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This paper is based on modifications implemented in the protection and grounding systems of a large paper mill and describes selective ground fault protection for a 13.8-kV system with multiple bus-connected generators, synchronous bus ties, and utility interconnections. The ground fault current in the system is reduced from the existing 3400 A to 500 A, and a hybrid grounding system is implemented for each of the generators. As the ground fault currents are reduced to limit the fault damage, the sensitivity and selectivity of the ground fault protection become important. Directional ground fault relays with coordinating pickup settings are applied to achieve this objective. The new platform for directional elements (numerical relays) drives its performance from sequence impedance measurements. [ABSTRACT FROM AUTHOR]

For forest-products-based industries, the significant benefits of preemptive arc-flash protection and online condition monitoring of electrical equipment are not well known. This paper provides a summary of the research surrounding the development and testing of new advanced sensor technologies for this purpose. This paper builds on the authors' initial research and their supporting publications providing more extensive and detailed field measurements supporting the preemptive detection of significant defects that can lead to an arc-flash event. The early detection of impending faults and the prediction of future arc-flash occurrences in medium voltage (MV) switchgears and motor control centers (MCCs) can be very beneficial. The development of new sensor technologies both for partial discharge measurement and thermal detection are discussed and evaluated. The two most common noncontact causes leading to an arc-flash event in MV switchgears and MCCs are insulation degradation and thermal stresses. This paper will highlight very detailed results measured under both of these conditions in laboratory and actual installed conditions. An effective signal processing method, which is used for extracting the essential indication data and for the integration of this system into existing protection programmable logic control or supervisory control and data acquisition (SCADA) systems, is outlined. [ABSTRACT FROM AUTHOR]

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

This paper discusses the protection requirements to interconnect a typical refinery to the utility system. However, the information provided is applicable to other industrial facilities that have generation. It covers applications involving service to a refinery that normally requires a transformation between the utility's supply voltage and the refinery's utilization voltage. This paper specifically addresses refineries with generation that are connected to utility transmission circuits. The protection discussed must protect the refinery from the effects of utility system faults, but must also protect the utility from the effects of refinery faults. Coordination between these two systems is essential to minimize the effects of fault-induced outages. This paper specifically addresses typical refinery–utility interconnections system one-line designs, determining utility supply performance expectations, impact of generation on interconnection protection, relay functional requirements for typical interconnections protection, relay communication requirements, and grounding of the interconnection transformer(s) and its impact on protection. In addition, this paper will discuss the North American Electric Reliability Corporation requirements and their effect on refinery interconnection protection. [ABSTRACT FROM AUTHOR]

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]

This paper discusses some of the main issues that are generally found in protection systems of low-voltage electrical installations and presents a methodology that can be used to analyze and upgrade the existing power system protective devices in these low-voltage distribution systems. The upgrades of existing operating systems, especially low-voltage systems, always face an economic challenge where the monetary value spent on upgrades has to be justifiable against the benefit derived. If understood clearly, the benefit of upgrades to existing protective systems is larger than just making these systems safer. A gated approach for the upgrade and proper management of such systems can help in planning for future expansions, provide reliability of equipment, and decrease the overall risk for the operation of any facility. [ABSTRACT FROM AUTHOR]

The operational availability of mining shovels is the focus of this paper. The hypothesis is that energy quality is responsible for the frequent shutdowns of the shovels. Previous engineering studies have highlighted a large presence of harmonics and reactive power in the mine loop electric system. A common solution proposed was to use a combination of active filters, larger mobile substations, shorter mining cables, and equipment location constraints. The aim of this paper is to produce a precise diagnosis of the source and nature of the energy quality issues. Mine loop electric quality monitoring, system modeling, equipment technologies, and shovel's histograms are considered. Results are measured against IEEE standards and shovel's voltage regulation susceptibility. With the diagnosis, the goal was to produce a reliable cost-effective solution. Different alternatives are crosschecked with this paper proposal. The solution presented provides energy quality well within the shovel's susceptibility and improves energy efficiency. The lower energy consumption pays the investment required and is currently under construction. [ABSTRACT FROM AUTHOR]

This paper suggests an advanced approach in the verification of the adequacy of a grounding system (GS) located in a common zone of influence with other GSs, taking into account the mutual interferences between the GSs. In fact, the presence of other GSs can transfer inadmissible touch and step voltages on the testing GS, particularly sensitive for critical power systems as data centers and hospitals. The safety of a local GS or of a global GS (GGS) does not admit uncontrolled interferences. Simulation programs assume a relevant importance, because they allow analyzing the interferences of GSs, particularly in operational difficulties for the tests. GSs have to maintain within the installation lifetime their characteristics of integrity and continuity and their safety performances; hence, they require a management program. This paper highlights the relevance of intrinsically safe GSs that guarantee safe touch/step voltages lower than permissible permanent voltages such as GGSs. GSs in city centers and urban and industrial areas evolve in time. Each installation of a new GS can influence the performance of the GSs existent in the area. Inspections and measurements are also necessary, following variations that can influence essential requirements. [ABSTRACT FROM AUTHOR]

