Reduction of the double-circuit flashovers on a 400 kV overhead line

Double circuit flashovers may cause very severe system disturbances when taking place on some critical double-circuit lines of an electrical network. Line arresters offer an efficient solution to protect these specific lines against double circuit outages due to lightning. This paper will study, on a double-circuit 400-kV line, the protection provided by line arresters against double circuit outages due to lightning. The efficiency of several configurations of line arresters will be compared. For that purpose, the double-circuit lightning flashover rates of the line with and without line arresters will be calculated using a newly developed software which includes a three-dimensional electro-geometric model and is able to take into account the random nature of lightning. This software automatically launches EMTP-RV (restructured version of EMTP) for analyzing fast front overvoltages impressed on line insulation. The energy stressing the line arresters will also be calculated in order to evaluate the risk of failure of the line arresters due to excess energy absorption. Furthermore, the effects of several other parameters such as the tower footing resistances, the lightning withstand voltages of insulator strings as well as the protective levels of line arresters will also be investigated

Effect of uncertainties on the precision of lightning studies

The specification of the withstand voltage of apparatuses as well as the location and characteristics of overvoltage limiting devices to be installed to protect them, requires a careful estimation of the fast front over-voltages, which might potentially exist on the system. This is usually done using an EMTP-like software program. The components of the electrical system located in the vicinity of the apparatuses under consideration are modeled to represent their high-frequency behavior. The precision on the results provided by this approach is limited by the uncertainty in the knowledge we have of key-parameters like, for instance, the value of the grounding resistance of towers or the value of the stray capacitance of some elements. We propose in this paper to examine the consequence of these uncertainties upon the precision of the final results provided by EMTP-like software program\u2019s simulations, using stochastic collocation on a practical case of lightning study

COMPORTEMENT DES PRISES DE TERRE DES PYLONES EN HF

L'objet de ce travail est la recherche de la meilleure mod\ue9lisation du comportement fr\ue9quentiel des prises de terre de pyl\uf4nes HT r\ue9els. Some of the mod\ue8les propos\ue9s dans la litt\ue9rature et actuellement utilis\ue9s sont bri\ue8vement pr\ue9sent\ue9s et analys\ue9s. Les caract\ue9ristiques principales et le domaine de validit\ue9 de chaque approche nous ont conduit \ue0 choisir le mod\ue8le \ue9lectromagn\ue9tique pour notre cas. Ce mod\ue8le est descried, valid\ue9 par des comparaisons avec des mesures r\ue9elles, et appliqu\ue9 \ue0 diff\ue9rentes configurations de prises de terre form\ue9es d\u2019ensembles de 3 boucles enterr\ue9es. Une \ue9tude param\ue9trique permet de constater que leur r\ue9ponse est plus ou moins capacitive selon les caract\ue9ristiques \ue9lectriques du sol et qu\u2019elle peut \ueatre am\ue9lior\ue9e aussi bien en basse fr\ue9quence qu\u2019en haute fr\ue9quence par l\u2019ajout d\u2019antennes de faible longueur

Use of Unbalanced Insulation forthe Limitation of Double-Pole Lightning Flashovers in Double Circuit HVDC Overhead Lines

International audienc

Phenylacetylene and Carbon Dioxide Activation by an Organometallic Samarium Complex

International audienceSmall molecule activation is a topic of growing importance and the use of low-valent f-elements to perform these reactions is nowadays well established. The complex Cp tt 2 Sm(thf) (1, Cp tt = 1,3-(t Bu) 2 Cp) is shown to activate the alkyne C-H bond of phenylacetylene to form the Cp tt 2 Sm(C≡C-Ph)(thf) complex. The subsequent reaction of this Sm(III) complex with CO 2 leads to the CO 2 insertion, yielding a dimeric [Cp tt 2 Sm(O 2 C-C≡C-Ph)] 2 complex (2), in which the carbon dioxide has been inserted in the Sm-C bond. Along with the experimental chemical structure analysis, theoretical calculations have been performed in order to rationalize the formation of 1 and 2

Representation du champ electrique du a un coup de foudre par une serie de termes exponentiels

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : 26165 B, issue : a.1998 n.10 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc