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The groundings of the power distribution, signaling, and power systems of a railway system are individually performed to realize fail safe, and the groundings are often installed in close proximity. Thus, when a grounding electrode is invaded by a lightning current, its ground potential rises together with the potential of the adjacent grounding electrodes; hence, there is a possibility of a large overvoltage being applied to the connected devices. In this paper, we have investigated the potential spread between two rod-shaped electrodes widely used in the grounding of the power, signal, and distribution systems of a railway system using the finite-difference time-domain method. The results of this paper are organized in such a way that the extent of the potential spread to the neighboring grounding electrodes can be understood from information such as the grounding resistivity at the installation location of the ground electrode and the wavefront duration of the lightning current, and these findings will be useful for grounding design. We also investigate the effect of the insulator between two neighboring electrodes to prevent the potential spread. [ABSTRACT FROM AUTHOR]

High resistance grounding (HRG) is a well-proven technology for improving electric reliability for many industrial and utility facilities such as used in petrochemical, automotive, and generating plants. Many such facilities require the increased reliability for production and operational reasons. This paper will discuss the improved personnel safety aspects of using HRG on low-voltage systems. In particular, this paper will discuss the following: 1) the probability of the three common faults occurring within an industrial plant, namely, three-phase, phase-to-phase, and ground faults; 2) how the probability of a ground fault can be used to improve electrical safety with HRG; 3) the impact of a ground fault on a system and the speed at which the ground fault on a solidly grounded system may propagate into a multiphase fault; 4) the risk reduction of a ground fault on an HRG system propagating into a multiphase fault; 5) the potential reduction in serious and fatal arc blast injuries through the use of an HRG system; and 6) potential single-pole breaker clearing issues when a second ground fault occurs on a second phase. This paper will include comments from recent testing, which was conducted at the KEMA Laboratories and presented in a recent IEEE Industry Applications Society Petroleum and Chemical Industry Committee paper in September 2014. [ABSTRACT FROM AUTHOR]

Recently, voltage-source converter (VSC)-based high-voltage dc (HVDC) transmission systems have gained more attention. In this paper, a control method for a modular VSC-based HVDC transmission system with high-frequency isolation referred to as high-frequency isolated modular converter is proposed. In the high-frequency isolated modular converter configuration, several floating dc capacitors in all three phases are connected in series, and voltage balancing control of these floating dc capacitors is required. In this paper, an appropriate control structure with the capacitor voltage balancing controller is proposed. The proposed control scheme consists of three layers to control terminal dc bus voltage and balance dc capacitor voltages of each building block. Detailed PSCAD simulation results are presented to evaluate the performance of high-frequency isolated modular converter. Controller hardware-in-the-loop simulation of the high-frequency isolated modular converter is also performed by real-time digital simulator (RTDS), and RTDS results are presented to verify the control structure. Finally, laboratory-scale experimental results are presented to validate the proposed control method. [ABSTRACT FROM PUBLISHER]

This paper is concerned with the use of a three-level inverter for a synchronous reluctance machine (SynRM). The SynRM suffers from a poor power factor due to poor machine saliency. This makes it harder to operate the three-level neutral-point-clamped inverter due to a strict requirement to have the two dc-link capacitor voltages balanced. This paper proposes a new nearest three vector modulation algorithm which can balance the two dc-link capacitors even at poor machine saliency ratio (poor power factor). In this paper, a method of sizing the two dc-link capacitors based on the machine power is also proposed. A comparison between two- and three-level inverters was conducted. The SynRM registered lower $d$-axis current ripple with a three-level inverter, indicating lower core losses in the machine. [ABSTRACT FROM PUBLISHER]

The grounding system in a solar farm has unique characteristics due to its extended footprint and varying type of grounding components. The changing physical properties of the soil within the perimeter of a solar farm result in the nonuniform resistivity of the top soil layers. Measurements of the as-built grounding grid could indicate higher grounding resistance than that predicted by design. Once this difference is detected, it is the duty of the designer to modify the existing grounding grid such that the touch potential is below the limits specified by the applicable codes. This paper presents the analysis of the touch potentials in solar farms and also provides some recommendations to reduce these potentials when the grounding resistance is higher than that predicted by the design. An actual grounding grid design and field measurements are used in an example to illustrate the concepts introduced in this paper. [ABSTRACT FROM PUBLISHER]

It is common practice in the industry for electrical workers to be exposed to shock and arc blast and arc flash hazards as they perform routine maintenance and diagnostic testing on equipment enclosed in motor control centers (MCCs). This paper will illustrate the influence that various IEEE conferences, including the Electrical Safety Workshop, has had on changing the electrical safety culture related to equipment diagnostics. End users are now requesting manufacturers of low- and medium-voltage MCCs to develop or add features and functionality into their products that enhance the ability of electrical maintenance and operating personnel to conduct routine diagnostic and troubleshooting tasks without being directly exposed to energized electrical equipment. This paper will explore some of these features and provide some examples of routine maintenance and diagnostic tasks that can be performed while doing troubleshooting and diagnostic tasks on operating equipment without opening enclosure doors and exposing workers to the hazards associated with exposed energized equipment. [ABSTRACT FROM PUBLISHER]