To minimize ground fault during a line-to-ground fault condition, it has been a common practice to use high-resistance grounded (HRG) power systems, both at low voltage and at medium voltage (MV). The criteria for designing HRG systems are very well known to the industry; however, the opinion of industry experts has been divided on limiting the use of HRG systems for MV systems to voltages of less than 4.16 kV and phase-ground fault currents of less than 10 A without clarifying that it applies to systems that require continuous operation upon first detecting line-to-ground fault, as it is now in the Recommended Practice for Grounding of Industrial and Commercial Power Systems. This paper will review the background history of HRG power systems and their application to MV systems for specific industries and will make the case that voltages need not be limited to less than 4.16 kV and the phase-ground fault current to less than 10 A, so long as the faulted power system is isolated within ten cycles and that there are no directly connected motors. This paper will discuss the potential damage and protection requirements of HRG systems for MV applications to ensure that a line-to-ground fault is cleared before it involves other phases to make a multiphase arcing ground fault. [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]

Direct current (dc) motor drive systems are extensively used in paper, steel, mining, material handling, and other industrial applications due to the high starting torque and easy speed control over a wide range. They could account for 10%–20% load demand in some industrial facilities and thus have significant impact on the overall system dynamics. However, an adequate dynamic model for this type of loads is not available for power system dynamic studies. In this paper, a comprehensive modeling method for dc motor drive systems is proposed considering two scenarios: 1) The drive will trip when subjected to severe voltage sags, and 2) the drive can ride through when experiencing mild voltage sags. The dc drive trip curve and a simple procedure to determine if the drive needs to be included for dynamic studies are proposed for Scenario 1. The dynamic model for dc motor drive systems, which can be readily inserted in the simulation software, is developed and verified through case studies for Scenario 2. [ABSTRACT FROM AUTHOR]

The more electric aircraft concept aims to improve the fuel consumption, the weight, and both the maintenance and operating costs of the aircraft, by promoting the use of electric power in actuation systems. According to this scenario, electromechanical actuators for flight control systems represent an important technology in next generation aircraft. This paper presents a linear-geared electromechanical actuator for secondary flight control systems, where the safety and availability requirements are fulfilled by replicating the electric drive acting on the drivetrain. Indeed, the architecture considered consists of two power converters feeding as many electrical machines coupled to the same mechanical system. The design of both the permanent magnet synchronous machine and the power converter are addressed. Preliminary results on the electric drive prototype are also provided and compared to the design requirements. Finally, the electromechanical actuator performance at system-level is evaluated in Dymola environment, analyzing different operating modes. [ABSTRACT FROM AUTHOR]

In this paper, the static and dynamic behaviors of a power system feeding an oil/gas plant with superconducting (SC) cables are investigated. SC cables have been expected to provide more efficient power supply and less space utilization for power systems compared to conventional cables. On the other hand, their compatibility with the existing power systems has not yet been clarified. In this paper, taking a typical distribution system in an oil/gas plant as an example, we designed high-voltage SC cables and investigated their compatibility with the system from the viewpoint of static and dynamic performances. The voltage distribution under steady-state operation and the transient voltage and current during fault conditions were examined and compared with the case of conventional cables. The results show that, in addition to the efficiency enhancement, SC cables could be applied without any further constraint on circuit breaker duties and insulation coordination requirements. [ABSTRACT FROM AUTHOR]

Power system protections are highly sensitive to decaying dc offset that could appear when a fault occurs. The consequences of this effect represent a challenge in the coordination of protection devices that have been widely studied. The elimination of the dc offset component of current transformers (CTs) measurements is the objective of this paper, including a new autonomous detector based on mathematical morphology. The idea enhances the digital signal processing to prepare the information before the protective device takes a decision. The detection and fast elimination of the decaying dc offset on current signals could improve the speed of protection, coordination, and selectivity. The paper presents the proposed algorithm and assesses the solution using alternative transient program. The model of the CT used for this validation is also presented. Results show the potential of the mathematical morphology for signal processing to delete the dc offset component. [ABSTRACT FROM AUTHOR]

Probabilistic wind generation forecast results are crucial for power system operational dispatch. In this paper, a nonparametric approach for short-term probabilistic wind generation forecast based on the sparse Bayesian classification (SBC) and Dempster–Shafer theory (DST) is proposed. This approach is composed of the following four steps. 1) A spot forecast of wind generation is performed based on support vector machine (SVM). 2) The range of SVM forecast error is discretized into multiple intervals, and the conditional probability of each interval is estimated by a sparse Bayesian classifier. 3) DST is applied to combine the probabilities of all the intervals to form a unified probability distribution function (pdf) of the SVM forecast error. 4) The pdf of wind generation is achieved by combining the SVM wind generation spot forecast result and corresponding forecast error distribution. The distinguishing features of the proposed approach are as follows. 1) The approach is a nonparametric one and the forecast error caused by the misjudgement of probability distribution type can be avoided. 2) The proposed approach has good generalization capability by using the sparse learning mechanism. 3) The range constraint of wind generation can be systematically considered in the approach by applying DST. Tests on a 74-MW wind farm illustrate the improvement of spot forecast accuracy of the proposed approach and validate that this paper provides better calibrated and sharper probabilistic forecasts than the empirical approach and quantile regression model. Comparison to the state-of-the-art of the Global Energy Forecasting Competition 2014 demonstrates the probabilistic forecast performance of the proposed approach. [ABSTRACT FROM AUTHOR]

Energy storage systems provide viable solutions for improving efficiency and power quality as well as reliability issues in dc/ac power systems including power grid with considerable penetrations of renewable energy. The storage systems are also essential for aircraft powertrains, shipboard power systems, electric vehicles, and hybrid electric vehicles to meet the peak load economically and improve the system’s reliability and efficiency. Significant development and research efforts have recently been made in high-power storage technologies such as supercapacitors, superconducting magnetic energy storage (SMES), and flywheels. These devices have a very high-power density and fast response time and are suitable for applications with rapid charge and discharge requirements. In this paper, the latest technological developments of these devices as well as advancements in the lithium-ion battery, the most power dense commercially available battery, are presented. Also, a comparative analysis of these high-power storage technologies in terms of power, energy, cost, life, and performance is carried out. This paper also presents the applications, advantages, and limitations of these technologies in a power grid and transportation system as well as critical and pulse loads. [ABSTRACT FROM PUBLISHER]

Growing system sizes and complexity, along with the large amount of data provided by phasor measurement units (PMUs), are the drivers to accurate state estimation algorithms for online monitoring and operation of power systems. In this paper, a distributed weighted-least-square state estimation method using an additive Schwarz domain decomposition technique is proposed to reduce the computational execution time. The proposed approach divides a data set into several subsets to be processed in parallel using a multiprocessor architecture considering data exchange among distributed areas. The slow coherency method and balanced partitioning are utilized to reduce the communication overhead and increase accuracy. Moreover, bad data analysis is also investigated in a distributed manner. The performance of the proposed distributed state estimator, along with the speed-up for several test systems, was compared with the traditional centralized state estimator. The simulation results show a speed-up of 6.5 for a 4992-bus system. [ABSTRACT FROM AUTHOR]

Ground faults are among the major causes of disrupting the safe, secure, stable, and profitable operation of doubly fed induction generator (DFIG) based wind energy conversion systems (WECSs). On one hand, minimizing the possible damage in a DFIG-based WESC, caused by ground faults, requires accurate detection and fast response of ground protective devices. On the other hand, the responses of ground protective devices are highly dependent on ground currents and potentials, especially during high-impedance ground faults. This paper investigates the influences of grounding configurations on the responses of ground protective devices used in DFIG-based WECSs during high-impedance ground faults. Investigated influences are observed through the ability of ground protective devices, used in DFIG-based WECSs, to quickly and accurately respond to high-impedance ground faults for different grounding configurations. In this paper, the solid, low-resistance, high-resistance, and open grounding configurations are tested for DFIG-based WECS in order to establish comprehensive investigations. The results of the investigations show that the responses of ground protective devices vary depending on ground fault currents, which can have different levels due to the grounding configuration. Moreover, the results of the investigations reveal that the frequency-selective grounding configuration can offer a minimum impact on the responses of ground protective devices used in DFIG-based WECSs. [ABSTRACT FROM AUTHOR]

Oversizing electrical distribution equipment is a concern in industrial facilities. It adds cost and can increase fault levels. IEEE Std 141-1993 provides guidelines on how to size electrical equipment, but at the early stage of the project, when the equipment is being purchased, much of the process information necessary to properly size the equipment is preliminary at best. In addition, much is left to the discretion of the individual design engineer, who is often not an employee of the facility's eventual owner and, therefore, may have no incentive to reduce equipment size. In fact, depending upon the contractual relationship and due to the preliminary data, compressed schedule, and long delivery, design engineers tend to oversize the equipment. This paper describes an approach for establishing a load-based upper size limit to control oversizing of electrical equipment. This paper will demonstrate that establishing this upper limit can effectively control oversizing of the electrical equipment with information available at the early stage of the project. The resulting safety and economic benefits of the properly sized electrical equipment cascade throughout the power system. [ABSTRACT FROM AUTHOR]

