Study of voltage stresses in arc furnace transformers due to switching operations

摘要

The present thesis is concerned with the possibility of calculating transient voltages at the terminals of an arc furnace transformer due to switching operations of the circuit breaker in front of the arc furnace transformer. Sufficient accurate models of the admittances of the components are needed to calculate the transient voltages. The first part of the thesis is concerned with the modelling of the admittance of the arc furnace transformer. Two methods of modelling have been developed. The second part is a case study of the steel work ''Fundia Norsk Jernverk''. Measurements of transient overvoltages during switching operations of the circuit breaker were carried out. The components of the steel work were modelled to calculate transient overvoltages due to switching operations. The circuit breaker was modelled by simple time controlled switches since the exact time points when the circuit breaker is opened or closed were known from the measurements. The arc furnace transformer was modelled by the method based on data of the windings. It was not possible to calculate the transient voltages due to the common switching operations with the models currently available. In a future work it is recommended to focus directly on the few cases in which the severe transient overvoltages occur. 60 refs., 98 figs., 16 tabs.