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HVDC cable systems are growing in number. This is a result of globally defined targets leading to an increase of investments in renewables. The HVDC cable systems enable us to integrate these new energy sources in a manner that reduces losses and stabilizes operations. In this paper, the focus is on extruded HVDC cables. Starting from a general description of the forces that drive us toward more cables, this paper quantifies the push for higher voltages. The extruded cable system on a product level is described followed by design aspects. Particularly, the effect of thermal runaway is highlighted. The accessories, joints, and terminations are described. The advantages of the concept nonlinear field grading are described. This paper ends with some words on realized commercial projects and future trends.

This paper presents original records of distributed-generation unintentional islanding events in three categories. The islands were formed by naturally occurred faults without the transfer trip initiated to generation facilities. Hydraulic, natural gas, and wind generators were involved in the events. The records exemplify important issues in DG anti-islanding planning, such as coordination with underfrequency (or undervoltage) load shedding, reactive power compensation, generation-to-load ratio, reclosing coordination, etc. The events reported in this paper can serve as first-hand references in applying IEEE Standard 1547 to distributed generation anti-islanding planning and operation.

This paper presents a physically consistent dual model applicable to single-phase two-winding transformers for the calculation of low-frequency transients. First, the topology of a dual electrical equivalent circuit is obtained from the direct application of the principle of duality. Then, the model parameters are computed considering the variations of the transformer electromagnetic behavior under various operating conditions. Current modeling techniques use different topological models to represent diverse transient situations. The reversible model proposed in this paper unifies the terminal and topological equivalent circuits. The model remains invariable for all low-frequency transients including deep saturation conditions driven from any of the two windings. The proposed model is tested with a single-phase transformer for the calculation of magnetizing inrush currents, series ferroresonance, and geomagnetic-induced currents (GIC). The electromagnetic transient response of the model is compared to the π model and to laboratory measurements for validation.

The mechanism of vertical-arrayed double-bundle transmission-line conglutination is studied in this paper through experiments on a laboratory-based physical model with a 230-m span. Based on the equivalence principle, the conglutination problem in real-world transmission lines has been reproduced in high-voltage and heavy-current experiments where the test circuit is compensated by a series capacitor, so that the output current is continuously adjustable by the voltage regulator and power current transformer. This paper presents, in detail, the experiments carried out, and demonstrated the threshold factors associated with the conglutination phenomenon. The investigation revealed that the number one factor contributing to transmission-line conglutination is the electromagnetic force, which, in turn, is affected by the space between the lines; initial sag and ambient temperature also play important roles. The research results with a thorough understanding of the mechanism of transmission-line conglutination can help provide an understanding of the mechanisms and will enable conduction of numerical analysis of the phenomenon.

During the switching of disconnectors in gas-insulated switchgear (GIS), repeated strikes occur in the contact gap and lead to very fast transient overvoltage (VFTO). Severe VFTO may bring damage to transformers and other equipment. The switching speed of the disconnector is one of the important factors which influences VFTO. There are still different opinions on this factor. Very little quantitative study was done before this paper. In this paper, the whole repeated strike process associated with the switching operation of the disconnector was simulated and analyzed. The polarity and the probability characteristics of breakdown voltage were analyzed. The impacts of the switching speed of the disconnector on VFTO were studied by statistical methods. Comparisons were made between simulated and measured results. The simulation result shows that within a certain range of speed, disconnectors with a lower switching speed generate lower trapped charge voltage after opening operation and lower VFTO magnitude during the opening and closing operations.

This paper presents a three-phase transformerless structure of modular multilevel converters based on cascaded pulsewidth-modulated chopper cells in medium-voltage D-STATCOM application. It is suggested for installation on unbalanced medium-voltage power-supply systems to achieve higher performance in improving power quality. This paper proposes a new control strategy based on power-flow analysis with a focus on dc capacitor voltage control that is insulated from the source voltage fault. This control strategy enables the D-STATCOM system to compensate unbalanced nonlinear load even under asymmetrical grid fault conditions and it has no limitations on the cascaded number. Experimental results obtained from a 60-V 3-kVA downscaled prototype verify that this D-STATCOM system performs satisfactory, not only compensating for unbalanced nonlinear load but also keeping the capacitor voltages maintained at the given value even in unbalanced power systems.