In this paper, an investigation into an alternative topology for reluctance synchronous machine rotor flux barriers is presented. The investigated topology employs a high number of flux barrier variables with an alternative asymmetric rotor structure. The focus in this paper is on maximizing average torque and minimizing torque ripple, using finite element-based design optimization, in order to study the possibility of achieving acceptably low torque ripple. A subsequent investigation into the effect of rotor skew on the proposed optimized design to reduce torque ripple even further is also conducted, as well as the manufacturing and testing of the proposed flux barrier prototype. [ABSTRACT FROM PUBLISHER]

This paper will discuss potential safety issues of lighting in an industrial setting. We will explore lighting safety factors that help mitigate such safety concerns. This paper will also highlight lighting design, maintenance, location, installation, maintenance ergonomics, and hazardous location concerns for lighting systems. The goal of this paper is to assist end users during their design, operation, and maintenance stages. [ABSTRACT FROM PUBLISHER]

This paper presents an algorithm for detection, classification, and characterization of voltage sags and swells in electricity networks using three-phase voltage ellipse parameters. The proposed method employs the instantaneous magnitude of three-phase voltage signals in three axes, which are separated from each other by 120 ^\circ . Thus, the resultant rotating vector, namely, the three-phase voltage vector, traces an ellipse. Then, the parameters of the ellipse, which include minor axis, major axis, and inclination angle, are used to develop the proposed algorithm for classification and characterization of voltage sags and swells. The proposed method is validated using real data of the IEEE working group and some measured real data of the Belgian transmission grid. The method is further tested for the sags and swells generated due to balanced and unbalanced faults at different buses, in test distribution networks (radial and mesh type) embedded with distributed generation and in a practical distribution network of Australia. This paper also demonstrates the proposed algorithm as a real-time sag/swell monitoring tool. [ABSTRACT FROM PUBLISHER]

The articles in this special section focus on grounding systems for industrial, commercial, and residential installations. [ABSTRACT FROM AUTHOR]

Synchronous reluctance (SyR) machines are a high-efficiency alternative to induction motors for variable-speed applications. To mitigate the well known downside of their lower power factor, permanent-magnet-assisted topologies, in which either rare-earth or ferrite magnets are inserted into the rotor in suitable quantities, are often adopted. The design and optimization procedures for PM-assisted topologies have been thoroughly discussed in the related literature. This paper compares SyR machines assisted with NdFeB and ferrite magnets, focusing on torque overload capability and feasibility of saliency-based position estimation algorithms. Three prototypes were realized and tested. They all have the stator of a commercial induction motor and the same custom-designed SyR rotor laminations. Among the three prototypes, one is a pure SyR motor, and the other two have NdFeB and ferrite magnets, respectively; both are designed to give the same torque at rated current. Results from simulations and experiments are presented comparing the transient overload capability of the three machines, in terms of torque capability and de-magnetization limit. A dynamic thermal model of the machines was developed within this scope. Moreover, the feasibility of saliency-based sensorless methods was investigated and is presented here for the three machines, both at high- and low-current loads. The results of the paper suggest that the ferrite-assisted solution is the best candidate for replacing induction motors in variable-speed applications, for its optimal tradeoff between performance and cost. [ABSTRACT FROM AUTHOR]

This paper presents the comparative study of coreless-type permanent magnet linear synchronous machines with non-overlapping windings. An analytical expression that can be applied to any combinations of pole and coil numbers is developed for evaluating the electromagnetic performances. Subsequently, a simple factor called thrust factor is introduced to find the best ${\boldsymbol{C}_{\boldsymbol{pp}}}$ family depending on the variation of coil width ratio. From the comparative study, a significant result is reported that ${\boldsymbol{C}_{\boldsymbol{pp}}} = 1/4$ , i.e., multiple 4-pole/3-coil, is the best non-overlapping winding configuration of coreless-type permanent magnet machines owing to the highest value of thrust factor. Finally, the validity of the key analyses is confirmed by optimal results, finite element results, and experimental results from prototype machines. [ABSTRACT FROM AUTHOR]

This paper examines computer virtualization as a solution to issues encountered in maintaining HMI and SCADA systems based on commercial off-the-shelf computing hardware. Following a brief primer, this paper outlines issues arising from the rapid advancement of personal and server computing hardware, including automation software conflicts with new operating systems, device driver availability for old operating systems, and migrating backup images to new hardware. Opportunities for improvement are identified in backup and recovery, operator access to computing resources, and prototyping HMI and program changes. The concept of a virtual machine is introduced, and common architectures are examined, followed by the description of an example virtualized control room. Finally, this paper examines the experiences of a multisite cement producer in implementing virtualization in two of their plants. This examination explores the reasoning, advantages, disadvantages, and limitations encountered in moving existing systems to a virtualized platform. [ABSTRACT FROM AUTHOR]

