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The conservative power theory (CPT) is a time-domain theory applicable to any periodic signal single- or polyphase system with or without a neutral conductor. The principle operation is the orthogonal decomposition of electrical variables, resulting in electrical quantities with physical meaning. An important feature of the CPT is the current decomposition. It consists of decomposing any current into five parts. The label of these parts is active current, reactive current, scattered active current, scattered reactive current, and generated current. This paper proposes the application of the current decomposition of the CPT in distributed energy resources (DERs). A supervisory controller (SC) uses the current decomposition in a load power-sharing strategy. The combination of these two issues is the main contribution of this paper. Moreover, the proposal of this paper is more attractive than the conventional droop strategy since the DERs follow their current reference in a current-controlled mode, making the load sharing faster, more reliable, and more accurate. A clear understanding of how the CPT decomposes load currents into its parts is presented, as well as the drawback found in droop strategy when dealing with load power sharing. Later, the SC load power-sharing strategy is described, indicating that the proposal of this paper makes an SC to have a broad option when managing a smart grid with dispatchable DERs. A case study with experimental results shows the efficacy of applying current decomposition of the CPT in load power-sharing strategies. [ABSTRACT FROM AUTHOR]

Microthrusters are used for microsatellites to provide precise motion control in space by applying very low thrust pulses, which must be properly calibrated on earth. The range of thrust levels required varies from one thruster to another, depending on its use. Thus, microthrusts that stand capable of reading thrusts of multiple ranges, depending on the configuration, are in demand. This paper discusses the features and the calibration method for a typical miniaturized thrust stand. This device is essentially a torsional pendulum whose sensitivity can be varied. As a source of torsion, a piece of wire is used. For the purpose of this paper, the thrust stand was configured to achieve a micro-Newton resolution. [ABSTRACT FROM AUTHOR]

An online approach based on application of search coil for transformer winding fault detection is presented in this paper. Earlier attempts report use of search coil for the detection of transformer interturn fault. This paper extends application of search coil for detection of winding displacement in addition to interturn fault identification. Experimental results based on specially designed 10-kVA transformer are presented to analyze search coil voltages during healthy and faulty conditions. The algorithm detects phase ($U$ , $V$, $W$), side (LV, HV), and precise location of the fault. Discrimination between interturn fault and winding radial displacement is also achieved by search coil voltage analysis. The results are experimentally verified based on impedance analyzer plots. Experimental analysis indicates that the proposed method is independent of load on the transformer, vector group, nature of winding, balanced or unbalanced source voltage, source voltage harmonics, inrush, and overexcitation conditions. [ABSTRACT FROM AUTHOR]

In Australia and many other countries, distribution network service providers (DNSPs) have an obligation to their customers to provide electrical power that is reliable and of high quality. Failure to do so may have significant implications ranging from financial penalties theoretically through to the loss of a license to distribute electricity. In order to ensure the reliability and quality of supply are met, DNSPs engage in monitoring and reporting practice. This paper provides an overview of a large long-running power-quality monitoring project that has involved most of Australia's DNSPs at one time or another. This paper describes the challenges associated with conducting the project as well as some of the important outcomes and lessons learned. A number of novel reporting techniques that have been developed as part of the monitoring project are also presented. A discussion about large-volume data management, and issues related to reporting requirements in future distribution networks is included. [ABSTRACT FROM PUBLISHER]

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]

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]

This paper presents a wide area control (WAC) method to coordinate the local controllers of generators and renewable energy sources (RESs), for robust power oscillation damping. The WAC signals are synthesized by a two-level hierarchical controller, which utilizes wide area measurements from all the installed synchronous generators and RESs for maximizing the performance of their corresponding local controllers. In the resulting WAC scheme, the generators are “aware” of the RES oscillations and vice versa, the RESs are “aware” of the generator oscillations. Further, the WAC signals intended for the RESs are adjusted in order to require only slight modifications on the RES local controllers. This study illustrates that the correct coordination of generators and RESs, through the WAC, improves the damping performance of the entire system even under high penetration of renewables. The performance of the proposed scheme has been tested and validated in the IEEE 9-bus and 39-bus test systems. [ABSTRACT FROM AUTHOR]

