ALBERT

Notizen: Power systems optimization problems are very difficult to solve because power systems are very large, complex, geographically widely distributed and are influenced by many unexpected events. It is therefore necessary to employ most efficient optimization methods to take full advantages in simplifying the formulation and implementation of the problem. This article presents an overview of important mathematical optimization and artificial intelligence (AI) techniques used in power optimization problems. Applications of hybrid AI techniques have also been discussed in this article.

Notizen: As large load disturbances with changing frequency in the vicinity of the inter-area oscillations mode occur in an interconnected power system, a system frequency may be heavily perturbed and oscillatory. To stabilise frequency oscillations, the active power controlled by a superconducting magnetic energy storage (SMES) unit placed in a power system, can be utilised. However, it may not be feasible to locate a SMES unit in every area of a multi-area interconnected power system due to the economic reason. Therefore, it should be advantageous if a SMES unit located in an area is available for frequency stabilisation of other interconnected areas. To implement this concept, a static synchronous series compensator (SSSC), can be applied to coordinate with a SMES unit to stabilise frequency oscillations. On the other hand, variations of system parameters, several load changes etc., cause system uncertainties. To enhance the robustness of frequency stabilisers against uncertainties, this paper focuses on a robust frequency stabilisation by SMES in co-ordination with SSSC. To take system uncertainties into account, the multiplicative uncertainty is included in system modeling. As a result, the system robust stability can be easily guaranteed in terms of the multiplicative stability margin (MSM). The structure of frequency stabiliser equipped with SMES and SSSC is a second-order lead/lag compensator. Based on the proposed optimisation technique, control parameters of frequency stabilisers can be automatically tuned by a tabu search. Consequently, the desired damping ratio of the target inter-area mode and the best MSM are achieved. Simulation studies in a two-area interconnected power system confirm the high robustness of the coordinated SMES with SSSC against several uncertainties.

Notizen: This paper presents a novel wavelet-based travelling wave fault location algorithm for aged underground cables in transmission systems. Such transmission systems consist of overhead lines combined with underground power cables. Applying the singularity detection feature of wavelets as a powerful signal processing tool, the first and second initial arrival of the voltage travelling waves at the first end of the overhead as well as at the terminal end of the aged cable line can be identified reliably without the need for detection the sign of these waves. In this paper modal signals, rather than the phase signals, are the inputs to the relay. The proposed algorithm is capable of eliminating the effect of the change in the propagation velocity of the travelling waves over the age of the cable. It can be used on-line following the operation of digital relays or off-line using the data stored in the digital transient recording apparatus. Extensive simulation studies carried out using ATP/EMTP show that the proposed algorithm provides an accepted degree of accuracy in fault location under different fault conditions.

Notizen: Availability Based Tariff (ABT) has been implemented in all the regional grids of India for improving grid discipline by frequency dependent pricing. Currently it is limited to short-term energy transactions between the beneficiary States and Central generating stations without the need for negotiations on price or quantum in real time. In the present scenario, Independent Power Producers (IPP), Captive Power Plants (CPP), small Distributed Generation (DG) like mini-turbine, fuel cell, etc., are not considered under ABT. DG units are normally modular in size and they can be placed close to consumers so as to reduce the T&D costs and losses. Hence, they need to be encouraged so as to meet the ever-increasing electricity demands of Indian power sector within the financial constraints. In this paper, impact of IPPs, CPPs and DGs on intra-State ABT is studied. This paper also proposes to study the impact of grid connected DG on network availability and reliability. The improvement in system reliability is studied after evaluating reliability indices like SAIFI, SAIDI, etc., with the inclusion of DG.

Notizen: The paper deals with an optimized Unified Power Quality Conditioner (UPQC), which aims at the integration of series active and shunt active power filters with minimum VA loading of the UPQC. The series active filter is a Dynamic Voltage Restorer (DVR), which is operated in twofold functioning mode. During the unbalanced voltage sag, the DVR compensates the unbalance in the voltage sag. It also regulates the voltage at the load end with minimum VA loading of the overall UPQC by optimum angle voltage injection. Validity of the proposed scheme is proved through extensive simulation results.

Notizen: Concentration of greenhouse gases in the atmosphere is steadily increasing leading to global warming. India is expected to be one of the major contributors to Green House Gases (GHGs) due to increased share of thermal power generation, which is a major contributor to carbon dioxide (CO2) emission. One way to limit these emissions is by implementing some economic instruments like carbon tax or energy tax. This study has been carried out to analyze the impact of carbon tax on the complete Indian power sector network. An Integrated Resource Planning and Analysis (IRPA) model and CPLEX software has been used to carry out the present study.

Notizen: A multi-level dc voltage reinjection concept is described that multiplies the pulse number of the twelve-pulse dual parallel converter. The ideal reinjection waveform for complete elimination of the harmonic content is first derived, and a practical approximation is proposed which converts the standard dual converter into a sixty-pulse scheme, thus meeting the strictest harmonic standards without the assistance of filters or Pulse Width Modulation.

Notizen: The goal of this paper is to evaluate performances of a new hysteresis current control strategy for autonomous three phase parallel active filter in harmonic currents elimination (by simulation an experiment) as well as the reactive power compensation (by simulation). This strategy, called the Optimized Hysteresis Control Strategy, is based on currents errors and their derivatives calculation each time the zero voltage vector is set at the AC side of the inverter of the active filter. The harmonic currents are identified using the method of the instantaneous real and imaginary powers. A voltage regulation loop is used to regulate the condenser DC voltage which ensure a constant DC voltage to the inverter. A digital software C++ simulation program was developed and implemented via the data acquisition board (AT-MIO-16X DAQ from National Instruments). Simulation and experimental results are presented.

Notizen: Currently, evolution of energy sector is being characterized by liberalization, increase of energy needs and technological advances. This evolution has eliminated the scale economy on which the generation, transmission and distribution systems are based. So, tendency of generation systems is oriented to integrated devices, which will supply the customers demand, either in medium voltage or low voltage networks. The interconnection of small modular generation sources to the low voltage distribution network establishes a new concept, the electrical micro-grid. These micro-grids can be connected to the electrical distribution network or work in an autonomous way and can include different technologies, such as: micro-turbines, wind mills, fuel cells, photovoltaic cells, etc., together with energy storage devices, such as: batteries, condensers, fly-wheels, etc. The content of this paper cover different aspects related with generation and distribution of electrical power in a small scale, and horizontal technologies for industrial, commercial and domestic energy systems. So, this paper presents a revision of current developed technologies, which can be used for electrical microgeneration installations.

Notizen: The increases in power flows and environmental constraints are forcing electricity utilities to install new equipment to enhance network operation. Some application of Flexible AC Transmission System (FACTS) technologies to existing high-voltage power systems has proved the use of FACTS technology may be a cost-effective option for power delivery system enhancements. Amongst various power electronic devices, the unified power flow controller (UPFC) device has captured the interest of researchers for its capability of regulating the power flow and minimizing the power losses simultaneously. Since for a cost-effective application of FACTS technology a proper selection of the number and placement of these devices is required, the scope of this paper is to propose a methodology, based on a genetic algorithm, able to identify the optimal number and location of UPFC devices in an assigned power system network for maximizing system capabilities, social welfare and to satisfy contractual requirements in an open market power.In order to validate the usefulness of the approach suggested herein, a case study using a IEEE 30-bus power system is presented and discussed.

Notizen: The flexible AC transmission system (FACTS) in a power system improves the stability, reduces the losses, reduces the cost of generation and also improves the loadability of the system. In the proposed work, a non-traditional optimization technique, a Genetic Algorithm (GA) is conjunction with Fuzzy logic (FL) is used to optimize the various process parameters involved in introduction of FACTS devices in a power system. The various parameters taken into consideration were the location of the device, their type, and their rated value of the devices. The simulation was performed on a 30-bus power system with various types of FACTS controllers, modeled for steady state studies. The optimization results are compared to the solution given by another search method. This comparison confirms the efficiency of the proposed method which makes it promising to solve combinorial problem of FACTS device location in a power system network.

Notizen: This paper introduces some field analyses of the wooden pole fire reports and online condition monitoring recorded data for line insulators of 33kV and 132kV overhead power lines of Petroleum Development Oman (PDO). From the statistical analysis of PDO pole fire reports, it was found that PDO southern directorates had higher number of pole fires during May-September 2004. Pole fires mostly occur for single poles of 33kV distribution lines close to graded roads, where the most common burning locations are at crossarm fixation and at ground foundation. Pollution monitoring systems provide very useful information which can be used to predict the pole fire events.

Notizen: The aim of this paper is to present a novel method for the optimal placement of capacitor and reactor banks, with the objective of maximizing network capacity to absorb new generation. The method is an extension of the Optimal Power Flow used as a tool for network capacity analysis. It can be used to a) plot graphs of the bank investment cost with respect to the increase in network capacity and b) find the optimum investment for the network operator in order to maximize his revenue. A 12-bus low voltage network was used as a test case. The results demonstrate the efficiency of the method to allocate new banks. At a small investment cost, network capacity could nearly double.

Notizen: In recent years, renewable energy generation has been coming up for effective use of natural energy, such as wind energy. Induction generators consisting squirrel-cage rotors are widely used as wind generators because of their salient features like robust rotor design, simplicity in the construction, maintenance free operation, etc. In this paper, it is derived that the transient current, electromechanical torque, and active power taking into account rotor speed change of induction generators at three-phase fault conditions. The output equations of the induction generator has nonlinearity, and the speed-time characteristic in a fault period is also expressed by the nonlinear equation. The approximation to derive analytical formulas for transient conditions is proposed, and the transient behavior of the induction generator is analyzed by the developed equations. The simulation block diagram in MATLAB/SIMULINK is constituted using the system equation in consideration of the nonlinearity of the induction generator. The simulation results obtained from each theoretical analysis are in close agreement with that of results obtained using MATLAB/SIMULINK simulation. Furthermore, theoretical discussion also developed to determine the fault phase angle and the time at which maximum transient currents flow in the system.