The integration of drive components is becoming increasingly desirable in global industrial applications. End users want the ability to control the speed of their drivetrain while ensuring that their drive components operate at a high level of reliability and safety. When an electric motor and a variable frequency drive are designed to operate harmoniously, there is an opportunity to optimize cost and reliability of a drivetrain package. This paper provides examples of the improvements in drivetrain component size and cost when motors and drives are sized together as one package, as opposed to having them sized separately without consideration of each other. This paper also provides examples of how cost of ownership due to efficiency improvements can be enhanced when taking into account the entire drivetrain package. Finally, the application considerations required to ensure drivetrain reliability over the life of the installation are discussed. [ABSTRACT FROM AUTHOR]

This paper presents a new power electronic topology that aims to reduce switching losses in hard-switched inverters for brushless dc (BLDC) motor drives. This is achieved by extending the benefits of synchronous rectification used in low-voltage switch-mode dc–dc conversion to high-voltage motor drive applications and by minimizing the reverse conduction behavior of the intrinsic body diode of the synchronous rectifier MOSFET. The proposed topology for reducing body diode conduction includes the addition of a MOSFET in series with the rectifying switch and a SiC Schottky diode around the series switch combination. This paper focuses on theory, simulations, and experimental results and validates the benefits of proposed new topology for BLDC motor drive applications. An extension of this topology for sinusoidal back electromotive force permanent-magnet motors is also presented. [ABSTRACT FROM PUBLISHER]

For the past decade, the discussion of occupational electrical safety in the U.S. has largely focused on compliance with NFPA70E, Standard for Electrical Safety in the Workplace. Without taking away from the importance of the requirements in the standard, this paper describes a more comprehensive solution, based on proven concepts derived from systems safety engineering. This paper provides an overview of systems safety engineering and includes a 20 $+$ year case history of a global Fortune 500 company's effort to change the electrical safety culture in its operations to demonstrate results of applying systems safety techniques to electrical safety. [ABSTRACT FROM PUBLISHER]

This paper deals with a hybrid energy source consisting of a proton exchange membrane fuel cell, two storage devices, and a load. Generally, this type of source constitutes of nonisolated dc–dc converters. In order to have galvanic isolation for safety reasons and a high voltage ratio, we introduce another system based on the use of three-port isolated dc–dc converters. The storage device can be either a battery or a supercapacitor. This paper presents a control strategy for the hybrid source and includes a global efficiency analysis of power sharing between modules. The proposed system is validated through different simulation results. Additionally, some experimental results are given for the single module operation. [ABSTRACT FROM AUTHOR]

This paper proposes a vector control strategy for independent control of two permanent-magnet synchronous motors (PMSMs) using a single four-leg inverter (4LI). An expanded two-arm modulation to obtain a balanced three-phase output voltage is described. This paper also proposes a method to compensate for the fluctuations in the neutral point voltage of two split capacitors in the dc link. The experimental results show that independent speed and position control of two PMSMs can be achieved using a single 4LI with the proposed vector control method. [ABSTRACT FROM AUTHOR]

This paper presents a novel nonintrusive protection scheme for fault classification of power transmission networks in a wide-area measurement system using fault information for decision making. The protection scheme is a noncommunication without global positioning system as it depends completely on locally measured currents for the nonintrusive fault monitoring (NIFM) using the power-spectrum-based hyperbolic S-transform (PS-HST). In this work, the HST is used to extract the high-frequency components of the current signals generated by an electric fault. To effectively select the HST coefficients (HSTCs) representing fault transient signals with increasing performance, a power spectrum of the HSTCs in different scales calculated by Parseval's theorem is proposed in this paper. Finally, back-propagation artificial neural networks and PS-HST are used to identify fault classes in power transmission networks. The proposed method is tested for different breaker on/off conditions by simulations using electromagnetic transients program software. The results obtained have proved that the proposed method is promising and demonstrate a high success rates and reliability for considering different fault resistances and inception times in NIFM applications. [ABSTRACT FROM AUTHOR]

With the wind power energy largely interconnected with power grid, it is necessary to develop a robust dynamic equivalent model of the wind farm for the system stability analysis and control. In this paper, a detailed wind farm model with doubly fed induction generators is established according to Western Electricity Coordinating Council benchmark test system. Then, the parameters identification process based on aggregation technique consisting of a hybrid algorithm combined improved-particle swarm optimization with improved-genetic algorithm is proposed for dynamic equivalent model development by using the measurement data from phasor measurement unit at the point of interconnection. Additionally, the robustness of the developed equivalent model is analyzed. The simulation results of the benchmark test system and IEEE-9 bus system demonstrate the effectiveness and robustness of the proposed equivalent modeling and identification methodology. [ABSTRACT FROM AUTHOR]