This paper proposes a stochastic control strategy, namely the unsynchronized Addictive Increase Multiplicative Decrease (AIMD) algorithm, to manage the power flow of interconnected microgrids (MGs). The proposed control aims at achieving a tradeoff between the individual utility function of each MG while ensuring the stability of the grid. Both centralized and decentralized AIMD approaches are considered and compared. Extensive Monte Carlo simulations are performed on the IEEE 39-bus system, and show that the proposed control strategy is able to provide the sought tradeoff. [ABSTRACT FROM AUTHOR]

In order to support an appropriate level of resource adequacy in the long term and also to achieve a reliable operation in the short term, a new pricing design and mechanism is needed as a key success factor of real-time energy-only market. This paper proposes optimization-based mathematical models to explore operating reserve demand curves (ORDCs) and two price adders in real-time energy-only market, including dispatch correction and extended security-constrained economic dispatch. The Lagrangian multipliers of the dispatch correction problem are used to construct the ORDCs. Then, the derivative of the ORDCs’ social welfare is formulated as real-time online reserve price adders such as the scarcity adder and the price-lift adder. In case studies, we justify the effectiveness of the proposed ORDCs and two price adders by a simple example with two aggregated units and the Electric Reliability Council of Texas data. [ABSTRACT FROM AUTHOR]

The penetration of distributed renewable energy sources in the distribution grid is increasing considerably in the last years. This is one of the main causes that contributed to the growth of technical problems in both transmission and distribution systems. An effective solution to improve system security is to exploit the flexibility that can be provided by distributed energy resources (DER), which are mostly located at the distribution grids. Their location combined with the lack of power flow coordination at the system operators interface creates difficulties in taking advantage of these flexible resources. This paper presents a methodology based on the solution of a set of optimization problems that estimate the flexibility ranges at the distribution and transmission system operators (TSO-DSO) boundary nodes. The estimation is performed while considering the grid technical constraints and a maximum cost that the user is willing to pay. The novelty behind this approach comes from the development of flexibility cost maps, which allow the visualization of the impact of DER flexibility on the operating point at the TSO-DSO interface. The results are compared with a sampling method and suggest that a higher accuracy in the TSO-DSO information exchange process can be achieved through this approach. [ABSTRACT FROM AUTHOR]

Problem of the local damage detection is a crucial task in modern condition monitoring. However, most of the classical methods rely on being tested in laboratories in the isolated test stands. In case of the real world data, there are outer sources of the noise (for instance nearby machines). Such noise can affect shape of the signal and increase the level of difficulty in finding information about the fault. Thus, one can define problem of the fault detection as a finding cyclic impulses in the signal. In this paper, the authors propose a procedure for the local damage detection based on the time-frequency decomposition and distance between distributions. Local damage in bearings/gearbox provides specific response in the vibration signal. It can be further investigated via time-frequency decomposition where one can track energy distribution change in time. Applying measure of distances between distributions to absolute value of short time Fourier transform (STFT) matrix of the vibration signal, one can find deviation of subsequent samples from one used as a referential sample. Furthermore, thresholding of the absolute value of the STFT matrix, based on the log-variance of this matrix with respect to frequency allows for the enhancement of the results. In the extension of the proposed methods, we also use normalization of the spectrogram to omit additional step of the log-variance thresholding. Knowledge, which one needs to set appropriate threshold, can set this step to be difficult in the industrial application and thus, normalization of the spectrogram is proposed. Analyzed real signals were acquired from the belt conveyor driving unit in the mining facility. [ABSTRACT FROM AUTHOR]

Global environmental variations in the past two decades have contributed to a significant deviation of classic ecological patterns, leading to severe electricity outages triggered by extreme weather-driven phenomena. This has highlighted an urgent need for enhancing the resilience and robustness of the interconnected electricity grid against such high impact low probability (HILP) incidents. From the electrical safety point of view, it is essential to increase the operators’ awareness on a better understanding of such hazards and grid vulnerabilities, and enhance their preparedness on how to respond or mitigate the probable outages. This paper proposes a temporary, yet agile, restoration strategy in response to the forecasted HILP events, founded based on efficient utilization of the grid existing infrastructure, and aimed at improving its resilience against such extreme emergencies. The applied concept of reconfiguration is proactively planned to recover the electricity outages in a timely manner. In the meantime, two sets of metrics are proposed to quantify both the grid operational and infrastructure resilience. The presented framework aids the system operator to evaluate the outage recovery plans considering their impacts on system resilience and decide on the final implementation. The proposed approach is applied to the IEEE 118-bus test system facing an HILP event, where results reveal its applicability and efficiency. [ABSTRACT FROM AUTHOR]