Notizen: The tariff is the best incentive factor for the industrial customer today to reduce the peak load. This paper describes different methods of pricing electricity. It is important to study the influence of the tariff on the industrial loads and the costs of electricity before ILM can be implemented. This paper is interested in studying the economic aspects of fixed and operating cost, other factors affecting the generation economy, distribution of power, etc. Costs of supplying electricity to consumers are also considered. A utility can influence its customers' load by providing financial incentives through the prices charged for electricity at different times of use. By designing discriminatory time of use tariffs in which the prices of electricity corresponds to the marginal cost of supply, a utility provides appropriate signals to the customer to increase consumption of electricity at off peak periods. The proposed algorithm is implemented to a real system in operation.

Notizen: A novel simulation-based spectral technique for power quality and electromagnetic compatibility (EMC) design of an independent electrical power system (EPS) has been proposed. Power filter optimization problem has been formulated to provide full solution of the electric power quality and conducted EMI problems in the EPS. The spectral technique has been implemented within a CAD tool. An example of power quality and EMC design has been provided for an independent EPS where an AC power source generates a power, which is comparable to the consumed power, and an additional power filter is calculated for an electronic product including a switch-mode power supply. Current and voltage spectra calculations have been verified with a block-oriented simulation program Simulink. Numerical experiments revealed a number of important features of the proposed spectral technique.

Notizen: With more emphasis being laid on clean and renewable sources of energy, engineers look for the best possible ways to harness the wind energy to the maximum extent. FACTs controllers that were earlier being used at the transmission level find their use at generation level when it comes to extracting reliable and quality power from Wind Energy Conversion Systems (WECS). This article presents a review of the important modeling techniques employed for developing FACTs controllers and examines the role of HVDC-Light transmission in exploiting the Off-shore wind energy resources.

Notizen: In this paper, a proportional plus integral (PI) type sliding surface has been proposed for designing a fuzzy variable structure controller to solve load-frequency control problem in presence of load disturbances. It is shown that the proposed controller is effective and robust enough when the system suffers from mismatched condition but the model uncertainty and disturbance are assumed to be bounded. Furthermore, the proposed control strategy drives the states to the sliding surface and also maintains the sliding motion. To illustrate the approach presented has been tested on load-frequency control of power systems and the analytical claims have been justified under the uncertainty involved in the load demand of inter-connected power systems.

Notizen: Accurate electricity load and pool-price forecasting can provide a set of vital predicted information that helps generation, transmission and retailer participating companies to bid strategically into a deregulated electricity market in order to maximize their profits and increase returns to their stakeholders. Although a number of forecasting methods have been proposed to solve the short-term and long-term electricity load forecast, pool-price forecasting is a relatively new research area. In this article, we propose an autoregressive approach, based on a wavelet multiscale decomposition, for the prediction of one-hour ahead load and pool price based respectively on historical electricity load, and pool-price data. This approach is based on a multiple resolution decomposition of the signal using the redundant Haar à trous wavelet transform whose advantage is taking into account the asymmetric nature of the time-varying data. There is an additional computational advantage in that there is no need to re-compute the wavelet transform (wavelet coefficients) of the full signal if the electricity and pool price data (time series) is regularly updated. We assess results produced by this multiscale autoregressive method, in both linear and nonlinear variants, with single resolution autoregressive, multilayer perceptron, Elman recurrent neural network and the general regression neural network models. The input data consists of historical load and pool price data, which is collected over a period of 3 years (1999-2001), used for training, and 1 year (2002) used for testing. Experimental results are based on the New South Wales (Australia) electricity load and pool price data that is provided by the National Electricity Market Management Company.

Notizen: This paper investigates the use of trajectory sensitivity analysis (TSA) technique for assessing the transient stability of a power system at various operating conditions. The effect of placement of a thyristor controlled series compensator (TCSC) as well as the influence of the change in firing angle is also discussed. The TCSC is modeled by a variable capacitor, the value of which changes with the firing angle. The systems studied are the WSCC 3-machine, 9-bus system and IEEE 16 machine 68 bus system. The results using TSA are validated by PSCAD/EMTDC simulation.

Notizen: A range of techniques has been proposed to define the optimal locations and capacities of distributed generation (DG) as a means of ensuring that the maximum amount of DG can be connected to existing and future networks. However, there are limitations inherent in these methods, not least in finding the best combination of sites for connecting a predefined number of DGs. Here, a method combining optimal power flow and genetic algorithms aims to meet this requirement. Its use would be in enabling Distribution Network Operators to search a network for the best sites and capacities available to strategically connect a defined number of DGs among a large number of potential combinations. Some applications of the proposed methodology confirmed its effectiveness in sitting and sizing an assigned number of DG units.

Notizen: This paper presents an approach for identifying the faulted line section and fault location on transmission systems using support vector machines (SVMs) for diagnosis/post-fault analysis purpose. Power system disturbances are often caused by faults on transmission lines. When fault occurs on a transmission system, the protective relay detects the fault and initiates the tripping operation, which isolates the affected part from the rest of the power system. Based on the fault section identified, rapid and corrective restoration procedures can thus be taken to minimize the power interruption and limit the impact of outage on the system. The approach is particularly important for post-fault diagnosis of any mal-operation of relays following a disturbance in the neighboring line connected to the same substation. This may help in improving the fault monitoring/diagnosis process, thus assuring secure operation of the power systems. In this paper we compare SVMs with radial basis function neural networks (RBFNN) in data sets corresponding to different faults on a transmission system. Classification and regression accuracy is reported for both strategies. Studies on a practical 24-Bus equivalent EHV transmission system of the Indian Southern region is presented for indicating the improved generalization with the large margin classifiers in enhancing the efficacy of the chosen model.

Notizen: This paper presents a new decision tree (DT) based approach for fast voltage contingency screening and ranking for on-line applications in energy management systems. The hybrid decision tree model is developed to learn all the selected contingencies simultaneously, therefore fewer DTs are required. To reduce the size and improve the accuracy of the decision tree, the K-class problem is converted into the set of K two-class problems, and separate decision tree modules are trained for each of the two class problems. All the selected contingencies are presented to the filter module, which is trained to separate them in critical and non-critical contingency classes, which reduces the burden on ranking modular DT. The critical contingencies screened out by the filter module are presented to the ranking modular decision tree for their further ranking. To measure the severity of contingencies, bus voltage violation based scalar performance index is used. Full AC load flow is performed to generate the training and testing patterns for the proposed hybrid decision tree, under each contingency. The effectiveness of the proposed approach is tested on IEEE test systems. Once trained, a hybrid decision tree method gives fast and accurate screening and ranking of contingencies for unknown load patterns.

Notizen: In this paper, a novel control algorithm is proposed to compensate the unbalanced and non-linear loads in a three-phase four-wire system using active power filters. The algorithm results in balanced and sinusoidal source currents under unbalanced and distorted three-phase supply voltages. The algorithm makes use of the positive sequence extraction of the supply voltage and the theory of instantaneous symmetrical components. To illustrate the concept, a three-phase four-wire system with unbalanced and non-linear load is considered for compensation. The detailed simulation and experimental results are presented to validate the proposed method.

Notizen: The necessity of dynamic equivalents for power system analysis has been well known since the expansion of large interconnected power networks, and has been discussed during the last decades. The present paper proposes a new method for constructing dynamic equivalents of power systems. In this method, at the first step the ``study system" is modeled completely via a single machine-infinite bus modeling procedure. Then the ``external system" is identified as a MIMO feedback block of this model in such a manner that can include dynamic effects of the latter on the behavior of the former. The method is successfully experimented on a part of the Iranian southern network.

Notizen: In this paper a comprehensive dynamical assessment of a high order synchronous generator plant is carried out using the Individual Channel Analysis and Design (ICAD) framework -a multivariable control engineering tool that allows robustness and system performance evaluations. The great benefits of ICAD are elucidated and contrasted to those provided by the long-time honored block diagram representations. Several models used for the small signal stability analysis of synchronous generators are evaluated under the framework of ICAD. The study, which builds on pioneering work, reveals the great advantages of carrying out control system analysis and design with higher order generator models. Moreover, careful analysis of the ICAD's Multivariable Structure Function (MSF) helps to explain, formally, why some operating conditions of the control system are more critical than others. Furthermore, correct interpretations of MSFs are amenable to robust and stable control system designs. Two kinds of studies are considered in the paper; one assesses operation under various power factor conditions and the other under a varying tie-line reactance. The control system design and stability and structural robustness assessment of the system are presented in the second part of this paper. Moreover, results obtained under the ICAD framework are compared with those arising from conventional controllers.

Notizen: For high-frequency (HF) interference in an HVDC converter station, the modeling of the noise source which causes interference with the power line carrier (PLC) remains a problem. Based on the profound analysis of the basic principles on which HF noise in PLC band is produced during the commutation process, the equivalent model of the HVDC valve with a snubber circuit is applied to the simulation of the GUI-GUANG HVDC project in PSCAD/EMTDC. Then spectrum plots of the noise source in the frequency domain are obtained by FFT analysis of the voltage waveforms gained from the simulation. Through analyzing the spectrum characteristics of the noise source in various operating modes, the main factors influencing the level of HF noise are found. Furthermore, a modified empirical model used to calculate the level of the noise source is introduced, with particular explanation of the physical quantities used in the model. The spectra of the noise source gained from the modified empirical model and from the simulation are compared with an actual spectrum based on the GUI-GUANG HVDC project. The results show that the modified empirical model can meet the requirement of HF interference calculation.

