Julieta Z. Vernieri

Consequence of an unbalanced supplying condition on a distribution transformer

Most of the time transformers work under balanced supplying conditions. However, after some fault conditions or anomalous switching operations, zero sequence component in excitation may be expectable. Transformers behavior under zero sequence excitation may be very different from usual behavior and might become dangerous. Some simulations are performed with the Alternative Transients Program (ATP), representing a three-legged core type three-phase transformer with a model available in the ATP library. Results show overvoltages and high saturated currents on the unloaded transformer. The proper use of the three-legged core type transformer model, shows evidence of the influence of the characteristics of zero sequence transformer on the development of such overvoltages and high transformer currents. Besides, regardless of load conditions, important homopolar currents are observed flowing to ground from the transformer high voltage neutral. The resultant homopolar fluxes could cause heating and damage in a three-legged core type transformer.

Comparison of TUPÃ risk assessment software with SIRAC software applied to a heritage building in Argentina

This paper analyses virtues and limitations of a new risk assessment software tool called TUPÃ developed by the IEE-USP (Institute of Electrotechnics and Energy — University of São Paulo) in Brazil, compared to the widely distributed Software Risk Assessment Calculator (SIRAC), developed by IEC. Besides, it checks its accordance with the risk evaluation methodology proposed by the IEC 62305-2 ed1.0 standard, through manual calculations applied to the selected example. An analysis of the data entry interface of the TUPÃ software tool, including accessibility, limitations and different alternatives for the parameter values is developed in comparison with the SIRAC tool. Aiming to compare the performance of both software, the document includes a risk assessment calculation against lightning for a building belonging to our University in La Plata, Argentina. In order to limit the extension of the paper, just some of the risk components are considered. Final results are compared, as well as partial results, when available. As simplified tools, the overall advantages and limitations of both software were fairly balanced. For instance, the SIRAC software allows for more than one service, while TUPÃ only considers one at a time. On the other hand, TUPÃ allows for the influence of an adjacent structure, which SIRAC ignores. Meanwhile, an interesting contribution of the TUPÃ software includes the possibility to introduce a manual calculation of the collection area in the case of more complicated structures.

Theoretical and practical comparison of shielding wire's position in 132 kV and 500 kV transmission lines in Argentina

The aim of this paper is to analise theoretical methods of shielding protection techniques in transmission lines and their correspondance with practical use in Argentina. The frequent practice of shielding wire positioning observed in the field is compared with the position obtained by applying classic and modern methods. The paper concludes that the “Electrogeometric Model” (EGM) matches pretty well with practical use in 500 kV power lines, while this method leads to unpractical and uneconomic results in 132 kV lines.