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This paper presents frequency domain (FD) Norton-type equivalents of single- and three-phase photovoltaic (PV) generators, aimed at transient calculations. The proposed equivalents can be interfaced with a general frequency-dependent network and/or nonlinear loads and include voltage/current sources representing initial conditions aimed at partitioned-time transient simulation. The transient solution is performed via the numerical Laplace transform (NLT) in a sequential scheme by using time sub-windows with corresponding initial conditions and using reduced number of samples. The proposed approach overcomes the issue of computationally heavy simulations as in classical implementations of NLT. Two case studies involving PV generator and nonlinear load are presented to illustrate the performance of the proposed FD PV models. [ABSTRACT FROM AUTHOR]

This paper proposes a new passive Islanding detection approach for the Inverter Interfaced Distributed Generators (IIDGs) operating under different control modes. First, a novel index is formulated using Root Mean Square (RMS) value of the voltage and the frequency information, acquired at the Point of Common Coupling (PCC) of the target DG. The index is then post-processed by estimating the number of peaks and valleys $(N_{p_{k}-v})$ in a cycle using the sliding window concept, which indicates the occurrence of an event. Finally, the nature of the event, i.e., Islanding or non-Islanding, is decided by exploiting the two statistical features viz., Square of RMS $(S_{RMS})$ of $N_{p_{k}-v}$ and Average Crest Factor $(ACF^{m})$ of the proposed index. The performance of the proposed method (P-IDM) is demonstrated through comprehensive studies in PSCAD/EMTDC for the single-bus and IEEE 34-bus Active Distribution System (ADS). Also, the real-time validation is performed for the IEEE 34-bus using Controller Hardware-in-the-Loop (CHIL) setup comprising of Real-Time Digital Simulator (RTDS) and dSPACE1104. The simulation and hardware results for different test systems indicate that the proposed scheme, being generic in nature, sustains its efficacy under various interface controls of IIDGs. Finally, a comparative assessment with the other existing Signal Processing (SP) based passive methodologies shows the supremacy of the proposed method in terms of accuracy and faster detection. [ABSTRACT FROM AUTHOR]

The possibility of operating distributed generation (DG) in islanded mode brings several benefits but still faces some problems, especially related to the transition from a grid-connected to an islanded operating condition. When connected to the main grid, DG units operate in PQ mode. During this transition, their controls must be changed to regulate frequency and voltage. The delay for islanding detection, associated with abrupt changes in the control references, may result in large and detrimental transients. This paper proposes a new control structure for a distributed synchronous generator (DSG) to allow a smooth transition from the grid-connected to the islanded operation mode. The proposed control structure uses a compensation loop that was conceived based on the main ideas of the anti-windup bumpless transfer (AWBT) theory (although it is not, strictly speaking, an AWBT controller). The results show that the proposed structure ensures smaller excursions of the DSG variables during the transition and, therefore, the possibility of a successful formation of the islanded system is extended to a wider range of operating conditions. Moreover, with the proposed control, the success of this transition does not depend on the islanding detection time, which is the main contribution of this paper. [ABSTRACT FROM AUTHOR]

Natural calamities always have been a serious threat to energy systems. In this regard, this paper constitutes a stochastic mixed integer linear programming (SMILP) model to enhance the resilience of power distribution systems to deal with disastrous events. In particular, the proposed model is developed to enhance both survivability and restoration capability of distribution systems. In this regard, to increase the preparedness of the power distribution system, the system operator reconfigures the network by utilizing remote-control switches (RCSs), manual switches (MSs), and distributed generations (DGs) before the natural calamity hits. The proposed model contemplates the traveling time of crew teams to the MS sites in the transportation system in order to achieve the best switching sequence. In addition, it pre-positions the crews and mobile emergency generators (MEGs) in staging locations to hasten the likely post-disturbance operations. To do so, likely post-event operations are included in the model using the scenario generation technique. To validate the performance of the developed model a distribution system is employed. The results of simulations confirm the effectiveness of the proposed approach in declining the interruption of electric energy for customers. [ABSTRACT FROM AUTHOR]

Traditional connection of a generating station to the transmission grid typically requires either a new transmission line to an existing substation or building a new substation to segment an existing transmission line. Both of these options are capital intensive which often hurts economic viability especially small- or medium-size nonconventional generating stations. The direct connection to an existing transmission line, without the switching station, is the most economical solution to interconnect the generating station but it desensitizes the line protection and poses a risk to the ability of the protection to detect faults, particularly ground faults involving fault resistances. Multifunction relays, combined with communication-assisted schemes, now offer innovative solutions to overcome protection desensitization concerns. This paper describes these solutions which are successfully implemented by a large Canadian electric utility over the last two decades to tap connect numerous generators to the transmission grid. [ABSTRACT FROM PUBLISHER]