Notizen: In India, apart from state owned generators, a central sector power pool has been created consisting of central sector power stations. The Central Transmission Utility (CTU) has built an EHV network to transfer this power to the constituents of the regional network. To recover the costs incurred, the CTU levies the Transmission Service Charges (TSC) over the constituents. The constituents are billed for network usage charges which are proportional to their allocated share in the central sector power generation. An ideal pricing mechanism would have been to find out the usage of the network by the constituents and charge accordingly. In this paper, a real power tracing based method for recovery of Transmission Service Charge (TSC) from the constituents of Western regional grid in India is proposed. The method uses proportionality based real power tracing to find out the network usage by various constituents. Loss allocation on EHV network to the various constituents is also done. Actual data of power flows over the EHV network of Western regional grid for one day is considered.

Notizen: In this paper we explain how to design intelligent agents able to process the information acquired from interaction with a system to learn a good control policy and show how the methodology can be applied to control some devices aimed to damp electrical power oscillations. The control problem is formalized as a discrete-time optimal control problem and the information acquired from interaction with the system is a set of samples, where each sample is composed of four elements: a state, the action taken while being in this state, the instantaneous reward observed and the successor state of the system. To process this information we consider reinforcement learning algorithms that determine an approximation of the so-called Q-function by mimicking the behavior of the value iteration algorithm. Simulations are first carried on a benchmark power system modeled with two state variables. Then we present a more complex case study on a four-machine power system where the reinforcement learning algorithm controls a Thyristor Controlled Series Capacitor (TCSC) aimed to damp power system oscillations.

Notizen: Design and successful operation of wind energy conversion systems (WECs) is a very complex task and requires the skills of many interdisciplinary skills, e.g., civil, mechanical, electrical and electronics, geography, aerospace, environmental etc. Performance of WECs depends upon subsystems like wind turbine (aerodynamic), gears (mechanical), generator (electrical); whereas the availability of wind resources are governed by the climatic conditions of the region concerned for which wind survey is extremely important to exploit wind energy. This paper presents a number of issues related to the power generation from WECs e.g. factors affecting wind power, their classification, choice of generators, main design considerations in wind turbine design, problems related with grid connections, wind-diesel autonomous hybrid power systems, reactive power control of wind system, environmental aspects of power generation, economics of wind power generation, and latest trend of wind power generation from off shore sites.

Notizen: In bilateral transaction market, the congestion relief cost should be allocated in an equitable manner among all the market participants contributing to the congestion. Unfortunately in the allocation of the congestion relief cost to the congested lines, which is the first step of cost allocation, the previously proposed shadow price method and the aggregated allocation method both have some shortcomings. To overcome these shortcomings, a cost allocation method based on the Aumann-Shapley value is proposed. By means of the Aumann-Shapley value, a solution concept in the cooperative game with infinitely many players, the proposed method takes all orders of relieving congestion on the lines into consideration and satisfies the consistency of the allocation, thus guarantees equitable allocation of the congestion relief cost to the congested lines. In addition, the calculating procedure is both simple and accurate due to the use of the Gauss Integration method. Test results show that this method can lead to better allocation than do the shadow price method and the aggregated allocation method.

Notizen: In this paper, a novel neural network controlled Hybrid Parallel Active Power Filter has been presented. The neural network controller comprises two similar adaptive linear neurons (ADALINE), and it has been designed to extract fundamental frequency components from non-sinusoidal and unbalanced currents. It has been shown that the proposed neural controller is simple, fast and accurate. The proposed system is implemented using Digital Signal Processor (DSP). Experimental results with different nonlinear loads are presented to confirm the validity of the proposed technique.

Notizen: A dynamic voltage restorer is a power quality (custom power) device used to correct the voltage disturbances by injecting voltage as well as power into the system. The compensation capability of a dynamic voltage restorer (DVR) depends primarily on the maximum voltage injection ability and the amount of stored energy available within the restorer. In this paper a new phase advance compensation (PAC) strategy for the DVR is proposed in order to enhance the voltage restoration property of the device. Also a method of determining the exact amount of voltage injection required to systematically correct a specific voltage drop with minimum active power injection is proposed. Using the proposed method it can be shown that a particular disturbance can be corrected with less amount of storage energy compared to that of existing in-phase boosting method. Analytical expressions for both the magnitude and angle of the injected voltage are also derived. A closed-loop controller that consists of an inner current loop and an outer voltage loop is also incorporated into the DVR system.

Notizen: This paper proposes a new bid based redispatching method to relieve congestion in a pool type market, based on bilateral generation exchanges between generation units. Sensitivity analysis is used to find and implement the cheapest consecutive bilateral exchanges that would remove congestion in an iterative process. Congestion cost is calculated as exchange cost during congestion removal and is divided between congested parts using load flow results in each iteration. Divided cost is recovered from consumers, based on their relative contributions on congested parts using generalized load distribution factors. IEEE 39 and 118 bus test systems are used for case study to evaluate the merits of proposed method and the results are discussed in comparison with other conventional methods.

Notizen: This paper proposes an agent based integration strategy for software elements at the Distribution Control Centre (DCC). The proposed agent-based software integration enables to "plug-and-play" new software applications developed by any vendor or developer with no or minimal changes in the existing software system at DCC. Consequently, it permits the development of the distribution automation system in a phased manner by different vendors. The strategy has been successfully implemented and tested in an actual 10 MVA, 33 kV distribution system to validate its efficacy.

Notizen: This paper presents two mathematical models based on graph theory, and a fuzzy logic approach for the steady state analysis of three phase self excited induction generator with and without series compensation. The first model is developed using nodal admittance method and the second model is developed using loop impedance method. Both models results in simple matrix form which are convenient for computer solutions. Since these models are more generalized the steady state performance of the three phase self excited induction generator can be easily obtained with and without series compensation along with fuzzy logic algorithm. These models are so flexible, wherein an element like core loss component can be included or eliminated if required and also the leakage reactance of the stator (Xls) and rotor (Xlr) can be handled separately, by avoiding the assumptions Xls=Xlr without any modifications in the models. Next to carry out the steady state analysis, a fuzzy logic approach is used first time to find any combinations of unknown variables using above models. The analysis presented is validated by experimental results.

Notizen: Reactive Power Dispatch (RPD) is one of the important tasks in the operation and control of power system. The objective is to apply Particle Swarm Optimization (PSO) algorithm for arriving optimal settings of RPD problem control variables. Incorporation of PSO as a derivative free optimization technique in solving RPD problem significantly relieves the assumptions imposed on the optimized objective functions. The proposed algorithm has been applied to find the optimal reactive power control variables in IEEE 30-bus system and in a practical Indian power system with different objectives that reflect loss minimization, voltage profile improvement and voltage stability enhancement. The results of this approach have been compared with the results of Genetic Algorithm (GA). The results are promising and show the effectiveness and robustness of the proposed approach.

Notizen: In this paper, an adaptive fuzzy PI-sliding mode control (AFPISMC) is proposed for induction motor (IM) speed control. First, an adaptive sliding-mode controller (APISMC) with a proportional plus integral equivalent control action is investigated, in which a simple adaptive algorithm is utilized for generalised soft-switching parameters. The proposed control design uses the fuzzy logic techniques to dynamically control parameter settings of the SMC equivalent control action. The theoretical analyses for the proposed fuzzy PI-sliding-mode controller are described in detail. Simulated results show that the proposed controller provides high-performance dynamic characteristics and is robust with regard to plant parameter variations and external load disturbance.

Notizen: Most tracing algorithms have used variants of proportionality based tracing algorithm. However, proportional sharing is not an inherent characteristic of the system. It is a rule enforced to arrive at a solution in a simple and fair manner. We propose a multi-commodity network flow optimization approach for optimal tracing of power flows. The resulting optimization formulation is shown to be sparse linear programming (LP) problem. The paper is devoted to the constraint modeling of this optimization approach. A unified formulation that models lossy MW flow network and provides consistent results for generation and load tracing is presented. Optimal tracing provides complete power audit information like share of loads in generation, generators' contribution in loads, loss allocation to generators and loads, and decomposition of branch flows into generation and load components. Illustrative examples and results on IEEE 30 bus system show the workability of the proposed approach.

Notizen: Optimal power flow (OPF) is one of the nonlinear problems of power system. The various algorithms for solving optimal power flow problem are found in the literature. The genetic algorithm (GA) based solution techniques are found to be most suitable because of their ability of simultaneous multidimensional search for optimal solution. This paper presents a novel GA-Fuzzy based approach for solving OPF. The GA parameters e.g. crossover and mutation probabilities are governed by fuzzy rule base. Algorithms for GA-OPF and GA-Fuzzy (GAF) OPF are developed and compared. The results obtained for these systems demonstrate that the GAF-OPF has faster convergence and lesser generation costs as compared to various methods tested for above systems.

Notizen: This article investigates the various damping controls of the unified power flow controller (UPFC). A detailed dynamic model of the UPFC including the possible damping control parameters has been derived. A method of determining the stable operating states of the nonlinear system model has been presented. Fixed parameter robust controllers for the identified controls have been designed satisfying the robustness conditions on performance and stability. The robust controller design has been carried out with the aid of a simple graphical 'loop-shaping' construction procedure. Simulation studies show that both robust series converter voltage magnitude and shunt converter phase angle provide extremely good damping. Combined application of the above two controls, however, gives the best damping profile over a wide range of operation. PI controllers having optimized gain settings were employed to evaluate the robustness of the proposed controllers.

Notizen: This paper presents particle swarm optimization based interactive fuzzy satisfying method for bi-objective generation scheduling of fixed head hydro plants and thermal plants with nonsmooth fuel cost and emission level functions. The bi-objective problem is formulated considering two objectives (i) economy and (ii) emission. These two objectives are mutually conflicting and equally important. Assuming that the decision maker has imprecise or fuzzy goals for each of the objective functions, the bi-objective problem is transformed into a minimax problem, which is then handled by the particle swarm optimization technique. The solution methodology can offer a global or near-global noninferior solution for the decision maker. Numerical results for a sample test system have been presented to demonstrate the performance and applicability of the proposed method. The results obtained from the proposed method are compared to those found by interactive fuzzy satisfying method based on evolutionary programming technique.

