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Availability of wind energy which differs across locations primarily determines the appropriate location for installing windfarms. However, the grid location of windfarms must always be considered in an attempt to accurately quantify the benefits which can be achieved from windfarms during their lifetime operation to the supply network. The value of wind power is significantly affected by their penetration and concentration, and is further affected by their location within a network. This is because the location and penetration level of wind generation will result in a significant impact on power-flow distribution across the network. The objective of this paper is to measure the impact of grid location of windfarms on economic and operational parameters of a power system in the lifetime of a windfarm project. This paper first develops an assessment tool to quantify the economic and operational impact of wind power in the grid. This is followed by developing different scenarios in which different penetrations of wind power are installed at different locations in the grid, and it shows how the value of wind power is affected by location and network constraints.

This paper proposes a single-stage three-phase photovoltaic (PV) system that features enhanced maximum power point tracking capability, and an improved energy yield under partial shading conditions. Further, the proposed PV system can effectively double the maximum permissible dc voltage of a grounded conventional single-stage PV system, with no need for insulators, fuses, disconnects, and switchgear of a higher voltage class, with respect to safety/insulation standards or common system integration practices exercised for conventional grounded single-stage PV systems. The proposed PV system is realized through the parallel connection of an auxiliary half-bridge converter to the dc link of a conventional single-stage PV system and, therefore, is also an option for retrofit applications. This paper presents the mathematical model, principles of operation, and the control loops of the proposed single-stage PV system. The performance of the proposed single-stage PV system is demonstrated by time-domain simulation studies conducted on a detailed switched model in the PSCAD/EMTDC software environment.

Positive feedback anti-islanding methods have been widely applied to inverter-based distributed generators recently due to their high cost-performance ratio. The effectiveness of these anti-islanding methods is usually demonstrated by means of steady-state non-detection zones (NDZs) represented in a load parameter space (LPS). However, these NDZs cannot accurately describe the impact of the inverter interface controls on the anti-islanding methods' detection performance, especially in multi-inverter systems. In addition, the intrinsic destabilization characteristic of the positive feedback anti-islanding scheme cannot be exhibited by these NDZs. This paper proposes an improved dynamic NDZ in the LPS to evaluate the islanding detection effectiveness of the positive feedback anti-islanding methods. The modal analysis approach is employed to determine the critical RLC load quality factor which is defined as the small-signal stability limit index of the islanded distributed generation (DG) systems for the dynamic NDZs. The sensitivity analysis of the dynamic NDZs for different DG system parameters is conducted in this paper. The applications of the proposed dynamic NDZs in multi-DG systems are also presented.

The contribution of this paper is the application of subspace system identification techniques, to derive a low-order black-box state-space model of a power system with many controllable devices using global signals. This model is a multiinput, multioutput open system model describing the power oscillatory behavior of the power system. The input signals are the controllable setpoints of the controllable devices, the output signals are the speed of selected generators measured by a wide-area measurement system. This paper describes how to achieve and preprocess the data to use subspace techniques to estimate and validate to finally assign an accurate model. This new approach can be used directly to design a central coordinating controller for all of the relevant controllable devices, with the aim to increase the damping of the modes in the system. Previously presented methods use local measurements or output signals dependent on the actual operational point. The benefit of the presented method is that the used output signals are independent of the system state. This makes it possible to use state-feedback control to combine the controllable devices to coordinately damp the modes. The presented method is applied in the CIGRE Nordic 32-bus system including two HVDC links. The case study demonstrates that accurate low-order state-space models can be estimated and validated by using the described method to accurately model the system's power oscillatory behavior.

International Electrotechnical Commission (IEC) standard 61850 proposes the Ethernet-based communication networks for protection and automation within the power substation. Major manufacturers are currently developing products for the process bus in compliance with IEC 61850 part 9-2. For the successful implementation of the IEC 61850-9-2 process bus, it is important to analyze the performance of time-critical messages for the substation protection and control functions. This paper presents the performance evaluation of the IEC 61850-9-2 process bus for a typical 345 kV/230 kV substation by studying the time-critical sampled value messages delay and loss by using the OPNET simulation tool in the first part of this paper. In the second part, this paper presents a corrective measure to address the issues with the several sampled value messages lost and/or delayed by proposing the sampled value estimation algorithm for any digital substation relaying. Finally, the proposed sampled value estimation algorithm has been examined for various power system scenarios with the help of PSCAD/EMTDC and MATLAB simulation tools.

The high-frequency domain characterization of overhead three-phase cables is a critical issue as far as power line carrier communications is concerned. In many instances a detailed knowledge of the electric and magnetic parameters of the cable is not available. Even if manufacturer cable-data are available, strong proximity effects among cable conductors do inhibit the utilization of closed-form expressions for the determination of the cable constitutive parameters, namely, the entries of the per-unit-length R, L, G , and C matrices. However, the determination of such parameters can always be made experimentally. In this paper, new measurement principles based on the cable excitation by independent propagation modes are presented and discussed. In the case of symmetric cables, the eigenvectors associated to the propagation modes are frequency independent, however, the propagation constants and surge impedances are not. The entries of the frequency-dependent R, L, G , and C matrices are retrieved from open and short-circuit cable measurements involving information on the modal propagation constants and modal surge impedances. For exemplification purposes, experimental results concerning a shielded three-phase cable for low voltage applications are provided. The results in this paper do not apply to buried cables where ground return phenomena would need to be accounted.

This paper shows one way to calculate grounding potentials in high voltage substation fences coupled by soil to a grounding grid in a two-layer soil. This problem is of special concern due to the presence of passers-by near metallic fences, whose potentials usually have not been evaluated, not directly connected to the grounding grid. In this context, the paper presents a general analytical formulation aiming to estimate the possible risk to human beings close to the substation. In order to do that the generated potentials originating from a short-circuit in the electric power system are calculated considering the coupling by soil between the main grounding system and the adjacent electrode (the metallic fence). Finally, the proposed methodology is tested and validated using different grounding topologies.

This paper evaluates the effectiveness of different commercial relay functions in a local passive anti-islanding process for a permanent-magnet synchronous generator (PMSG)-based wind farm which is interfaced with a radial distribution network. The results are obtained through a comprehensive set of real-time simulation studies, conducted on a detailed topological model of a single-machine equivalent of the PMSG-based wind farm and the network, using three different commercial relays. The paper introduces the study set-up and methodology and, additionally, details of the mathematical and simulation models of the PMSG-based wind farm. The models and the methodology presented in this paper can be used, directly or with minor modifications, for many other impact-assessment studies.

This paper is concerned with calculating the optimum rating for two dynamic voltage restorers (DVRs) when used in an interline DVR (IDVR) structure. An IDVR consists of two or more DVRs which have a common dc link and, thus, can exchange active power. This can increase the compensation range of an IDVR compared with separate but otherwise similar DVRs. The basic operation of the DVR and IDVR is briefly explained. The limitations of IDVR operation in terms of active power exchange are explained and, based on that, the expressions governing the steady-state operation of IDVR are derived. The compensation range of an IDVR is compared with that of two separate DVRs. This paper also explores how the limitations in absorbing power from a healthy feeder can narrow the compensation range of an IDVR. After identifying and formulating various limitations in IDVR operation, a design procedure is presented to determine the optimum size (or rating) of the DVRs in an IDVR structure. In the proposed approach, all possible scenarios concerning healthy and faulty feeders are taken into consideration. Examples along with graphs and tables aid in conveying the proposed approach.

This paper presents and analyzes a selection of 21 “myths” identified from the authors' experience as being the most common in power utilities and the most harmful to their cybersecurity posture. For each one, tangible and referenced elements, typically sparse and dispersed, are presented in this single and up-to-date reference to support their rationalization. This paper also provides generic recommendations supporting power utilities on the ongoing and challenging process of dispelling the identified myths.

The number of semiconductor switches in a modular multilevel converter (MMC) for HVDC transmission is typically two orders of magnitudes larger than that in a two or three level voltage-sourced converter (VSC). The large number of devices creates a computational challenge for electromagnetic transient simulation programs, as it can significantly increase the simulation time. The paper presents a method based on partitioning the system's admittance matrix and deriving an efficient time-varying Thevenin's equivalent for the converter part. The proposed method does not make use of approximate interfaced models, and mathematically, is exactly equivalent to modelling the entire network (converter and external system) as one large network. It is shown to drastically reduce the computational time without sacrificing any accuracy. The paper also presents control algorithms and other modelling aspects. The efficacy of the proposed method is demonstrated by simulating a point-to-point VSC-MMC-based HVDC transmission system.

