Line fault analysis of ungrounded distribution systems

This paper proposes a new method for line fault analysis of ungrounded distribution systems. The fault condition of a line fault is integrated into the nodal admittance matrix of the faulted line to be modeled. The zero-impedance branch is merged into adjacent impedance branches to be taken into account, and one of its terminal buses with zero neutral-to-ground voltage is chosen as a slave bus when it is an ideal transformer or a voltage regulator with ungrounded winding connection. The three-phase jointly regulation of a distributed generation source is embedded into nodal admittance model of its internal impedance branch by combining three phases of its internal bus into one equivalent phase. The distribution system is partitioned into a main network and a set of lateral networks to be solved. The main network is formed by the connected paths between the terminal buses of the faulted line, and generation sources, and solved by a Gauss-Seidel method. A lateral network is formed by one of the buses of main network and all buses and branches downstream to the bus, and solved by a backward and forward sweep method. The numerical examples are provided to prove the effectiveness of proposed method.