Full Time Scale Research Articles

A two-time scale simulation for dynamic analysis of power systems

This paper proposes a two-time scale simulation approach of both short-term and long-term dynamics in power systems. The short-term transient period is analyzed by a full-time scale simulation while a quasi-steady state model of the power system is used to simulate long-term dynamics. The proposed method is inspired of Singular Perturbation theory to model the interaction between the short-term and long-term dynamics. Based on this interaction, a suitable criterion to determine when the quasi-steady state model of a power system can be considered as a uniform approximation of the full-time scale model is proposed, which also determines the appropriate switching time between models. The proposed method is demonstrated on the 10-machine, 39-bus New England system and a 46-machine, 190-bus equivalent Mexican system.

Determination of Kinetic and Diffusional Parameters for Sodium Borohydride Oxidation on Gold Electrodes

Direct borohydride fuel cells are among the latest fuel cell types under considerable research and development. There is a clear need for further elucidation of the borohydride electrochemical oxidation. From this perspective, potential step experiments were carried out with a Au disk electrode in alkaline sodium borohydride solutions of varying concentrations and temperatures. Analysis of the current transients for the full time scale enabled the delimitation of the domains where diffusion, electron transfer, and mixed control prevail. Chronoamperometric measurements in the diffusion-controlled region led to current responses exhibiting Cottrellian behavior, from which accurate diffusion coefficients, , were estimated. Arrhenius plots of allowed determination of the diffusion activation energies and maximum diffusion coefficients. Chronocoulometric measurements generated Anson plots from which the kinetic rate constants and charge transfer activation energies were calculated. Analysis of the current densities in conditions of infinite mass transfer led to Tafel plots from which exchange current densities, transfer coefficients, standard rate constants, and standard activation energies for charge transfer were determined. Purely charge-transfer regimes were not recognized in the studied system under the imposed potentials.

Determination of Kinetic and Diffusional Parameters for Sodium Borohydride Oxidation on Gold Electrodes

Potential step experiments were carried out with a Au disc electrode in alkaline sodium borohydride solutions of varying concentrations and temperatures. Analysis of the current transients for the full timescale enabled the delimitation of the domains where diffusion, electron transfer, and mixed control prevail. Chronoamperometric measurements in the diffusion controlled region led to current transients exhibiting Cottrellian behaviour, from which accurate diffusion coefficients, D, were estimated. Arrhenius plots of D allowed determination of the diffusion activation energies, Ed, and maximum diffusion coefficients, D0. Chronocoulometric measurements generated Anson plots from which the kinetic rate constants, k, and charge transfer activation energies, Ect, were calculated. Analysis of the current densities in conditions of infinite mass transfer led to Tafel plots from which exchange current densities, i0, transfer coefficients, α, standard rate constants, ks, and standard activation energies for charge transfer, Ect0, were determined. Purely charge transfer regimes were never observed for the studied applied potentials.

Simulation on binding efficiency of immunoassay for a biosensor with applying electrothermal effect

The working principle of immunoassays is based on the specific binding reaction of an analyte-ligand protein pair in physiological environments. However, for a diffusion-limited protein, the diffusion boundary layer of the analyte on the reaction surface of a biosensor would hinder the binding reaction from association and dissociation. The formation of such association and dissociation layers thus limits the response time and the overall performance of a biosensor. In this work we have performed a two-dimensional full time scale finite element simulation on the binding reaction kinetics of two commonly used proteins, C-reactive protein (CRP) and immunoglobulin G (IgG). By applying a nonuniform ac electric field to the flow microchannel of the biosensor, the electrothermal force can be generated to induce a pair of vortices to stir the flow field. With the aid of the vortices and a suitable choice of the location of the biosensor, the fluids flowing over the reacting surface can be accelerated fast enough to depress efficiently the growth of the diffusion boundary layer on the reaction surface, and enhance the association or dissociation of analyte-ligand complex. The interference patterns of the flow field due to the existence of the sensor at different locations of the microchannel could cause different degrees of enhancement to the association and the dissociation. By changing the location of the sensor the largest enhancement is found at the position near the negative electrode. For the configuration of the microchannel we studied, the initial slope of the curve of the analyte-ligand complex versus time can be raised up to 5.17 for CRP and 1.93 for IgG in association, and 3.74 for CRP and 1.28 for IgG in dissociation, respectively, under the applied ac field 15 Vrms peak-to-peak and operating frequency 100 kHz. At this optimal sensor location, we also studied the effect of various settings of temperature boundary conditions on the top and bottom walls, including the two limiting cases, namely, constant temperature and thermal insulation on both walls. We show that varying the temperature boundary conditions can cause an essential effect on the enhancement of the binding reaction and can be employed to find an optimal binding enhancement. Utilizing these simulation results, an improved design incorporating a pair of electrodes and a neck region near the reaction surface is demonstrated. The sensor is fixed to locate at the middle of the bottom side. With the existence of the stirring flow field, the association rate of the 30 μm neck is 2.73 times faster than that of the original channel with no neck.