The active power distribution network operation with the integration of various renewable distributed generations (DGs), storage units, and dynamic loads are attracting a lot of interest due to substantial benefits in maximizing the penetration of available renewable energy resources (RES). However, the risk of voltage violation in the active distribution system (ADS) is exacerbated due to increasing penetration of DGs. It has become a bottleneck to maximize the DG penetration into the system. This bottleneck can be handled by effective voltage regulation and reactive power support into ADS. Nowadays, power electronic devices are frequently used for voltage and reactive power support over the conventional approaches. In this paper, an approach to maximize the penetration of RES, such as solar, wind, etc., into ADS by maximum utilization of existing solar photovoltaic inverters (SPVI) in the system is presented. Optimal utilization of SPVI may enhance the voltage stability of the ADS and wind power penetration into the system. The proposed SPVI control approaches are depended on active power generation of solar photovoltaic (SPVG), rating and capability of SPVI, and required reactive power in the ADS. In this paper, the problem of maximum penetration of RES is formulated as an optimal power flow embedded nonlinear optimization problem subject to the physical limitations of the SPVI. The results of the analysis performed on an IEEE 33 bus system show that the proposed SPVI control strategies can improve the voltage profile of the ADS with minimization of curtailment of wind power generation. [ABSTRACT FROM AUTHOR]

This paper presents a novel power flow control strategy, combined with an economic analysis, for an energy management system (EMS) involving a hybrid energy storage. The EMS operates a remote microgrid and directs the power flow to either batteries or supercapacitors to increase the life of the batteries. This paper demonstrates how the use of supercapacitors increases the lifetime of the batteries and ultimately how it affects the economics of the system. The proposed EMS controller also compensates for the 120-Hz ripple on the dc bus. Modeling, simulations, and experimental verification are presented together with the procedure to perform the assessment of the battery lifetime, according to the tuning parameters of the controller. [ABSTRACT FROM AUTHOR]

This paper presents theoretical and experimental discussions on low-voltage-ride-through operation of a modular multilevel single-delta bridge-cell (SDBC) inverter intended for utility-scale photovoltaic (PV) systems. Modern grid codes require grid-tied inverters to provide dynamic grid support during grid-fault events by injecting reactive current. This paper discusses decoupled positive- and negative-sequence reactive-current control, focusing on asymmetric voltage sags with imbalanced magnitude and phase relationships. The main objective is to present a feedforward control method based on calculation of the zero-sequence current required for achieving power balance during normal and grid-fault conditions. Moreover, this paper demonstrates a practical method that minimizes overcurrent stress in the three inverter clusters by adjusting active power drawn from PV arrays. Experimental results on a three-phase 12.6-kVA system prove that the SDBC inverter is capable of seamlessly operating through asymmetric voltage sags. [ABSTRACT FROM AUTHOR]

The pump-back test is widely adopted in the industry for characterizing and qualifying high-power converters. One popular pump-back test configuration is to tie the dc links of two converters together and circulate the current through the inductor connected between the ac terminals. In this configuration, one of the converters operates in the voltage mode to generate the virtual grid and the other converter regulates the circulating current, where hysteresis control could be applied. However, the switching characteristics of hysteresis control are unique due to the pulsewidth modulation type voltage being the virtual grid. This paper contributes to analyzing the switching frequency characteristics of the hysteresis control in this pump-back test configuration. The switching frequency tracking phenomenon is revealed and reported in this paper for the first time. Theoretical analysis, simulation validation, and experimental demonstration are provided to support the major conclusions. [ABSTRACT FROM AUTHOR]

Estimation of induction machine parameters, which are commonly used in efficiency evaluation and control methods, can be effectively achieved by utilizing genetic algorithms (GAs). One of the difficulties of using GAs for efficiency estimation is the determination of variable (parameter) constraints (ranges). This paper focuses on the range determination of the parameters (variables) for GA applications. A wide range of variables can cause unstable outcomes. Hence, it is essential to determine an acceptable range for each variable prior to a GA run to produce stable and repeatable results. In this paper, relationships based on the nameplate information and a large database of tested induction motors provided by Hydro-Québec are proposed to determine reasonable induction motor parameter ranges. The proposed method is applied to three different cases. The results of the three cases are compared to each other and also against the corresponding experimental results, which validate the effectiveness and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

The paper deals with the accurate flux map modeling of synchronous reluctance motors, using finite element analyses. Non-negligible discrepancies were initially observed by comparing two-dimensional (2-D) finite element method (FEM) simulation results with measured flux maps of real machines. Conversely, the three-dimensional (3-D) FEM-based flux mapping offers more accurate estimation of the aforementioned flux linkage characteristics and gives evidence of the 3-D end effects being also a function of the relative position between the magneto-motive force waveforms of the rotor and the stator. The paper investigates such 3-D end effects for different rotor geometries and winding structures, utilizing 2-D and 3-D FEM analysis in comparison to experimental data. The paper confirms that the 3-D effects are non-negligible both in concentrated and distributed winding machines. A simple mathematical approach is proposed for the concentrated winding machine, capable of off-line correction of the 2-D FEM flux maps. The proposed closed-form equation is validated through 3-D FEM and experiments. [ABSTRACT FROM AUTHOR]