Strict limits of the revised noise ordinance of New York City require power transformers to have ultra-low levels at each of the frequencies of transformer noise at full load and overexcitation. This paper describes the development of the technology that allowed successful design and production of ultra-low-noise power transformers recently delivered to Consolidated Edison of New York City. The paper presents results achieved by this development effort in the areas of accurate calculation of core resonance frequencies, frequency spectrum of core noise, and load noise. It also presents other aspects of the technology development, such as de-coupling of active parts vibrations from the tank, proper design of tank-plate fields and tank bracing, proper transformer mounting techniques, and accurate measurement of low noise levels in the factory. Finally, this paper presents the difference in design of the generations of these transformers produced at different stages of this development effort.

Included angle selection for a V-shape insulator string applied in 750-kV compact transmission line is studied in this paper. The mechanical performance of V-shape insulator string is demonstrated from calculation and experiment. A new solution, which is based on the finite-element method and applied to calculate the deformation of V-string, is presented. This paper discusses the relation between deformation (displacements and force) and load on V-string. Loading experiment for V-string is conducted in order to verify the calculation results. Experimental data of displacements for V-shape composite and porcelain insulator string are obtained. Finally, combined with the calculation and experiment results, the selection of included angle for V-shape insulator string is discussed, and recommendations for the included angle value of V-shape insulator string in 750-kV compact transmission line are made.

This paper provides new ideas for the synchronization between an electric power system and a synchronous generator. If an individual ac generator is to be operated with another ac power system, the synchronization is an essential process for the parallel operation. For small combined heat and power cogeneration, the synchronization is a very frequent event and one of the most important jobs in daily operation. There are several types of traditional devices that support or control the breaker closure within the synchronizing criteria. However, the actual break closing is not controlled exactly on a zero point phase-angle difference. In this paper, we introduce new ideas that will lead two ac systems to a smooth and soft synchronization. With these ideas, a soft synchronizer that provides the perfect phase-angle matching is realized. To verify the effectiveness of this newly proposed soft synchronizer, we had conducted simulation studies using MATLAB as well as experimental tests with an actual synchronous diesel generator.

This paper proposes the use of an intrusion detection system (IDS) tailored to counter the threats to an IEC61850-automated substation based upon simulated attacks on intelligent electronic devices (IEDs). Intrusion detection (ID) is the process of detecting a malicious attacker. It is an effective and mature security mechanism. However, it is not harnessed when securing IEC61850-automated substations. The IDS of this paper is developed by using data collected by launching simulated attacks on IEDs and launching packet sniffing attacks using forged address resolution protocol (ARP) packets. The detection capability of the system is then tested by simulating attacks and through genuine user activity. A new method for evaluating the temporal risk of an intrusion for an electric substation based upon the statistical analysis of known attacks is also proposed.

Single-phase diode-bridge converter-based loads have become a common load type in power distribution systems. It has become very important to consider their harmonic impact on the power quality (PQ) of power distribution systems because they now represent a large percentage of residential loads. One of the challenges in modeling these loads for harmonic analysis is the lack of model parameters. This paper proposes an approach to estimate the model parameters, suitable for use in frequency-domain harmonic analysis, through a measurement-based technique. Both the proposed method and the resulting harmonic model have been verified by simulations and measurements in this paper. In addition, this paper analyzes the sensitivities of the model parameters on the accuracies of predicting harmonic currents generated by these loads. An application of the frequency-domain model is also presented in this paper.

Series capacitor imposes problems to line protection and other online decisions. The directional relaying issues during voltage and current inversions in a series-compensated line are addressed in this paper. A conventional directional relaying algorithm uses fault voltage and current phasors to derive the decisions and, thus, finds its limitation at voltage or current inversion. This paper proposes a fault direction estimation technique for a series-compensated line using phase change in positive-sequence current and magnitude change in the positive-sequence voltage at fault. The technique is evaluated by using data simulated with EMTDC/PSCAD for a series-compensated line, and the dynamic performance of the algorithm is also studied.

This paper presents a novel algorithm to recognize magnetizing inrush condition in power transformers by analyzing average differential power signal. The algorithm is independent of the value of transformer parameters and consumed power and relies only on the waveshape properties of the average power signal. These distinctive properties are obtained from the power signal by determining its instantaneous frequency. Extensive simulation studies presented in this paper demonstrate the merits of the proposed technique in discriminating between fault and inrush cases accurately in less than a quarter cycle. The accuracy and speed of the method is unaffected by changing parameters of the transformer or for different operating conditions of the power system, since it is based on a fundamental difference between iron-core saturation and other operating conditions. Since the employed signatures are extracted from the low-frequency spectrum of the power signal, the algorithm is robust against high-frequency noise.

