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This paper presents a novel method for finding coherent groups of generators in large power systems, based on graph partitioning and clustering methods commonly used in other areas like image processing and gene expression analysis. First, the power system is modeled as a graph in order to obtain a maximum spanning tree that represents the strongest connections between generators in the system. Then, inconsistent edges are removed from the tree according to proposed criteria. This leads to the identification of the coherent groups of generators. Two algorithms are proposed for the elimination of the edges in the maximum spanning tree, both based on Fukuyama-Sugeno validity index. The method is tested on 68-bus test system and 678-bus Italian equivalent system. Results are compared with classical approaches.

Current and traditional methods of load shedding are based on threshold values of frequency and voltage; thus, when the power system falls below these values, some mechanical control actions are activated as countermeasure against stability problems. Nevertheless, in many cases the traditional mitigation methods based on load shedding cannot ensure that the network remains in continuous operation after the presence of suddenly and severe perturbations. In addition, the development of control systems of wide area based on PMU’s measurements has allowed the development of different kinds of indices for the stability prediction. Thus, on-line diagnosis of the power system about angular stability and voltage stability gives better information about the system’s situational awareness. This paper proposes a methodology that allows the system operator to take a decision if applying the load shedding as a countermeasure for system instabilities caused by severe contingencies. In addition, the methodology identifies which are the nodes where the load shedding must be applied and the quantity of load shedding to be applied. The proposed load shedding methodology is based on a fuzzy logic decision method using the stability prediction index (SPI) and fast voltage stability index (FVSI). These indices can be computed on-line and they give the stability status of several operating areas. The methodology is tested on the NYPP-NETS of 68 nodes and it is illustrated with a cascade.

This paper proposes a methodology for the computation of robust controls that guarantee robustness in a wide range of operating condition of a power system; such as contingencies, uncertainties and delays in the signals. This paper proposes a detailed modeling of uncertainties of the power system as additive uncertainties of the plant under the theory of robust control, and also a methodology for defining in a correct way sensitivity matrices used in the computation of robust controls and based on the model uncertainties and control purposes (damping of electromechanical oscillations). It is also proposed the computation of robust controls in two stages guaranteeing robustness and damping, and the analysis of performance of the control against delay times in control signals.

Power systems control strategies that use global signals have shown better results than those based on local signals, but the remote signals are usually taken far away from the control center. Because of that, wide area power systems controlled using global signals are inherently delayed, and time delays jeopardize the stability of power systems. This paper presents a Kalman based time delay compensation strategy, which feed a Model Predictive Control (MPC) scheme to damp inter-area oscillations in power systems with latencies in their communications. A Kalman state estimator is employed to get the states. The proposal uses a dynamic reduced order model obtained using Hankel singular values. The methodology is promissory because it considers time delays in control schemes design processes, useful for either centralized or distributed wide area power system controllers based on widespread metering. This approach was validated for controlling inter-area oscillations in a test power system with two areas, 4 generators and a tie power line. Results suggest an enhancement of the power system dynamic performance upon the application of the method proposed.

Traditionally, repairs has been modeled in power system reliability as part of the component reliability models; an alternative way is to represent them by means of queuing theory concepts. One of the advantages of this approach is that it allows assessing the performance of crews, a feature not offered by any other method. However, the application of this modeling approach arises the following question: ?what is the correct way to generate the times to repair, using a global model for all components or using one for each component or component class? To reply this question, in this paper reliability of a power transmission system is assessed using both approaches and considering for power transformers the cases of repair, replacement with a local spare and replacement with a spare taken from a remote location. The conclusion is that if repair durations of the components are very different is not valid to use a global model for generating the repair times for all components, i. e. the approach commonly used in QT is not valid here; instead, it is necessary to generate them using a model for each component or component class and this demands more computational time.

Normally, the trains of a UMTS requires a DC power supply by means of rectifier AC/DC substations, know as traction substations (TS); that are connected to the electric HV/MV distribution system of a city. The DC system feeds catenaries of tramways or the third rail of metros, for example. The DC voltage is selected according to the system taking into account power demand and length of the railway’s lines. Typically, a 600 Vdc – 750 Vdc is used in tramways; while 1500 Vdc is used in a metro system. Some interurban-urban systems use a 3000 Vdc supply to the trains.

In this paper graph theory is used to identify coherent groups of generators and to locate PMUs for Inter-Area monitoring. Initially, the problem of identifying coherent groups is presented as a graphical problem. Then, three graph clustering methods are implemented to group coherent generators. Finally, when the electric network is separated in coherent regions, a placement of PMU based on centrality criteria is proposed. This can be used as a first stage in the implementation of a plan of monitoring in a large electric power system. Dynamic simulations and phasorial representation of simulations are done with the reduced order equivalent of the interconnected New England system (NETS) and New York power system (NYPS). The results show that graph theory can be applied to identify coherent groups and to locate PMUs to Inter-area monitoring.