Notizen: Dynamic economic emission dispatch is an extension of the conventional economic emission dispatch problem that takes into consideration the ramp rate limits of the generators. Evolutionary programming based fuzzy satisfying method has been proposed to determine the optimal noninferior generation schedule. This paper treats economy and emission as competing objectives for optimal dispatch, which requires some form of conflict resolution to arrive at a solution. The multi-objective problem is configured as a minimax problem under the assumption that the decision-maker has fuzzy goals for each of the objective functions. The present algorithm employs evolutionary programming technique in solving this problem. The solution methodology can offer a global or near-global noninferior solution for the decision-maker. Numerical results of a sample test system have been presented to demonstrate the performance and applicability of the proposed method. Results obtained from the proposed method are compared to those obtained by fuzzy satisfying method based on simulated annealing technique.

Notizen: Flicker is an important power quality disturbance and has received an increasing concern from power system researchers. Interharmonics are the non-integral frequencies other than harmonic frequencies. Nowadays, research has shown that interharmonics and flicker seem to be closely related. To clarify this relationship, flicker is characterized in the frequency domain. The traditional Fourier-based methods have shown some drawbacks in representing non-stationary, non-periodic power signals and therefore other methods should be investigated for accomplishing this task. This paper introduces the most common signal processing approaches to assess the problem, power spectrum estimation methods and linear transforms. The wavelet transform has shown superior performance comparing to other methods and circumventing the problem time-frequency resolution.

Notizen: This paper presents a study of market design issues for the future Electricity Supply Industry of countries in transition from monopolistic to more competitive structures. An approach is developed to apply a standard measurement of market concentration, such as Herfindahl Hirschman Index (HHI) within the market design context. Typically, HHI is used to study market power issues in established electricity markets. The approach presented in this paper indicates that HHI can also be used as a primary method to study market design ahead of implementation. A dynamic simulation of the Thai market is used to confirm the applicability of the approach presented in this paper.

Notizen: It is well known to electricity authority worldwide of difficulty in meeting an ever increasing demand of a rural load center tens to hundred kilometers away from the interconnected grid. In many cases, upgrading sub-transmission system seemed appropriate in technical, economic and environmental aspects. Nevertheless, there are cases where addition of local generation is the only means to meet the increasing demand. For more than ten years, Thailand's Provincial Electricity Authority has been tackling complications of adding more and more local generations until exceeding the local off peak demand. These generations consist of four small hydro, one geothermal and one fuel oil power plants. Unfortunately, the unplanned attempts made to resolve problem concerning provision of electricity supply to meet the demand without conducting any pre-engineering study had proved ineffective and sustainable solution could not be attained. This paper described, analyzed and discussed in details the development of PEA's distribution system planning to supply quality and reliable electricity to a small rural and remote community in the country Northern province. Extensive field surveys and technical analyses were carried out to investigate impacts of distributed generation on the performance of the network. Finally, recommendations were given as guideline for further study in search of feasible and sustainable solutions.

Notizen: There is no unique definition of non-active power for nonsinusoidal systems. A new definition of non-active power is proposed in this paper. This definition is based on energy transfer and provides a unique solution for non-active power of single-phase systems under both sinusoidal and non-sinusoidal conditions. An example is used to illustrate the use of this new definition. Energy transfer calculated using the new definition provides the same energy transfer determined from the non-sinusoidal non-active instantaneous power. This is consistent with the existing definition of active power that is also based on energy transfer.

Notizen: Dynamic behaviour analysis of electric power system has always played a vital role in operation and planning of power systems. This analysis relies on computer simulation which are usually based on simplifying assumptions which aim at rendering system modelling more amenable to numerical solution. However, it is well known that uncertainties and unmodelled dynamics could in some cases lead to unexpected results. In the paper a simplified dynamic model of transmission network is employed to evaluate the influence of network transients on dynamic behaviour of power systems. Although simplified, this model can easily capture usually neglected dynamics. Applications of this modelling is proposed with respect to two test systems, highlighting the effects of usually unmodelled dynamics.

Notizen: HVDC and FACTS devices have been widely applied in power system for their excellent and flexible control ability. Their contributions to the damping of system oscillations are of great importance for achieving satisfactory system performance. However, previous experience has shown that there may be negative interactions among FACTS devices whose supplementary controllers are designed separately. This may deteriorate system performance and even make system unstable. The interactions of HVDC and SVC during system oscillation were analyzed in this paper. The coordinate supplementary damping controller for HVDC and SVC were then designed based on projective control principle. The criterion of synthetic residue is adopted in choosing the proper input wide area signals. Eigenvalue analysis and time domain simulations were performed on a two-area system and the results demonstrated the effectiveness of the proposed controller.

Notizen: This paper describes how the phase sequence and voltage level (132 kV, 275 kV or 400 kV) of single-circuit overhead conductors can be calculated from measurements made by passive, non-contact sensors situated on a moving platform at ground level. The investigation relies on sensing the electric field along the profile of the conductors through the use of passive sensors. The fabrication of the passive sensor is described together with an analysis of its performance. The variation of the vertical component of electric field strength along the lateral profile beneath single-circuit conductors has been studied using finite element modeling software, ANSYS. The results of this simulation have led to a proposed method of determining the magnitude and phase sequence information from overhead conductors via analysis of the induced voltages on the sensors. The paper concludes with an investigation made in a 400 kV substation in the UK. Analysis of the experimental results shows that the proposed technique can successfully evaluate the phase sequence, voltage level, the spacing between phases and the orientation of high-voltage overhead conductors.

Notizen: There are IEC 60060-1 requirements on three impulse current waveforms. For the damped-oscillating waves, margins of the front time T1 and the time to half the peak T2 are 10 per cent whilst any value after the polarity reversal has to be less than 20 per cent of the peak value. Authors have tried to construct impulse current calibrator for reference measuring system, which would generate a waveform having the time parameters quite close to ideals. After numerous simulations in selecting values for circuit composing components, authors came to an impression that a damped-oscillating current generator whose output waveform has parameter values close to standard, cannot be realised. In the paper, authors' "impression" is theoretically proved and mathematically possible margins for the parameters are to be presented in detail.

Notizen: A dc-ripple reinjection concept, described in the literature with reference to the line-commutated current source converter, is applied in this paper to the self-commutated current source converter. This is achieved by means of a reinjection converter fed, via a single-phase transformer, from the triple frequency ripple signal. It is shown that the three-phase bridge can be made to operate effectively at any multiple of the six-pulse number and, thus, presents an effective alternative to the use of ac and dc side filters.

Notizen: This paper presents the design, analysis and development of a novel tapped star connected autotransformer based twenty-four-pulse ac-dc converter for improving power quality at the point of common coupling (PCC) in vector controlled induction motor drives (VCIMD's). A star connected autotransformer with four windings per phase at different phase angles is used to realize the proposed twenty-four-pulse ac-dc converter. The basic design equations are derived to calculate the number of turns in different windings for achieving the harmonic reduction in the proposed autotransformer. The design of autotransformer is further modified for making it suitable for retrofit applications to replace presently used 6-pulse diode bridge rectifier. The proposed 24-pulse ac-dc converter is able to eliminate up to 21st harmonics in the supply current along with the power factor improvement close to unity in the wide operating range of the drive. The effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed ac-dc converter. Different power quality indices on input ac mains and on dc bus for a VCIMD fed from a 12-pulse and a 24-pulse ac-dc converters are also given to compare their performance. Various tests are conducted on the developed prototype of proposed autotransformer based 24-pulse ac-dc converter. Different power quality indices are measured on developed 24-pulse ac-dc converter to validate the design and simulation model.

Notizen: Brushless doubly-fed machines (BDFMs) allow the use of a partially rated inverter and therefore offer reliable, maintenance-free operation at low cost, especially in large power variable speed applications with limited speed ranges such as off-shore wind turbines, pumps etc. However, with a special cage rotor design, the machine has substantial rotor losses, poor efficiency and complicated control being difficult to implement.The BDFM reluctance type, the brushless doubly-fed reluctance machine (BDFRM), can overcome most of the above BDFM deficiencies while retaining all its merits. It has a "cold" reluctance rotor, which makes it more efficient and much easier to model/control than the BDFM.A theoretical study of the BDFRM is very important to gain proper understanding of its unusual operation, the main control features and compromises between optimal performance and the size of the inverter and machine required. This paper will attempt to develop, and provide a comprehensive comparative analysis of, different control strategies for the machine that are suitable for digital implementation.

Notizen: One of the most important tasks of System Operator (SO) is to manage congestion as it threatens system security and may cause rise in electricity price resulting in market inefficiency. In corrective action congestion management schemes, it is crucial for SO to select the most sensitive generators to re-schedule their real and reactive powers and the loads to curtail in extreme congestion management. This paper proposed the selection of most sensitive generators and loads to re-schedule their generation and load curtailment based on the improved line flow sensitivity indices to manage congestion. The impact of slack bus on power flow sensitivity factors has been determined to encourage fair competition in the electricity markets. Effect of bilateral and multilateral transactions, and impact of multi-line congestion on congestion cost has also been studied. The generators' reactive power bid has been modeled by a continuous differentiable tangent hyperbolic function. The proposed concept of congestion management has been tested on a practical 75-bus Indian system and IEEE-118-bus test system.

