Power system analysis requires a model of the power system. With PowerWorld, you can either build a new case (model) from scratch or start from an existing case. Most of the time, including here, we’ll start from an existing case. In ECE 466 using PowerWorld we’ll be assuming a balanced three-phase, 60 Hz ac system. The model of the system can be shown using a oneline diagram. As the name implies, on a oneline the actual three phase conductors are shown using a single line. The initial oneline used here is shown