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Reliability and power quality are two of the most discussed topics in the utility industry today. Many groups have performed power quality studies with varying results. One large industrial customer (Champion International) in northern New York State, which experienced numerous process interruptions in its paper mill due to power system disturbances, is the focus of this study. Monitoring methods, results, inadequacies of standards, and unique mitigation techniques used to conquer their problems are discussed in this paper.

This paper briefly describes the special publication, "Fault and Disturbance Data Requirements for Automated Computer Analysis", prepared by working group III of the Relaying Practices and Consumer Interface Protection Subcommittee of the IEEE Power System Relaying Committee. The publication describes the analysis objectives and the data necessary to facilitate automated analysis.

This paper describes a systematic method for determining an area of vulnerability (AOV) to fault induced voltage sags. The concept of an AOV is very useful for evaluating vulnerability and the relationship between sensitive loads and system voltage sag performance. In general, a system performance assessment pertaining to voltage sags requires a determination of AOVs for system buses. Because voltage sags can be caused by remote faults in a transmission system, to completely identify an AOV, a large part of the power system including adjacent circuits and remote supply systems should be considered. Therefore, accurately calculating critical points and identifying AOVs are challenging tasks. In this paper, we present an effective numerical method to determine an accurate AOV in a large scale power system and to overcome limitations of other well-known methods.

A saturated core fault current limiter (SCFCL) is a promising device for limiting the fault currents effectively, and improving the safety and reliability of power systems. Due to the core structure and the coupling effect between the ac and dc windings, traditional SCFCLs suffer the drawbacks of insufficient clipping performance and large size. Moreover, theoretical analysis of fault clipping performance has received little attention. Therefore, this paper proposes a novel bridge-type SCFCL (BSFCL). Compared with the traditional type, the BSFCL effectively reduces size and cost by using a bridge-type structure. In addition, the proposed additional limiting inductor improves the fault clipping performance of SCFCL. This paper first presents the principle and characteristics of BSFCL. Then, a theoretical analysis of clipping performance and parameter design method of BSFCL are presented in detail. Finally, the principle and performance of BSFCL are validated through electromagnetic simulation and experiments. The simulation and experimental results demonstrate the effectiveness of the theoretical analysis and the structure. The influence of different BSFCL parameters on fault clipping performance is also discussed.

This paper presents and discusses the concepts of a gapless-power-quality disturbance recorder (G-PQDR) and a novelty detector. In the G-PQDR, power signals are divided into continuous frames and the energy difference between an actual frame and a reference frame is used for comparison. If the current frame is different from the reference frame, it will be recorded in the equipment and it becomes the new reference frame; otherwise, the frame is discarded and the frequency of the fundamental component is stored. The G-PQDR is able to detect and record the waveforms of the previously known PQ disturbances as well as those of the PQ disturbances not yet observed in power systems, thanks to the novelty detection concept. This characteristic is important in the context of smart grids where hidden disturbances can be detected by this methodology. For efficient data storage by minimizing the volume of the data stored, the G-PQDR uses lossy and lossless compressors. This paper describes the entire process of detection and compression, and compares the performance of the proposed method with that of a commercial-power-quality data recorder. In addition, some of the prototype implementation details are presented.

This paper proposes a probabilistic method aimed at estimating the voltage sag frequency of nonmonitored sites given the number of sags recorded by a limited set of voltage sag monitors. The proposed method is based on simulating a representative database of feasible pseudomeasurements by using probabilistic values of fault coefficient, fault impedance, fault type, and fault location. This information is processed through Bayesian filtering based on the Bayes' probabilistic theorem. This enables obtaining the most probable voltage sag index at nonmonitored busbars given the index measured at monitored busbars. This statistical estimation of sag indices at locations where there are no monitors constitutes the main contribution of this paper. This study is developed in three power systems: the IEEE 24-busbar reliability test system, the IEEE 118-busbar test system, and the transmission network of Ecuador with 357 busbars.