Notizen: Very Fast Transient Overvoltages (VFTO) and the associated Very Fast Transient Currents (VFTC) generated during switching operations in a Gas Insulated Substation (GIS) couple conductively and inductively to the secondary equipment connected to the GIS. The frequency spectrum of the VFTC gives the dominant frequencies present but cannot provide the time varying current amplitude w.r.t. any particular frequency. Since the transient response of the control circuits is a function of the frequency content of the VFTC, it becomes necessary to segregate the VFTC waveform both in time and frequency scale simultaneously. This has been achieved by employing the GABOR wavelet function and the time-frequency spectrum of the VFTC waveform has been calculated at various locations for a 245 kV GIS during a switching event. The validity of the wavelet model is confirmed by reconstructing the VFTC signal at the GIS-cable termination as well as at the switching point using the time varying current waveforms obtained for different frequencies. Finally, the transient current vs frequency as well as the current vs distance charts are developed for the 245 kV GIS under study during various switching operations.

Notizen: During the last two decades, renewable wind energy has become increasingly popular as a consequence of strong ecological concerns and appealing advantages with regard to economical energy solutions in remote communities. Furthermore, with very large wind farms emerging, the dispersed renewable wind energy is required to be fully connected to the electrical distribution networks. However, the integration of dispersed renewable wind energy will pose a great challenge to the power quality in the distribution networks when the weak nature of the grid in remote areas and the uncertainty of wind are taken into consideration.This paper presents a novel Modulated Power Filter Compensator (MPFC) for the distribution networks with dispersed renewable wind energy interfaced. A tri-loop error driven controller is used to adjust the PWM switching of the modulated power filter compensator. Full power factor correction and power quality improvement is validated under different operation conditions, like load switching and wind velocity excursions. The MPFC device is a member of novel FACTS based compensators developed by the first author.

Notizen: The importance and conduct of necessary studies on grid reliability evaluation have become increasingly important in recent years due to the number of blackout events occurring throughout the world. Additionally, quantitative evaluation of transmission system reliability is very important in a competitive electricity environment. The reason is that successful operation of an electric power under a deregulated electricity market depends on transmission system reliability management. This paper suggests that the important input parameters of a probabilistic reliability evaluation tool for the KEPCO-system by sensitivity analysis of high reliability level operation. Simultaneously, it also presents sensitivity analysis probabilistic reliability evaluation of practical KEPCO-system long-term transmission system expansion planning (2006-2010). The tool utilized a Transmission Reliability Evaluation for Large-Scale Systems (TRELSS) which was developed by EPRI and Southern Company Services Inc.

Notizen: The electric power industry in the United States and in other countries is undergoing profound regulatory and operational changes. The underlying rationale behind these transformations is to move once highly monopolized vertically-integrated industry from a centralized operation approach to a competitive one. The emerging competitive markets and an increase in the number of market participants have, in turn, fundamentally changed not only electricity trading patterns but also the structure of the electric power supply chains. This new framework requires new mathematical and engineering models and associated algorithmic tools. Moreover, the availability of fuels for electric power generation is a topic of both economic importance and national security. This paper uses the model developed by Nagurney and Matsypura (2004, 2006) as the foundation for the introduction of explicit fuel suppliers, in the case of nonrenewable and/or renewable fuels, and their optimizing behavior, into a general electric power supply chain network model along with "direct-supply" generation. We derive the optimality conditions for the various decision-makers, including fuel suppliers, power generators, suppliers, as well as the transmission service providers and the consumers at the demand markets. We establish that the governing equilibrium conditions satisfy a finite-dimensional variational inequality problem. We provide qualitative properties of the equilibrium flow pattern; in particular, existence of a solution and uniqueness under suitable assumptions. Finally, we discuss how the equilibrium fuel supply and electric power flow pattern can be computed.

Notizen: The steady state thermal rating of overhead transmission lines is limited by the conductor`s maximum design temperature, which is related to the maximum sag and the loss of tensile strength of the conductors. Traditionally, this overhead transmission lines rating is computed using a deterministic approach, with reference to severe weather conditions. Thus, the application of this method leads to conservative results resulting in under-utilization of conductors. In this paper, a new method based on an hourly probabilistic index is proposed to predict the line thermal rating for each hour of the day; this index is evaluated using the conductor current limit probability density function (pdf). The method uses Bayesian time series models for the weather parameters (ambient temperature, wind speed and wind direction) and calculates the conductor current limit pdf using a Monte Carlo simulation. The probabilistic index is applied by considering measured weather data of both hot and cold seasons; the corresponding lines ratings are reported and analyzed.

Notizen: The framework of transformer condition assessment system is proposed in this paper through mainly using data warehouse techniques, data mining techniques, and Open Agent Architecture. In this system, a data warehouse is used to collect transformers' testing data, a multi-agent system is used to design the framework of the software, and data mining techniques are used to evaluate transformers' conditions. The present framework is open and flexible, so the objective system is easy to be developed and maintained. The system can support transformers' condition-based maintenance to reduce electric utility's cost. Because the condition of a transformer depends on its design, present and historical operating data, and relates to its installation environment, load amounts, and so on, it is necessary to integrate all above information to evaluate transformer's condition. However, the off-line testing results, operational data, fault records and weather conditions have been stored in different systems, so finding an effective method to utilize all this information for condition assessment is difficult. Therefore, a data warehouse has been set up to integrate all of the above data, and some data mining techniques have been used to find the pattern and trend of the condition of a transformer. Then whether it is healthy can be determined. In order to make the system open and flexible, Open Agent Architecture (OAA) is employed to compose the multi-agent system. Seven application agents are designed to evaluate transformers' conditions synthetically. The Grey correlation method, grey theory prediction model GM(1,1), Bayesian network classifier and Bayesian network are employed in the agents.

Notizen: The objective of this paper is to optimize maintenance scheduling of generating units of a captive thermal plant using intelligent optimization techniques such as genetic algorithm (GA) and simulated annealing (SA). A multi-class maintenance scheduling has been considered to incorporate statutory safety regulations for maintenance of boilers, turbines and generators. Such multi-class maintenance scheduling in terms of mathematical formulations necessitates a planning horizon of five years compared to the conventional one to two year horizon. As the utilities catered by captive power plants are very sensitive to power failure, the reliability of power supply has been evaluated by loss of load probability (LOLP) index. The significant contribution of this paper is to evaluate confidence intervals of LOLP instead of conventional point estimate of LOLP. A point-estimate of LOLP uses expected values and provides no information about the range of values over which LOLP may vary. Some variations from optimum schedules are anticipated while executing maintenance schedules due to different real-life unforeseen exigencies. Such exigencies are considered in terms of near-optimum schedules obtained from SA during the final stages of convergence. LOLP evaluated from such sub-optimum schedules forms the basis to treat LOLP as a random variable for subsequent evaluation of confidence intervals. Case studies pertaining to a captive power plant for an aluminium smelter corroborate that the schedules obtained from two optimization techniques yield the same optimum schedule and thus the efficacy of the proposed algorithm is validated. Also the interval of confidence for LOLP denotes the possible risk in a quantified manner and it is of immense use from perspective of captive power plants intended for quality power.

Notizen: This paper presents the design of a Linear Quadratic Gaussian (LQG) regulator for the frequency control of a multi-area power system in a restructured competitive electricity market environment. A general model of the LQG regulator has been developed for multi-area system (with hydro and thermal generators) having Poolco and bilateral transactions. To account for the modeling uncertainties and non-measurable states, a Kalman filter has been designed to estimate the state variables. The controller uses these estimates, optimizes a given performance index, and reschedules the generators' outputs according to their bids for the frequency regulation. The functioning of the proposed LQG regulator has been demonstrated on a four area test system and the results have been compared with those obtained by using an optimal PID controller.

Notizen: Many analytical solution methods are incapable of dealing with modern power system planning, operation and control problems due to various uncertainties involved in the system. Generation output from most of renewable energy (RE) sources is uncertain which varies with time. Therefore, appropriate solution methods need to be considered in light of the uncertainty of RE generation. In this paper, a generation duration curve approach has been presented in order to handle the uncertainty of RE generation output while solving a combined dispatch problem of fossil fuel (FF) units and RE sources. A cost minimisation scheduling problem of FF units along with forecasted quantities of RE sources is formulated and solved considering the probability of meeting or exceeding anticipated shortfalls of RE outputs. Due to the complexity of the problem a genetic algorithm (GA) based solution approach is considered for solving the problem. A test problem with five FF units and three RE sources is formulated and solved under various considerations. It is demonstrated that the combined operation of FF units with RE sources gives better results, which can also manage uncertainty associated with RE generation outputs.

Notizen: This article presents a solution model for the unit commitment problem (UCP) using fuzzy logic to address uncertainties in the problem. Hybrid simulated annealing (SA), particle swarm optimization (PSO) and sequential quadratic programming (SQP) technique (hybrid SA-PSO-SQP) is used to schedule the generating units based on the fuzzy logic decisions. The fitness function for the hybrid SA-PSO-SQP is formulated by combining the objective function of UCP and a penalty calculated from the fuzzy logic decisions. Fuzzy decisions are made based on the statistics of the load demand error and spinning reserve maintained at each hour. SA is used to solve the combinatorial sub-problem of the UCP. An improved random perturbation scheme and a simple method for generating initial feasible commitment schedule are proposed for the SA method. The non-linear programming sub-problem of the UCP is solved using the hybrid PSO-SQP technique. Simulation results on a practical Neyveli Thermal Power Station system (NTPS) in India and several example systems validate, the presented UCP model is reasonable by ensuring quality solution with sufficient level of spinning reserve throughout the scheduling horizon for secure operation of the system.

Notizen: This paper presents novel, simple and efficient method for ranking line outage contingencies from network loadability limit considerations. The method follows conventional optimal multiplier based Newton Raphson power flow. The simulation of line outage contingencies is carried out near pre-contingency critical loading using the above power flow. A salient feature of the method is the use of the pre-contingency power flow Jacobian factors for simulation of all contingencies. Results for two sample test systems have been obtained with the new method and continuation power flow method in order to verify the potential of the former method for practical use.