Emerging environmental awareness, government subsidies, and deferred utility investments have created an environment that favors the proliferation of distributed energy resources (DERs) in distribution systems. While beneficial, these DERs create operational challenges to the power utility, ranging from additional safety risks to unstable system operation. Among those, traditional feeder overcurrent protection can become desensitized due to the additional fault contribution output by DERs. In some cases, it may not be possible to protect the entire distribution line. This effect is introduced in this paper as the Apparent Effect, which accounts for the reduction in fault contribution from the substation. Its extent varies depending on the DER technology, i.e., synchronous, induction, doubly-fed induction generators, or inverter-based DERs. Substantial investment may be required to overcome this effect and maintain feeder protection dependability. This paper characterizes this issue analytically and suggests the application of system reconfigurations that can result in mitigating the problem. [ABSTRACT FROM AUTHOR]

Large induction motors used in variable speed industrial applications (digging, traction, etc.) undergo dynamic stresses at high power levels. Their lifetime is reduced as compared with constant speed motors and downtime costs are very high. To monitor the condition of such motors, advanced sensor instrumentation is considered, including installation of Hall effect flux sensors inside the motor airgap. Such an advanced instrumentation enables continuous measurement of the airgap flux in both time and space domains simultaneously. This allows for advanced fault detection algorithms. This paper presents a method for early diagnosis of stator turn-to-turn faults and static eccentricity, and differentiation between these two conditions. The paper demonstrates that the proposed method detects, localizes, and quantifies both faults with high accuracy and sensitivity. Furthermore, each fault can be detected at an incipient stage and its development can be predicted. The results of the presented study have been supported by both simulation and experimental results obtained on a laboratory scale induction motor. Based on the results presented in the paper, a real-time condition monitoring system has been developed. [ABSTRACT FROM AUTHOR]

The next big change in various industry applications is associated with power dense motors, such as permanent magnet synchronous motors (PMSMs). Utilization of multiphase PMSM can offer an additional fault-tolerant capability to their applications. Combining both advantages, this paper proposes a simple yet robust current control strategy for a five-phase PMSM under normal operation and in a case of a loss of one phase. Traditional linear current controllers successfully applied to reference tracking of a healthy motor may become less efficient during postfault operation due to additional unmodeled dynamics. This paper proposes a modified angular transformation to a special rotating frame in which the postfault permanent magnet flux linkage remains unchanged and the motor model remains decoupled. Following this, a nonlinear current control scheme based on sliding mode control is proposed, which successfully treats model inaccuracies and provides good dynamic performance and tracking accuracy. Feasibility of the proposed control strategy is experimentally validated on a laboratory scale PMSM motor with a digital signal processor/field programmable gate array based drive. [ABSTRACT FROM AUTHOR]

Doubly fed induction machine (DFIM) is increasingly being preferred in large rated variable speed pumped storage power plants (PSPP), because it provides better energy efficiency due to optimization of pump/turbine efficiency. Increased efficiency results from the flexibility of operating speed at different hydraulic heads. In doubly fed configuration, partial rated power converters feed the rotor circuit. Parallel-connected back-to-back voltage-source converter on rotor side is responsible for starting, braking (dynamic/regenerative), and speed (real power) control of the unit. This paper presents smooth starting and regenerative braking, and assesses performance under power converter and sensor faults of a 250-MW DFIM pump turbine unit to be commissioned in Tehri PSPP, India. Survivability of the unit during faults is analyzed based on current, speed, and dc-link voltage. Further, this paper investigates fault-tolerant operation of 250-MW DFIM unit at open-circuit fault in converters. A 2.2-kW DFIM is tested in the laboratory to corroborate the simulation. [ABSTRACT FROM AUTHOR]

Large-scale wind farms (WFs) are gradually required to participate in power system frequency regulation, especially in a weak grid. Corresponding ancillary frequency control functionalities and the contribution of the WF to system frequency stability are well studied. However, the impact of WF ancillary frequency control on wind turbine generators (WTGs) is rarely considered. It is found in this paper that the ancillary frequency control deteriorates drive-train torsional oscillation of the WTG, which restricts application of the ancillary control. To overcome this problem, this paper proposes an adaptive damping control scheme based on reactive power modulation of the WTG to suppress the drive-train torsional oscillation, which can assist the WF to meet the grid code requirements. Superior to the traditional active power modulation method, the proposed adaptive control scheme can achieve satisfactory damping improvement with less control effort. Furthermore, the adaptive scheme with a torsional frequency updating mechanism can effectively counteract torsional damping deterioration caused by parameter uncertainties, operating condition or control mode variations. Feasibility and effectiveness of the proposed damping control are validated by simulations and real-time experiments. [ABSTRACT FROM AUTHOR]

This paper presents a novel system that allows elevating large structures by using a set of lifting towers that, adequately controlled with a synchronized operation, succeed in pulling the spatial mesh up to the height where it should stay. By doing so, the mounting of the spatial mesh can be carried out on the ground in an easier and, most important of all, safer way; it also gives rise to a shorter final time and, thereby, a cost reduction. This paper deals with the elevation system designed to pull the mesh up and specifically focuses on the electronic system that allows controlling their movement. Comments about the overall control that coordinates the operation of all of the mechanical structures involved are also provided. [ABSTRACT FROM AUTHOR]