This paper presents a novel finite-control-set model predictive control (FS-MPC) approach for grid-connected converters. The control performance of such converters may get largely affected by variations in the supply impedance, especially for systems with low short-circuit ratio values. A novel idea for estimating the supply impedance variation, and hence the grid voltage, using an algorithm embedded in the MPC is presented in this paper. The estimation approach is based on the difference in grid voltage magnitudes at two consecutive sampling instants, calculated on the basis of supply currents and converter voltages directly within the MPC algorithm, achieving a fast estimation and integration between the controller and the impedance estimator. The proposed method has been verified, using simulation and experiments, on a three-phase two-level converter. [ABSTRACT FROM PUBLISHER]

Intentional islanding operation of distributed generation (DG) can increase system reliability and reduce customer outage costs. Guidelines for the impact study and operation of DG for islanding operation should be implemented. The Provincial Electricity Authority (PEA) plays more attention to intentional islanding operation. To perform islanding operation, PEA has established islanding operation and impact study guidelines for DG. This paper presents the development of these guidelines. A case study was conducted to demonstrate the results of both steady-state and dynamic analyses. Operational issues are also taken into account in this paper. [ABSTRACT FROM AUTHOR]

Deployment of renewable energy sources in power grid causes an undesirable characteristic in the voltage profile due to its stochastic nature. Such electrical perturbations may impact the performance of equipment or machines connected to the grid, especially large rated machines (e.g., 250 MW). This paper investigates the electrical, thermal, and mechanical stresses on large rated doubly fed synchronous (fixed speed) and doubly fed asynchronous (variable speed) machines used in pumped storage power plants under voltage unbalance. Also, the lifespan of the drive train considering thermal stress is estimated. In this paper, considering the medium voltage distribution system (15.75 kV), the magnitude of voltage unbalance is opted as 2.5% and 5% to test the performance of doubly fed machines. With respect to these considerations, the impacts on machine parameters such as rotor current, stator current, input power, torque, and losses are comprehensively investigated. To observe the performance of large rated doubly fed machine drive system under voltage unbalances, the MATLAB/Simulink environment is adopted. Also, to realize the real-time impact on doubly fed machines, a prototype rig (with 2.2-kW synchronous and asynchronous machines) are experimented. The practical significance of this relative analysis is to minimize voltage collapse in the system and for developing the robust system with countermeasures. [ABSTRACT FROM AUTHOR]

Critical process loads need to be safeguarded against power system disturbances and erroneous operations caused by human factors. During such events, a fast synchronism-supervised transfer scheme is required to ensure continuous operation. This paper discusses the implementation of a fast motor bus transfer scheme using existing protective relays. The scheme is designed to respond to local and remote (upstream) events in the substation. This makes possible an attempt to initiate a fast transfer for events that are remote to the motor bus. On a failure to achieve a fast transfer, the scheme resorts to an in-phase transfer and, if that fails, finally a residual transfer. Real-time dynamic modeling was performed to simulate motor bus decay and reacceleration. This paper provides the results of the simulations and the response of the transfer scheme. [ABSTRACT FROM AUTHOR]

This paper deals with an innovative design strategy of building power systems by introducing criteria based on both the “installation approach” and the “operating approach” applying plan–do–check–act (PDCA) cycle. The In-Op design of the electrical power systems takes care of the worst cases of configurations, adequate gaps on load in selecting the rating of components, the actual mean losses to evaluate their energetic operation, and to avoid excessive gaps on the lifetime of components. With this aim, the authors suggest consideration of the thermal aging model of Arrhenius to review the actual gap on load in selecting the rating of components. In reference to IEC standards, this paper underlines in the circuits design the cable steady and transient current densities, the load current torque density as “natural” parameters that allow applying a thumb rule in the classic sizing of the cross-sectional area of circuit conductors. Microsystem criteria in power systems design allow structuring their configuration with components of smaller size to reduce radically the volume of circuit conductors with more sensitive results in the branch distribution. The authors suggest why not reconsider the series of commercial cross section areas of power cables. [ABSTRACT FROM PUBLISHER]

Shipboard control systems equip an expert operator with the ability to safely open and close breakers to facilitate electric plant operations. In more advanced systems, ship integrated power systems are equipped with automatic control systems that provide power management by automatically connecting and disconnecting power generation sources based on plant's present load and online generation capacity. What is generally lacking, however, is an effective manner to provide autonomous reconfiguration of the power system in response to electric plant casualties and ship's mission changes when the ship's electric plant is in a degraded condition. This paper explores the use of graph theory principles as they apply to developing automation control system algorithms to provide electric plant operations full autonomous control in the event of electric plant casualties and/or ship's mission changes. [ABSTRACT FROM AUTHOR]