This paper proposes an efficient solution approach based on Benders’ decomposition to solve a network-constrained ac unit commitment problem under uncertainty. The wind power production is the only source of uncertainty considered in this paper, which is modeled through a suitable set of scenarios. The proposed model is formulated as a two-stage stochastic programming problem, whose first-stage refers to the day-ahead market, and whose second-stage represents real-time operation. The proposed Benders’ approach allows decomposing the original problem, which is mixed-integer nonlinear and generally intractable, into a mixed-integer linear master problem and a set of nonlinear, but continuous subproblems, one per scenario. In addition, to temporally decompose the proposed ac unit commitment problem, a heuristic technique is used to relax the inter-temporal ramping constraints of the generating units. Numerical results from a case study based on the IEEE one-area reliability test system (RTS) demonstrate the usefulness of the proposed approach. [ABSTRACT FROM AUTHOR]

Recent years have witnessed significant interest in convex relaxations of the power flows, with several papers showing that the second-order cone relaxation is tight for tree networks under various conditions on loads or voltages. This paper shows that ac-feasibility, i.e., to find whether some generator dispatch can satisfy a given demand, is NP-hard for tree networks. [ABSTRACT FROM AUTHOR]

Oscillations threaten the stability of a power system. Timely detecting oscillations can improve operators' situational awareness of system stability and enable remedial reactions. To detect oscillations during their early stages, this paper proposes a cross-coherence method using multiple-channel phasor measurement unit (PMU) data. Oscillations are related to the peaks in coherence spectra and can be detected by visual inspection and setting up a threshold. Using simulation data, it is shown that the proposed coherence method can detect oscillations even under low signal-to-noise ratios. Three algorithms for estimating coherence spectra are implemented and evaluated. Their performances are compared using Monte Carlo methods. Based on the comparison, this paper makes some recommendations for proper use of the algorithms. [ABSTRACT FROM AUTHOR]

This paper proposes a bi-level branch-and-bound ((B&B) method to solve the economic dispatch problem with prohibited zones and network losses. The approach employs binary variables for each prohibited zone and utilizes the B-coefficient for network losses, which can be transformed into a mixed-integer quadratically constrained quadratic programming (MIQCQP), where linear relaxation technique is applied on each bilinear term. Due to the complexity in solving the MIQCQP problem, this paper proposes a bi-level B&B method to achieve global optimum. A spatial B&B method is utilized in the higher level to solve the quadratically constrained quadratic programming (QCQP) problem, whereas a simple B&B method is employed in the lower level to solve a mixed-integer quadratic programming (MIQP) problem. The bi-level B&B algorithm that combines spatial and simple B&B methods is actually a deterministic optimization method and can produce global optimal solutions. Numerical results on 6-unit, 15-unit, and 40-unit test systems show that the bi-level B&B method can solve the MIQCQP problem with superior solution quality and convergence characteristics. [ABSTRACT FROM PUBLISHER]

This paper proposes a generalized approach of the per unit normalization, named complex per unit normalization (cpu), to improve the performance of fast decoupled power flow methods applied to emerging distribution networks. The proposed approach takes into account the changes envisaged and also already faced by distribution systems, such as high penetration of generation sources and more interconnection between feeders, while considering the typical characteristics of distribution systems, as the high R/X ratios. These characteristics impose difficulties on the performance of both backward-forward sweep and decoupled-based power flow methods. The cpu concept is centred on the use of a complex volt-ampere base, which overcomes the numerical problems raised by the high R/X ratios of distribution feeders. As a consequence, decoupled power flow methods can be efficiently applied to distribution system analysis. The performance of the proposed technique and the simplicity of adapting it to existing power flow programs are addressed in the paper. Different distribution network configurations and load conditions have been used to illustrate and evaluate the use of cpu. [ABSTRACT FROM PUBLISHER]