Harmonic pollution of the traction power-supply system (TPSS) has become a vital concern for its adverse impacts on the tractive drive system of the train and power-quality issues of TPSS and connected power system. Harmonic modeling is the precondition to evaluate the harmonic pollution for TPSS. This paper systematically discusses the main harmonic sources in TPSS as well as their characteristics based on accurate field measurements. Moreover, the background harmonic voltage of the connected utility system and the harmonic of the train are compartmentalized and modeled with consideration of the stochastic and statistical features. This paper studies the background harmonic voltage with time slicing and probability statistics technique. Meanwhile, the harmonic of the train is described with the Norton equivalent model, which considers the interaction between harmonic voltage and harmonic current. Moreover, the influence of the working conditions and power output on the harmonic distribution is mentioned in the low-order harmonic modeling of the train. The results suggests the proposed methods can effectively restore the distribution and characteristics of the harmonics in TPSS.

In this paper, typical strengths, fault levels, and source impedances are thoroughly analyzed and calculated for the study of quality of supply in 230/400 V 50 Hz distribution systems. Considering all the disparity in distribution network design, this study is based on a comprehensive database containing typical arrangements and equipment in U.K./European systems, as well as on fully documented generic network models supplying four residential load subsectors in the U.K., i.e., from metropolitan to rural areas. Thus, this paper proposes an alternative method for determining reference values of network supply impedances and short-circuit fault levels at different points and locations of the medium-to-low voltage distribution system. The aim of this study is to provide a wider range of benchmark values than those stipulated in the IEC 60725 Standard, which only defines a single-reference threshold of public supply impedances for all types of distribution systems and residential customers. In order to assist network operators in the planning and design of their distribution systems, these values are further disaggregated and classified in this paper according to network/demand type.

This paper presents analytical and simulation studies of wind farms (WFs) connected to power system through a unified interphase power controller (UIPC), which should control power flow and the short-circuit contribution of WF. The UIPC is based on an interphase power controller (IPC) in which the phase-shifting transforms are replaced by two series converters (SECs). In this paper, the UIPC model is developed based on phase angles of injected SEC voltage and a control scheme is proposed to control power flow and limit the short-circuit contribution of WF. The WF model is based on an equivalent aggregated variable-speed double-fed induction generator. The PSCAD/EMTDC simulation results show that the UIPC is an effective and novel solution for power-flow control and limitation of short-circuit contribution of WF in power systems.

Proliferation of distributed generations (DGs) and power-electronics-based loads is bringing about more harmonic-polluted power signals. While some failures may occur as a consequence of nonsinusoidal current or voltage waveforms, existing reliability models of protection relays have not taken the harmonic-related failures into consideration. This paper develops a comprehensive Markov reliability model to categorize the possible functional states of a component, say a transmission line, protected by a relay, operating in a harmonic-polluted environment. In order to make the proposed model practically tractable, it is further simplified in two ways, through merging the states of the same consequence. The first simplified model focuses on the power component reliability assessment; while the other is built for reliability analysis of a protection system. Calculation of transition rates and how the resultant model is mathematically evaluated are then discussed. Numerical analyses and outcomes are based on the real-world data taken from Canadian substations. Accordingly, the results and conclusions drawn in this paper would be interesting to both academia and industry. Moreover, the proposed reliability assessment methodology is readily applicable in scrutinizing the impacts of harmonic pollution on the protection devices of other power components.

This two-part paper is intended to clarify definitions in dual transformer modeling that are vague, provide accurate modeling guidelines, clarify misconceptions about numerical instability, provide a unified dual model for a specific type of transformer, and introduce new paths of research to the power systems/electrical machinery community for low-frequency transients. Part I discussed the topology of duality-based models and some important issues, such as the most common approaches to derive dual models and their variety, the equivalence of negative inductance and mutual couplings to represent the leakage inductance of three-winding transformers, and the numerical oscillations caused by the use of nontopological models. This part of the paper discusses and compares white-, gray-, and black-box models. The paper also reviews hysteresis models (static and dynamic) and highlights the differences between the air-core inductance and saturation inductance. The available dual models for the representation of the transformer tank are then presented. A unified and accurate model of a three-phase core-type transformer adequate for all low-frequency transients is presented. Finally, concrete guidelines are presented for the appropriate selection of the model topology and parameters for different low-frequency transient studies.