This paper discusses the design criteria for the electrical systems of roadway tunnels with particular regard to the safety in the daily operation and in the case of fire events. It proposes a fit distribution system and an adaptive criterion for the support lighting system in order to minimize costs and energy impact. Electric systems of roadway tunnels need sophisticated architecture to allow the presence of extensively distributed loads and more stringent installation requirements due to the presence of fire hazard. Mechanical and electrical design criteria must be based on equipment qualification categories (EQCs), which are characterized by thermal inherent resistance and environmental parameters. Design criteria must include variable configurations to simplify installation, allow flexible operation, and optimize the cost–benefit ratio. A special power distribution, herein defined as “brush distribution,” and a temperature zone classification are proposed for road tunnels with a higher risk in the case of a fire event. Therefore, this paper suggests as design parameters the temperature exposure levels characterizing the thermal demand in each zones and the EQCs in order to choose the equipment with adequate thermal resistance. [ABSTRACT FROM PUBLISHER]

The integration of distributed generation (DG) or distributed resources in the distribution system poses technical constraints for the electrical power system owner or manager. The addition of relatively large amounts of generation to the distribution system can potentially challenge the historical setting principles and design assumptions made in developing protection and control strategies based on overcurrent protection. The necessity and complexity of additional protection and control measures increase as the aggregate DG capacity within a potential island approaches or offsets the load within that island. In addition, the varying nature of DG availability and fault current capability must also be considered. The key issues discussed and associated with DG on the distribution feeder include anti-islanding, temporary overvoltages during fault conditions, and loss of sensitivity of feeder overcurrent protection for long feeders. As the distribution system evolves to accommodate more DG, the design and implementation of the feeder protection must also evolve. This paper presents the use of distance relays for distribution protection to solve some of the DG integration problems. This paper provides real-world event report data to further demonstrate the performance of distance protection on the distribution system. A relative cost comparison between various feeder protection solutions is presented along with a discussion on options for education of distribution companies challenged with implementing distance protection for the first time. [ABSTRACT FROM PUBLISHER]

Main–tie–main (MTM) transfer schemes increase reliability in a power system by switching a load bus to a secondary power source when power interruption occurs on the primary source. Traditionally, the large number of physical I/O lines required makes MTM schemes expensive to design and implement. Using Ethernet-based IEC 61850, these hardwired I/O lines can be removed and replaced with generic object-oriented substation event (GOOSE) messages. Adjustment of the scheme for optimal performance is done via software that saves redesign and rewiring times. Special attention is paid to change-of-state GOOSE only; no analog GOOSE messages are used, making the scheme fast and easy to configure, maintain, and troubleshoot. Applications such as fast motor-bus transfer are discussed with synchronization remaining at each breaker relay. Simulation test results recorded GOOSE message latencies on a system configured for an MTM scheme. This paper presents the details of open and closed manual and automatic transfers. [ABSTRACT FROM AUTHOR]

This paper describes the application of remote isolation applied in mining industry conveyance systems. Remote isolation removes personnel from potentially dangerous electrical lockout tasks by removing the element of human error. Safe verified isolation of electrical systems has proved to increase production output by reducing the required time to electrically isolate industrial systems where zero energy is required prior to performing work. Time saved to both isolate and de-isolate is converted to production time and increased manufacturing throughput. This paper describes the application of remote isolation systems, discusses implementation of enhanced safety systems and the necessary engagement with local regulating authorities. Finally, a case study of an actual installation discusses specific details where these systems have been installed. [ABSTRACT FROM AUTHOR]

The increasing penetration of distributed and renewable generation presents power systems with a challenge of accommodating multiple inverter-based generators. Distributed generators (DGs), capable of operating in the islanded mode, are often installed in microgrids. However, a control system for operating multiple DGs in the islanded mode using voltage-sourced converters is a real challenge under uncertainties in load parameters, unbalanced phase conditions, and transients. This paper proposes a novel approach to decentralized control of multiple DGs. This approach is based on a combination of a voltage controller using model predictive control and a fast current controller using a discrete-time sliding-mode controller for limiting the inverter currents under overload conditions. Performance of the proposed control system is compared with a robust servomechanism program controller. The proposed control strategy provides fast tracking, robustness, and fast transient recovery in voltage and current under: 1) short-circuit conditions; 2) load transients; and 3) unbalanced loads. Various scenarios including reference signal tracking and robustness against the load perturbations are considered. Results are presented and discussed. [ABSTRACT FROM PUBLISHER]

The successful mission of CubeSat require reliable and fault-tolerant electrical power system (EPS) that powers all the other subsystems and payloads. Several studies have shown that EPS failure has been one of the main contributors for the CubeSat mission failure. The main objective of this paper is to enhance the lifetime of CubeSats EPS by proposing a distributed EPS architecture and power-down mode. The distributed architecture consists of independent converters for maximum power point tracking operation of photovoltaic (PV) panels. This is possible by using gallium nitride field-effect transistors to reduce the converter footprint and placing the converters on the back-side of the PV panels. Also, single-inductor based $N$ -1 redundant converters for generation and load-side are proposed to provide uninterrupted operation during component failures. Thus, the proposed distributed architecture not only improves the reliability but also facilitates placement of redundant converters to achieve the fault-tolerant capability. To further reduce the electrical and thermal stresses on the semiconductor devices and thus, improve the EPS life span, a novel power-down mode is proposed for the power converters. In this mode, semiconductor devices are switched-off whenever the power processed is below the threshold level and/or no-load operation. Reliability block diagrams are illustrated to demonstrate the reliability improvement and calculations shows that the proposed distributed architecture has higher reliability than the conventional EPS architecture. All the proposed concepts are validated using a prototype developed based on the specifications of MYSAT-1, which is an 1U CubeSat launched by Khalifa University. [ABSTRACT FROM AUTHOR]