A new wind turbine transformers protection method against high du/dt switching transients taking place during a wind turbine operation is described. High-frequency transients, characterized by a high rate of voltage rise (du/dt) and overvoltage at the wind turbine transformer high-voltage terminals may be a result of operations of the turbine switchgear typically comprising a vacuum circuit breaker. The protection concept described in this paper is a follow up of research activities on a transients suppressing method dedicated for distribution transformers. The principle of operation of the protective device proposed and parameters optimization procedures for windmill transformers are provided in this paper. The performance of the device was verified by means of Alternative Transients Program–Electromagnetic Transients Program simulations. The physical device was built and experimentally verified by full-scale functional tests reflecting a real wind turbine power network. [ABSTRACT FROM AUTHOR]

This paper presents an economic study to find the switches that should participate in a switch upgrade plan, based on the results of reconfiguration. The traditional reconfiguration problem trend considers only one loading condition (mostly maximum demand), in order to find the optimum reconfiguration. However, as the distribution loading condition has hourly and daily variations, the optimum configuration continuously changes. Consequently, considering only one loading condition might lead to inefficiency of the results. In this paper, daily load curves of different types of distribution consumers, during various types of days (weekdays and holidays) and seasons (summer and winter), are used to obtain the best reconfiguration hours during a day. Then, genetic algorithm (GA) is used to obtain the optimum configuration during each time interval. The objective function applied to GA consists of loss and energy not supplied. The switches that contribute to reconfiguration should be remotely controlled in order to have the capability of immediate mode alteration. In order to evaluate the feasibility of automated switch installation, the benefit-to-cost ratio is calculated. The entire procedure is applied to a test distribution system, and the results are discussed in this paper. [ABSTRACT FROM AUTHOR]

Prioritizing equipment maintenance activities has been an important and challenging task in developing an equipment maintenance strategy for electric power utility companies. This paper presents a RankBoost-based data-driven approach for determining the maintenance priority of circuit breakers. Compared with conventional methods, the proposed method can consider both equipment-level condition-monitoring parameters and system-level reliability impacting indices, automatically create the rational weights among the multiple parameters/indices, and handle missing and invalid data. The simulation results based on the data of 33 circuit breakers indicate that the maintenance priority list obtained using the proposed method is closer to reality than the ranking lists obtained using a subjective weighting method or only using system-level reliability indices. [ABSTRACT FROM AUTHOR]

This paper proposes a data-driven affinely adjustable distributionally robust method for unit commitment considering uncertain load and renewable generation forecasting errors. The proposed formulation minimizes expected total operation costs, including the costs of generation, reserve, wind curtailment, and load shedding, while guaranteeing the system security. Without any presumption about the probability distribution of the uncertainties, the proposed method constructs an ambiguity set of distributions using historical data and immunizes the operation strategies against the worst case distribution in the ambiguity set. The more historical data is available, the smaller the ambiguity set is and the less conservative the solution is. The formulation is finally cast into a mixed integer linear programming whose scale remains unchanged as the amount of historical data increases. Numerical results and Monte Carlo simulations on the 118- and 1888-bus systems demonstrate the favorable features of the proposed method. [ABSTRACT FROM AUTHOR]

Voltage–current (V–I) droop control has been proposed for real and reactive power sharing. Compared with the conventional droop control using real power/frequency and reactive power/voltage, it enhances stability since adding a V–I droop is equivalent to providing a resistor. However, for a system with parallel converters with V–I droops, oscillations are observed when small droop coefficients are adopted. In this paper, a multi-input multioutput (MIMO) model of the system is derived in the frequency domain. This model is based on the $dq$ -reference frame and consists of converter control and the power network model, which is represented by an admittance matrix. Linear system analysis is carried out to identify the root causes of oscillations in both grid-connected mode and autonomous mode. Analysis results are validated by simulation results of detailed model-based systems built in Matlab/Simpowersystems. [ABSTRACT FROM AUTHOR]