This paper presents an extended harmonic domain (EHD) model of a wind turbine generator (WTG) system based on a doubly fed induction generator. The proposed EHD WTG model includes both electrical and mechanical subsystems and permits monitoring step-by-step the harmonics time variation; this allows, among other applications, to detect contingency scenarios, such as resonance problems caused by a specific harmonic. Moreover, control efficiency can be improved by means of the power-quality indices which are instantaneously available by the EHD WTG model. The proposed model is capable of accounting for an arbitrary number of harmonics; however, the more harmonics that are included, the larger the system becomes. This affects the central-processing unit time by the transient simulation. An efficient heuristic remedy is proposed in this paper which consists of accounting for “high-impact” harmonics only, based on the converter's frequency spectrum. The EHD WTG model is validated with the power system computer-aided design/electromagnetic transients including dc (PSCAD/EMTDC) software tool via a case study.

In this paper, we propose an idea to integrate more renewable energy into the existing China power grid and to provide remote islands with a reliable power supply. The idea is to expand the existing point-to-point line-commutated converter (LCC) HVDC transmission link into a hybrid multiterminal HVDC (hybrid MTDC) system, which contains LCC stations and voltage-source converter (VSC) stations. Accordingly, this paper proposes a novel control strategy for this system called active voltage feedback control, which does not need any high-speed communication system under various disturbances, such as wind speed variations, load fluctuations, faults, etc. This paper also adds secondary frequency regulation to the synchronverter, which is one way of combining the VSC converter with synchronous machine behavior. Then, this paper applies an approach to limit its current under fault conditions. Finally, the entire hybrid MTDC system is modeled in PSCAD/EMTDC. Simulation results show that the improved synchronverter is able to achieve secondary frequency control, and the presented active voltage feedback control works very well when exposed to various disturbances.

Series impedance and shunt admittance parameters of transmission lines are fundamental data for various online and offline power system studies. This paper shows that the active power, reactive power, and voltage magnitude ( $P$ , $Q$ , $V$ ) data measured at the two ends of a transmission line are sufficient to determine the positive-sequence line parameters. The phase-angle information is not essential. Since the $P$ , $Q$ , and $V$ data are readily available from the supervisory control and data-acquisition systems, the proposed method can be easily implemented in existing control centers. Algorithms, characteristics, performances, and potential applications of the proposed method are presented in this paper. Simulation study and field test results show that the proposed technique can be a useful addition to the energy-management systems of utility companies.

Systematic principal component analysis (PCA) methods are presented in this paper for reliable islanding detection for power systems with significant penetration of distributed generations (DGs), where synchrophasors recorded by Phasor Measurement Units (PMUs) are used for system monitoring. Existing islanding detection methods such as Rate-of-change-of frequency (ROCOF) and Vector Shift are fast for processing local information, however with the growth in installed capacity of DGs, they suffer from several drawbacks. Incumbent genset islanding detection cannot distinguish a system wide disturbance from an islanding event, leading to mal-operation. The problem is even more significant when the grid does not have sufficient inertia to limit frequency divergences in the system fault/stress due to the high penetration of DGs. To tackle such problems, this paper introduces PCA methods for islanding detection. Simple control chart is established for intuitive visualization of the transients. A Recursive PCA (RPCA) scheme is proposed as a reliable extension of the PCA method to reduce the false alarms for time-varying process. To further reduce the computational burden, the approximate linear dependence condition (ALDC) errors are calculated to update the associated PCA model. The proposed PCA and RPCA methods are verified by detecting abnormal transients occurring in the UK utility network.

Having unveiled the problems associated with distance protection of lines connected to full-scale converter-interfaced renewable energy power plants (CIREPPs) due to remote and intermediate infeed in Part I of this paper, Part II describes why the countermeasures currently deployed by commercial relays to tackle these problems in a conventional power system fail in the presence of a CIREPP. Then, a new formula to calculate impedance is devised for the phase element of the relay to prevent maloperation in the event of line-to-line to ground faults. In addition, a communication-assisted method with minimal bandwidth requirement is proposed for balanced and line-to-line faults. The issues that should be taken into consideration for single-line-to-ground faults are also discussed. The solutions presented in this paper are simple and independent of the host system grid code, and can be applied to industrial memory-polarized distance relays. A comprehensive performance evaluation is presented to verify the reliable operation of the proposed methods.

