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FACTS Controllers Impacts on Security Margin Enhancement in Power System

In this paper, voltage stability of power system has been investigated in the presence of three types of FACTS controllers including SVC, STATCOM and UPFC. Voltage stability and voltage collapse point and the loading amount are calculated with and without FACTS controllers. Simulations have been carried out on 33-bus network test system in PSAF software. It was found that without the installation of FACTS controllers, the maximum loading amount is 1.71 (p.u), which by installing any of these FACTS controllers and changing their installation place, loading value is also changed. In this paper, the installation of various types of FACTS controllers has been examined simultaneously as well as by installing several numbers of just one of these FACTS controllers.

Conjugation of hydroxyapatite nanocrystals with human immunoglobulin G for nanomedical applications

Inorganic nanosized drug carriers are a promising field in nanomedicine applied to cancer. Their conjugation with antibodies combines the properties of the nanoparticles themselves with the specific and selective recognition ability of the antibodies to antigens. Biomimetic carbonate–hydroxyapatite (HA) nanoparticles were synthesized and fully characterized; human IgGs, used as model antibodies, were coupled to these nanocrystals. The maximum loading amount, the interaction modelling, the preferential orientation and the secondary structure modifications were evaluated using theoretical models (Langmuir, Freundlich and Langmuir–Freundlich) spectroscopic (UV–Vis, Raman), calorimetric (TGA), and immunochemical techniques (ELISA, Western Blot). HA nanoparticles of about 30 nm adsorbed human IgGs, in a dose-dependent, saturable and stable manner with micromolar affinity and adsorption capability around 2.3 mg/m 2. Adsorption isotherm could be described by Langmuir–Freundlich model, and was due to both energetically homogeneous and heterogeneous binding sites on HA surface, mainly of electrostatic nature. Binding did not induce secondary structure modification of IgGs. A preferential IgG end-on orientation with the involvement of IgG Fc moiety in the adsorption seems most probable due to the steric hindrance of their Fab domains. Biomimetic HA nanocrystals are suitable substrates to produce nanoparticles which can be functionalized with antibodies for efficient targeted drug delivery to tumours.

Preparation and Release Properties of a pH-Tunable Carboxymethyl Cellulose Hydrogel/Methylene Blue Host/Guest Model

pH-sensitive carboxymethyl cellulose hydrogel beads were prepared in spherical form by a suspension-crosslinking technique with epichlorohydrin as a crosslinking agent and fluid wax as the suspending solvent. The hydrogel beads are spherical in shape with a diameter of about 4 mm, which exhibits reversible pH-sensitive behavior. The hydrogel beads have good behavior for adsorption and release. The ability of the hydrogel beads to uptake and release a positively charged cationic guest molecule, such as methylene blue, could be tuned by controlling the extent of carboxylate ionization via pH. At 25°C, the maximum loading amount for methylene blue exceeded 1350.6 g/g with 56.27% adsorption ratio.

Hydrotropic Polymeric Micelles for Enhanced Paclitaxel Solubility: In Vitro and In Vivo Characterization

The purpose of this investigation was to characterize the in vitro stability and in vivo disposition of paclitaxel in rats after solubilization of paclitaxel into hydrotropic polymeric micelles. The amphiphilic block copolymers consisted of a micellar shell-forming poly(ethylene glycol) (PEG) block and a core-forming poly(2-(4-vinylbenzyloxy)-N,N-diethylnicotinamide) (P(VBODENA)) block. N,N-Diethylnicotinamide (DENA) in the micellar inner core resulted in effective paclitaxel solubilization and stabilization. Solubilization of paclitaxel using polymeric micelles of poly(ethylene glycol)-b-P(D,L-lactide) (PEG-b-PLA) served as a control for the stability study. Up to 37.4 wt % paclitaxel could be loaded in PEG-b-P(VBODENA) micelles, whereas the maximum loading amount for PEG-b-PLA micelles was 27.6 wt %. Thermal analysis showed that paclitaxel in the polymeric micelles existed in the molecularly dispersed amorphous state even at loadings over 30 wt %. Paclitaxel-loaded hydrotropic polymeric micelles retained their stability in water for weeks, whereas paclitaxel-loaded PEG-b-PLA micelles precipitated in a few days. Hydrotropic polymer micelles were more effective than PEG-PLA micelle formulations in inhibiting the proliferation of human cancer cells. Paclitaxel in hydrotropic polymer micelles was administered orally (3.8 mg/kg), intravenously (2.5 mg/kg), or via the portal vein (2.5 mg/kg) to rats. The oral bioavailability was 12.4% of the intravenous administration. Our data suggest that polymeric micelles with a hydrotropic structure are superior as a carrier of paclitaxel due to a high solubilizing capacity combined with long-term stability, which has not been accomplished by other existing polymeric micelle systems.