A fault protection and location method for a dc bus microgrid system is presented in this paper. Unlike traditional ac systems, dc bus systems cannot survive or sustain high-magnitude fault currents. And if a fault causes the dc bus to de-energize completely, it makes locating faults very difficult. The main goal of the proposed scheme is to detect and isolate faults in the dc bus without de-energizing the entire system and identifying the fault location. In order to achieve this, a ring-type bus was used in this paper. The bus was segmented into overlapping nodes and links with circuit breakers (CBs) to isolate the segment in the event of a fault. Backup protection is implemented for circuit breaker failures to improve system reliability. A noniterative fault-location technique using a probe power is also presented in this paper. This probe power can also be used for a pilot test before main CB reclosing to avoid system issues that can be expected when the reclosing fails due to a permanent fault. The proposed algorithm can be implemented and executed by an intelligent electrical device for individual node. The proposed concepts have been verified with computer simulations and hardware experiments.

For phase-controlled vacuum breakers, the acting time of the actuator should be precise. The variation of capacitor voltage, capacitance, and environmental temperature impact the dispersion of closing time seriously. A new technology has been put forward in this paper. It is the speed control of the vacuum breaker. This technology can be used for phase-controlled operation of vacuum breakers. By using this technology, the deviation of displacement can be corrected in real time. So the permanent-magnetic actuator (PMA) can move along with the given displacement curve. Also, the closing time is stable when the external factors, such as capacitor voltage, capacitance, and environment temperature change. The closed-loop system has been established in this paper. The proportion-differentiation (PD) algorithm and fuzzy algorithm are used in the system. The PD algorithm adjusts the coil current to ensure that different actuators have the same excitation time. And the fuzzy algorithm is used to adjust actuator displacement. With the use of the algorithm, the closing time of the breaker is stable, and mechanical properties are optimal. Based on the aforementioned theory, many experiments have been performed when external factors change, such as environment temperature, capacitance, and so on. The results prove that the displacement deviation can be corrected using this method and the closing time can be stabilized within ±0.5 ms. Therefore, not only can the accuracy of phase-controlled operation can be ensured, but the lifespan of the circuit breaker can also be prolonged.

This paper assesses the impact of conventional and renewable distributed generation (DG) on the reliability of future distribution systems, even when the connection may not be simply radial. The variability of the power output of renewable DGs, such as wind and solar is included. The stochastic nature of the renewable resources and their influence on the reliability of the system are modeled and studied by computing the adequacy transition rate. An integrated Markov model that incorporates the DG adequacy transition rate, DG mechanical failure, and starting and switching probability is proposed and utilized to give accurate results for the DG reliability assessment. The main focus in this paper is conventional generation, solar, and wind DG units. The technique used appears to be applicable to any renewable energy source.

Calculating electric loss and planning a strategic plan in loss reduction is a main activity in the asset management of an electric distribution network. In usual methods, offloss calculation load flow as well as placed meters in different parts of the network are used. However, electric loss in distribution network is estimated rather than calculated due to reasons, such as the absence of network databases or load meters and computation burden in large-scale distribution networks. This paper proposes a new heuristic method for loss estimation of the low-voltage sector of a large-scale distribution network faced by a scarcity of network data. This method uses load characteristics similarity for feeder clustering. Extracting a loss model for each cluster subject to a small fraction of network data is the main step followed in this paper. Finally, the extracted loss model would be used as an instrument to estimate the copper loss of the considered network. Moreover, a computer program is developed in order to evaluate the accuracy of the method. The proposed method is employed to estimate copper losses of Gilan distribution network in Iran.

This paper analyzes series impedances of screenless cables enclosed by a common conducting pipe. Established analytical formulas for pipe-type cables parameters are analyzed by taking finite pipe thickness and proximity effect into account. Analytical low-frequency approximations are developed and analyzed. The analysis shows that a classical formulation by mixing infinite and finite pipe thickness can result in incorrect inductance and even negative self-resistance at low frequency. This paper analyzes corrections to take a finite pipe thickness into account. Finite-element simulations reveal that the core-to-core proximity effect is substantial for the analyzed cable design with much lower high-frequency inductance than that obtained from analytical formulas. This paper also analyzes given proximity-effect formulations and proposes corrections based on analytical low-frequency approximations. The proposed proximity effect corrections improve resistance and inductance in common and differential mode.

The proper and reliable operation of circuit breakers (CBs) directly affects the reliability and continuity of electricity services in a power systems. Condition-based maintenance (CBM) is the best economic CB maintenance strategy through its online monitoring (OLM) possibilities. Since there is a large number of CBs in a power system, to equip all CBs with OLM systems is not economically justifiable however. This paper, as the second part of a two-part paper, presents an effective optimization framework to find the optimal number of CBs to be monitored online as the kernel of CBM process. To prove its feasibility, the proposed approach is applied to the IEEE Roy Billinton Test System, which includes 32 CBs. The impacts of interest rate and load interruption cost variations as well as nonoptimum selection of CBs for monitoring on the results are also discussed in this paper. The results of numerical analyses of the case study presented in this paper demonstrate how the proposed method can be employed for maintenance management of power system CBs.

