Voltage security and reactive power management

The focus of this paper is on voltage security as a functionof ancillary services that can be described in the context ofreactive power markets and associated pricing mechanisms. Firstly,an introduction to voltage security and reactive power managementis presented and the consequences of recent electricity industryrestructuring in the UK are highlighted. Finally, several recentlydeveloped algorithmic techniques are presented in detail. Thetechniques will introduce the concepts of transition-optimizationand congestion management in the context of a complete frameworkfor the monitoring, assessment and control of voltage security.     

Kinetics and mechanism of the reaction between thiosulfate and chlorite ions at 90°C

The kinetics of the oxidation of S₂O₃^2? by ClO₂^? have been studied in aqueous alkaline solution at 90⁰C using classical titrimetric methods to follow the course of the reaction. The reaction takes place according to the stoichiometry S₂O₃^2? + 2ClO₂^? + 2OH^? = 2SO₄^2? + 2Cl^? + H₂O even in large S₂O₃^2? excess. There is some indication of a complex reaction pattern, but 70% of the ClO₂^? disappearance can be best described by the autocatalytic rate equation -d[ClO₂^?]/dt = k[S₂O₃^2?] [ClO₂^?] [H⁺] with k = (1.3 ± 0.2) ×10⁸ M^?2 sec^?1. The mechanism is explained by postulating nucleophilic attack of S₂O₃^2? on HClO₂ to form a chlorine-containing intermediate.     

Geometric phases in dissipative systems

It is shown that a phenomenon analogous to the geometric phase shifts of Berry and Hannay occurs for dissipative oscillatory systems and can be detected in numerical simulations of chemical oscillators. The approach herein to the theory of geometric phases begins with a study of simple first-order differential equations on the circle (circle dynamics). It is shown how more complicated systems exhibit geometric phases through reduction to a circle dynamics. In this way, the various manifestations of the phenomenon are seen from a single unified perspective. The results are illustrated in numerical experiments on several model systems ranging from analytically solvable, but contrived, to realistic models of chemical oscillators.     

The initiation process in the polymerization of tetrahydrofuran with carbonium ion salts

The initiation process for the polymerization of tetrahydrofuran with (C₆H₅)₃C⁺SbCl₆^? has been studied. Two mechanisms have been considered: a cation-addition process, and a process in which tetrahydrofuran donates a hydride ion to the cation of the initiator to form triphenylmethane. The biscarbonium salt [(C₆H₅)₂C⁺C₆H₄CH₂]₂(SbCl₆^?)₂ has been synthesized and used to initiate the polymerization of tetrahydrofuran. The results are consistent with the hydride-ion mechanism but may be inconclusive because of chain transfer. NMR experiments with 0.05–0.2M solutions of initiator in tetrahydrofuran show that triphenylmethane is rapidly produced in an amount equal to the molar amount of initiator originally present. Some NMR evidence for the presence of an acetal end group in the polymer has been obtained. It is concluded that the initiation process in this system definitely involves the formation of triphenylmethane, although a detailed, unique mechanism cannot be selected at this time.     

Polymerization of isobutylene by the adamantane bromide–diethylaluminum chloride catalyst system

Isobutylene has been polymerized in a continuous stirred tank reactor using a catalyst system comprised of 1-bromoadamantane and diethylaluminum chloride. The polymerization was carried out in hexane solvent at ?15 to ?27°C and gave 100% conversion to polyisobutylene (PIB) of 1000–3000 M_w. The results of pyrolysis–gas chromatography–mass spectrometry analyses are consistent with a mechanism involving the formation of the adamantyl cabocation and its addition to an isobutylene molecule to initiate polymerization. ¹³C-NMR analyses show that the PIB products contain R₂C? CR₂ and R₂C? CHR olefin types. Information on the nature of these olefins and the route to their formation has been developed.     

Cocatalysis by epoxides in the polymerization of tetrahydrofuran with trityl hexachloroantimonate initiator

The polymerization of tetrahydrofuran (THF) with (C₆H₅)₃C⁺SbCl₆^- initiator is markedly accelerated by small concentrations of propylene oxide or other epoxides. Molar concentrations of propylene oxide 4 to 10 times those of the carbonium-ion salt showed increasing conversion to polymer. The equilibrium conversion level at different temperatures with epoxides is the same as in their absence; the approach to equilibrium is first-order in THF. NMR experiments in the presence of propylene oxide indicate the formation of a trityl ether intermediate. The cocatalysis effect is interpreted on the basis of an acceleration in the initiation process in the system.     

Convenient synthesis of NCS-chromophore metabolite isosteres: binding agents for bulged DNA microenvironments

A designed molecule with capacity to bind DNA bulges (20) has been prepared from readily available starting materials. The spirocyclic template was modeled on a metabolite of neocarzinostatin chromophore (NCSi-gb) and is equipped with functionality to enable convenient bioassay. Preliminary studies confirm binding at specific bulged sequences and induction of polymerase-mediated slippage events. The target compound offers a convenient means to study affinity for unique bulged motifs and for use as a molecular biology reagent.     

A study of some problems in determining the stoicheiometric proton dissociation constants of complexes by potentiometric titrations using a glass electrode

Possible errors in the measurement of acid dissociation constants by potentiometric titration techniques have been considered, with particular references to nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA). Unknown junction potentials can arise when pH measurements are carried out using a glass electrode with saturated calomel reference electrode which have been previously calibrated with a standard buffer solution. The magnitude of the influence of these unknown potentials has been demonstrated and an experimental procedure recommended which gives meaningful results.The precision of calculated acid dissociation constants will also be influenced by the presence of cationic species (e.g. H₄L⁴), the total acid strength, the absolute values of the constants and the value accepted for the auto-dissociation constant of water (K_w). All these factors have been considered quantitatively and their effect on metal complex formation constants, calculated from these acid dissociation constants, noted. The proton dissociation constant of the cationic species of NTA (i.e. H₄L⁺) has been found to have the value of pK₀=0.80 at 20° and μ=0.10 M.     

An absorptiometric determination of perchlorate by means of a novel coloured liquid anion exchanger

A novel liquid anion exchanger can be prepared from tetra-n-hexylammonium iodide and Erdmann's salt, (NH₄)[Co(NH₃)₂(NO₂)₄]. When a solution of this quaternary erdmannate in a suitable organic solvent (e_max = 15,700 at 355 mμ) is equilibrated with an aqueous solution of a salt, the coloured ermannate ion is displaced to a greater or less extent; the effect decreases in the order ClO₄^- > ClO₃^- > NO₃^- > Cl^- > SO₄^2- etc. The effects of changes in the organic solvent composition, of ionic strength, and of other variables on the position of equilibrium have been studied with a view to defining the optimum conditions for the absorptiometric determination of perchlorate ion (≧25 μ) in the presence of chlorate and other ions. Methods are proposed for eliminating those ions that form insoluble silver salts and to allow for the presence of substantial proportions of chlorate or nitrate ions.