This paper discusses the various aspects involving the research and development of smart grids. Discussed are applications, from large grid renewable integration, wide-area monitoring, protection, and control systems to microgrids. Load scheduling and power balance, communications issues, understanding customer behavior, large-area protection, and distribution control are only some aspects of the challenge of making power grids more robust and more intelligent. The potential complexity of such smart grids requires careful study and analysis before actual realization. This paper explains how such challenges are addressed using real-time simulation technologies in different laboratories around the world. [ABSTRACT FROM AUTHOR]

The goal of all circuit protection devices is to mitigate and minimize collateral damage when a failure occurs to either the source (ac line) or the equipment. The circuit protection device is often given little attention, i.e., until erroneous trips hamper performance or unexpected damage occurs within the equipment. Then, the devices are often reviewed for performance characteristics and operating conditions. To meet this need, various devices have been designed for this purpose, and various standards have been written to provide guidance for the usage of those devices. The focus of this paper will be on the interplay between adjustable-speed drive (ASD) short-circuit current rating and protective device sizing, as well as the scaling of such systems, i.e., if a fuse sized for a 10-A circuit should have the same guidelines as that used for a 1000-A circuit. This paper will review the impact of Underwriters Laboratories 508A and 508C, and the National Electric Code on the ASD protection requirements. This paper evaluates a test setup scheme to measure the fuse performance. The peak current and I^2\t test results with both test schemes from three protection devices, a time-delay (TD) Class J fuse along with two non-TD Class J and T fuses, are presented and explained. A novel method of comparing the results is offered by viewing the collateral damage associated with a failure. This methodology has a minor impact at low power ratings, but it has major implications with high power ratings, where equipment is often field repairable. [ABSTRACT FROM AUTHOR]

This paper depicts an accident that happened in 2010 in a Brazilian chemical plant. A combination of different events, installations, and commissioning errors coupled with equipment failures involving the primary substation resulted in catastrophic failure. A single-phase failure of a 138-kV disconnect switch, during closing, initiated events and phenomena that resulted in a complete plant shutdown. This paper will walk the reader through the events, forensics analysis, and power system analysis that allowed the authors to identify what happened, how it happened, and what to do to prevent it from happening again. This paper will show how the anatomy of the problem, involving equipment failure, single-phase arcing, switching transients, overvoltage, capacitive coupling, transferred surge voltages, ungrounded system, transient overvoltage due to an arcing ground fault on an ungrounded system, insulation coordination, flashover, and lack of adequate surge protection, all of which resulted in a catastrophic failure of an arc resistant switchgear and a potentially serious arc flash incident. The research followed some steps that will be commented on here as well as the lessons learned. [ABSTRACT FROM AUTHOR]

The ever growing penetration of distributed generation (DG) in a distribution network has a profound impact on network protection and stability. Traditional protection schemes and algorithms need to be extensively investigated as more and more DGs get introduced into the network. The current version of IEEE Standard 1547 does not present a comprehensive solution for fault current detection in the presence of various kinds of DGs. Power electronic inverter-based DGs (IBDGs) are of special concern in distribution network protection as they are often incapable of providing sufficient fault current and their controllers play a principal role in the DG behavior. In this paper, the effects of voltage and current controllers for IBDGs on industrial and commercial power system protection schemes are investigated. It is shown that the inverter control mode has a direct impact on its fault current levels and duration. A simplified distribution network model with IBDG operating under voltage and current control modes was tested to verify the effects of these controllers. This paper also proposes an adaptive relaying algorithm to detect the faults in the presence of IBDGs with various types of controllers. [ABSTRACT FROM AUTHOR]

In this paper, concentrator photovoltaics (CPVs) were used to integrate the extraction of light energy and thermal energy. The water cooling system that is proposed in this paper provides effective cooling by circulating cold water to remove heat in the photovoltaics. The experimental results were subsequently analyzed and compared with the power generation efficiency of the examined photovoltaics. The use of a water-circulation cooling system improves the power capacity of the photovoltaics by 2%–15% and enhances the power generation efficiency of the photovoltaics by 2.29%–3.37%. Through the combined application of photovoltaic and thermal technologies, the total energy of the overall system can be improved by 37%–59% even after accounting for the energy consumption of the cooling system. As a result, environmental protection, energy savings, and an increase in the efficiency of sunlight utilization can be achieved. Finally, a neural network was used to optimize this increase in efficiency. [ABSTRACT FROM AUTHOR]

The delta-connected cascaded H-bridge converter has been applied to compensate flicker and unbalance load to meet power quality requirement. Based on the detailed power analysis, this paper presents a dc capacitor voltage-balancing technique for the converter. This paper also proposes a current limit control technique to avoid overstressing the power semiconductor devices of the converter. The control techniques in this paper are verified in a 220-V, 1-kVA laboratory test bench. [ABSTRACT FROM PUBLISHER]