In recent years, there has been a growing interest in incorporating microgrids in electrical power networks. This is due to various advantages they present, particularly the possibility of working in either autonomous mode or grid connected, which makes them highly versatile structures for incorporating intermittent generation and energy storage. However, they pose safety issues in being able to support a local island in case of utility disconnection. Thus, in the event of an unintentional island situation, they should be able to detect the loss of mains and disconnect for self-protection and safety reasons. Most of the anti-islanding schemes are implemented within control of single generation devices, such as dc-ac inverters used with solar electric systems being incompatible with the concept of microgrids due to the variety and multiplicity of sources within the microgrid. In this paper, a passive islanding detection method based on the change of the 5th harmonic voltage magnitude at the point of common coupling between grid-connected and islanded modes of operation is presented. Hardware test results from the application of this approach to a laboratory scale microgrid are shown. The experimental results demonstrate the validity of the proposed method, in meeting the requirements of IEEE 1547 standards. [ABSTRACT FROM PUBLISHER]

In addition to supplying electrical power to the transmission grid, nuclear generating stations rely on the grid to provide power into the facility to support critical equipment during upsets. Although backup power supplies exist, such as diesel generators, the offsite power circuits are considered to be the “preferred power supplies” and must be kept at a high state of readiness. During certain operating conditions, the nuclear unit's generator is utilized to help support the voltage of the nearby high-voltage transmission system. If the offsite power circuits are served from the same high-voltage system, events that would result in tripping of the generator could also cause a depression of voltage on the offsite circuits due to loss of this voltage support. Nuclear operators must ensure that post-trip voltage levels are adequate to support critical equipment, such as emergency pumps and valves, during extreme postulated events, such as the rupture of reactor coolant system piping. Nuclear engineers utilize analytical models of their generating station electrical distribution system to determine the switchyard voltage level needed during various scenarios, but usually rely on outside organizations, such as transmission system operators and planners, to predict the change in switchyard voltage as a result of a nuclear generator trip. These organizations utilize complex models of the transmission system to make this determination. This paper proposes a simplified approach to predicting post-trip switchyard voltage utilizing data that do not rely heavily on outside organizations. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to propose and analyze the high-performance control strategies for a novel current source converter (CSC)-based wind turbine-superconducting magnetic energy storage system (SMES) hybrid system, which will, in turn, improve the operating performance for the wind farm not only in the grid-connected operation, but also in the islanding mode. The key is to design the effective active power controller and the ac bus voltage controller for the CSC-based hybrid system in grid-connected operation. Thus, better power smoothing and robust operation can be achieved. For the islanding mode operation, the capacitor voltage control scheme is proposed for the CSC hybrid system to offer efficient operation when the wind farm is disconnected from the grid. Based on simulation, the performance of the proposed control for the CSC-type wind turbine-SMES hybrid system in the wind farm has been verified. [ABSTRACT FROM PUBLISHER]

This paper presents an innovative generalized systematic approach and related analytical formulation to evaluate distribution system reliability in smart grids where islanded operation of microgrids helps to improve local and overall reliability. In order to do this, the analytical formulation involves the adequacy calculation of conventional and renewable distributed generators supplying microgrids by using probabilistic models. Adequacy is computed by means of a new general analytical expression which takes into account load shedding (user load disconnection) and curtailment (user load reduction) policies. [ABSTRACT FROM PUBLISHER]

A power-failure event occurred at the third nuclear power plant (TNPP) in Taiwan in 2001. A chain of events began at 09:36 p.m. on March 16 due to insulation failure associated with flashovers on the 345-kV transmission line. As a result, the 4.16-kV engineered safety features (ESF) buses at the TNPP experienced a loss of power for 2 h and 8 min. This accident was a class 3 emergency (e.g., a class 4 emergency will lead to an overall evacuation of local residents) based on the declared class of emergency in Taiwan. The purpose of this paper is to describe and analyze the chain of events leading to the loss of electrical power. Conclusions on the causes of the outage are drawn and modifications of the system structure are made to improve safety and reliability in a nuclear power plant. [ABSTRACT FROM PUBLISHER]

Typically, telecom power systems are connected to the grid and diesel generator. This paper represents a new telecom power system using local microsources (fuel cell and microturbine). Some benefits of this system are effectively eliminating batteries, diesel generator, and automatic transfer switch. In this study, a new multiple input buck-boost converter is utilized as an interface between the microsources and the dc bus. The peak current-mode control is used to control the current of fuel cell while the voltage-mode control is used to regulate the output voltage. A model for the proton-exchange membrane fuel cell (PEM FC) and microturbine (MT) along with their subcomponents and internal controls are presented. Furthermore, the parallel operation of FC and MT by using the proposed multiple-input dc/dc converter is investigated. In addition, the dynamic response of the system to the dynamic behavior of the load is analyzed. Using an inverter, the common bus of the system also connected to the distribution network in order to supply the excess power to the grid. For grid interconnection, an LC filter, double-tuned filters, and a C-type high-pass filter are developed for eliminating high-frequency switching oscillations, selected harmonics, and high-order harmonics, respectively. [ABSTRACT FROM PUBLISHER]