Dynamic voltage stability constrained ATC calculation by a QSS approach

The evaluation of Available Transfer Capability (ATC) in deregulated power system should take into account thermal limits, transient, steady-state and dynamic angle stability as well as the voltage stability limit. The consideration of voltage stability in the determination of ATC, however, was not well researched before. On the other hand, under the power market environment, voltage instability becomes a more important consideration in many countries in recent years, especially when following a large disturbance in a heavily stressed power system over long distances. A new ATC determination scheme using Quasi-steady-state (QSS) approximation is proposed in this paper and implemented on a test system. The performance of the QSS approximation is also compared with the Full-Time-Scale (FTS) simulation. From the results, it is shown that the proposed scheme can evaluate ATC with dynamic voltage stability constraints accurately and the calculation speed is accelerated considerably to meet the real-time requirement.

Resolution of Simultaneous Kinetic Spectrophotometric Processes by the Full Time Scale Technique in the Fourier Domain

The full-time scale technique in the Fourier domain was studied for resolution of simultaneous kinetic spectrophotometric processes. Two programs, SPGRKIT and SPGRFTQ, were designed to perform kinetic simulation and resolution of simultaneous kinetic processes. The method made use of full kinetic information and matrix data processing. Data reduction and optimization were performed using principal-components analysis and Fourier transformation. Experimental results showed the method to be successful for both simulated and experimental data.

Diffusion models for gas production from coals: Application to methane content determination

Experimental studies of methane diffusion from coal cuttings have been analysed with both a unipore diffusion model and a bi-disperse pore structure diffusion model to determine the time range of each model's validity. Initial desorption, during the first 50% of volume desorbed, can be adequately described by the unipore model. For Fruitland coals of the San Juan Basin, the unipore diffusion coefficient varied by less than a factor of 2 from a value of 1 × 10 −5 s −1 despite large variations in sample depth and location. The unipore diffusion model has been successfully incorporated into a lost-gas-correction-factor determination as part of a new technique to delineate coal-bed methane. To describe methane diffusion over the full timescale of desorption, a more complex model which more accurately represents the observed bi-disperse pore structure of coal is required. Using that model the observed desorption rate is described over all the desorption. This model is especially applicable as a source term in describing overall well production.

The Galvanostatic Method: Analysis of Error and Computation of Parameters

Galvanostatic transients arising from multi‐step processes of the type: are treated mathematically for systems subjected to both activation and diffusion control. Analysis of error based on the error matrix is presented. The galvanostatic method is characterized by the information contents [ and ] for a single‐estimate analysis (i.e., estimate of for known or the reverse) and that for a two‐estimate analysis (simultaneous determination of and ). The correlation between the estimates of and is given as a function of the dimensionless scale . Information contents for and in single and two‐estimate systems are given and this permits the determination of the accuracy and the limits of the method as well as the choice of optimal experimental conditions. The optimal full time scale for estimation of depends on the value of . For between 0.5–500, varies from 6 to 18 (single‐estimate system) and from 4 to 25 (two‐estimate system). The upper limit for in a single‐parameter estimation is 3–12 A cm−2 (for ) and the upper limit for is 8 cm sec−1. This is three times greater than for the coulostatic method. For a given value of , the accuracy of the galvanostatic method is better than that of the coulostatic for systems when , but is not as good when . The upper limit of and the accuracy of the galvanostatic method for two‐estimate analysis ( and ) are considerably lower than those for single‐estimate analysis. An iteration method is developed with which a large improvement is achieved. Estimation of and with a computerized curvilinear regression analysis is proposed.