This paper presents theoretical, simulation, and experimental investigations of input current interharmonics in modern variable-speed drives based on voltage source inverters and diode input rectifiers that are caused by motor current imbalance. It investigates how a disturbance in the inverter dc side current created by unbalanced motor currents propagates from the inverter to the rectifier stage and appears as variable frequency interharmonic distortion in the rectifier input currents. Particular emphasis is given to theoretical analysis of the frequency transformations created by the inverter and rectifier stages and the magnification of the disturbance current caused by parallel resonance in the drive dc bus circuit. The theoretical results are confirmed by simulation and experimental results. They demonstrate that motor current imbalance can be responsible for high non-characteristic inter-harmonic distortion in the drive input currents. A calculation example outlines a procedure for estimation of the drive input current interharmonic distortion based on measurements of the motor currents. The paper should be helpful for people investigating the origin of problems caused by variable frequency interharmonic currents.

This paper presents the findings of an investigation concerning a calculation method for current-carrying capability (ampacity) of cables located in a shallow trough. The investigations proceeded in two parallel directions. On the one hand, an extensive search of published and unpublished records dealing with the subject was performed. The second path of investigation involved studies applying finite element analysis. Sensitivity analysis was also performed. In both cases, the recommendation is to use the same approach for determining the current rating of cables in a trough. They both use the cable rating in “free airv as the basis and add an extra thermal resistance to take into account the effect of the trough. Based on the investigation of the previous work and the finite element analysis, two new equations were developed for the external thermal resistance. The proper choice would depend on the field or laboratory tests that would confirm our findings or lead to the modifications of the rating formulae. In the absence of any additional information, it is recommended that the calculations be performed using one of three methods listed below. The methods are listed from the most to the least conservative. 1) method given by a new equation based on the finite element analysis; 2) method given in the IEC standard 60287; 3) method given by a new analytical equation presented in this paper. The comparison of the calculated results with the available test data shows that the method 3) above, the least conservative one, gives a good agreement with the measured values.

Probabilistic analyses of a wide-area measurement system (WAMS) would require equivalent reliability models for its components which include phasor measurement units (PMUs). In this paper, the reliability modeling of PMU is proposed and the proposed model is extended to consider options for the PMU hardware. The Markov process is employed to analyze the proposed model and to present an equivalent two-state model of PMUs. Reliability parameters of PMU are estimated with major difficulties associated with limited and uncertain data. In this paper, uncertainties are taken into account to achieve more realistic estimates of PMU characteristics. Fuzzy sets along with reliability analyses and fuzzy importance measures (FIMs) are utilized as a means of measuring the significance of PMU components on its availability. Numerical analyses are conducted and results are discussed.

This paper presents an analytical method for approximating the eddy current and hysteresis losses in a system of multiple sheathed cables placed in any configuration inside a steel pipe. The method is based on the theory of images, which this paper expands to apply to pipes having high magnetic permeability and high electric conductivity at the same time. The method of images, in combination with approximating the cable conductors and sheaths as multiple physical filaments, is used to compute the final current distributions in the cables and pipe and, thus, the associated losses. The accuracy of the proposed method is assessed against numerical solutions obtained using the Maxwell finite-element program by Ansoft.

The reliability and power-quality (PQ) expectations of the power distribution system are steadily increasing. Performance-based rates and/or incentives are being put into place in order to ensure that reliability standards are being met. The distribution system planners, designers, and operators are given the task of developing system upgrades that will successfully meet these new performance goals. This is not always an easy or straightforward task, particularly in cases where a system upgrade can impact the various reliability and PQ indices in different directions. This paper develops an incremental cost-based approach to providing linkage between the sustained and momentary interruption indices. This new approach is readily implementable, and also readily adjusted to meet local performance goals. This paper also presents a case study involving a distribution feeder, and assesses the use of the method in evaluating fuse saving/fuse melting and sectionalizing switch automation upgrades on the line.

Transformer inrush currents can lead to a reduction of transformer lifetime and inadvertent tripping of relays. This paper investigates a novel approach for minimizing the inrush current with a potential application in circuit-breaker (CB) control strategies without independent-pole operation and residual flux estimation. For the analyzed transformer, the worst-case inrush current is halved compared to the rapid-closing switching strategy. Measurements of inrush current transients are performed on an unloaded 11-kV distribution transformer varying disconnection and connection instants systematically. This reveals a characteristic pattern in the extremal value of the inrush current as a function of switching times. The pattern is reproduced with simulations and extended to alternative winding configurations. A condition for minimum inrush currents, consistent for all phases and winding configurations, is identified and explained physically. The impact of the current chopping capability of the CB is important and is discussed in this paper.