Notizen: This paper deals with a model to simulate the operating of an autonomous induction generator. The model used is a diphase one obtained by the application of the Park transform. This model permits, when adopting some simplifying hypothesis, to take account of the saturation effect. This is achieved using a variable inductance function of the magnetising current. The non linearity is then based on the approximation of the magnetising inductance with regards to the current. In our case, we use a polynomial function, of 12th degree to perform it. This approach is simple and very accurate. The developed model has been used to study the operating of an induction machine when a capacitive bank is connected to the stator windings. The simulation calculation was achieved using MATLAB®-SIMULINK® package. This paper presents transient analysis of the self-excited induction generator. In order to simulate the voltage build-up process and the dynamic behaviour of the machine, we first establish the machine's model based on a d-q axis considering the machine's saturation effect. Secondly, effect of excitation capacitors or load imbalances on voltage build-up process is investigated. Simulations results for a 5.5 kW induction generator are presented and discussed. Several experimentations are presented to validate simulations and verify the effectiveness of the developed model.

Notizen: Specially connected transformers can reduce the voltage unbalance in a High Speed Railway (HSR) power supply system. Differently connected transformers reduce unbalance differently. Traditionally, a two-dimensional figure is used to represent the degree of unbalance associated with specially connected transformers. However, such a figure cannot completely express the conditions under which the voltage unbalance factor (VUF) is maximized. This work proposes a new approach to creating figures that represent the VUF of specially connected transformers under different dispatch schedules. Besides helping engineers to estimate voltage unbalance associated with various connected transformers, the analytical results can also provide a valuable reference for train dispatchers of HSR to plan dispatching.

Notizen: The paper presents the application of web services in the SCADA systems. Efforts are made to develop web publisher and WAP publisher using web services. Web and WAP configurators are developed to configure these MMIs. Dot NET technology has been successfully used for efficient implementation of the web services. Some sample screens of Web MMI and WAP are shown in the results section.

Notizen: Security assessment of a power system is very important function to detect any violation in the system and to ensure secure operation of the system in deregulated environment. Contingency ranking is the process of indexing the possible contingencies of system on the basis of their severity. The contingencies of higher ranking are further analyzed for detailed analysis. The contingencies based on the real power flow and the voltage deviations should be dealt simultaneously for better ranking. The paper presents fuzzy approach to combine ranking based on MW and Mvar losses and a new rank list is prepared. The proposed approach is tested on IEEE-30 bus test system.

Notizen: To achieve a sustainable power generation industry it is necessary to study the environmental impacts and economic costs of all aspects of a power generation plants' lifecycle - from mining to electricity distribution, and, ultimately, decommission (from cradle to grave). One key component in improving and maintaining quality of life for consumers is the application of the Green Productivity Index (GPI) in order to evaluate the related factors of Life Cycle Assessment (LCA) and Life Cycle Costing (LCC). The goal of this research is to appraise the efficacy of decision-making tools in accurately assessing the potential results of 'green' improvements to coal-fired and natural gas-fired power plants in both ecological and economic terms. The recently developed Numerical Eco-load Total Standardization (LCA-NETS) evaluates environmental impacts by identifying and quantifying input energy and output waste released to the environment throughout the life cycle of a power plant. Environmental impacts caused by global and regional environmental issues are numerically calculated in the units of NETS. Environmental assessment tools such as LCA, LCC and GPI can be used to improve the 'environmental friendliness' of electricity generation by demonstrating the future sustainability of 'green' power generation plants and their contribution to the quality of life of consumer.

Notizen: This paper investigates the chaotic behavior exhibited by a typical ferroresonant circuit under two-phase open condition. The circuit includes multiple nonlinear elements that accounts for transformer core nonlinearities and arrester. In most of the ferroresonance studies the core loss of the transformer is neglected or modeled as linear resistor [1]. The basic model of the system under investigation and solution of the differential equations describing the model are corroborated against MicroTran [2]. Choice of state variables and formulation of state equations are accomplished through a topological approach [3]. Extensive simulations have been carried out to analyze the sensitivity of the state variables with respect to degree of core saturation, amplitude of the Thevenin voltage source and the presence of arrester. Time response plots, phase plots, Poincaré maps and conventional bifurcation diagrams are used to analyze the chaotic behavior. The results reveal that the nonlinear model of core loss has a significant effect on the onset of chaos. The simultaneous presence of arrester and nonlinear model of core loss effectively eliminates the chaotic region for lower value of transformer saturation exponent.

Notizen: In restructured environment, various transactions such as firm bilateral and multilateral transactions are taking place. An analysis is made on effects of transactions on Generation Expansion Planning (GEP). Some of the metaheuristic techniques such as Genetic Algorithm (GA), Differential Evolution (DE), Evolutionary Programming (EP), Evolutionary Strategy (ES), Particle Swarm Optimization (PSO), Tabu Search (TS), Simulated Annealing (SA), and Hybrid Approach (HA) are applied to solve the Transactions-GEP problem with the support of AC-Optimal Power Flow (OPF) for the modified IEEE-30 bus test system with 6-years planning horizon. The original GEP problem is modified using the proposed methods i) Virtual Mapping Procedure (VMP), and ii) Penalty Factor Approach (PFA), to improve the effectiveness of the Metaheuristic techniques. Further, Intelligent Initial Population Generation (IIPG) and 'Store and Retrieve approach' are introduced in the solution techniques to reduce the computational time. PFA is used to convert the constrained problem into an unconstrained one. The results of the metaheuristic techniques are compared and validated with that of Dynamic Programming (DP). The performances of each metaheuristic technique were compared in terms of their Success Rate (SR), Average Number of Generations (ANG), the error percentage and the mean execution time. The effects of various transactions on GEP are also analyzed.

Notizen: Due to the more stringent environmental requirements imposed on electric utilities, utilities must adopt new technologies for the cleaner production of electricity. This paper suggests the introduction of renewable energy and energy storage systems to fossil fueled existing electric utilities for the cleaner production of electricity with hourly emission target. A cost effective dispatching algorithm for clean and economic operation of electric utilities has been proposed. The efficacy of the proposed approach is illustrated with the help of a 25-bus, 6-generator sample utility. This paper would be useful for electric utilities, consultants, regulatory bodies, policy makers and planners.

Notizen: This paper presents a flow control approach for the speed control of hydro turbines. Power can be controlled by controlling the rotary motion of the spear valve. In this paper, a flow control based model is proposed for the automatic control of small hydro power plants. In the proposed model, a servomotor is used to control the flow of water by controlling the rotational motion of the spear valve. The spear valve causes a 'continuous' control of the flow of water. `Discrete' flow control is achieved by the use of butterfly gates which are activated by DC motors. The suitability of servomotors for the control of small hydro power plants is discussed and PI controllers are used to further enhance their governing capability. State space representation is used to mathematically model the proposed model. Extensive simulations are performed to analyze the behaviour of the proposed model. Parameter optimization is performed using Artificial Neural Networks.

Notizen: The availability of electrical energy ensures development and progress while its non-availability means stagnation or 'back tracking'. The condition of 'No Power' [1] is the costliest state and leads to social, economical and production loss. Power system blackout means inconvenience and hardship to society. Uninterrupted power supply is essential for the national productivity and social structure and hence system must be made flawless at any cost. Reliable and disturbance free electric power supply is recognized as a key to 'Societal progress throughout the world'. Grid failure occurs due to continued overstressing, low frequency operation, increased load demand, peaking characteristics of the demand, ineffective load control, reduced level of security due to opening of interstate lines and violation of grid discipline. After occurrence of severe system disturbances, the system may split into parts, which may or may not survive depending on the load generation balance. The part system containing the generation sources and certain loads, which are planned to be separated from the main grid during system disturbance at, preconceived points either through under frequency and / or directional power relays are called 'Islands'[2]. During restoration due to wide fluctuations in the frequency it becomes very difficult to maintain the load-generation balance. Inability to control the frequency may lead to unsuccessful restoration. Repeated collapse of the system island due to tripping of generators either due to over frequency or under frequency causes delay in getting normalcy. In this situation the computer-computer links between the State Load Despatch Centre (SLDC) and Area Load Despatch Centre (ALDC) play a key role [3]. The priority during the restoration period such as railway traction, essential consumers such as water supply scheme, hospitals etc and lastly to the civil societies should be given. It is also necessary to have provision of disturbance recorder and event logger at power generation stations and various interconnected substations. These and other major aspects are considered in proposing the islanding scheme of the Pune city.

Notizen: A new approach for power system event recognition and classification using HS-transform and RBFNN is presented in this paper. Different power system events (disturbances) like sag, swell, notch, spike, transient, and chirp are generated and processed through Hyperbolic S-transform (HS-Transform). The excellent time-frequency resolution property of HS-Transform is used to extract useful information (features) from the non-stationary signals for pattern recognition. Here HS-transform generates the S-matrix and S-matrix provides the time-frequency contours, phase contours and absolute phase of the corresponding signal. From the above extracted information, various numerical indices like standard deviation, variance, norm, energy are found out. Further these indices are used as inputs to the Radial Basis Function Neural Network (RBFNN) for classifying different power system events accordingly. The RBFNN provides accurate results even with inputs (indices) found out under high noise conditions (SNR 20 dB). Thus the proposed method provides a robust and accurate method for power system events classification.