This paper proposes an input voltage sensorless control algorithm for three-phase active boost rectifiers. Using this approach, the input ac-phase voltages can be accurately estimated from the fluctuations of other measured state variables and preceding switching state information from converter dynamics. Furthermore, the proposed control strategy reduces the input current harmonics of an ac–dc three-phase boost power factor correction (PFC) converter by injecting an additional common-mode duty ratio term to the feedback controllers’ outputs. This additional duty compensation term cancels the unwanted input harmonics, caused by the floating potential between ac source neutral and dc link negative, without requiring any access to the neutral point. A 6-kW (continuous power)/10-kW (peak power) three-phase boost PFC prototype using SiC-based semiconductor switching devices is designed and developed to validate the proposed control algorithm. The experimental results show that an input power factor of 0.999 with a conversion efficiency of 98.3%, total harmonic distortion as low as 4%, and a tightly regulated dc-link voltage with 1% ripple can be achieved. [ABSTRACT FROM PUBLISHER]

This paper presents the flexible dc capacitor voltages balancing control method for star-connected cascaded H-bridge converters. In this paper, the power flows are analyzed by investigating all the converter's control freedoms. Based on the analyses, users can accomplish the dc capacitor voltage balancing with both negative-sequence current and zero-sequence voltage. These two kinds of control options are further integrated together with the defined weighting factor $K$. The low-voltage ride-through operation of a proposed control method is also discussed in this paper. The control method is verified with a 220-V 1-kVA static synchronous compensators based on the star-connected cascaded H-bridge converters, and the experimental test results show that all the dc voltages are well regulated at the commanded value with different weighting factor $K$. [ABSTRACT FROM AUTHOR]

A constant on-time (COT) controller for dc converters has received much attention recently because of its unique feature of high light-load conversion efficiency. In this paper, a control model is developed for the boost converters with the current-mode COT controller. Models are developed for predicting the loop stability and the step-load transient response. Based on the model, a compensation design is proposed to achieve desired stability margin and step-load transient response. Simulations and experiments are used to verify the model. [ABSTRACT FROM AUTHOR]

During routine commissioning of a steam turbine load-sharing system, serious low-load frequency instabilities were discovered. These instabilities were causing undamped oscillations in power and frequency to escalate until protective relays tripped a generator offline. Root-cause investigation led to a robust solution and some rather startling revelations about the implications of electronic governor controls and small (micro) grids. There are basically two ways to form an electronic governor control loop with droop: 1) speed control with a MW droop; or 2) MW control with a speed droop. The analysis in this paper shows one method to be superior under low-load conditions. The results of this analysis have implications for the frequency stability of the power grid today. Microgrids, green energy, distributed generation, and isolated industrial plants can all be susceptible to this instability. The authors estimate that approximately 60% of today's generation is prone to destabilize the power system frequency under low-load conditions. [ABSTRACT FROM PUBLISHER]

This paper proposes a new method for measurement-based modeling of nonlinear loads in power systems. The proposed method includes a combination of a binary tree algorithm with nonlinear autoregressive with exogenous input (NARX) identification. This paper demonstrates that the new method performs well without any prior knowledge of the system structure. In contrast to other load modeling methods, which are typically aimed for particular studies or load types, the proposed method can be used with any load type and for any study. Accurate load modeling is particularly important for studies of industrial networks and grids. In the study described, a field data set was collected at a mine site from a large electrical rope shovel. This data set has been used to develop a model of the rope shovel based on the proposed binary tree—NARX algorithm. When compared to other known methods, such as wavelet and sigmoid networks, the proposed method has shown the fastest training time and the highest accuracy. Finally, the modeling results have been verified against another set of field measurements from an existing network and have shown a very good agreement. [ABSTRACT FROM PUBLISHER]

A drive train system (DTS) powered by an ideal voltage source and driving a permanent-magnet synchronous motor (PMSM) is discussed in this paper. A two-level three-phase voltage source inverter is used as a means of power conditioning. This converter is not equipped with any harmonic filters on neither the ac nor the dc side. The mechanical part of the DTS is modeled as a double oscillator according to a drive train in an electric vehicle (EV). Various inverter modulation schemes are applied, namely, a single-phase hysteresis scheme, two-space vector-based hysteresis control schemes, for one, a stator aligned hysteresis and for another, a rotor aligned hysteresis, a modulation scheme based on pulsewidth modulation (PWM), such as sinusoidal modulation (including zero-sequence components) and space-vector pulsewidth modulation (SVPWM). The hysteresis-based pulsing methods are nondeterministic and build a current controller in their structure by nature. The other pulsing methods are deterministic due to their underlying PWM and require a separate control unit. The influence of these modulation schemes on the performance of the DTS is determined by assessing the level of inverter generated harmonics flowing to the PMSM and to the tires [downforce, (mechanical part)] as well as the resulting switching frequency (electrical part). The simulated results presented in the paper indicate that the pulsing frequency can be reduced by means of the hysteresis controller. In addition, the dispersion of the harmonic energy of the inverter generated spectrum partly compensate the absence of filters. [ABSTRACT FROM PUBLISHER]