The power swing caused by various disturbances will affect distance relay behavior and may result in relay misoperation. This paper provides a fast detection scheme for symmetrical fault during power swing for distance relay, which is based on extracting the high-frequency component energy of forward and backward traveling waves induced by faults. The multiresolution analysis based on wavelet transform has the ability to decompose the analyzed signals into different frequency bands. The selection of mother wavelet and the number of levels of wavelet transform are carefully studied. The fault can be identified by feature extracting from the d1 component of Daubechies-8 (Db8) wavelet transform. The proposed approach is verified by using the IEEE reference model implemented by using the Alternate Transients Program and the test results have been presented in this paper. This proposed method can be used for distance relay operation blocking or monitoring.

This paper discusses various aspects of unified power flow controller (UPFC) control modes and settings and evaluates their impacts on the power system reliability. UPFC is the most versatile flexible ac transmission system device ever applied to improve the power system operation and delivery. It can control various power system parameters, such as bus voltages and line flows. The impact of UPFC control modes and settings on the power system reliability has not been addressed sufficiently yet. A power injection model is used to represent UPFC and a comprehensive method is proposed to select the optimal UPFC control mode and settings. The proposed method applies the results of a contingency screening study to estimate the remedial action cost (RAC) associated with control modes and settings and finds the optimal control for improving the system reliability by solving a mixed-integer nonlinear optimization problem. The proposed method is applied to a test system in this paper and the UPFC performance is analyzed in detail.

Retrofitting condition monitoring systems to aging plant can be problematic, since the particular signature of normal behavior will vary from unit to unit. This paper describes a technique for anomaly detection within the context of the conditions experienced by an in-service transformer, such as loading, seasonal weather, and network configuration. The aim is to model the aged but normal behavior for a given transformer, while reducing the potential for anomalies to be erroneously detected. The paper describes how this technique has been applied to two transmission transformers in the U.K. A case study of 12 months of data is given, with detailed analysis of anomalies detected during that time.

The modular multilevel converter (MMC) is a newly introduced switch-mode converter topology with the potential for high-voltage direct current (HVDC) transmission applications. This paper focuses on the dynamic performance of an MMC-based, back-to-back HVDC system. A phase-disposition (PD) sinusoidal pulsewidth modulation (SPWM) strategy, including a voltage balancing method, for the operation of an MMC is presented in this paper. Based on the proposed PD-SPWM switching strategy, a mathematical model for the MMC-HVDC system, under both balanced and unbalanced grid operation modes, is developed. Dynamic performance of the MMC-based back-to-back HVDC converter system, based on time-domain simulation studies in the PSCAD/EMTDC environment, is then evaluated. The reported time-domain simulation results show that based on the adopted PD-SPWM switching strategy, the MMC-HVDC station can respond satisfactorily to the system dynamics and control commands under balanced and unbalanced conditions while maintaining voltage balance of the dc capacitors.

An algorithm based on the concept of combining Kalman filter and Least Error Square (LES) techniques is proposed in this paper. The algorithm is intended to estimate signal attributes like amplitude, frequency and phase angle in the online mode. This technique can be used in protection relays, digital AVRs, DGs, DSTATCOMs, FACTS and other power electronics applications. The Kalman filter is modified to operate on a fictitious input signal and provides precise estimation results insensitive to noise and other disturbances. At the same time, the LES system has been arranged to operate in critical transient cases to compensate the delay and inaccuracy identified because of the response of the standard Kalman filter. Practical considerations such as the effect of noise, higher order harmonics, and computational issues of the algorithm are considered and tested in the paper. Several computer simulations and a laboratory test are presented to highlight the usefulness of the proposed method. Simulation results show that the proposed technique can simultaneously estimate the signal attributes, even if it is highly distorted due to the presence of non-linear loads and noise.

This paper presents a flexible ac transmission system device under development for the management of power flow under steady-state and dynamic conditions, the bundle-controlled line-impedance modulator (LIM). In its simplest form, an LIM is made of switching modules connected in series with transmission-line segments whose bundles have subconductors insulated from each other. A module contains one switch in series with each subconductor of a bundle and the modules are anchored to dead-end towers in place of yoke plates. Together, with the measurement of sensors and controls, these modules can be used to change series impedances of transmission lines and implement functions, such as deicing, power-flow control, stability control, and line monitoring. In order to illustrate the LIM capabilities, two load-flow studies and one stability study are presented in this paper. Finally, the LIM performance is qualitatively compared to the thyristor-controlled series compensator technology.

