototaxis behavior of fireflies, and enables solving the optimization problem effectively. In this study, by formulating high relationships among connected reactors, sheath loss, and induced voltage, the HFA method is employed to determine the appropriate reactor placement in an underground transmission systems. Through the tests made on different transmission lines along with the results compared to other methods, the proposed approach provides satisfactory decision support for reactor placement and serves as a beneficial reference for underground transmission planning and design. [ABSTRACT FROM AUTHOR]

This paper discusses system-level impacts of temperature-dependent transmission line models based on given ambient temperature profiles. In order to capture nonuniformity of line parameters caused by ambient temperature gradients, a line model characterized by multiple nonuniform segments is used. An automated tool has been developed to obtain appropriate system models, given a set of temperature measurements and their locations along each system branch. Using these models, the impacts of temperature variations are investigated with respect to line terminal behavior (bus voltage) and maximum power transfer characteristics. Results for the IEEE 30-bus test system are presented. [ABSTRACT FROM AUTHOR]

This paper proposes strategies to reduce the number of variables and the combinatorial search space of the multistage transmission expansion planning problem (TEP). The concept of the binary numeral system (BNS) is used to reduce the number of binary and continuous variables related to the candidate transmission lines and network constraints that are connected with them. The construction phase of greedy randomized adaptive search procedure (GRASP-CP) and additional constraints, obtained from power flow equilibrium in an electric power system are employed for more reduction in search space. The multistage TEP problem is modeled like a mixed binary linear programming problem and solved using a commercial solver with a low computational time. The results of one test system and two real systems are presented in order to show the efficiency of the proposed solution technique. [ABSTRACT FROM PUBLISHER]

A general formulation for the calculation of the influence of the earth return path on the impedances and the admittances of underground multiconductor power cable arrangements is presented in this paper. The expressions for the self and mutual earth correction terms are derived by a rigorous solution of the electromagnetic-field equations. The involved semiinfinite integrals are calculated by using a suitable numerical integration technique. The propagation characteristics of a single insulated conductor and of a typical three-phase single-core cable arrangement are investigated and are compared to the corresponding ones obtained by other approaches. Finally, the cable parameters calculated by the proposed method are used in a simulation of a fast transient in a three-phase single-core cable. [ABSTRACT FROM AUTHOR]

This paper proposes a powerful high-speed traveling-wave-based technique for the protection of power transmission lines. The proposed technique uses principal component analysis to identify the dominant pattern of the signals preprocessed by wavelet transform. The proposed protection algorithm presents a discriminating method based on the polarity, magnitude, and time interval between the detected traveling waves at the relay location. A supplemental algorithm consisting of a high-set overcurrent relay as well as an impedance-based relay is also proposed. This is done to overcome the well-known shortcomings of traveling-wave-based protection techniques for the detection of very close-in faults and single-phase-to-ground faults occurring at small voltage magnitudes. The proposed technique is evaluated for the protection of a two-terminal transmission line. Extensive simulation studies using PSCAD/EMTDC software indicate that the proposed approach is reliable for rapid and correct identification of various fault cases. It identifies most of the internal faults very rapidly in less than 2 ms. In addition, the proposed technique presents high noise immunity. [ABSTRACT FROM AUTHOR]

The general aim of this paper is to develop an accurate fault-location scheme that can solve the problems affecting the accuracy of the existing conventional fault locators achieving easier maintenance and restoration time reduction as well as economical aims. This consequently helps to fit the new deregulation policies and competitive marketing. This investigation successfully applies zero-sequence current (3I0) from the two terminals for earth high impedance fault (HIF) location, or negative-sequence currents from the two terminals of one faulted phase for line-to-line fault location. The HIF location is determined within only a maximum time of one cycle. The proposed scheme is insensitive to variations of different parameters, such as fault type, HIF behavior, wide-range transmission-line parameters variation, and fault inception angle. Staged fault testing results demonstrate that the proposed algorithm has feasible performance. [ABSTRACT FROM AUTHOR]

Lightning overvoltages coming from overhead lines, such as power distribution lines, telecommunication lines, and antennas to residences have been actively studied. However, the relation between a lightning strike to the ground and overvoltages in residences remains unclear. This paper proposes a simulation model to estimate lightning overvoltages caused by ground potential rise due to the lightning strike to the ground. The proposed model is derived on the basis of the Thevenin theorem, and can be realized in the Electromagnetic Transients Program. [ABSTRACT FROM AUTHOR]

Significant penetration of distributed generation in many distribution systems has opened an option of operating distribution systems in island mode for economical and technical reasons. However, balancing frequency of the islanded system is still an issue to be solved, especially when the demand exceeds the generation in the power island. This paper presents a strategy to shed an optimal number of loads in the island to stabilize the frequency. The load shedding strategy is based on frequency information, rate of change of frequency, customers' willingness to pay, and loads histories. Different scenarios have been simulated with results showing that the proposed method is effective in shedding the optimal number of loads while stabilizing frequency. [ABSTRACT FROM AUTHOR]

This paper presents a method for locating faults on HVDC transmission lines using two terminal data. Different from those based on the traveling wave principle, the new fault-location algorithm can use any section of the postfault data to locate faults. The proposed method is developed based on the distributed parameter line model in which the voltage distribution over the line can be obtained from the voltage and current measurements at both terminals and point where fault occurs can be identified from the calculated voltage distribution. The fault-location algorithm is performed in time domain and thus a short data window is sufficient for it to achieve satisfactory accuracy in practice. The proposed algorithm is simulated using data of the frequency-dependent line model in EMTDC and data of an existing HVDC line as well. The simulations have shown that this method is valid and is capable of locating the faults occurring on HVDC transmission lines quickly and accurately. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of identifying the optimal location for voltage sags monitors. The proposed approach is based on using a monitor reach matrix obtained from the solution of analytical expressions which are valid for any location of faults in the power system. This method provides the optimal number of monitoring devices and the best positions to place them in order to guarantee the observabiity of the whole system considering any type of fault (balanced or unbalanced). That is, the location of monitors obtained by means of the proposed algorithm ensures that any event leading to a voltage sag is captured by, at least, one voltage sag monitor. Several examples are provided showing the performance of the proposed formulation compared to other approaches. [ABSTRACT FROM AUTHOR]