Statistical distributions of switching overvoltages have been used for decades for the determination of insulation levels of extremely high voltage (EHV) systems. Existing statistical distributions obtained in the 1970s are for overhead lines, and statistical distributions of switching overvoltages of EHV cables are not available to date. This paper derives the statistical distribution of energization overvoltages of EHV cables. Through the comparison of the statistical distributions of EHV cables and overhead lines, it has been found that line energization overvoltages on the cables are lower than those on the overhead lines with respect to maximum, 2%, and mean values. As the minimum value is almost at the same level, standard deviations are smaller for the cables. The obtained statistical distributions in this paper are of a great importance in considering insulation levels of cable systems.

The increase of harmonic current circulation in electric system affects the shunt capacitor banks protection arrangement, causing false alarms and trips and leading to a reduction of the relay sensitivity. This paper analyzes the behavior of the protection system on a reduced-scale model, which reproduces the main features of grounded wye shunt capacitor banks. In such experiments, high levels of current harmonic distortion, voltage unbalance, and bank inherent unbalance were considered. This paper brings experimental analyses for protection arrangements considering robustness and sensitivity.

The new standard C37.118.1 lays down strict performance limits for phasor measurement units (PMUs) under steady-state and dynamic conditions. Reference algorithms are also presented for the P (performance) and M (measurement) class PMUs. In this paper, the performance of these algorithms is analysed during some key signal scenarios, particularly those of off-nominal frequency, frequency ramps, and harmonic contamination. While it is found that total vector error (TVE) accuracy is relatively easy to achieve, the reference algorithm is not able to achieve a useful ROCOF (rate of change of frequency) accuracy. Instead, this paper presents alternative algorithms for P and M class PMUs which use adaptive filtering techniques in real time at up to 10 kHz sample rates, allowing consistent accuracy to be maintained across a ±33% frequency range. ROCOF errors can be reduced by factors of >40 for P class and >100 for M class devices.

The key techniques employed in this paper reflect on a comprehensive method for calculating the cost of the electric power and energy needed to supply the life-cycle losses of power transformers. The method is applicable to transformer users who possess their own generation and transmission facilities. The proposed loss evaluation method is based on factors derived from relevant historical and forecasted data that are combined to determine the total ownership cost of power transformers. Finally, in a companion paper, the method is evaluated on a small-scale real system.

This paper proposes a new approach for obtaining parameters of the zero-sequence equivalent circuit of three-phase three-legged three-winding YNynd transformers (i.e., transformers with two wye windings and a third delta stabilizing winding). The methodology proposed in this paper includes a complete set of onsite field measurements using commercial equipment (traditionally used for onsite transformer leakage reactance tests). An easy-to-implement determination of the zero-sequence behavior of the YNynd transformer is achieved by means of separating the equivalent T-circuit into two different circuits, one of them to be used when the delta stabilizing winding is closed and the other when this is open. The effect of the resistive component of the zero-sequence impedances is also analyzed and quantified. Onsite measurements on a 45/16.05/10-kV 25-MVA power transformer and their comparison with high-voltage factory tests are presented to demonstrate and validate the proposed methodology.

The current transformer (CT) is prone to the magnetic core saturation during the power system faults. The CT saturation can prolong and/or miscoordinate operation of relays and thus may result in the system stability problems and equipment damage. This paper proposes a new hardware-based method to suppress or prevent the CT saturation. The proposed approach is based on adding a controllable resistor at the CT secondary circuit which dynamically generates a flux to oppose the time varying flux associated with the decaying dc component of the fault current. Part I of this two-part paper presents the concept, the controllable-switch operational strategy, the design steps, and the parameters of the controllable resistor. Part II provides a comprehensive evaluation of the controllable resistor based on offline digital time-domain simulation and control-hardware-in-the-loop studies.

This paper proposes an algorithm for determining the optimal composition which means number of links and section switches in a feeder and placement of automatic switches in a distribution automation system (DAS). A DAS is configured by automatic switches and reclosers on a power distribution line. The composition and placement of switches affect the operational applications of a DAS. More switches lead to better DAS operation but also to increased cost and maintenance. Thus, this paper proposes an approach to determining the optimal composition and placement of automatic switches. Additionally, the proposed algorithm is developed considering various system topologies in a real field. The algorithm was tested on an example power distribution system with eight-feeders and on a real power distribution system operated by KEPCO in Young-Deung-Po and Jeju, South Korea.