Power system loads are one of the crucial elements of modern power systems and, as such, must be properly modelled in stability studies. However, the static and dynamic characteristics of a load are commonly unknown, extremely nonlinear, and are usually time varying. Consequently, a measurement-based approach for determining the load characteristics would offer a significant advantage since it could update the parameters of load models directly from the available system measurements. For this purpose and in order to accurately determine load model parameters, a suitable parameter estimation method must be applied. The conventional approach to this problem favors the use of standard nonlinear estimators or artificial intelligence (AI)-based methods. In this paper, a new solution for determining the unknown load model parameters is proposed—an improved particle swarm optimization (IPSO) method. The proposed method is an AI-type technique similar to the commonly used genetic algorithms (GAs) and is shown to provide a promising alternative. This paper presents a performance comparison of IPSO and GA using computer simulations and measured data obtained from realistic laboratory experiments.

Hopf bifurcation phenomenon of a power system results in oscillatory dynamics which can lead to instabilities in the system. Therefore, it is desirable to operate the system such that a sufficient margin to Hopf bifurcation is ensured. This paper presents a methodology based on the adjustment of the setpoint values of the HVDC link controllers, to prevent instability or increase the stability margin of the system subject to Hopf bifurcation. In this paper, the first-order sensitivities of the Hopf stability margin to the setpoint values of the HVDC links are presented. These sensitivities identify the optimum direction to change the HVDC setpoints to steer the system away from instability, increase the stability margin, and improve the damping of oscillatory modes. The proposed method is evaluated on various system configurations subject to Hopf bifurcation phenomena caused by a variety of events, such as load and line impedance variations. Simulation results show that at the optimum operating point, for a variety of Hopf bifurcations, the stability margin and damping of the oscillatory modes improve.

in the companion paper (Part I), a new tool for lightning-induced voltage calculations, called CiLIV, has been presented. In this paper (Part II), predictions made with the new tool are compared to experimental data and to outputs of analytical procedures/numerical codes found in the literature.

Multiterminal dc (MTDC) systems are drawing a lot of interest lately in applications related to distributed generation, especially in those that integrate wind or photovoltaic (PV) generation with energy storage (ES). Several approaches for controlling the operation of such systems have been proposed in the literature; however, the existing structures are mainly application specific and, thus, can be still improved in order to provide a more generic approach. This paper proposes an improved primary control layer for an MTDC system. The concept is based on the combination of a droop control method and dc bus signaling in order to provide a more generic and flexible solution. In this paper, different droop characteristics are proposed for the various elements connected to the dc bus. All of them are specifically tailored around five operation bands, which depend on the dc bus voltage level. Special attention is paid to the integration of ES: the state of charge (SoC) is considered at the primary control level, yielding a surface characteristic that depends on the SoC and the dc bus voltage. The scaling of the system has been analyzed together with the proposed control strategy and the overall operation has been validated through simulations by considering a 100 kW PV system with energy storage. Experimental results were obtained on a scaled laboratory prototype rated at 10 kW.

This paper presents the work carried out by the IEEE Working Grou[ on field-measured overvoltages and their analysis for validating power system component models to be used in switching transients studies. The work uses measurement data obtained from field tests performed by Bonneville Power Administration in June 1995 where switching overvoltages were measured on one of its 230 kV lines. This paper includes a description of the switching tests and the main results derived from field measurements. Details of the switching procedures that were followed to calibrate component models used to match field-recorded waveforms can be found in the Part II paper.

This paper proposes a technique for preventing saturation in series transformers from dynamic voltage restorer (DVR) systems. The method consists in correcting the voltages which are injected through the transformers into the power system to compensate voltage sags. It restricts the compensating voltages during the sag whenever it predicts that a maximum limit for the flux linkage is about to be exceeded. The prediction is carried out at the beginning of a stabilized voltage sag. Moreover, the technique allows a certain level of sag compensation even when the estimated flux is expected to exceed the saturation limit. The voltage sag level and phase are computed through an adaptive recursive least squares (RLS). The RLS estimation incorporates a transient period before it achieves a stable state whenever there is a sag event. The DVR is not supposed to operate in this period. Therefore, this paper also outlines a simple procedure for detecting the RLS estimation stable level. Simulation of different scenarios of voltage sags and the results from the experimental implementation of a DVR show the effectiveness of the method.