The rapidly quenched soft magnetic materials have found many practical applications in power electronics, electric engineering, telecommunications, and other industrial sectors. The aim of this paper was to present the results of a research on fabrication technology of the amorphous and nanocrystalline cores intended for: 1) soft magnetic cores for the stators of the high-speed permanent magnet brushless direct current (PMBLDC) motors; 2) nanocrystalline soft magnetic cores for application in high-frequency power conversion; and 3) three-limb amorphous cores for the three-phase distribution transformers. The cores intended for the stator of the high-speed PMBLDC motor were made from the Metglas 2605 SA1 ribbon and then subjected to the performance tests in a model of an electric motor. The research on soft magnetic materials for high-frequency high-power conversion was concentrated on the Finemet rectangular cores with a gap and the composite ones with distributed gap, and the comodified Finemet cores with the induced transverse magnetic anisotropy. The three-limb cores for 400 kVA three-phase distribution transformer were made from the Metglas 2605 SA1 ribbon and subjected to the performance tests in electricity distribution network. It was found that all the amorphous and nanocrystalline cores fabricated under this paper enable considerable reduction in power losses. [ABSTRACT FROM PUBLISHER]

Performance in copper electrowinning is directly linked to the electrode's hanger bar designs and plate assembly methods. The actual physical condition of the plate, hanger bar assembly, and the internal resistance of electrodes are critical factors in this process. Internal electrode resistances affect parallel anode–cathode pair resistances. Therefore, it also alters balanced copper deposits, current efficiency, and cell voltage and power consumption of electrowinning cells. This paper summarizes the design characteristics of commercial stainless steel cathodes and cold-rolled lead–alloy anodes. It includes the evaluation of electrode performances under typical operating conditions using 3-D finite-element method analysis. The proposed evaluation of internal electrode resistance comprises nonlinear effects of electrical conduction, heat generation, and electrode position. The analysis of the design robustness of electrodes considers the most important elements, which help to maintain high current efficiency and electrical performance in the long term; that is to say, mechanical strength, inherent straightness, resistance to dissolution of copper coating on hanger bars, galvanic corrosion of weld joints, and hanger bar resistance to annealing. Results are based on industrial measurements, test work by vendors, and tankhouse operating data for benchmarking. The performance evaluation considers internal electrical resistance, contact shape design, contact loading, average contact resistance, and lifetime current efficiency. The results highlight the relationship between the robustness of electrode design and long term performance. [ABSTRACT FROM PUBLISHER]

This paper discusses a new paradigm of real-time simulation of power systems in which equipment can be interfaced with a real-time digital simulator. In this scheme, one part of a power system can be simulated by using a real-time simulator, while the other part is implemented as a physical system. The only interface of the physical system with the computer-based simulator is through data-acquisition system. The physical system is driven by a voltage-source converter (VSC) that mimics the power system simulated in the real-time simulator. In this paper, the VSC operates in a voltage-control mode to track the point of common coupling voltage signal supplied by the digital simulator. This type of splitting a network in two parts and running a real-time simulation with a physical system in parallel is called a power network in loop here. This opens up the possibility of the study of interconnection of one or several distributed generators to a complex power network. The proposed implementation is verified through simulation studies using PSCAD/EMTDC and through hardware implementation on a TMS320F2812 DSP. [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 considers the effect of the complex permeability of a power transformer core on the frequency response analysis (FRA) test spectrum. Current work in FRA generally neglects the core beyond a few hundred kHz. This research demonstrates that the effective complex permeability is significant at 1 MHz and greater than unity at frequencies exceeding 15 MHz. The paper also shows that for broadband small signal testing, such as FRA, the lowfield conditions induced by the injected signal result in a relative permeability that approaches the initial permeability of the core. This ensures that the relative permeability remains approximately constant over a large range of frequencies and will have a degree of independence with respect to the amplitude of the injection voltage. [ABSTRACT FROM AUTHOR]

A wooden pole is the most popular choice as the physical support structure for an electrical distribution network. A recent increase in the failures of wooden poles that lead to pole fires warrant further investigation into the performance of wooden poles and pole design. This paper examines the leakage current distributions on the radial, heartwood and sapwood section of the wood pole and the effect of the metal insertion in wooden structures using an electrical ladder network model. This paper presents the findings from two wooden pole models: a basic wooden pole and a complete wooden pole with cross-arm and supporting bars attached. The results show that the bulk of the leakage current flows through the internal section under wet weather conditions and the metal insertion along the radial of the wood increase the magnitude of the leakage current. The model takes into consideration the pole dimension, rain parameter, moisture content, air resistance, and preservative effect (chromated copper arsenate) on the wooden pole. [ABSTRACT FROM AUTHOR]