This paper conducts an analysis of subsynchronous resonance (SSR) phenomena in doubly-fed induction generator (DFIG)-based wind farms interconnected with series compensated networks. A dynamic model is developed to analyze the induction generator effect (IGE) and torsional interaction (TI) in such systems. A test system derived from the IEEE first benchmark model is considered for the analysis. The effect of two factors namely: 1) series compensation level and 2) wind speed on the IGE and TI are studied. In addition, impact of the inner current converter controller parameters and turbine parameters on SSR is also addressed. Small signal (eigenvalue) analysis is conducted to assess the damping of network and torsional modes followed by dynamic (time domain) simulations. The major contribution of this paper is the analytical investigation on SSR phenomena presented in DFIG-based wind farms interconnected with series compensated networks. The paper clearly demonstrates that IGE instead of TI is the major reason for SSR in such systems.

Acoustic emission monitoring is often used in the diagnosis of electrical and mechanical incipient faults in high-voltage apparatus. Partial discharges are a source of failure in power transformers, and the differentiation from other sources of acoustic emissions is of the utmost importance. This paper reports the development of a new sensor concept-mandrel-based fiber-optic sensor-for the detection of incipient faults in oil-filled power transformers, taking direct measurements inside a transformer. These sensors can be placed in the inner surface of the transformer tank wall, not affecting the insulation integrity of the structure, and improving fault detection and location. The applicability of these acoustic sensors in air, water, and oil is investigated and the paper presents the promising results obtained, which will enable the industrial development of practical solutions.

This paper presents a three-phase power-flow algorithm, in the sequence-component frame, for the microgrid (μgrid) and active distribution system (ADS) applications. The developed algorithm accommodates single-phase laterals, unbalanced loads and lines, and three/four-wire distribution lines. This paper also presents steady-state sequence-component frame models of distributed energy resource (DER) units for the developed power-flow approach under balanced/unbalanced conditions. The DER models represent the synchronous-generator based and the electronically-coupled DER units. Both constant power (PQ) and regulated-voltage (PV) modes of operation of DER units are considered. The application of the developed power-flow method for two study systems is presented. The study results are validated based on comparison with the detailed solution of the system differential equations in time domain, using the PSCAD/EMTDC software tool.

The transfer function (TF) these days is a well-known method to detect different types of mechanical damage in power transformers. The most important mechanical faults mentioned by the authors and researchers, which are most likely to be detected using the TF and occur frequently in transformers, are disc-space variation, radial deformation, and axial displacement. These faults are investigated in this paper using three different similar-size test objects. Since the TF method is a comparative method and the measured results should be compared with the reference results, some mathematical methods are studied to compare different TFs. A complete fault detection, which means determining the type, location, and level of the faults by using TF analyses is the main aim of this paper.

This paper introduces the concepts of 1) dynamic inductance and 2) effective inductance based on the magnetic energy, and provides a new insight on the transformer core behavior during steady-state and transient regimes. Based on a newly developed core modeling approach, which is described in references one to four, this paper also: 1) addresses the intrinsic limitations of the single-valued magnetization characteristic-based core model; 2) uses the dynamic inductance as the key parameter to fully and accurately represent the core behavior; and 3) explains the reason for discrepancies among the reported core behavior based on the simulated and experimental results. In contrast to the widely accepted belief that a single-valued magnetization characteristic-based model can accurately represent the transformer core behavior, this paper demonstrates the necessity of a dynamic and physically correct hysteresis core representation. This paper also compares various core representations in terms of their accuracies for the ferroresonance simulation. This paper shows that: 1) the single-valued core model not only cannot accurately represent the core behavior under asymmetric excitation conditions, it may provide erroneous results even under symmetric excitation conditions and 2) the accuracy of specific transients highly depends on the precise representation of the hysteresis minor loops and the core dynamic inductance.

Reliability evaluation of multiterminal HVDC systems has received very little attention in the past. This paper presents reliability modeling and analysis of an HVDC transmission system incorporating a voltage-sourced converter (VSC) tapping station. The use of VSC tapping stations enables the supply of power along the route to areas with comparatively little consumption. In this paper, a comprehensive detailed reliability model is developed and then converted to a manageable and computationally efficient model. Using this equivalent reliability model, various reliability indices are calculated at the load point of the system and the impacts of the VSC tapping station on these indices are illustrated. Sensitivity analyses are conducted to investigate the impacts of the load level and the location of the tapping station on the reliability indices. The conducted studies are numerically applied on a typical HVDC system and thorough discussions are presented.