This paper presents a practical assessment and validation for the new proposed approach based on the continuous wavelet transform (CWT) to obtain the frequency response from online transient signals for an actual transformer. Apart from the mathematical procedure, an electronic system was also designed and implemented in order to inject superimposed controlled pulses to the power system (50/60 Hz) wave. The results show improved performance of the wavelet transform compared to the Fourier transform, for transient signal analysis to be applied on a nonintrusive transformer monitoring approach. Particularly, this new approach enables overcoming some problems related to the signal filtering and the signal processing in an online frequency-response analysis transformer diagnosis. This paper is presented in three parts. Part I showed the main theoretical basis of this approach. The current Part II shows a practical assessment based on tests performed in a three-phase transformer of 1150/345 V-5 kVA and in a single-phase transformer of 13200/240 V-15 kVA. Part III shows the performance of this new approach on transformers being diagnosed under real conditions.

This paper presents a new technique for wideband characterization and modeling of multiport large grounding systems in the form of an accurate Electromagnetic Transients Program-compatible model. This helps to consider the exact behavior of grounding systems in the electromagnetic transient analysis of power systems. The methodology involves three stages. First, a general electromagnetic approach based on the method of moments solution to Maxwell's equations is utilized to obtain the grounding system admittance matrix over the frequency range of interest. In the next stage, a rational approximation of the grounding system admittance matrix is inferred by making use of a modified matrix pencil method (Modified-MPM) developed in this paper. The Modified-MPM is well suited to the matrix fitting applications with a common set of poles selected for all matrix elements. The obtained rational approximation is finally employed to construct a multiport time-domain model of the grounding system expressed in the form of state-space equations. The proposed modeling approach is applied to the lightning transient analysis of a real subtransmission (63/20 kV) substation considering its grounding system as an integrated part of the electrical system. It is shown that the traditional method of using a simple resistive model for representing the grounding system results in a noticeable underestimation in the calculation of lightning-generated overvoltages in electrical systems.

The geomagnetically induced currents (GICs) produced in power systems during magnetic storms are a function of the electric-field amplitude and direction, and the characteristics of the power system. This paper examines the influence of a number of power system characteristics, which include the resistances and structures of the conductors; the length of the transmission lines; the number, type, and resistances of transformers, the substation grounding resistances, and the topology of the network. It is shown that GIC grows with increasing line length but approaches an asymptotic constant value, and a more relevant parameter than the individual line length is the length of the entire system. This paper also derives the effective GIC for a conventional transformer and an autotransformer, and analyzes the behavior of GIC when the network topology changes illustrated with the GIC-Benchmark Model. The results of these studies provide a guide to estimating GIC impacts on a power network.

In this paper, an adaptive pole-shift control technique for a FACTS device, namely Thyristor Controlled Series Capacitor (TCSC), is presented. Adaptive pole-shift techniques have been successfully implemented for power system stabilizer applications in the past, but one of the difficulties in extending such a technique for transmission line control devices has been its inability to handle large disturbance conditions such as three-phase faults. In recent literature, random walk technique has been suggested during the system identification process, to overcome this problem. This paper presents a simple parameter constrained RLS identification procedure to track the large disturbance conditions. The effectiveness of the proposed methodology is demonstrated using (i) a three-area six-machine power system with a TCSC, and (ii) a IEEE 12 bus power system configuration with a TCSC.

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

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

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

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

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

This paper presents a game-theoretic communication structure, which is a network constructed among distributed controllers in the microgrid. This helps to share local controller information, such as control input, individual objectives among controllers, and finds a better optimized cost for the individual objectives. The modeling follows a game-theoretic framework for the energy conversion and control elements inside small-scale power systems (SSPS) or microgrids. These elements form teams to optimize performance and operation based on available information and communication. The team players are able to minimize a common objective when there is communication, and shift to the individual local objectives when communication fails. This paper also presents analysis to determine the minimal performance standards for the given level of communicated information. Then it shows optimal information mixing for team player modeling. In addition, a Stackelberg model is proposed for the microgrid with a leader-follower modeling approach. The last part of this paper shows possible examples with network contingency study with team player participation.