As the penetration of wind energy into the power system continues to grow, wind energy conversion systems (WECSs) are increasingly expected to be able to control their output real power, while retaining their maximum power-point tracking (MPPT) capability. This paper proposes a simple real power control strategy, which augments the MPPT feature of modern WECSs, and is based on rapid torque control as opposed to the traditional pitch-angle control. This paper presents the implementation of the proposed control strategy for a direct-drive WECS that employs the permanent-magnet synchronous generator, even though the proposed method can also be extended to other classes of electronically interfaced WECSs. The paper also presents a parameter-tuning procedure for the proposed control strategy. The effectiveness of the proposed control strategy is demonstrated through mathematical analysis and time-domain simulation studies.

The reduced-scale model of HVDC transmission lines in the laboratory is widely used to investigate the ionized fields. This paper is aimed at analyzing impact factors of the ion-current density measurement system based on Wilson plates in the laboratory. Both experimental and numerical simulation methods are used to obtain the characteristics of the measurement system. The results show that measurement data can be calibrated with different Wilson plates, and suitable parameters are proposed in this paper to meet the requirement of measurements. The measurement system described in this paper can be used in other similar applications.

The numerical results detailed in this paper reflect on a method proposed to accurately appraise the energy and the demand component of the cost of losses for evaluating the total ownership cost of power transformers. Specifically, the proposed method is evaluated on a small-scale real system, by incorporating realistic financial data and system characteristics through appropriate technoeconomic models as well as statistical evaluations. The calculated loss components of this paper are compared to the methodology detailed in IEEE C.57.120-1991.

Single-pole tripping (SPT) operation imposes problem to many power network relaying schemes. In this paper the directional relaying issue for faults during SPT condition is addressed. Algorithms applying negative sequence components of fault voltage and current for directional relaying find limitation during SPT as the prefault signals also contain negative sequence components. This paper proposes a directional relaying algorithm during SPT using phase-change in negative sequence current. The proposed technique is an attractive option as it does not use the fault voltage signal in the decision process. The technique is evaluated using data simulated with EMTDC/PSCAD for single and double circuit lines and the performance of the algorithm is also evaluated.

This paper introduces a new theoretical method to obtain the frequency-response curve with the transformer in service (online) from the transient signals analysis by applying the continuous wavelet transform. To validate the method, the transient signals were simulated in the Alternative Transient Program for two cases: 1) under injection of pulses over the 60-Hz wave and 2) under switching operations, respectively. To simulate the transformer, a suitable wide-bandwidth model was employed. This study proposes a new setup of the Morlet wavelet, denominated Morlet-Modified, which showed the best results obtained for our application purpose (FRA On-line). This paper is a contribution for signal processing for the online frequency-response analysis technique on transformers.

This paper introduces a computationally efficient surrogate model-based approach for tolerance analysis of power systems. Surrogate models are heuristic, simple representations of complex systems that are obtained through an automated sensitivity analysis of electromagnetic transient simulations results. These simpler models are shown in this paper to be significantly faster than full-detail simulation models to obtain accurate statistical tolerance information about complex power networks. Usefulness of the proposed approach is demonstrated by two application examples. In the first example, surrogate models are used for determining the statistical distribution of undesired remnant harmonics produced by a voltage-source converter, given the uncertainty in the firing angles. In the second example, the impact of variations in the system parameters around the nominal values on the transient behavior of a static compensator is analyzed.

This paper presents a novel compensation technology of static synchronous compensator integrated with distribution transformer (DT-STATCOM). STATCOM is connected with the transformer taps at the high-voltage (HV) windings. By selecting the appropriate tap voltage level, it can help to make full use of the spare capacity of the distribution transformer, simplify the main circuit topology of STATCOM, and reduce the current level of power devices. The theoretical basis for DT-STATCOM reactive power compensation is explained. For the Dyn-type transformer, the structure of DT-STATCOM with multigroup taps at the transformer HV windings is mainly designed, and its influence on the current distribution in the transformer windings is analyzed. Besides, according to the characteristics of DT-STATCOM, this paper also proposes a reactive command current calculating method based on the principle of power balance, and adopts a hysteresis current control method with a variable hysteresis band. Simulation and experimental results verify the correctness of the proposed DT-STATCOM structure and its control method.