Notizen: This paper presents the design and implementation of a learning controller for the Automatic Generation Control (AGC) in power systems based on a reinforcement learning (RL) framework. In contrast to the recent RL scheme for AGC proposed by us, the present method permits handling of power system variables such as Area Control Error (ACE) and deviations from scheduled frequency and tie-line flows as continuous variables. (In the earlier scheme, these variables have to be quantized into finitely many levels). The optimal control law is arrived at in the RL framework by making use of Q-learning strategy. Since the state variables are continuous, we propose the use of Radial Basis Function (RBF) neural networks to compute the Q-values for a given input state. Since, in this application we cannot provide training data appropriate for the standard supervised learning framework, a reinforcement learning algorithm is employed to train the RBF network. We also employ a novel exploration strategy, based on a Learning Automata algorithm, for generating training samples during Q-learning. The proposed scheme, in addition to being simple to implement, inherits all the attractive features of an RL scheme such as model independent design, flexibility in control objective specification, robustness etc. Two implementations of the proposed approach are presented. Through simulation studies the attractiveness of this approach is demonstrated.

Notizen: Recently, using a non-linear programming method authors have demonstrated that based on certain criteria if some non-significant selectivity constraints are relaxed, all remaining constraints happen to be feasible but the solution of coordination problem is not possible with the conventional objective function as optimization procedure leaves the solution space [20]. In coordination studies solution with the conventional objective function provides minimum relay operating times. The present paper describes an additional criterion so that the solution with the conventional objective function can be achieved. This paper also achieves the acceptable speed of the primary protection while attempting to coordinate the maximum relay pairs. Complete results are presented in this paper in this regard. This paper uses the non-linear Random Search Technique to solve the coordination problem, which has been successfully applied in many problem areas.

Notizen: This paper studies, in a tutorial form, the impact of location of the TCSC on the degree of compensation and the transmitted power of a radial power system. The voltages of the two terminals of the TCSC have been examined at different locations with increase in the degree of compensation and transmitted power. The objective is to limit these voltages to 1.05 pu and obtaining maximum degree of compensation. Two cases were studied: (1) The case when the receiving end is a large AC system where the receiving end voltage is always maintained at 1.0 pu which is designated as case # 1 and (2) The case when the receiving end is an inductive load (R-L) load and it is designated as case # 2. For case #1, it has been found that sitting the TCSC at the sending or receiving end causes a large overvoltage. In contrast, sitting it at the midpoint could not cause overvoltage up to 0.5 degree of compensation. If it is higher than this value, overvoltage has been found. Thus placing the TCSC at the midpoint provides a compensation range up to 0.5. If the TCSC are disparted in two or three smaller TCSCs, which are equal in size and equally spaced along the transmission line, it has been found that higher degree of compensation can be obtained. This scheme has been found to be best compensation scheme to obtain a wide compensation range. In case 2, the sending end positioning has been found to cause overvoltage while the receiving end positioning provides a wide compensation range up to 1 without overvoltage at any point. Similar to case # 1, sitting the TCSC at the midpoint causes overvoltage at a degree of compensation greater than 0.5. For distributed TCSCs, a degree of compensation greater 0.5 can be obtained and the maximum degree of compensation depends upon the number of TCSCs. For case # 2, the best position has been found to be at the load end. In addition to the two study cases, a relation between the number of the distributed TCSCs and the maximum degree of compensation has been developed.

Notizen: This paper presents a Digital Signal Processor (DSP) based implementation of Hybrid of Fuzzy Logic Controller (FLC) and Proportional-Integral (PI) speed controller for Direct Torque Controlled (DTC) Permanent Magnet Synchronous Motor (PMSM) drive. The fuzzy membership function is used for hybrid control of these two FLC and PI speed controllers in such a way that at the time of dynamic conditions such as starting, the degree of belonging for FLC speed controller is higher than the PI speed controller and near set point the degree of belonging of PI controller is having higher weightage. The simulation model of the drive system is developed in MATLAB environment with simulink, PSB and FLC toolboxes to analyze the performance of the PMSM drive system. This hybrid speed controller is found suitable for DTC based PMSM drive to maintain the high level of performance while maintaining the excellent response at the time of starting, speed reversal, load perturbation and steady-state operating condition of the drive.

Notizen: The operating cost of a radial distribution system may be minimized by reducing the amount of real power and reactive power drawn from the transmission system. Presently, real power is being priced through a market clearing scheme all over North America. Reactive power is an ancillary service and its supply would be priced appropriately in the near future through a clearing market structure. A recent US Federal Energy Regulatory Commission staff report [1] has initiated a discussion on the formulation of a reactive power market. When such a market is designed and operated, large customers (distribution corporations) will have to purchase reactive power along with real power from the transmission corporation through an independent system operator. Envisaging such a prospect, this paper proposes a new method of reconfiguring radial systems considering costs of real and reactive power while maintaining an appropriate voltage profile and level of reliable power supply. The proposed method is tested on sample test systems and reported.

Notizen: Competition has been introduced in the last decade into the electricity markets and is presently underway in many countries. A centralized approach for the dispatching of the generation units has been substituted by a market approach based on the biddings submitted by the supply side and, eventually, by the demand side. Each producer is a player in the market acting to maximize its utility. The decision making process of the producers and their interactions in the market are a typical complex problem that is difficult to be modeled explicitly, and can be studied with a multi agents approach. This paper proposes a model able to capture the decision making approach of the producers in submitting strategic biddings to the market and simulate the market outcomes resulting from those interactions. The model is based on the Watkins' Q (lambda) Reinforcement Learning and takes into account the network constraints that may pose considerable limitations to the electricity markets. The model can be used to define the optimal bidding strategy for each producer and, as well, to find the market equilibrium and assessing the market performances. The model proposed is applied to a standard IEEE 14-bus test system to illustrate its effectiveness.

Notizen: Electrical energy planning of modern electric power system requires great attention for the air pollution problem. This is in accordance to the increasing tendency to optimise the production processes in the respect of their sustainability. Moreover, the advent of the deregulation in the electric energy market has involved substantial modifications of philosophy in planning and managing the electrical power system. These aspects together offer new challenge in defining proper system study methodologies and suitable planning strategies. One of the most complex problems in the planning strategies is the data management uncertainty related to load forecasting and environmental modelling. In this paper a robust optimal planning procedure is formalized, taking adequately into account the problem of stochastic variables presence, allowing to satisfy the air quality and load demand forecast constraints in spite of uncertainties. The proposed approach addresses generation planning, where the various aspects have been integrated to solve the problem in a feasible and realistic way. A numerical application to an electrical power system with respect to a regional area is reported in the final part of the paper, showing the applicability of the proposed methodology.

Notizen: In an Inductively Coupled Power Transfer (ICPT) system, a multiplicity of (moving) loads take power from an elongated conductive loop (track) excited by a current in the range of 15-125A by magnetic induction at a VLF frequency of between 5-50kHz. In this application, the track performs the same function as a distribution line in a power system. However, frequency deviations cannot be tolerated in ICPT systems and therefore there are difficulties with inrush power surges as loads switch on. In severe cases, the inrush surge may compromise the security of the whole system.This paper proposes a solution to this problem using an ICPT pickup controller with input shaping where the poles that can cause an inrush are not excited. The paper is supported by theoretical analysis and experimental measurements and is applicable across a wide range of ICPT sizes and applications. The solution reduces the inrush effects to 10% of an uncontrolled system.

Notizen: Since the development of the first control strategy for the active power filters (APF) introduced by H. Akagi [H. Akagi, Y. Kanazawa,A. Nabae, Generalized theory of the instantaneous reactive power in three-phase circuits, in: Proceedings of International Power Electronics Conference, Tokyo, Japan (1983) 1375-1386.], many efforts have been concentrated to improve their performances. However, when electrical networks supplies high current non-linear loads, a single inverter-based APF has limited power capability. In this paper, we studied parallel operation achieving high power level. More particularly, we examined a modular APF based on two three-phase inverters. This structure allows zero-sequence current circulating through the inverters, as demonstrated by using averaged modelling of the APF. To solve this problem and based on previous averaged model, we proposed a new optimal control strategy, suppressing the zero-sequence circulating current. Simulation results validate the proposed control.

Notizen: The aging of insulators often results in corona discharge, and the measurement of the ultraviolet light (UV-light) can be used to detect insulator defects. This paper introduces a new tester, the ultraviolet detector, which can detect defective insulators by measuring the UV-light from the discharging insulators. Some tests were carried out. The results indicated that the detector can identify the existence of corona discharge with good performance. And it can be used for discharge detection of power system and transformer substation.

Notizen: Electrostatic and electrodynamic field analyses of 33kV line insulators were introduced to compare the electric-field and the current density profiles of commonly used line insulators in Oman; namely, silicone rubber (SiR) and porcelain line post insulators, and porcelain cap and pin insulator string. SLIM software package was used for such simulation, which is a fully integrated collection of software modules that provides facilities for the generation and solution of electromagnetic finite element models. The simulation results reveal that for the electrostatic simulation under pollution conditions, SiR and porcelain line-post insulators give maximum values of the electric field of 360kV/m and 1700kV/m, respectively. The latter value exceeds the recommended electric field level of 500kV/m. For the electrodynamic simulation under pollution conditions, the electric field and the current density are much higher for porcelain insulator compared to those of SiR insulator. The simulation of four cap-pin standard insulator string reveals that there is high electric field (1250kV/m) at the cap-insulator gap which can cause high current density for polluted case. Finally, the trend of the simulation results has been verified by experimental tests, which has been conducted on different 33kV line insulators having different designs and materials.

Notizen: This paper presents an approach for short-term electricity price and load forecasting using the artificial neural network (ANN) computing technique. The described approach uses the three-layered ANN paradigm with back-propagation. The publicly available data, acquired from the deregulated Victorian power system, was used for training and testing the ANN. The ANN approach based on similarity technique has been proposed according to which the load and price curves are forecasted by using the information of the days being similar to that of the forecast day. A Euclidean norm with weighted factors is used for the selection of similar days. Two different ANN models, one for load forecasting and another for price forecasting, have been proposed. Test results show that average price and load MAPEs for the year 2003 by using the ANN approach are obtained as 14.29% and 0.95%, respectively. MAPE values obtained from the price and load forecasting results confirm considerable value of the ANN based approach in forecasting short-term electricity prices and loads.