Distance relays, in the power transmission systems, are susceptible to the maloperation under certain system events, such as power swings and voltage instability, which drive the apparent impedance trajectories into the protection zones of the relay. Fast and reliable detection of the symmetrical faults, occurring during power swings, poses another challenge to operation of the distance relays. This paper introduces a new classification and protection scheme based on support vector machines (SVMs) for offering supervisory control to the operation of the conventional distance relays. The proposed scheme segregates the power system events into faults, power swings, and voltage instability. This paper also proposes a new index, called the relay ranking index, for identifying the relays most vulnerable to the maloperation due to power swings and voltage instability. The proposed SVM classifiers can work in unison with the conventional distance relay unit. The performance of the proposed scheme has been tested on a nine-bus WSCC system and 39-bus New England system.

Of particular interest to restrict the short-circuit level of interconnected power systems is to exploit fault current limiter (FCL) technologies. FCLs let the system planners devise new reliable and rather economical substation configurations and provide the possibility of proposing a promising cost-effective and prompt solution to the fault current over duty problem in the existing substations. This paper attempts to assess reliability of substation architectures accommodating the FCL operation and, besides, numerically investigates the FCL's impacts on the substation reliability indices. In order to clarify the proposed approach, two case studies with and without FCL are analyzed and compared. Although the discussions raised here are applicable for reliability modeling of all structures, five common substation configurations, namely: (1) single-bus single-breaker; (2) double-bus single-breaker; (3) ring bus; (4) one breaker and a half; and (5) double-bus double-breaker are considered in this paper. Numerical studies reveal that FCL deployment, while keeping the maximal flexibility of substation, may deteriorate the reliability indices of the substation due to the possible failures of FCLs.

This paper shows two applications for using vacuum circuit breakers (VCBs) in flexible ac transmission systems in the high-voltage (HV) power grid. This is first a mechanically switched reactor, which is series connected to a thyristor-controlled series compensator in order to enhance the inductive working range. Nevertheless, the switching frequency of VCBs is limited by their mechanical properties. In order to achieve a higher switching frequency, more VCBs are switched in parallel to each other. Second, a device is investigated, which consists of mechanically switched capacitors and a mechanically switched reactor. It is connected to a node in the HV system in order to enhance the voltage quality and to avoid a voltage collapse. Since VCBs are mainly available in the medium-voltage range, a transformer is used to connect the mechanically switched device to the HV system. In this paper, it could be shown that the mechanically switched series reactor is able to enhance the damping progress of power oscillations and that the mechanically switched device using VCBs can stabilize the voltage of the node in case of disturbances, such as faults in the power system. Furthermore, the electrical stress on the VCBs has been assessed for different simulation cases with PSCAD.

This paper extends the concept of dynamic average-value modeling to power-electronic-intensive hybrid-electric vehicular power trains. Hybrid vehicles with plug-in capability are becoming increasingly important in the study of emerging smart power grids, and their simulation using digital programs has gained widespread attention. This paper demonstrates the usefulness of averaging in preserving the dynamic characteristics of the vehicular system while reducing the computational intensity of its simulation on an Electromagnetic Transients Program-type simulator. This paper presents an example of averaging for modeling, simulation, and system-level studies of a power-split gear hybrid drive-train.

The feasibility study of a power system is aimed at determining whether the system can adequately satisfy the load. The study will usually include other purposes, such as estimating the life-cycle cost of the system. This paper summarizes the main capabilities of current software packages for feasibility analysis of distributed energy resources. The document presents a short description of models, dispatch strategies, and economic indicators implemented in some packages. The test cases included in this paper will illustrate the scope of a feasibility study considering off-grid and grid-connected distributed resources.

New opportunities for optimally integrating the increasing number of distributed-generation (DG) units in the power system rise with the introduction of the microgrid. Most DG units are connected to the microgrid via a power-electronic inverter with dc link. Therefore, new control methods for these inverters need to be developed in order to exploit the DG units as effectively as possible in case of an islanded microgrid. In the literature, most control strategies are based on the conventional transmission grid control or depend on a communication infrastructure. In this paper, on the other hand, an alternative control strategy is proposed based on the specific characteristics of islanded low-voltage microgrids. The microgrid power is balanced by using a control strategy that modifies the set value of the rms microgrid voltage at the inverter ac side as a function of the dc-link voltage. In case a certain voltage, which is determined by a constant-power band, is surpassed, this control strategy is combined with P/V -droop control. This droop controller changes the output power of the DG unit and its possible storage devices as a function of the grid voltage. In this way, voltage-limit violation is avoided. The constant-power band depends on the characteristics of the generator to avoid frequent changes of the power of certain DG units. In this paper, it is concluded that the new control method shows good results in power sharing, transient issues, and stability. This is achieved without interunit communication, which is beneficial concerning reliability issues, and an optimized integration of the renewable energy sources in the microgrid is obtained.