Fault location is considered as one of the essential techniques enabling a smart grid. This paper presents a novel fault location approach for double-circuit transmission lines. Various existing algorithms usually require measurements recorded from one or two terminals of the faulted line. However, when such measurements are not available, these methods are not applicable. To fill this gap, this paper proposes a fault location method by harnessing current measurements from one or more branches, which may not be necessarily taken from the faulted section. The currents from multiple branches are synchronized and can be obtained from phasor measurement units installed in the system. The bus impedance matrix technique is exploited to develop the new method. The shunt capacitance of the line is fully considered by utilizing the distributed parameter line model. The network data are assumed to be available. When multiple synchronized current measurements are available, an optimal estimator capable of identifying possible bad measurement data and, thus, further enhancing the fault location is also proposed. Quite accurate results have been achieved based on simulation studies.

Although reliability-centered maintenance (RCM) has proven its noticeable merits in many industries, has not been yet furnished with efficient analytical methods in the power engineering context. The first of this two-paper set presents a practical framework by which the RCM procedure can be implemented in power distribution systems. The proposed algorithm consists of three main stages. The prerequisites of the analysis are outlined in the first stage. In the second stage, an approach is developed to identify the network's critical components, from the reliability point of view. Having practically modeled the components' failure rates, an efficient cost/benefit evaluation approach is then proposed to distinguish a variety of maintenance plans. The optimal set of maintenance strategies is next adopted for implementation. The algorithm is terminated in the third stage by recording both technical and economical outcomes for tuning the forward maintenance activities. The proposed methodology, although tailored to distribution networks, is generic enough to be applied to other power system areas. In the companion paper, the proposed methodology is examined by application to the Birka distribution system of Stockholm City, Sweden, and more practical aspects are discussed.

A distribution automation system (DAS) is a power automation system to operate a power distribution network efficiently through remote control and monitoring. The most important function of the DAS is the restoration of a stable power supply to the customer when a fault occurs. Since the DAS has a centralized structure, the restoration time of the DAS takes place in about 5 min. This is too long for a customer in the digital age, so a distributed restoration system, which can shorten the restoration time from 5 min to less than 1 min is proposed in this paper. The concept of a multiagent system (MAS) for a distributed control system is applied to the proposed system to enhance its operational reliability, but there is a belief that the MAS-based distributed operations system is just a future technology. So an application method is proposed in this paper for an MAS-based distributed restoration system without significant changes to the existing DAS. The proposed system was applied to an existing DAS and tested in the Gochang Power Testing Center. The test results showed that in the most complex case, the DAS restoration time was 48 s using a code-division multiple-access module and 10 s using an Ethernet communication module.

This paper presents a methodology for modeling the load behavior of electric vehicles. This information is needed to make a more accurate prediction of the technical potential of electric vehicles which might be used in the future as dispersed energy storages or controllable loads. For this purpose, a simplified stochastic model is established based on nonhomogeneous semi-Markov processes. This model is capable of describing the grid connectivity of electric vehicles over the period of one day. In addition, it provides information about the driven distance and the state of charge. This makes it possible to generate information about the load behavior of the vehicles at different times and locations. The fundamentals of the model are given in this paper as well as the basic results. As proof of validation, a comparison between the results and real data are presented. Finally, a synthetic load profile is generated based on the proposed model.

The main purpose of this series of papers is to provide methodology and best business practices to assess the risk posed by geomagnetic disturbances. This paper addresses the methodology used by Dominion Virginia Power to model geomagnetically induced currents. An extreme 100-year geoelectric-field scenario is utilized as a baseline. The impact of topology changes in a large 497-bus system is investigated. Subsequent papers-Parts II and III-will address transformer vulnerability and system voltage stability, respectively.

Shield wire segmentation has been used for quite some time as an effective method for reducing transmission-line power losses, with most segmented shield wire applications on extra high-voltage lines utilizing phase-to-phase power-line carrier (PLC) coupling. As transmission system efficiency becomes more of a priority, some utilities may consider applying segmented shield wires to lower voltage lines, such as 115-kV and 230-kV lines, which most often utilize single-phase-to-ground PLC coupling. Thus, knowledge of the effects of segmented shield wires on PLC signal attenuation for various coupling methods would be useful to relay engineers. The purpose of this paper is to present a generalized method to model transmission lines for signal attenuation calculation at PLC frequencies, with special consideration given to shield wire connections. Terminating impedance and phase wire transposition are considered as well. The modeling method presented is validated with field measurements. In a companion paper, signal attenuation results considering the effects of various parameters are analyzed.

A previous paper has been written on the generalized modeling method of overhead transmission lines for use in power-line carrier (PLC) systems. Knowledge of the effects of shield wires on PLC signal attenuation for various coupling methods would be useful to relay engineers. In addition to the effect of the coupling method on PLC signal attenuation, other problems, such as resonance conditions resulting in high signal attenuation may also occur depending on the PLC signal frequency and the length of the shield wire segments. Therefore, the purpose of this paper is to provide awareness to relay engineers of problems that may arise when applying PLC systems on transmission lines with segmented shield wires.