On multiple tap blocking to avoid voltage collapse

This article discusses some aspects related to long term stability analysis of power systems. In particular, it is studied the effect of the tap changes in the instability process. For this sake, instability may be obtained as a consequence of a contingency, assuming the transient period as stable. In this sense, some discrete actions are taken in order to enhance the post–fault equilibrium point. These control actions may be temporarily effective, but eventually, may trigger the system collapse. In order to preserve the system stability, a technique to determine the instant to block the tap changes is proposed. Such a technique focuses on keeping the stability and recovers the maximum amount of voltage-varying load. The idea is tested using the IEEE-14 bus system.

Voltage collapse risk assessment

Abstract Several approaches have been proposed in the literature to analyze system voltage collapse, based on indices that can efficiently evaluate the load margin for which the system remains stable. All this discussion, including possible methods of solution, is being carried out under deterministic assumptions; load, generation and transmission are defined for each operating condition. The basic idea is to obtain the maximum amount of load the system can support, and what distance it is from this condition. In this work, the voltage collapse problem is reviewed, considering the stochastic nature of the load. A probabilistic methodology is developed to provide risk indices of voltage collapse, based on a combination of the tangent vector and Monte Carlo simulation methods. It is also shown how a probabilistic load flow analysis can be adapted to evaluate the proposed risk indices. In order to illustrate the proposed approach, a modification of the IEEE reliability test system is used and the applicability of the results to operation and expansion planning is discussed.

Abridgment of transient torque-angle characteristics of synchronous machines

Mechanical oscillations of synchronous motors following the application of abrupt shaft loads have not heretofore been easily calculated for cases of large angular swings, taking into account the damping currents in the rotor, except by tedious point-by-point methods. The chief difficulty has been due to the form of the basic differential equation upon which the solution of hunting problems depends. Within the last few years, Doctor V. Bush and others at the Massachusetts Institute of Technology have devised the integraph which is capable of solving the equations of the synchronous motor. Into the integraph are put curves representing the non-linear differential equations and the boundary conditions. The desired results come from the integraph as curves. In this paper, the problem of sudden load on the non-salient pole alternator is solved by the integraph for enough different conditions so that the performance of practically any machine of this type may easily be predicted from the compiled results. Knowing the moments of inertia of the machine and its load, the characteristics of the machine running as a synchronous motor and as an induction motor, the maximum amount of sudden load for which the machine will remain in synchronism may be determined for different values of initial load. Other curves give the maximum angle of the first swing of the rotor and the time interval for the rotor to change from Us initial position to this maximum angle. The simplest type of equation representing an ideal synchronous machine is solved in this paper. The integraph is capable of solving problems of a much more complicated nature than those presented. The more complicated problems pertaining to machines with unsymmetrical excitation and salient-pole rotors will probably be the subjects of future papers.

Transient Torque-Angle Characteristics of Synchronous Machines

Mechanical oscillations of synchronous motors following the application of abrupt shaft loads have not been hereto-fore easily calculated for cases of large angular swings, taking into account the damping currents in the rotor, except by tedious point-by-point methods. The chief difficulty has been due to the form of the basic differential equation upon which the solution of hunting problems depends. Within the lastfew years Dr. V. Bush and others at the Massachusetts Institute of Technology have devised the integraph which is capable of solving the equations of the synchronous motor. Into the integraph are put curves representing the non-linear differential equations and the boundary conditions. The desired results come from the integraph as curves. In this paper the problem of sudden load on the non-salient pole alternator is solved by the integraph for enough different conditions so that the performance of practically any machine of this type may be easily predicted from the compiled results. Knowing the moments of inertia of the machine and its load, the characteristics of the machine running as a synchronous motor and as an induction motor, the maximum amount of sudden load for which the machine will remain in synchronism may be determined for different values of initial load. Other curves give the maximum angle of the first swing of the rotor and the time interval for the rotor to change from its initial position to this maximum angle. The simplest type of equation representing an ideal synchronous machine is solved in this paper.