Matti Lehtonen

Dynamic thermal modelling of power transformers

Summary form only given. The aim of This work is to introduce hot-spot and top-oil temperature thermal models for more accurate temperature calculations during transient states, based on data received in a normal heat run test (i.e. the top oil in the tank of transformer and the average winding-to-average oil gradient). Oil viscosity changes and loss variation with temperature are taken into account. The new thermal models will be validated using experimental (fiber optic test) results obtained at varying load current on a 250 MVA-ONAF-cooled unit, a 400 MVA-ONAF-cooled unit and a 605 MVA-OFAF-cooled unit. The results are also compared with the IEEE-loading guide (1995) Annex G method.

Travelling waves based earth fault location in 400 kV transmission network using single end measurement

This paper investigates the problem of fault location based on transient signals obtained at single-end of the transmission line. Current travelling waves are utilized to locate faults on transmission system. In this paper a review of different travelling wave methods in fault location is presented. The wavelet transforms is used for analyzing power system fault transients to determine the fault location and to provide time resolution for the high frequency components of the fault transients. These signals are decomposed into their modal components. The aerial and the ground mode. Wavelet transform is found to be an excellent tool for identifying the travelling wave reflections from the fault. Validation of fault location is carried out by ATP/EMTP simulations for typical 400 kV power system faults.