Power-line communication (PLC) allows establishing digital communications without adding any new wires. It will turn one's house or neighborhood grid into a smart grid. PLC has some issues, namely, high noise at low frequencies and varying characteristic impedance. This paper addresses these issues to improve the signal-to-noise ratio by increasing the signal or reducing the noise. PLC MODEMs are subject to legislations that limit the signals in the line. The radiated signal is proportional to the current, but not to the input current, since the current forms a standing wave along the line. However, better performance can be achieved if the input current is measured. The receiver circuit of the transmitting MODEM can be used to estimate the input impedance. This paper presents a technique to use this new information to achieve better performance and to follow legislation changes in the band above 30 MHz. A study of the viability of using impulsive noise reduction techniques to further increase performance is also presented. The short noise pulses result in high correlation between the noises in different carriers. Impulse position detection should result in an increase in capacity.

The restricted earth fault (REF) relay is one of the protection units of the transformer digital protection system which typically has a fast response and thus is prone to maloperation. Based on measurement results and time-domain simulation results, this paper provides a comprehensive performance evaluation of the REF relay which is an augmented-based adaptive restraint current approach for performance stabilization. The investigation results provide justifications to introduce modification to the relay to improve its performance during transients and, thus, improve the relay security. This paper also introduces and evaluates a scheme to modify the REF relay performance. The proposed scheme has been implemented in the field, and the results indicate performance improvement.

This paper presents a technique for simulation of transient skin effect of the dc railway system based on MATLAB/Simulink. The classic calculation of skin effect based on frequency domain is not suitable for time-domain simulation. The aim of this paper is to develop a time-domain calculation method which can be realized in MATLAB/Simulink. Through the analysis of the step series algorithm, results are applied to the calculation of frequency voltage signal and compared with skin effect impedance of frequency. Accurate simulation of the transient skin effect produces accurate modeling of the remote fault current. This is important for the dc railway protection researchers to develop techniques for discriminating remote short-circuit currents from locomotive starting currents.

In this paper, for the first time, a high-impedance fault indicator (HIFI), to be mounted on the poles of distribution feeders, is proposed to detect and track down the location of high-impedance faults (HIFs). The main contribution of this paper is the investigation of employing the magnetic-field strength signal, measured in the vicinity of the conductors of a feeder, to detect HIFs based on a novel pattern recognition method. The proposed HIFIs should be installed so that the faulted branch identification becomes possible and simple (i.e., at the sending ends of branches). Applying the data for HIFs, insulator leakage current and harmonic load from field tests and for other similar phenomena from simulations has shown high security and dependability of the proposed method as a computational model for HIFI.

This paper studies the harmonic impact of modern residential loads on the secondary power distribution systems. Several issues of concern to utilities, such as the neutral-to-earth voltage rise, the overloading of service transformers, the impact of compact fluorescent lights (CFL), and the benefits of adopting IEC 61000-3-2 limits, have been investigated. A bottom-up probabilistic harmonic assessment method proposed in the companion paper was applied to conduct the study. Several interesting results have been obtained. For example, the adoption of CFLs based on market trend could result in an increase of voltage total harmonic distortion by about 10% per year over the next couple of years. Adopting the IEC limits on CFLs will drop the growth rate to 2% per year. In addition to the results of interest to utility companies, this paper demonstrates the usefulness and necessity of a bottom-up-based approach to conduct harmonic assessment for residential loads.

In this paper, some useful features are extracted from voltage signals measured at one terminal of the transmission line, which are highly efficient for accurate fault locating. These features are the amplitude of harmonic components, which are extracted after fault inception through applying discrete Fourier transform on one cycle of three-phase voltage signals and then are normalized by a transformation. In this paper, the location of single-line-to-ground faults as the most probable type of fault in the transmission networks is considered. The SLG fault locator, which is designed based on the simple algorithm of k-nearest neighbor (k-NN) in regression mode, estimates the location of fault related to the new input pattern based on existing available patterns. The proposed approach only needs the measured data from one terminal; hence, data communication between both ends of the line and synchronization are not required. In addition, current signals are not used; therefore, the proposed approach is immune against current-transformer saturation and its related errors. Tests conducted on an untransposed transmission line indicate that the proposed fault locator has accurate performance despite simultaneous changes in fault location, fault inception angle, fault resistance, and magnitude and direction of load current.

