A Distributed State Estimator Utilizing Synchronized Phasor Measurements

With the creation of balancing authorities by the North American Reliability Council that span large portions of the North American interconnection, and stringent requirements for real time monitoring of power system evolution, faster and more accurate state estimation algorithms that can efficiently handle systems of very large sizes are needed in the present environment. This paper presents a distributed state estimation algorithm suitable for large-scale power systems. Synchronized phasor measurements are applied to aggregate the voltage phase angles of each decomposed subsystem in the distributed state estimation solution. The aggregated state estimation solution is obtained from the distributed solution using a sensitivity analysis based update at chosen boundary buses. Placement of synchronized phasor measurements in the decomposed subsystems is also investigated in this paper. Test results on the IEEE 118-bus test bed are provided     

Mechanical State Estimation for Overhead Transmission Lines With Level Spans

Electric power transmission lines face increased threats from malicious attacks and natural disasters. This underscores the need to develop new techniques to ensure safe and reliable transmission of electric power. This paper deals with the development of an online monitoring technique based on mechanical state estimation to determine the sag levels of overhead transmission lines in real time and hence determine if these lines are in normal physical condition or have been damaged or downed. A computational algorithm based on least squares state estimation is applied to the physical transmission line equations to determine the conductor sag levels from measurements of tension, temperature, and other transmission line conductor parameters. The estimated conductor sag levels are used to generate warning signals of vertical clearance violations in the energy management system. These warning signals are displayed to the operator to make appropriate decisions to maintain the line within the prescribed clearance limits and prevent potential cascading failures.      

Power system transient stability analysis: Formulation as nearly Hamiltonian systems

In this paper we formulate power systems as nonlinear nearly Hamiltonian systems. Using the invariance principle for ordinary differential equations, necessary and sufficient conditions for asymptotic stability are established and a new method of estimating the domain of attraction of the stable equilibrium point is developed. The present results constitute a novel approach to stability analysis and involve the following three steps:

1. Given a system with dissipation, the stability of its equilibrium is ascertained by determining the stability of the associated conservative system.
2. Attractivity of the stable equilibrium of the entire system (with dissipation) is determined from the system topology.
3. An estimate of the domain of attraction of the asymptotically stable equilibrium is obtained by making use of results obtained in (a) and (b).

The stability criterion developed in this paper sheds new light on the mechanism of instability in power systems and it provides analytical verification to the concept of the potential-energy boundary surface (PEBS). The PEBS is a hypersurface which makes up a part of the boundary of the domain of attraction of the stable equilibrium in a power system. The existence and properties of the PEBS have thus far been deduced primarily via simulations and heuristic methods.     

Attachment and biofilm formation of Pseudomonas fluorescens PSD4 isolated from a dairy processing line

The effects of different nutrient sources and temperatures on attachment and biofilm formation of Pseudomonas fluorescens PSD4, a dairy isolate, were studied. Initial adherence and attachment capabilities among different strains were studied using microtitre plate assays. Biofilm development was observed using confocal microscopy. Strongly adherent cells were seen in protein rich media. Citrate as a carbon source enhanced biofilm formation. Glucose did not favor biofilm development. Psychrotrophic P. fluorescens PSD4 formed strongly adherent biofilms having high metabolic activities at low temperatures. P. fluorescens PSD4 with spoilage potential was capable of forming strong biofilms in dairy processing environments. Biofilm formation was influenced by nutrient availability and growth conditions. These factors should be considered for design of effective anti-biofilm strategies.     

Direct transient stability assessment with excitation control

The authors extended the applicability of the transient energy function method by incorporating the exciter effects in the energy of a multimachine power system during the first swing transient. The generator was represented by the two-axis model and the exciter was represented by one gain, one time constant, and one limiter. In this study they compute the parameters of the extended transient energy function, which assumes a constant average internal EMF. The critical value of this transient energy is determined. A procedure for its use in transient stability assessment has been developed and successfully applied to fault disturbances in two test networks     

An approach for research and training in enterprise information system with RFID technology

Successful implementation of Radio Frequency Identification (RFID) in Enterprise Information System (EIS) depends on exploring the knowledge of RFID technology and providing EIS software training to potential users. The restriction of RFID technology and huge amount item-level data collection via RFID potentially increases the complexity of integrating with EIS. It raises several concerns such as reduced data accuracy, and increased exceptions leading to processes requiring more time to be developed, tested and maintained. However, this approach has not been entirely investigated so far. This paper proposes an integrated research on EIS and a training approach for students and employees who intend to integrate RFID with EIS software in an organization. This integrated research approach applies a typical EIS project workflow from automatic shop floor data collection to customer order fulfillment. This research identifies these stages as transaction, planning and scheduling, integration, execution and control, and automatic identification and data collection. For training and demonstration purpose, this research proposes prototype information systems that emulate the systems used in any organization. This ensures that the logic of the proposed methodology of integrating RFID and EIS software is consistent with that in the business organization. This paper discusses some of the important case studies that were conducted with the suggested prototype systems.     

Effect of nonlinear modal interaction on control performance: useof normal forms technique in control design. II. Case studies

This is part II of a two part paper dealing with control design in power systems using the normal forms technique. The companion paper (part I) describes the general theory and control procedure. Also, the proposed procedure was applied to the Base Case of the 50-generator IEEE Test System. This paper depicts the case studies to show the validation of the proposed method and to observe the effects of controller setting changes. In addition the results dealing with the design of the controller are given and verification of the controller design using nonlinear time simulation is provided     

An on-line contingency filtering scheme for dynamic securityassessment

This paper describes the philosophy and development of a contingency screening system for the selection and ranking of dynamic security assessment. The most severe cases are identified and ranked high on the contingency list for more exact analysis. The nonsevere cases are filtered out of the list. In the proposed system, a cascade of more restrictive filters is developed based on the sparse transient energy function method     

Analyzing dynamic performance of power systems over parameter spaceusing normal forms of vector fields-part I: identification of vulnerableregions

This is the first part of a two-part paper discussing the dynamic performance of power systems over parameter space using the method of normal forms. A new normal form transformation is derived under the second order resonance condition. By using the resonance condition as a guide to indicate detrimental system dynamic performance, the authors propose a computationally efficient method to study the system under varying parameters. An approach to determine the resonance and near-resonance region in the parameter space is developed. For the resonance case, conclusions are drawn by simply examining the analytic solutions. For the near-resonance case, the machine states showing poor performance can be found by tracing the dominant nonlinear modal interaction and mode-machine interaction. The method is tested on the IEEE 50-generator system. The results reveal many interesting characteristics of the system related to resonance and near-resonance, which validates the effectiveness of the method as a useful analytical tool for system operation and design. Further work on quantifying the effect of the modal interactions on the machine states is presented in Part II     

Robust design of a damping controller for static VAr compensatorsin power systems

This paper presents a systematic procedure for the synthesis of a supplementary damping controller (SDC) for static VAr compensators (SVC) in multimachine power systems. The robust performance in terms of the structured singular value (SSV or μ) is used as the measure of control performance. A wide range of operating conditions are used for testing. Simulation results on standard test systems show that the resulting SDC effectively enhances the damping of the interarea oscillations, providing robust stability and good performance characteristics both in frequency domain and in time domain