The first five-phase induction motor drive system was proposed in the late 1970s for adjustable speed drive applications. Since then, a considerable research effort has been in place to develop commercially feasible multiphase drive systems. Since the three-phase supply is available from the grid, there is a need to develop a static phase transformation system to obtain a multiphase supply from the available three-phase supply. Thus, this paper proposes a novel transformer connection scheme to convert the three-phase grid supply to a five-phase fixed voltage and fixed frequency supply. The proposed transformer connection outputs five phases and, thus, can be used in applications requiring a five-phase supply. Currently, the five-phase motor drive is a commercially viable solution. The five-phase transmission system can be investigated further as an efficient solution for bulk power transfer. The connection scheme is elaborated by using the simulation and experimental approach to prove the viability of the implementation. The geometry of the fabricated transformer is elaborated in this paper.

Mass production of total electric vehicles capable of traveling longer distances results in a need for electric service stations that can satisfy the requirements for a significant amount of power provided in a time duration similar to that of filling a car with oil-based fuel. These vehicles would pull into the station, and need a large amount of power delivered over a short period of time for the rapid recharging of batteries which serve as their “fuel tank.” This paper investigates the effect of fast-charging electric vehicles on an existing utility company distribution system at several specified sites. This paper will cover power-flow, short-circuit, and protection studies at these sites using utility-grade software packages. In addition, the analysis of simulations of a recharging station where up to eight rapidly rechargeable vehicles come online at once will be presented.

An analytical method of calculating the steady-state and transient temperature rises (T.R.s) for round cable bundles is proposed in this paper. The main feature of the proposed approach, which distinguishes it from the models published earlier, is that the cables in a bundle can be loaded with different currents and the heat-source density does not have to be uniform in all conductors. This paper also presents an experimental verification of the proposed model. It is also shown that the proposed method gives almost identical results with the IEC approach for a steady-state load and a uniform current density in all cables.

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

This paper discusses the need to simultaneously monitor voltage unbalance and harmonic distortions in addition to root-mean-square voltage values. An alternative way to obtain the parameters related to voltage unbalance at fundamental frequency as well as voltage harmonic distortions is here proposed, which is based on the representation of instantaneous values at the dq axes and at the instantaneous Euclidean norm. A new power-quality (PQ) index is then proposed to combine the effects of voltage unbalance and harmonic distortions. This new index is easily implemented into existing electronic power meters. This PQ index is determined from the analysis of temperature rise in induction motor windings, which were tested for long periods of time. This paper also shows that these voltage disturbances, which are harmful to the lifetime expectancy of motors, can be measured by alternative ways in relation to conventional methods. Although this paper deals with induction motors only, the results show the relevance for further studies on other pieces of equipment.

This paper proposes an analytical algorithm for the computation of the magnetization and loss curves for a transformer from standard no-load test report data. This is the input to standard transformer models for power system simulation. In the case of delta-coupled windings, the conversion from test-report root-mean-square line quantities to peak phase values requires processing of the triplen harmonics in the current. This is handled analytically in the paper with utilization of the concept of incremental inertance and conductance. The analysis shows that only the third harmonic needs to be treated to reach sufficient accuracy within the measurement errors. The test case with a 290-MVA generator stepup transformer shows an increase in the calculated current of above 10% at rated voltage with proper triplen harmonic handling. This difference will increase considerably with excitation voltage.

This paper deals with the detection of incipient faults in underground distribution systems using online voltage and current measurements. The approach presented in this paper is based on the numerical modeling of incipient fault patterns established from the oscillographic data. Specific energy features in the wavelet domain were extracted and used in the modeling task using the self-organizing map technology. The modified modeling errors are used as a chronologically ordered sequence in the change detection problem specifically formulated for this application. Three modified change detection algorithms, namely, cumulative sum, exponentially weighted moving averages, and generalized likelihood ratio were investigated and assessed as to the performance using field-recorded data from an underground cable lateral. The detection results demonstrate the detectability of these faults and application of the approach for real fault scenarios.