Rectifier substations in DC electric transportation systems are an important source of harmonic distortion. One of the best compensation actions is to use active power filter due to its adaptation capacity to different load conditions. This paper presents a computational model of DC traction supply systems that allows the presentation of the current distortion in the distribution system under several traction load cases. The compensation is developed using active power filter with a control system based on the p-q theory. Simulations without and with active compensation shows the effectiveness of active power filter in DC traction systems.

The present paper develops a methodology to choose the best connection scheme for traction substations of a Massive Electrical Railway System (MERS) and distribution substations in urban areas using graph theory and economical optimization.

This paper presents a decentralized robust control scheme for two types of FACTS devices: SVC and TCSC, to enhance the voltage and angular stability in a power system. The robust control scheme is based on reduced order models, which are computed using the Hankel reduction theory. After that, computation of decentralized robust controls is proposed and tested in a two-area 68 nodes system.

In power systems are normally localized linear controllers placed at several subsystems located in different geographical zones. In addition, there have been introduced new technologies of non-linear control, with applied methodologies of feedback linearization, where all the system is transformed to a linear system. Nevertheless, the decentralized scheme is not possible because all the information of the entire system is required when that transformation is done. That is why it must be developed a controller that maintains the decentralization at the same time as the robustness. The procedure detailed in this paper consists of the utilization of reduced dynamical models computed at each FACTS device useful for the computation of supplementary controls. So, a decentralized model is done from a linear model, where there are the local controls for each device and a central control that gives the reference. The paper also describes the methodology used for computing optimal LQG/LTR decentralized controls for FACTS and, previously, it is outlined the problem to locate the FACTS devices and know its dimensions.

Power quality phenomena originated in power distribution systems impact on the electrical power supply system of railway systems, such as the tramway, and in the same way, power electronics used in the traction system impacts on the power quality service of the distribution system. This paper presents a study of the main power quality phenomena involved in the interaction between the power distribution system and the tramway's power supply system. In addition, the paper presents an alternative method to study the PQ phenomena using time simulations of power demand of a set of trains in a tramway system.

This paper compares a traditional fuzzy logic controller with two new proposals of defuzzification based on Boolean relations. The objective of the controller is to reduce the electromechanical oscillations like a classical power system stabilizer. The design of controllers begins from of a previous developments in fuzzy logic and fuzzy logic type 2 tested in simulation before, each one is presented including a justified theoretical and methodology explanation of the contribution mentioned and modified with the defuzzification proposals. Time response is evaluated in a multimachine system of two areas for each method.

a security scheme of the power systems should protect the integrity of the electric networks and carry out fast operations on the entire power system to prevent a possible blackout. Blackouts started as local failures led to electrical disturbances, and the complete collapse of the power systems. This work proposes a security scheme based in two stages. In the first stage, the controlled separation of the power system allows to isolate the failure area. In the second stage, under frequency load shedding control actions should be applied to maintain a balance between consumption and generation power. This work presents some schemes in the IEEE-39 test system.

Reliability assessments of electrical power substations have been traditionally performed assuming that the failure and repair processes are stationary and making a great simplification on the protective systems modeling. Thus, in order to improve the level of detail of these assessments, this paper presents a method that combines the modeling of failures and repairs as stochastic point processes and a procedure of sequential Monte Carlo simulation for computing the reliability indexes. Its main features are: i. It can manage time varying rates, a necessity for those scenarios considering improvement/deterioration of component reliability, preventive maintenance and repair process performance. ii. It allows the explicit representation of the protective systems, its operating sequence and the effect of their failures. iii. It does not require an exhaustive list of operating states as other methods do. Of course, this improvement in modeling detail has a price; it is the long computational time required by the simulation.

This paper presents a method for studying the occurrence of loss of component scenarios in a power system using stochastic point process modeling. It can manage stationary and non stationary failure and repair rates, common mode failures of any order, components with any number of operating states and diverse repair logistics. The failure and repair sequences in each maintenance zone of the power system are generated using Monte Carlo simulation. A list of possible loss of component scenarios is therefore not required as in other methods. Loss of component scenarios are studied in terms of probability of occurrence, expected frequency and mean duration. By means of two examples, it is shown how the proposed method is a more flexible modeling tool than those based on Markov chains.

