Clarke transform based fast assessment of switching overvoltages in an MV distribution network

The paper investigates the use of the Clarke transform in time-domain simulations, namely the evaluation of transient overvoltages in medium voltage (MV) distribution networks. A simplified Clarke equivalent circuit can be set up using readily available symmetrical components data used in steady-state studies, such as line series impedances and the aggregate MV network capacitance. Attention was focused on an existing 20 kV radial distribution system, a large mixed cable/overhead network operated with ungrounded neutral. The worst-case scenario of a single-line-to-ground (1LG) fault occurring at the end of a long overhead line was simulated by means of equivalent lumped-parameter Clarke circuits which were implemented and solved by means of ATP-EMTP. An extensive transient simulation parametric study was carried out using Clarke circuits with different degrees of simplification, and results were compared with those yielded by a complete 3-phase ATP model, evidencing a very good agreement and a drastic reduction of computation times.