The simulation of an electromagnetic transient is only as good as the model's data and the level of detail put into the modeling. One parameter with influence in the results is the size of the modeling of the area around the switched-on line. If the area is too small, the results are inaccurate. If the area is too large, the simulation requires a long period of time and numerical problems are more likely to exist. This paper proposes a method that can be used to estimate the depth of the modeling area using the grid layout, which can be obtained directly from a PSS/E file, or equivalent. The simulation of electromagnetic transients in cable-based networks requires larger computational effort than in an equivalent overhead-line (OHL)-based network. Therefore, the method is demonstrated for the former, with the cases of OHL-based networks and hybrid cable-OHL networks addressed in a future paper. One of the main reasons behind the long simulation times of a cable-based network is the simulation of all the cross-bonded sections. The introduced method can also be used to minimize the modeling of the cross-bonded sections.

This paper proposes an enhanced control strategy for electronically coupled distributed energy resources that improves the performance of the host microgrid under network faults and transient disturbances. The proposed control strategy does not require controller mode switchings and enables the electronically coupled distributed energy resources to ride through network faults, irrespective of whether they take place within the host microgrid or impact the upstream grid. Moreover, the proposed control ensures acceptable power quality for the duration of the faults, which is an important feature for protection against certain classes of faults, as well as for sensitive loads. Further, the paper proposes a supplementary control loop that improves the microgrid post-fault recovery. The effectiveness of the proposed control strategy is demonstrated through a comprehensive set of simulation studies, conducted in the PSCAD/EMTDC software environment.

This paper proposes a short-circuit diagnosis tool for electrical low-voltage (LV) distribution networks. The tool relies on analyzing Park's vector representation of the LV phase voltage in the sag produced by a short circuit. Park's vector representation is considered to be an identification mark for the type of short circuit that the installation is exposed to and the phases that it affects. In addition, it shows whether the fault is located in the medium voltage or LV network. The characteristics of the vector representation corresponding to the different types of short circuits are analyzed in this paper. Finally, the relationship between Park's vector representation and the location of the defect is also studied. The results can be used as part of an expert system for the automatic classification of disturbances.

In Part I of this two-part paper, a power-management and a control strategy for the microgrid autonomous mode of operation were presented. The strategy consists of 1) open-loop frequency control of the system and synchronization of DER units based on a GPS signal; 2) voltage reference setpoint determination for the DER units by the central power-management system; and 3) tracking the assigned setpoints and rejecting disturbances by robust, decentralized, local controllers of DER units. This Part II paper applies the envisioned strategy to a three-DER microgrid. Offline digital time-domain simulation studies in the EMTDC/PSCAD software environment demonstrate the robustness of the local controllers to parametric, topological, and unmodelled uncertainties of the microgrid, its fast performance in tracking the setpoints with zero steady-state error, and rapid disturbance rejection. The results also show the effectiveness of the proposed power-management system in achieving prescribed load sharing of DER units. The digitized algorithms of the proposed control system of the three-DER microgrid are also implemented in NI-cRIO industrial-grade platforms and tested in an RTDS-based real-time hardware-in-the-loop (HIL) environment to demonstrate the feasibility of the strategy for hardware implementation and hardware-based performance validation.

International audience; Broadband power-line communication (PLC) technologies are one of the main parameters of digital convergence voice-data-video in the home environment. These technologies use the power-line network as a propagation and a communication medium. Its transmission quality depends on the frequency behavior of the propagation medium and the connected household electrical appliances. The impedance of those devices and noise levels has a great impact on the PLC systems. In this paper, a simulator for indoor power-line channels is presented. In this paper, a new approach is presented for modeling temporal variations of noise and channel on indoor power lines. A three-conductor power cable (phase, neutral, and ground) is modeled by a circuit of four elements (resistor R, inductor L, capacitance C, conductance G). The RLCG parameters are deduced from the impedance measurement in open circuit and in short circuit. The cable model is validated in time and frequency domains. Then, the temporal variation of periodic noise is modeled by a stochastic approach. The global model, combining both channel and noise variations, is validated by comparing SPICE simulation and measurement results.