This paper investigates the nonuniformed distribution of leakage current in a wooden pole with the cross arm attached by using the network ladder model and evaluates the effectiveness of leakage current shunting arrangements that could minimize the occurrence of pole fire. The mitigation method that is proposed in this paper diverts excessive leakage current from a fire-prone hotspot along the wooden structure by using a special shunting method. A comparison between the existing shunting methods and the new cost-effective shunting method is presented. The findings in this paper will be beneficial toward the understanding of the current flow in the internal wooden power pole and, thus, help us to find new methods that can effectively mitigate the pole fire. [ABSTRACT FROM AUTHOR]

This paper presents the problem of power penetration of photovoltaic (PV) systems in urban networks. After a qualitative problem description, two different environments for PV systems have been analyzed: rural and urban networks. Concerning the rural network, a single line has been simulated in order to evaluate the relation between the number of PV systems installed along the line and the maximum PV power installable. In the second part of this paper, possible problems due to power penetration have been examined concerning a clustered PV system that will be installed in the city of Torino (Italy) within the ambit of the EU project called POLYCITY. [ABSTRACT FROM AUTHOR]

This paper describes important aspects of partial discharge (PD) diagnostics of distribution power cables. PD parameter were discussed under consideration of attenuation and dispersive effects of cable characteristics. Field experiences with PD diagnosis on paper insulated cables (PILC) and cables with cross linked polyethylen insulation (XLPE) by energizing with Damped AC Voltage demonstrate relevant demands and the effective outcome for asset management decision support. The main difficulty is to evaluate the risc of PD occurrences on the reliability of the cable system. If an sufficient amount of PD diagnostic data for the cable components is available statistical methods can be used for determing threshold levels and relevant condition indexes for the asset management. [ABSTRACT FROM PUBLISHER]

This paper develops a representation of the Northeastern U.S. bulk electric power system, with an emphasis on New York and New England. The representation has two parts: a 36-bus electrical model in PTI-23 format and market data in the form of generator bids and load demands. The market data are distilled from historical data on public web sites. Since the historical data are available on an hourly basis over many years, the representation is quite rich. In addition, this paper includes the mix of generation at each bus in the model so that generation cost (fuel and emissions) and unit commitment constraints can be deduced. The representation is intended to be a test-bed for formulating, simulating and analyzing the combined technical and economic objectives of the changing electric power industry. It is further intended to be a test-bed for comparing methods of simulating electric power systems and electricity markets operating under engineering constraints. It can, for example, be used for power flow, optimal power flow, reliability, market clearing, and other economic studies. The representation as described is intended only for steady-state equilibrium studies and does not account for inter-temporal effects such as unit commitment constraints. It can, however, be extended to account for those effects. [ABSTRACT FROM AUTHOR]

Accurate computation of electromagnetic transients for underground cables and overhead transmission lines requires the frequency domain characterization of two matrix functions: propagation and characteristic admittance. The propagation function constitutes a high order Wideband system with inherent time delays. In this paper a weighted fitting technique is presented and advocated for the identification of the propagation function as a rational transfer function. The paper also contributes to theoretical clarifications on vector fitting and orthonormal vector fitting. The application of orthonormal vector fitting is demonstrated together with weighted vector fitting. Although the presentation is also applicable to transmission lines, the numerical examples are focused on underground cables where the frequency dependency problems are more complex. [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]

This paper presents a gradient-based nonlinear optimization wrapper for an electromagnetic transient simulation program to assist in the design of hardware and control parameters of flexible ac transmission system (FACTS) apparatus. A new second-order sensitivity analysis method is introduced that quantifies the sensitivity of the optimal solution to parameter uncertainties. Using this approach, the sensitivity of the harmonic elimination capability of a pulsewidth-modulated voltage-source converter to variations in switching angles is investigated. This paper also adapts the method of Pareto optimization to the simulation-based design of FACTS apparatus when multiple design objectives are to be satisfied. The developed Pareto optimization tool generates a Pareto frontier plot to visualize the design tradeoffs between the multiple objectives. The effectiveness of the tool is demonstrated through a design example that selects optimal values for the dc-bus capacitor and the control settings of a STATCOM. [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]