This paper describes a method for implementing a gradient-based nonlinear optimization technique for optimal tuning of nonlinear power system controllers such as a flexible ac transmission system (FACTS) via a combination of hardware and software in the real-time digital simulator (RTDS). The RTDS offers fundamental advantages over other commercial software tools because it is a fully digital power system simulator that operates in real time. Therefore, nonlinear optimal parameters can be effectively determined under similar environments to actual physical systems by this real-time implementation. In this paper, the Broyden–Fletcher–Goldfarb–Shanno optimization algorithm, which has a quadratic convergence property, is implemented in order to design the nonlinear controllers in power systems. Its effectiveness is demonstrated with two design examples intended to improve low-frequency oscillation damping in power systems. After illustrating an example to optimize the nonlinear parameters of the power system stabilizer, this paper introduces the optimal design of an external controller for the series capacitive reactance compensator, which is one of the FACTS devices, in real-time simulation. [ABSTRACT FROM AUTHOR]

The selection of placement and size for multiple distributed generators based on renewable energies becomes an important issue in operating modern power systems safely and reliably. This paper extends the previous study in our earlier paper by treating the problems for their optimal locations and sizes in more realistic way based on the power loss sensitivities and Kalman filter algorithm, respectively. In particular, the proposed method is implemented by the simulation on a part of practical distribution network of 60 MVA scale, which is located at the Do-gok area in Seoul, Korea. The new factor, called as the optimal locator index, is developed to determine the optimal locations in a systematic and effective manner by the power loss sensitivities. Also, the Kalman filter algorithm is applied to determine the optimal sizes by choosing the step size of 10 KW, which is a much smaller increment than the 10-MW step used in our earlier paper, without requiring high computational efforts. This selected step size of 10 KW is realistic and suitable to apply in practical test systems. [ABSTRACT FROM AUTHOR]

Petrochemical industry not only consumes a large amount of electricity every year but also requires high-quality power supplies. Any unexpected power failure could shut down the entire production line and cause significant financial loss. Meanwhile, due to the large electricity consumption and intensive power demand, in-house cogeneration plants have been equipped for most petrochemical facilities. Thus, any power interruption or disturbance between a petrochemical facility and interconnected power grids could affect both sides of the power systems. Therefore, having high power quality becomes one of the most critical parts for petrochemical facilities. To avoid unexpected power failure and to provide a better understanding of the power system at petrochemical facilities, a fast, precise, and reliable power monitoring system is required. A novel real-time web-based power monitoring system on field-programmable gate array platform is developed in this paper for a power substation at the petrochemical facility. Besides the data collecting with event-triggering mechanism and measurement data recording functions, subsynchronous oscillation detection application is also developed in this system. This monitoring system could provide precise data to help engineers with insightful analysis of the electric system to prevent a power failure, and it also could help system operators to have a better understanding of the system operation characteristics. [ABSTRACT FROM AUTHOR]

This paper presents a new islanding detection method for synchronous distributed generation (DG). The proposed method is developed based on the combination of rate of change of exciter voltage (RCEV) and open–close circuit breaker (OCCB) at a DG connection point. Whenever the RCEV parameter is not sufficient enough to detect an islanding condition efficiently and correctly, the OCCB strategy will be triggered. The proposed OCCB strategy sends a switching command to one phase of the three-phase circuit breaker (CB), which connects the DG to the grid. In this way, the CB will be immediately opened and then closed. This switching condition will cause a variation in the value of RCEV. This variation is small for the conditions when DG operates in parallel with the main grid, whereas it will be large during the occurrence of islanding. The implementation of the proposed strategy is cost-effective because it only uses the CB at the DG output and does not require any extra equipment. The proposed approach is tested on two different systems including a hypothetical power system and the IEEE 33-bus test system in MATLAB/Simulink environment. The simulation results show that the proposed method eliminates the nondetection zone and also reveals high accuracy compared with previously introduced methods. Moreover, it has been proved that the performance of the proposed approach is not affected by DG capacity, DG location, the number of DG units, as well as network configuration. [ABSTRACT FROM AUTHOR]