This paper aims at evaluating the methods of multiclass support vector machines (SVMs) for effective use in distance relay coordination. Also, it describes a strategy of supportive systems to aid the conventional protection philosophy in combating situations where protection systems have maloperated and/or information is missing and provide selective and secure coordinations. SVMs have considerable potential as zone classifiers of distance relay coordination. This typically requires a multiclass SVM classifier to effectively analyze/build the underlying concept between reach of different zones and the apparent impedance trajectory during fault. Several methods have been proposed for multiclass classification where typically several binary SVM classifiers are combined together. Some authors have extended binary SVM classification to one-step single optimization operation considering all classes at once. In this paper, one-step multiclass classification, one-against-all, and one-against-one multiclass methods are compared for their performance with respect to accuracy, number of iterations, number of support vectors, training, and testing time. The performance analysis of these three methods is presented on three data sets belonging to training and testing patterns of three supportive systems for a region and part of a network, which is an equivalent 526-bus system of the practical Indian Western grid.

This paper investigates the behavior of power transformers under the occurrence of permanent or intermittent winding insulation faults. For the study of these phenomena, a simple and efficient permeance-based electromagnetic transformer model is proposed, which is based on the simultaneous consideration of magnetic and electric equivalent circuits. To incorporate the internal faults in this model, a suitable equivalent circuit of the faulty winding is described. With the aid of this transformer model, the onload exciting current Park's Vector Approach will be applied for diagnosing the occurrence of permanent and intermittent winding faults. Experimental and simulation tests results are presented in this paper, which demonstrate not only the adequacy of the digital transformer model for winding fault studies, but also the effectiveness of the proposed technique for detecting winding interturn insulation faults in operating three-phase transformers.

The design trades made in choosing an appropriate protocol for the conveyance of meter data are discussed. The paper identifies “context” as the mechanism by which communication efficiencies are sometimes obtained. This paper concludes that while generalized protocols are commonly used to communicate between utility back-office applications, specialized protocols can yield an optimum solution when reaching endpoints.

Optimal deployment, with respect to locations, capacity sizes, and types of distributed energy resources (DERs), which are the main components in a microgrid system, are chosen for study in this paper. For the selection of optimal locations of DERs, the loss sensitivity index of each bus is taken into account. Whereas optimal size and its separation among microturbines, diesel generators and combustion turbines at each bus location are performed on the basis of the maximum benefit-to-cost ratio of the microgrid owner, obtained by using the particle swarm optimization technique and with respect to their reliable catering and quality of power as well as heat (i.e., combined-heat-and-power (CHP) operation) for customers. This paper conducts four separate case studies-two on 6-bus systems (radial and meshed) and resting on 14-bus systems (the IEEE system and radial system)-to show how much these systems are economically feasible for investment planning when cost and CHP benefits of various types of DERs are taken into account. Load profiles, tariffs, as well as the constructional cost of the microgrid itself are addressed in the six-bus meshed network and its central DER location in a district-heating paradigm is also done separately.

This paper analyzes the feasibility and convenience of applying the efficient discrete Fourier transform (DFT) techniques for the computation of reference currents in active power filters. Existing methods designed for this purpose rely on a high-pass filter in order to obtain the harmonic components of the load current to be filtered. Among these methods, the stationary reference frame (SRF) method reveals itself as the most accurate one because of its inherent immunity to distorted voltage conditions. In this paper, two different implementations of the running DFT, including their recursive and nonrecursive versions, are compared to the SRF approach in terms of steady-state performance, adequacy of transient response, and computational effort. In addition to simulation results, an experimental setup is designed to prove the advantages of resorting to the DFT. Conceptual similarities between both schemes are also stressed in this paper.

Distance protection of the electrical power system is analyzed in the paper. Electrical power transmission lines are divided into sections equipped with protective relaying system. Numerical protection relays use specialized digital signal processors as the computational hardware, together with the associated software tools. The input analogue signals are converted into a digital representation and processed according to the appropriate mathematical algorithms. The distance protection is based on local and remote relays. Hazard is the event: remote circuit breaker tripping provided the local circuit breaker can be opened. Coordination of operation of protection relays in time domain is an important and difficult problem. Incorrect values of time delays of protective relays can cause the hazard. In the paper, the time settings are performed using probabilistic fault trees with time dependencies (PFTTD). PFTTD is built for the above mentioned hazard. PFTTD are used in selection of time delays of primary (local) and backup (remote) protections. Results of computations of hazard probabilities as a function of time delay are given.

This paper describes a new algorithm to calculate the per phase impedance between the measurement and fault points on a transmission line, featuring robustness to the uncertainties in load current and fault path resistance. The algorithm, which is ideal for distance relaying, is derived based on a justifiable assumption of the fault path being purely resistive, implying that the unmeasured fault point voltage and fault path current are in phase with each other. This paper illustrates the characteristics of the proposed algorithm and evaluates its performance by using PSCAD/EMTDC simulation.