The purpose of this paper is to present a framework for assessing information security in power communication systems. The framework consists of dividing the communication system to be analyzed into its subcomponents and linking these to relevant evaluation criteria. In this study, the information security standard ISO 17799 has been used as a point of reference to define such evaluation criteria. The framework involves collecting data to evaluate each individual criterion and aggregating these evaluations using a robust algorithm. To cater for the many uncertainties in evaluating information security, the evaluation of the individual subcomponents is aggregated using a Dempster-Shafer based algorithm for evidential reasoning. This algorithm incorporates the many insecure facts and incomplete data that are inherent in large scale systems. The overall result is a set of indicators which highlight the level of information security within a studied communication system. The paper is concluded with a description of a case study in which the framework was applied to a communication system used for automatic meter reading (AMR). Experiences from this application are described in the paper. [ABSTRACT FROM AUTHOR]

In this paper, the ultrasaturation phenomenon of power transformers during their energization is studied. It is shown that under special conditions, the currents observed after transformer switching on do not contain enough restraining information (e.g., second harmonic), which may lead to protection maloperation. This paper concentrates on a thorough explanation of the problem and possible causes of ultrasaturation. Theoretical investigations are supported and illustrated with simulation studies performed both with MATLAB and Electromagnetic Transients Program-Alternative Transients Program. The outcomes of this research can further be used as hints for substation operation personnel as well as for the development of new protection stabilization criteria, which is not discussed further in this paper. [ABSTRACT FROM AUTHOR]

An underground cable power transmission system is widely used in urban low-voltage power distribution systems. In order to assess the performance of such distribution systems as a low-voltage broadband power-line communication (BPLC) channel, this paper investigates the effects of load impedance, line length, and branches on such systems, with special emphasis on power-line networks found in Tanzania. From the frequency response of the transfer function (ratio of the received and transmitted signals), it is seen that the position of notches and peaks in the magnitude are largely affected (observed in time-domain responses too) by the aforementioned network configuration and parameters. Additionally, channel capacity for such PLC channels for various conditions is investigated. The observations presented in this paper could be helpful as a suitable design of the PLC systems for better data transfer and system performance. [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]

This paper introduces PJM Interconnection's new method to model and predict transformers' service lives. A simplified Perks' equation is used to model the hazard rates, which will be used synonymously with retirement rates in this paper, of transmission transformers. A Bayesian Method is used to model the uncertainty in the three parameters of Perks' equation. This method is different from the traditional Iowa Curve method in that: 1) it gives a continuous family of transformer life distributions as well as the extinction likelihoods, rather than a limited number of distribution patterns and 2) a closed-form distribution can also be deduced with only three parameters, which can assume all the three distribution patterns of Iowa Curves: right, left, and symmetrically modal. The method has been successfully applied to the statistics on hundreds of large electric transformers in PJM. Example problems are provided and solved with this new method. [ABSTRACT FROM AUTHOR]

Controlled islanding refers to the controlled separation of an interconnected power system into electrically isolated regions. The objective of this paper is to develop adaptive controlled islanding as a component of an emergency power system control strategy. There are two primary aspects of controlled islanding: 1) where to island and 2) when to island? Assisted by a decision tree (DT) approach, this paper seeks to address the ‘when to island’ aspect. A decision tree based tool is proposed to recognize conditions existing in the system that warrant controlled islanding. A 29-generator, 179-bus system is employed to demonstrate the tool. Simulation data are used to train DTs, and the online performance of DTs is then evaluated as part of a controlled islanding strategy. [ABSTRACT FROM AUTHOR]

The radial distribution feeder protection strategy is first presented in this paper without consideration for distributed generation (DG). Then, the addition of DG across the feeder (constrained in terms of power and/or energy capacity) is introduced in the model. If islanded operation of these DG sources is allowed on a feeder subjected to a disturbance, DG may reduce the number of interruptions and/or durations for customers residing within their protection zones, thus increasing the reliability of service. To that end, a procedure for finding optimal positions for DG and protection devices is presented for a feeder equipped with capacity-constrained distributed generators, using a custom-tailored genetic algorithm, and the improvement in reliability is demonstrated on a test feeder. Tuning of the genetic algorithm parameters and an adaptive algorithm that eliminates the need for parameter tuning are the subject of a separate paper by the same authors. [ABSTRACT FROM AUTHOR]