This paper investigates a method to increase fuel economy of motors for an electric vehicle (EV) traction system. The low-torque region of an EV motor is frequently used in everyday urban driving and in fuel economy measurement. Pulsewidth modulation (PWM) carrier harmonic iron loss accounts for a high percentage of total loss for EV motors in this region. This paper reveals the relationship between phase current and carrier harmonic iron loss for a permanent-magnet synchronous motor (PMSM) in the low-torque region. Thus, a novel carrier harmonic loss reduction technique is proposed and applied to two sets of three-phase windings for a concentrated winding PMSM. The loss is successfully reduced in a 70-kW EV motor as well as a two-dimensional finite-element method (2-D-FEM) calculation. The efficiency of the developed motor is calculated and compared with that of a conventional motor in the JC08 mode driving cycle. [ABSTRACT FROM PUBLISHER]

Wireless power transfer (WPT) technology has become a popular research direction in the field of industrial applications, with the advantages of contactless operation, high degree of freedom, and great controllability. However, there are still some challenging issues that need to be resolved. First of all, more advanced circuit topologies and magnetic coupling structures need to be designed to achieve the power conversion goals of diversified applications. Second, novel control methods, optimization algorithms, and modeling methods enable systems to be better controlled and designed. Finally, potential application scenarios need to be discovered so that this novel power transfer method can be applied in more suitable applications. Therefore, this topic is organized by the responsible editor to gather the power of more scholars. With reviewers' hard work and considerations, 32 papers were finally accepted for publication in this Special Issue. [ABSTRACT FROM AUTHOR]

The significant benefits of preemptive arc-flash protection and the online condition monitoring of electrical equipment are quite well known. Our continuing research focuses on the development of new advanced sensor technologies that are cost-effective, reliable, and efficient for the early detection of faults in order to predict impending arc-flash occurrences in mediumvoltage and low-voltage switchgear and controlgear. More extensive and detailed measurements regarding significant defects that lead to an arc-flash event have been completed since the original work in Part I was completed. A more detailed analysis of the results of this additional testing is presented in this paper. It has been documented that the two major noncontact causes that lead to an arc-flash event in switchgear are insulation degradation and thermal stresses. This paper covers the detailed measurement results under both of these conditions. New sensor technologies for both the partial discharge measurement and the thermal detection are introduced and evaluated. An effective signal processing technique, which is needed for extracting the essential indication of a developing fault, is also presented. Finally, this paper outlines how a preemptive arc detection system can be connected to protection, the programmable logic controller, or the supervisory control and data acquisition. [ABSTRACT FROM PUBLISHER]

Submarine cables are indispensable for offshore wind farms (OWFs) connected to a power grid. The submarine cable can cause certain degrees of impact on the system performance due to its different lengths, characteristics, electrical parameters, etc. This paper employs the power-system simulation software of Power System Simulator for Engineering (PSS/E) for modeling a future-scheduled OWF, i.e., a large-scale doubly-fed induction generator-based OWF of 200 MW, connected to Jang-Bin distribution substation of Taiwan Power System through five feeders, five circuit breakers, two step-up power transformers, a commercial submarine cable, and an underground cable. This paper simulates and compares the electrical quantities of the studied OWF with different operating capacities under various lengths of three types of commercial submarine cable. The transient surge peak voltages at the common bus of the OWF and the bus of Jang-Bin distribution substation subject to the switching of one of the five circuit breakers of the studied OWF under different lengths of the three types of commercial submarine cable are also compared using the power-system simulation software of ATPDraw in Alternative Transients Program (ATP) version of Electromagnetic Transients Program (EMTP). [ABSTRACT FROM AUTHOR]

This paper deals with the design and testing of an interior permanent-magnet (IPM) machine that exhibits advanced features. It adopts fractional-slot (FS) nonoverlapped coil windings that reduces the end winding length, i.e., the Joule losses and machine cost. As a consequence, higher rated current can be supplied so that higher torque density and higher efficiency in a wide operating region can be reached. The rotor saliency increases the performance in flux-weakening operating region and the fault-tolerance capability. In order to decrease the torque ripple, it is important to minimize the interaction between the magnetomotive force (MMF) harmonics due to the stator currents and the rotor anisotropy. To do that, the winding has been optimized so as to minimize the MMF harmonics, taking advantage from the higher degree of freedom of the four-layer winding. However, the so-called slot-harmonics cannot be minimized by rearranging the winding coils. Hence, the rotor geometry has been designed so as to minimize the impact of such slot-harmonics. A 12-slot 10-pole IPM FS machine has been designed and manufactured. The experimental tests confirm the expectations. [ABSTRACT FROM AUTHOR]

There are benefits if copper windings are replaced with aluminum in applications that are cost- and mass-sensitive, such as automotive traction; these include the low cost of aluminum, low mass of aluminum, and the ease of motor recycling at the end of life. However, the relatively low electrical conductivity of aluminum compared to copper needs to be overcome. Precompressed motor coils have been shown to produce very high fill factors ($ > 75\%$), reducing dc-winding losses, therefore enabling the use of aluminum conductors. However, the single-stranded conductors used can be prone to high ac losses due to skin and proximity effects. Therefore, a method of manufacture of precompressed coils made from stranded/Litz wire is needed, allowing ac losses to be reduced to low levels. This paper describes the development and test of stranded, precompressed aluminum coils, which have been developed for use in an automotive traction application. [ABSTRACT FROM AUTHOR]