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

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

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

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

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

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

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

This paper deals with modelling and analyzing specific transient states of voltages (i.e., of lightning surges in electric power systems of high voltages). The lightning surges arriving in a substation are impacted by more complicated wave effects. Those effects result from a complex spatial structure of each substation, and are determined by all equipment units mounted on it. A model of an electric power line and substation developed for computer software Electromagnetic Transients Program-Alternative Transients Program is presented in this paper. This model includes wave effects and nonlinear effects. It is based on a set of appropriately connected elements (i.e., distributed parameter elements and lumped parameter elements). Furthermore, the analysis results of lightning surges as well as the optimization results of a surge protection system installed in a 110-kV substation are presented in this paper.

The electromagnetic transient programs (EMTP-like tools) are based on the nodal (or modified nodal) equations that enable an efficient numerical solution and, subsequently, fast time-domain simulations. The state-variable-based simulation programs, such as Simulink, are also used for studying the dynamics of electrical systems. Both the offline and real-time versions of these two types of simulation tools are widely used by the researchers and engineers in industry and academia to study the transient phenomena and dynamics in power systems with rotating electrical machines. This paper provides a summary of the interfacing techniques that are utilized to integrate the general-purpose models of electrical machines with the rest of the power system network for these studies. The interfacing methods are broadly classified as indirect and direct approaches. The paper also describes the numerical properties as well as limitations imposed by the interfacing of the commonly used machine models that should be considered when selecting the simulation parameters and assessing the final results.

This paper presents an enhanced implementation methodology for the associated discrete circuit model of a power-electronic converter in a field-programmable gate array-based real-time power systems simulator. The simulator is intended for the testing and performance evaluation of digital control/protection platforms based on the hardware-in-the-loop concept. The salient features of the proposed implementation are: 1) It eliminates the need for corrective measures to reduce error due to the lack of synchronization between the simulation time-grid and output signals of the control/protection platform; 2) it provides scalability, that is, it maintains calculation time, within each simulation time step, nearly fixed irrespective of the system size; and 3) it enables the use of a small simulation timestep, for example, a couple of hundreds of nanoseconds for the overall system, in contrast to the microseconds range time-steps used in the existing simulators. Thus, it is also able to provide a wide frequency bandwidth for the simulation results. This paper also reports the implementation results and their verifications corresponding to real-time simulation of two converter units based on less than 60-ns calculation time within each simulation time step. The scalability property is also verified based on real-time simulation of six converter units.

This paper presents an application of a coordinated static VAr compensator (SVC) device as additional control for the reactive power (VAr) optimization problem and analyzes the impact on system loss and voltage profile. The coordinated SVC model controls internal, local, and remote devices simultaneously. It has two modes of operation: 1) voltage-control mode; and 2) Q control mode. This paper analyzes the functions of the coordinated SVC and implements them in the practical power systems. The impact of VAr optimization with coordinated SVC model on loss minimization and voltage enhancement are also discussed by comparing it with VAr optimization with general SVC model as well as VAr optimization without the SVC model.

The directional overcurrent relays (DOCRs) coordination problem is usually studied based on a fixed network topology in an interconnected power system, and is formulated as an optimization problem. In practice, the system may be operated in different topologies due to outage of the transmission lines, transformers, and generating units. There are some situations for which the changes in the network topology of a system could cause the protective system to operate without selectivity. The aim of this paper is to study DOCRs coordination considering the effects of the different network topologies in the optimization problem. Corresponding to each network topology, a large number of coordination constraints should be taken into account in the problem formulation. In this situation, in addition to nonlinearity and nonconvexity, the optimization problem experiences many coordination constraints. The genetic algorithm (GA) is selected as a powerful tool in solving this complex and nonconvex optimization problem. In this paper, in order to improve the convergence of the GA, a new hybrid method is introduced. The results show a robust and optimal solution can be efficiently obtained by implementing the proposed hybrid GA method.