This paper presents an active islanding detection method for electronically-interfaced distributed resource units at the distribution voltage level. The proposed method is based on injecting a disturbance signal into the system through either the direct axis (d-axis) or the quadrature axis (q-axis) current controllers of the interface voltage-sourced converter. Signal injection through the d-axis controller modulates the amplitude of the voltage at the point of common coupling (PCC), whereas signal injection through the q-axis controller causes a frequency deviation at PCC, under islanded conditions. Monitoring strategies to detect islanding are also presented for the proposed injection method. The feasibility of the proposed method is evaluated under the UL1741 anti-islanding test configuration. The studies reported in this paper are based on time-domain simulations in the PSCADIEMTDC environment. The studies show that the proposed islanding detection method succeeds in detecting the islanding phenomenon as fast as 33.3 ms for the parameter setting of the test system, and always meets the two-second UL detection requirement. The paper also concludes that the proposed method has the salient feature of offering a potential application in a micro-grid scenario, where fast "islanding detection" and not necessarily the "anti-islanding function" is required. [ABSTRACT FROM AUTHOR]

This paper is the second part of a joint paper aimed at predicting the voltage sag performance of distribution net- works by estimating voltage sag indices. This part explores the characteristics of voltage sags caused by faults in a distribution network considering the effect of the protective devices installed in the network. The work is based on a Monte Carlo procedure implemented in a time-domain simulation tool. Several scenarios with a different coordination between protective devices have been analyzed. As expected, the main conclusions are that the protection system can have a significant influence on voltage sag characteristics and proper coordination between protective devices can reduce voltage sag impact on end-user equipment. [ABSTRACT FROM AUTHOR]

This paper is the first part of a work aimed at predicting the voltage sag performance of distribution networks using digital simulation and an EMTP-like tool. The paper discusses modeling guidelines for representing power distribution components in voltage sag simulations and details the approaches selected in this work. Different models for representing some components can be used to obtain voltage sag characteristics with similar accuracy. Test results are included to illustrate the performance of the developed models and support the selection of different modeling approaches. [ABSTRACT FROM AUTHOR]

Power quality indices have been developed to assess the performance of a single site or an entire system. They can guide utilities to improve their systems and can be used by manufacturers to decide about equipment immunity. This paper is the third part of a joint paper aimed at predicting the voltage sag performance of distribution networks by estimating voltage sag indices. Two types of indices are analyzed in the present paper, they give, respectively, the average number of events and the average interruption duration of each kilovolt ampere served at the low-voltage level over the assessment period. Their values are obtained from a stochastic prediction using a time-domain simulation tool. The methodology used to obtain these indices and the analysis of the influence of the protective devices are the main contributions of this paper. The limitations of the present work are also discussed. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to the fuzzy unit commitment problem using the absolutely stochastic simulated annealing method. In every iteration, a solution is taken with a certain probability. Typically in the simulated annealing minimization method, a higher cost feasible solution is accepted with temperature-dependent probability, but other solutions are accepted deterministically. However, in this paper, all the solutions, both higher and lower cost, are associated with acceptance probabilities, e.g., the minimum membership degree of all the fuzzy variables. Be- sides, the number of bits flipping is decided by the linguistic fuzzy control. Excess units with system-dependent distribution handle constraints efficiently and reduce overlooking the optimal solution. To reduce the economic load dispatch calculations, a sign bit vector is introduced with imprecise calculation of the fuzzy model as well. The proposed method is tested using the reported problem data sets. Simulation results are compared to previous reported results. Numerical results show an improvement in solution cost and time compared to the results obtained from powerful algorithms. [ABSTRACT FROM AUTHOR]

The protective devices and switches play an important role in the reliability of electrical distribution systems by minimizing the impact of interruption. In this paper, a method for identifying the type and location for protection devices and switches on the prerouted distribution system using value-based optimization. is proposed. The proposed method is based on the contingency analysis of various components, e.g., the faults of line sections, switches, protective devices, and the restoration through switching actions such as upstream restoration and downstream restoration. The formulation of the optimization problem in this paper is appropriate for linear integer programming, where each nonlinear term can be translated by only two additional linear constraints. The detailed design of the protection devices and the switches are determined by minimizing the total cost of reliability that comprises apparatus investment, maintenance, and interruption cost. The efficiency and validity of the proposed method are demonstrated in case studies. [ABSTRACT FROM AUTHOR]