Notizen: The benefit to end-users of electricity, mainly in terms of low prices, is strictly related to the interaction among the consumers themselves and retailers. The literature on retail competition has highlighted possible distortions in market outcomes due to unresponsive demand and boundedly rational consumers. Hence, a model appropriate to represent this aspect of the market is needed. The paper proposes a general model of the interaction among retailers and consumers in the electricity market based on the theory of multi-agent systems. The model incorporates different assumptions concerning the behavior of the players that corresponds to different levels of interaction in determining the market outcomes. The model is validated interpretively by the results provided in terms of Game Theory equilibrium. The results of an extensive set of simulations on a population of 1,000 consumers is presented and discussed.

Notizen: Deregulation of the power industry, increases in consumer demand of electricity and mandates to reduce greenhouse gases has significantly heightened the interest in distributed generation (DG). Typical DG sources include wind turbines, fuel cells, micro gas/diesel turbines, small hydro generators and photovoltaics. Currently most of these generation sources are optimized for local operation and thus the potential of DG that is both dispatchable and cost-effective has yet to be fully realized. One key technical challenge is the development of low-cost communications for remote telemetry and control of individual DG sources. Along with cost, other key communication system requirements are modularity, range and reliability. This paper presents a distributed generation communication system (DGCS) that is based on a wide area network (WAN) and local area network (LAN) topology and utilizes two variants of low-cost radio modems (RM) to satisfy the desired connectivity between the DG sites and a centralized control center. For the LAN, low-cost RMs operating in the industrial, scientific, and medical (ISM) frequency band offers point-to-multipoint scalability to multiple DG sites within a limited range. Integration of the ISM RMs with a cellular RM provides connectivity to a WAN or Internet thus providing long-range access to DG sites from any facility that has internet-access. Given the LAN scalability requirement, an ISM field programmable gate array (FPGA) channel simulator was developed to assess DGCS performance using channel impairments such as free-space path loss, multipath reflections, additive white Gaussian noise (AWGN), multiple access interference, and narrowband interference. This study provides the evaluation of two commercially available ISM radio modems and recommendations are made based on LAN requirements such as cost and performance given difficult channel conditions.

Notizen: A stochastic multi-objective line security constrained problem is formulated to minimize non-commensurable objectives viz. operating cost, polluting gaseous emission and variance of active power generation and reactive power generation, with explicit recognition of statistical uncertainties in the thermal power generation cost coefficients, gaseous emission coefficients, power demands and hence power generations and bus voltages, which are considered random variables. Specific technique is put forth to convert the stochastic models into their respective deterministic equivalents. Fuzzy set theory has been exploited to evaluate the different objectives that are quantified by defining their membership functions. Security of transmission lines with respect to expected active power flow is considered in the form of fuzzy objective function. The solution set of such formulated problems is non-inferior due to contradictions among the objectives undertaken. The weighting method is used to simulate the trade-off relationship between the conflicting objectives in the non-inferior domain. Generally, the weights are either simulated or searched in the non-inferior domain. In the paper Evolutionary search technique is implemented to search the 'preferred' weightage pattern in the non-inferior domain, which corresponds to the 'best' compromised solution. Among the non-inferior solutions, the system operator selects the 'preferred' optimal operating point that provides maximum satisfaction level of the most under achieved objective in terms of membership function and is termed as fitness function. The validity of the proposed method has been demonstrated on an IEEE system comprising of 11-nodes, 17-lines and 5-generators.

Notizen: The security of the transmission system is dependent on the relays' performance after various disturbances. Undesirable relay operation will trip the lines and lead to cascading events. In this paper the operation margin of mho relays is equivalently redefined as function of bus voltages instead of line impedance. The sensitivities of the operation margin to bus voltage and bus power is applied to quantify the vulnerability of transmission system. The contribution of the shunt compensation by SVC is analyzed based on the sensitivities (control factors) of the operation margin to the shunt susceptance. It is found that the control effect of SVC is approximately linear when the mho relay has relative smaller operation margin. In this range the linear model based on the control factors is accurate enough to simulate the control effect. It is also found that the shunt compensations at different locations may yield opposite effect to the operation margin of the mho relays, which can be easily judged by the value of the control factors.

Notizen: This paper presents the design and analysis of a multi-phase ac-dc converter system for harmonic reduction at the point of common coupling (PCC) in vector controlled induction motor drives (VCIMD's). The design of the proposed 3-phase to 15-phase autotransformer is presented along with the VCIMD. The proposed 15-phase ac-dc converter is found capable of suppressing up to the 29th harmonic in the supply current, along with the power factor improvement close to unity in the wide operating range of the drive. The effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed ac-dc converter. A set of power quality indices on input ac mains and on dc bus for a VCIMD fed from existing 6-pulse and proposed 15-phase ac-dc converters are also given to compare their performance.

Notizen: This paper addresses the problem of curtailing the number of control actions using fuzzy expert approach for voltage/reactive power dispatch. It presents an approach using fuzzy set theory for reactive power control with the purpose of improving the voltage profile of a power system. To minimize the voltage deviations from pre-desired values of all the load buses, using the sensitivities with respect to reactive power control variables form the basis of the proposed Fuzzy Logic Control (FLC). Control variables considered are switchable VAR compensators, On Load Tap Changing (OLTC) transformers and generator excitations. Voltage deviations and controlling variables are translated into fuzzy set notations to formulate the relation between voltage deviations and controlling ability of controlling devices. The developed fuzzy system is tested on a few simulated practical Indian power systems and modified IEEE-30 bus system. The performance of the fuzzy system is compared with conventional optimization technique and results obtained are encouraging. Results obtained for a modified IEEE-30 bus test system and a 205-node equivalent EHV system a part of Indian southern grid are presented for illustration purposes. The proposed fuzzy-expert technique is found suitable for on-line applications in energy control centre as the solution is obtained fast with significant speedups with few number of controllers.

Notizen: This paper presents a novel concept of Static Var Compensator (SVC) damping control using a weighted sum of bus voltage angles of remote generators that are responsible for causing inter-area oscillations in power systems. These remote bus voltage angle signals are acquired through Phasor Measurement Units (PMUs). A time domain simulation study on a 39-bus New England multi-machine system is utilized to show that an SVC auxiliary damping control, based on the derivative of these remote bus voltage angles, is superior to the conventionally employed local signals in damping inter-area oscillations. The effect of transmission delay in the acquisition of remote signals is also presented and a simple mechanism to compensate this delay is proposed and validated. The robustness of the delay compensator is finally shown for a wide range of signal transmission delays. The designed SVC controller shows a superior performance in damping the inter-area oscillations despite the signal transmission delays.

Notizen: Series compensation at the midpoint of a transmission line creates problems to conventional protection approaches. A new fault classification technique has been developed for a transmission line with a series capacitor at the midpoint, having different percentages of compensation varying from 25% to 75%. The proposed technique requires three line currents and voltages at each end and computes fundamental phasors of these quantities using a modified version of Full Cycle Discrete Fourier Transform. Using these phasors, the absolute values of three phase impedances are calculated for faulted phase identification. Moreover, the involvement of the ground in the fault is identified using a zero sequence component of the fault current. Using a PSCAD/EMTDC software package, a large test data (28,800) set has been generated with different types of faults and system variables, which includes fault resistances, fault inception angles, fault positions (before and after series capacitor) and variable loading conditions along with wide variations in the source impedances at both ends of a transmission line. The proposed scheme is tested on the said data set and the results are found to be promising. The results indicate that the proposed technique is fast, accurate and robust for a wide variation in system and fault conditions.

Notizen: This paper presents an assessment of the vulnerability of the power grid to blackout using graph topological indexes. Based on a FERC 715 report and the outage reports, the cascading faults of summer WSCC 1996 are reconstructed, and the graphical property of the grid is compared between two cases: when the blackout triggering lines are removed simulating the actual sequence of cascading outages and when the same number of randomly selected lines are removed. The investigation finds that the critical path lengths of the triggering events of the July and August outages of 1996 WSCC blackout are higher than those of no-outage and arbitrary events. In addition, the small world-ness index for each of the outage triggering events is much smaller than that of normal or any no-outage scenario, indicating that events of shifting a network from small world to a random network would be more likely cascaded to wide area outage.

Notizen: An asynchronous parallel electromagnetic simulation method for large scale power system is developed, in which the original system is divided into two subsystems, A and B. Subsystem A is the local system including the disturbance source and any devices that should be simulated in details. Subsystem B is the external system consisting of all the other part of the system. The time domain digital simulation of subsystem A and B are executed by two independent processes with different time-steps. Signal transmission between A and B is implemented at each time step by a series of time varying Norton equivalent circuits and equivalent voltage sources. Because the digital simulation for subsystem A and B are processed in parallel, and simulation time of process B lags that of process A, so it's called asynchronous parallel electromagnetic simulation method. The basic principle, implementation procedure and error analysis of this new method are discussed, computer coding is also implemented in one version of EMTP program. Practical power system simulation and other application with the new method are also presented.

Notizen: This study aims to present a new approach to detecting high impedance faults (HIFs) in the distribution feeder. Discrete wavelet transformations (DWT) and neural networks (NN) have been widely applied in power system research. Consequently, this study developed a novel technique to discriminate effectively between the HIFs and the switch operations by combining DWT with NN. The proposed approach has three distinct features. First, the input signal of this algorithm is neutral line current, rather than the conventional currents based on three individual phases. Second, HIFs identification uses the details at levels 3, 4 and 5 and the approximations at level 5 of the neutral line current are utilized for. Third, the input signals of the three-phase voltages classify the faulty and healthy phases. The results of simulation and field staged fault clearly show that the proposed technique can accurately identify the HIFs in the distribution feeder.