Although stochastic point process theory has been successfully applied in many fields of knowledge, in power systems reliability it has not received so much attention what is reflected in the low number of reported applications. This may be due to some common misconceptions about the modeling of repairable components which falsely show this method is the same than other popular ones. All these misconceptions originate in the incorrect practice of analyzing the reliability of repairable components using concepts that were developed only for non repairable ones and, specifically, in the misleading idea that a stationary random process model can represent a non stationary random process. This paper discusses these misconceptions expecting clarity of concepts can foster the development of more applications of this theory in power systems reliability.

Power system security requires the modeling and simulation of catastrophic contingencies that could be present in the system collapse or blackouts. Thus, power system operators require analysis tools that give them information in order to take preventive and corrective actions to operate the system in a reliable way. Generally, this type of analysis involves simple componentpsilas contingencies based on a N-1 criteria. However, it has been shown that more than one component of the system has been involved in major blackouts. These major contingencies include simultaneous outages, cascade phenomena or a major outage that means the outage of complete power system installation with several components, i.e. a Super Component contingency, such as a full substation. So, an outage of a super component implies the multiple and simultaneous outages of many elements. This paper presents a methodology to model and to evaluate the severity of this kind of contingencies in the operative planning framework. The methodology has been implemented in MATLAB and tested using the IEEE 118 and IEEE 300 systems.

Currently, the voltage security assessment in the power system operating planning applies the N-1 criterion in order to evaluate the voltage security impact provoked by contingencies. This criterion could be applied in probabilistic and/or deterministic methodologies. At the same time, one of the most popular and used techniques to evaluate voltage security is the system loadability computation by means of the power flow computation (CPF). In consequence, the voltage security assessment in an operating planning scenario based on exhaustive enumeration takes much computational time. This paper proposes the utilization of statistical sampling techniques, such as stratified sampling, in order to reduce the computational time. Two sets or strata are defined based on aggregated modal analysis behavior; such as, the universe of single contingencies is separated in two sets: critical and non-critical.

Operation of power systems is subject to disturbances, such as faults, that increase the operational risk. Under a "day ahead" planning, it is useful to forecast system loadability capacity such an operational margin. This paper introduces a methodology for assessing and characterizing the maximum loadability of a power system when it undergoes contingencies on an hourly basis by means of Monte Carlo simulations and continuation power flow methods. In addition, the methodology allows the identification of weak areas in the system. The proposed methodology has been tested in the New England 39 bus system and the IEEE 118 nodes system.

Power system operating planning must determine adverse conditions that could affect the normal performance of the system. Load variations and contingencies could provoke these adverse conditions, which produce angular instability problems or voltage stability problems, among others. In addition, the short-term operating planning must evaluate risk of instability conditions for angular and voltage instability. This paper proposes a methodology to assess the angular instability risk due to load uncertainty based on modal analysis of the small signal analysis for short-term planning purposes. In addition, the risk assessment of angular instability is done for selected contingencies based on an eigenvalue variation contingency ranking proposed in this paper. The methodology is tested in the New England 39 nodes system.

A demonstration of ambipolar transistors of polymer-wrapped single-walled carbon nanotubes (SWNTs) provides an opportunity to scrutinize transport mechanism of electrons and holes in this system. Anomalous temperature-dependent nonlinear transport behavior is observed in large diameter SWNTs. This suggests an interplay between the intrinsic transport of individual tubes and the percolative network properties, highlighting the nature of polymer-wrapped SWNTs as a complex hybrid material.

This paper proposes a methodology through an optimization model that allows decisions about expansion of a power system considering intermittent renewable energy sources, like wind energy, and other random variables in transmission and generation expansion planning. So, the uncertainty of the risk of failure in the system components, uncertainty in demand and uncertainty in the availability of energy resources (wind speed for wind power generation) is included. The methodology is applicable to systems with a high level of hydroelectric sources. It is divided in two parts, the first one establishes the best location of intermittent sources, like wind energy. The second part optimizes the combination between renewable sources and conventional generation. After that, the transmission facilities are formulated and optimized.

