Análise de zeros atrasados em unidades offshore

Abstract

High asymmetric currents are expected to appear in electrical systems, whenever a short circuit occurs somewhere nearby electric generators buses. In the case of offshore production platforms, the so called asymmetry, along with other specific conditions, may give rise to the so called “delayed current zeros” phenomenon in the short circuit current wave, which in turn, can produce thermal stress in the circuit breaker in charge of clearing the fault. The aim of the present work is to analyze the mentioned phenomenon, as well as its possible aftermath in a typical electrical system of an offshore production platform. Firstly, a 25 MW, 13.8 kV electric generator was modeled, by using finite elements method, since this piece of equipment is the most important factor in the study under consideration. That model was added to the electrical system under study, and then several simulations were performed employing the software ATP (“Alternative Transient Program”), making possible the evaluation of the different elements affecting the formation of “delayed current zeros”, including the contribution of large induction motors.