Thyristor-based onload tap-changing ac voltage stabilizers can replace mechanical tap changers associated with transformers feeding medium-voltage (MV) lines (typically 69 kV primary, 34.5 kV line, 6.3-50 MVA), thus avoiding frequent contacts revision. As shown in a previous paper, the topology using a compensating transformer in the main circuit and a multiwinding coil in the commutating circuit give good technical and economical results independent of the coil operation mode (shared, nonshared, and mixed load). This second paper focuses on this topology and defines the criteria for an optimum design and the synthesis formulae that give the definition parameters of the components as a function of the equipment characteristics. Numerical results are added for a typical 10-MVA stabilizer. One of the best circuit solutions (single switch comb, mixed load, auxiliary short-circuit winding), which does not need a series association of thyristors, is developed in detail. Final synthesis formulae, effective power of the transformers and coil, and summatory of thyristors I·U products for all three operation modes are contrasted in a table as the final step of the iterative analysis and synthesis cost-comparative method followed along the research.

The method using the embedded electrode in a spacer to measure the very fast transient overvoltage (VFTO) is well applicable to the field measurement in a substation. However, the current measurement system has the disadvantage of low high-frequency cutoff frequency (2 MHz), and the problem of fallibility caused by a flashover from the embedded electrode to tank sheath. Based on the fundamental principle of the embedded electrode measurement system, a distributed parameter model has been established in this paper. With theoretical analysis and experimental verification, it is found that the major factors affecting bandwidth include the inherent inductance in external capacitors connected to an embedded electrode, the different port-distribution of external capacitors, and the nonconsistency of external capacitors on different ports. When the capacitors at four ports of an embedded electrode are highly consistent, the partial transient overvoltage of the electrode will be eliminated. In this paper, capacitors with low inductance, high stability, and highly consistency are chosen to be connected on four ports of an embedded electrode, and the consistency of four external capacitors is ensured. Hence, the high-frequency cutoff frequency increases to 10 MHz. The VFTO generated by disconnector operation in 1100-kV gas-insulated switchgear is both measured by the system based on the embedded electrode in a spacer and a broadband measurement system. The contrastive results indicate that the measuring system can meet the needs of VFTO measurement on some conditions.

This paper aims at developing a simulation method for the ion-flow field when HVDC transmission lines cross over HVAC transmission lines. A time-domain 3-D method is proposed in this paper, where the 3-D finite-element method and 3-D finite volume method are used to solve the Poisson's equation and the charge conservation law, respectively. The implicit temporal discretization scheme is used to accelerate the computation. An indoor test model is set up in this work, and the simulation results agree well with the measured results from this test model, which validates the proposed method. The proposed method is then used to calculate the ground-level electric field and ion current density under the crossing of ± 800-kV HVDC transmission lines and 500-kV HVAC transmission lines. The presence of HVAC transmission lines is found to have a significant influence on the ion-flow field under the crossing.

The conventional interphase power controller (IPC) can control the power flow of the transmission line. In this paper, a novel topology for IPC, called the unified interphase power controller (UIPC), is introduced. In this topology, the phase-shifting transformers (PSTs) are replaced by voltage-source converters. In this paper, the transient behavior of UIPC is modeled and investigated. The results are compared with the simulation results of IPC and UPFC. It is shown that UIPC has all of the capabilities of IPC and UPFC, such as power-flow control, fault current limitation, voltage isolation, and local bus voltage regulation simultaneously. The results also reveal that UIPC increases the variations range of control variables of IPC and, as a result, the range of variations of active and reactive powers.

This paper presents a comprehensive analysis of the possible impacts of different penetration levels of distributed generation (DG) on voltage profiles in low-voltage secondary distribution networks. Detailed models of all system components are utilized in a study that performs hundreds of time-domain simulations of large networked distribution systems using the Electromagnetic Transients Program (EMTP). DGs are allocated in a probabilistic fashion to account for the uncertainties of future installations. The main contribution of this paper is the determination of the maximum amount of DG that secondary distribution networks can withstand without exhibiting undervoltage and overvoltage problems or unexpected load disconnections. This information is important for network planning engineers to facilitate the extension of the maximum penetration limit. The results show that depending on the location, type, and size of the installed DGs, small amounts of DG may cause overvoltage problems. However, large amounts of DG may not cause any voltage problems when properly selected.

Cable parameter extraction is needed for many practical purposes. The main motivation for this research came from a need to extract high-frequency properties of cables used for indoor electricity distribution because they can be utilized for transmission of communication signals, too, by means of the power-line carrier (PLC) technology. These cables have relatively high specific losses, so that indoor broadband PLC applications can use frequencies up to some 30 MHz. In this paper, cable features in the frequency range from 5 to 30 MHz, belonging to the high-frequency band, were studied. The purpose of this paper is to describe a practical method by which the cable parameters in the mentioned indicated frequency range can be extracted rather accurately from measured complex reflection coefficients at a cable end when the other end is terminated by precise open and short terminations, using very simple equipment. The parameters extracted in this way can be used for very precise modeling of real-life multiterminal distribution networks.