An optimized system management of a commercial and industrial power system must take care of the actual operational and energetic duty of the power system distribution. A procedure based on the Arrhenius model of the thermal aging of insulating materials allows introducing the relative time coefficient and promoting a heuristic method, as a rule of thumb, to estimate the life loss and the residual useful life for insulated power cables. This paper deals with simplified models of low-voltage (LV) cable systems characterized by one and two time constants to evaluate the cable temperature behavior and the influences of the ambient and installation conditions. Furthermore, this paper proposes a device to count the “life loss hours” for LV power cables of main/critical circuits. [ABSTRACT FROM AUTHOR]

This paper presents an approach to design a contactless energy-transfer system to supply desktop computer peripherals. Energy is transferred using coreless transformers from an array of primary coils (placed on a table) to one or several secondary coils (placed under the peripheral). Knowing the geometrical structure of the coils of a coreless transformer, accurate calculations allow predicting the power that can be transferred to a load. By applying these calculations to one basic energy-transfer cell, it is then possible to design a whole table that is able to supply many consumers at any location. The main problem with such systems is that the energy transfer is not constant along the surface and may not be even enough to supply an electronic device. This paper proposes several solutions to solve this problem. [ABSTRACT FROM AUTHOR]

Power grid reliability impacts could be significant when a large amount of variable wind generation is integrated with the electric power system. The widely used deterministic reliability assessment method is invalid when modeling the intermittency of wind energy sources. The energy-based probabilistic reliability assessment models are required in system reliability impact assessment in order to consider the stochastic characteristic of wind resources. This paper investigates different stochastic characteristics in wind energy integration, including resource availability, generation facility outage, and transmission availability. A probabilistic framework of reliability modeling for renewable resource integration such as wind energy conversion system is proposed in this paper. Using the proposed reliability models and framework, the cost of wind energy integration with the power grid for maintaining system adequacy and reliability can be evaluated realistically. The IEEE Reliability Test System is utilized to demonstrate the developed models and methods. The methodology can be used for modeling the reliability of industrial and commercial facilities being serviced by wind farms and transmission lines. [ABSTRACT FROM AUTHOR]

Power electronic converter-interfaced distributed energy resources (DERs) are being increasingly deployed for achieving high energy efficiency, power quality, and flexibility of power system operation and controls. They facilitate access to a wide array of energy sources, including renewables, fuel cells, microturbines, variable speed engine-generator sets, etc. However, recent tests carried out at the Consortium for Electric Reliability Technology Solutions (CERTS) Microgrid have indicated that their deployment in the mixed source microgrid can cause a cascading collapse during extreme events. To investigate the problem, simulation models of two types of DERs are developed in PSCAD/EMTDC software and validated with the experimental test results. Furthermore, the validated models are used to study a cascading collapse problem in a large-scale mixed source microgrid on the benchmark IEEE 33-bus test system. In this paper, three alternative techniques are evaluated to prevent the cascading collapse in the large-scale microgrid caused by fast-acting inverter-based DERs. [ABSTRACT FROM AUTHOR]

Short-term load forecasting is always a popular topic in the electric power industry because of its essentiality in energy system planning and operation. In the deregulated power system, an improvement of a few percentages in the prediction accuracy would bring benefits worth of millions of dollars, which makes load forecasting become more important than ever before. This paper focuses on the short-term load forecasting for a power system in the U.S., where several alternative meteorological forecasts are available from different commercial weather services. To effectively take advantage of the alternative meteorological predictions in the load forecasting system, a new comprehensive forecasting methodology has been proposed in this paper. Specifically, combining forecasting using adaptive coefficients is applied to share the strength of the different temperature forecasts in the first stage, and then, ensemble neural networks have been used to improve the model's generalization performance based on bagging. The proposed load forecasting system has been verified by using the real data from the utility. A range of comparisons with different forecasting models have been conducted. The forecasting results demonstrate the superiority of the proposed methodology. [ABSTRACT FROM AUTHOR]

This paper describes a design study for the power system for an industrial plant with islanded gas turbine generators (GTGs) and large variable-frequency drives (VFDs). Examples discussed are based on the authors' experience of liquefied natural gas plants where VFDs are used as compressor drivers. The shaft of a GTG has mechanical torsional resonant modes which may be excited by the interharmonic currents produced by the VFDs. At the power levels considered, up to 90 MW for each compressor, the VFD converters should be arranged to give suitable harmonic and interharmonic characteristics. This paper describes real case studies and compares three load-commutated-inverter VFD arrangements. Their advantages and limitations are analyzed; this highlights features that are different for each design for both the "normal" harmonics as well as the interharmonics. It is shown that, in islanded operation, the GTGs cannot provide any electrical damping to the torsional vibration which implies that strict interharmonic limits should be applied in the design. PSCAD-EMTDC time domain simulation results are used to confirm the analysis and justify the considerations that are important in the design exercise. [ABSTRACT FROM AUTHOR]

Presents an abstract of the paper entitled `An Improved Model for Analyzing Industrial Power Systems,' by Matthew P. Oommen and Jeffrey L. Kohler,' which won the 1996 First Society Prize Paper Award of the Institute of Electrical and Electronics Engineers.