Noncovalent functionalization of carbon nanotubes by wrapping them using pi-conjugated polymers is one of the most promising techniques to sort, separate, and purify semiconducting nanotube species for applications in optoelectronic devices. However, wide energy bandgap polymers commonly used in this technique reduce charge transport through the nanotube network. To avoid the formation of insulating barriers between the tubes, challenging procedures for the removal of the polymer from the nanotube walls are necessary. Here, the use of two narrow bandgap polymers based on naphthalene-bis(dicarboximide) (NDI), namely, poly{[N, N'-bis(2-octyldodecyl)- naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,59-(2,29-bithiophene)}, (P(NDI2OD-T-2 or ActivInk N2200) and its molecular cousin, poly{[(N, N'-bis(2-octyldodecyl)-1,4,5,8-naphthalenedicarboximide-2,6-diyl)alt -5,5'-(2,2'-bithiophene)]-co -[(N, N'-bis(2-octyldodecyl)-1,4,5,8-naphthalenedicarboximide-2,6-diyl)-alt -5,5'-(2,2'-(4,4'-dimethoxybithiophene))]}(ActivInk PE-N-73), for selecting semiconducting single-walled carbon nanotubes (s-SWNTs) is demonstrated. The influence of the chemical structure of these polymers on the nanotube selectivity, as well as the effect of residual excess polymer and their band-gaps, are investigated through optical spectroscopy and charge transport measurements. While the electron transport of the devices fabricated with PE-N-73 and N2200 wrapped SWNTs is comparable, a substantial difference is observed in the hole transport. The better alignment of the HOMO level of PE-N-73 with that of the nanotubes allows achieving improved p-type characteristics even with a large amount of residual polymer in the network.

A strategy to estimate the power demand increment for Plug-in Electric Vehicles (PEV) penetration in residential customers is proposed. This is based on a stochastic model of arrivals and leavings of vehicles and has as goal to generate diversified load curves for every hour of a day, and so on, to estimate the power demand by Electric Vehicles. So, the proposed model is useful to be employed for planning purposes in distribution power systems. This study is divided in two cases, one of them has a limited number of chargers to be installed at residential customers and the second option has a free amount of charges related to number of Electric Vehicles; these represent different types of housing. This tool provides information for planning in distribution systems, based on specific information on mobility in the city to study.

Deterministic security criteria provide a degree of security that may be insufficient under some operating conditions and excessive for others. To determine an appropriate level of security, one should perform a probabilistic cost/benefit analysis that balances the cost of the security margin against its benefits, i.e., the expected societal cost of the avoided outages. This paper shows how a previously published method based on Monte Carlo simulation can be enhanced to take into account time-dependent phenomena (TDP) such as cascade tripping of elements due to overloads, malfunction of the protection system, and potential power system instabilities. In addition, the importance of using failure rates that reflect the weather conditions is discussed. Studies based on the South-Western part of the transmission network of England and Wales demonstrate the validity of the models that have been developed.

It is well known that the main disadvantage of centralized controls systems in power systems is the time delay that is produced by communication systems. This paper presents a design technique of decentralized LQG controllers, which conserves the optimality characteristic of an LQR regulator. The design of these controllers is based on a proposed structure of subsystems of low order, which can be calculated using either order reduction techniques or identification techniques. This structure is noncoupled in state variables, that allows the computation of independent LQR regulators. The paper presents the calculation of equivalent estimators for each subsystem taking into account the other optimal controllers. The proposed method is used to coordinate two SVC controllers. Results of simulations of the controlled system are shown.

This paper presents the results of the study that evaluates the incorporation of FACTS technologies in the expansion planning process of the Colombian National Transmission System (NTS). The application methodology uses as a starting point the optimization of the exploitation of the existing system by increasing its transmission capacity and it is based on steady-state analysis. The results of the feasibility study are also presented for a wide application of FACTS systems in the Colombian Transmission System, for improving transmission capabilities and reliability and security levels after year 2005.

This chapter outlines the role of target levels in the systematic design methodology, the scientific and technical grounds for assessing target levels for key parameters of industrial air technology, and the hierarchy of different target levels, as well as some examples of quantitative targets. Fulfillment of the target levels should be validated or measured by the individuals or organizations responsible at the end of the construction process. Occupational exposure limits (OELs) identifies the highest level of exposure concentration and the corresponding reference time period for which we can be confident that there will be no adverse effects on health. The need for the implementation of target levels for air quality in industrial workrooms stems from different concerns. The requirements on target levels due to type of premises can be divided in two parts: the effect of the different parameters and their target levels on the building, and the building's effect on the different parameters and their target levels. Requirements on parameters that may influence the building and its performance and target levels to be determined for occupational zones and nonoccupational zones are: temperature, humidity, air velocity, contaminant concentration, odors, biocontamination, fire/explosion risk, noise, vibrations, radiation, sunshine, loading on floors, and pressure differences. In industrial premises it is also important that the target level values are guaranteed and that the ventilation system operation can be secured so that the process is not violated because of the ventilation.

As part of the correct operation of any electrical system, it is necessary to guarantee the safety of the persons and the equipment or elements that constitute the system. Therefore, an electrical traction system must be furnished with a grounding system that takes into account their particularities and differences with regard to other electrical systems. This paper proposes a generalized multi-train model to simulate the behavior of the rail voltage and the stray currents in the grounding system, based on equivalent circuit models, processing the instantaneous power obtained from a multi-train DC transport systems electrical demand simulator.