When medium-voltage reduced-voltage autotransformer (RVAT) motor starters fail, also referred to as Korndorfer starters, particularly ones in which there is no clear failure to the core or tap-to-tap but just layer-to-layer deep down in the windings, the results are almost always catastrophic. An offshore platform is used as an example to discuss site-specific solutions that are based on the recently developed switching transient analysis, sweep frequency-response analysis, and state-of-the-art electromagnetic transient program (EMTP) simulation techniques. This paper will explain how the power system, interrupter, and transformer interact and outline the steps to solve this long-standing problem as well as present the newly applied solutions. Since the implementation of these new solutions, no further failures have occurred. [ABSTRACT FROM PUBLISHER]

The aim of this study is to introduce real-time hardware-in-the-loop (RT-HIL) techniques to test and study different protection systems on industrial distribution networks. The advantages of this implementation consist in the possibility to emulate the theoretical coordination results accordingly to the specifications of the real-system conditions, including the limitations from the protective device; certainly, the proposed methodology incorporates the feature to evaluate multiple scenarios, special fault cases, and equipment characterization, while thoroughly grasping the behavior or response of a protection setup. Therefore, the study achieves a more appropriate and reliable protection scheme and facilitates the coordination of abridged topologies. A selected case of study based on IEEE 242-2001 was implemented on two simulation softwares in order to analyze and compare the standard configuration and results; after the models are validated, the electrical system is implemented on an RT test bench. This paper also shows computational performance assessment of the RT-HIL implementation of the protection coordination system based on the standard. [ABSTRACT FROM PUBLISHER]

Power electronic devices are widely used in power grid associated with loads and renewable energy sources. With increasing penetration levels of these devices, their response characteristics to short-circuit events can have significant impact on power system dynamics. Power electronic devices are sensitive to voltage sags; they could trip off line under severe voltage disturbances. The ride-through capability of these devices determines if they will remain online. In this paper, a generic method is proposed on how to evaluate the ride-through capability of power electronic devices through trip curves. This method is a two-step procedure. Step 1 is to create a trip curve of the device. Step 2 is to conduct a ride-through evaluation based on the created trip curve and a short-circuit study. Creating a trip curve for a particular type of power electronic devices is critical and challenging. Three case studies are demonstrated in this paper on the trip curve creation for variable-frequency drives, dc drives, and solar photovoltaic inverters based on local and international standards, power grid interconnection requirements, and manufacturer specifications. The proposed method can serve as a general guideline for the trip curve creation for power electronic devices. [ABSTRACT FROM AUTHOR]

Cascaded on-load tap changers (OLTCs) are widely used for coarse control of voltages in largely interconnected electric power systems. There could be interactions between load dynamics and OLTC control under certain system operating conditions which may lead to the OLTC limit cycle phenomena, thereby resulting into long-term voltage oscillations in the system. In recent years, renewable and nonrenewable local generation (LG) units have been getting interconnected in modern power systems. The existence of OLTC limit cycles in the presence of LG has not been addressed in the literature in greater details. In this paper, the OLTC limit cycle phenomenon, which can occur due to interactions among load dynamics, OLTC controls, and LG operation in electricity networks, has been investigated. Also, a novel strategy is explored for mitigating the power system oscillations introduced by OLTC limit cycles, especially for a network embedded with LG. The proposed mitigation strategy including detailed investigations and analyses has been verified for a two-bus test system and successfully tested on a multibus system using MATLAB. [ABSTRACT FROM AUTHOR]

The arc flash hazard is related to electrical safety in work place and has gained much attention as part of the safety program for many facilities. An effective approach to reducing the arc flash hazard in existing industrial and commercial facilities is proposed in this paper. To illustrate the proposed approach and provide quantified results, computer simulation is conducted for a large oil field facility and a manufacturing facility in a commercial building as two case studies. The simulation results from the two case studies show significant reductions on the incident energy and the fault clearing time, which verifies the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

In this paper, the performance of a passive anti-islanding method is experimentally tested for three phase (3\phi) cogeneration systems. The tested method is based on determining the wavelet packet transform (WPT) high-frequency subbands present in the d– q-axis components of instantaneous 3\phi, when evaluated at the point of common coupling (PCC). This passive anti-islanding method is founded based on the nature of instantaneous 3\phi apparent powers that have components continuously exchanged between both sides of the PCC. An islanding condition can be considered as a transient disturbance that creates nonperiodic and nonstationary high frequency components in sd and sq. These frequency components can be parameterized by WPT high-frequency subbands, which can provide accurate detection of the islanding condition. The $d$– $q$ WPT-based anti-islanding method is tested for a $3\phi$ cogeneration system under various loading and power delivery conditions. Performance results reveal accurate, fast, and reliable detection and response to the islanding condition. [ABSTRACT FROM AUTHOR]