This app models faults at different points on a power system with different transformer connections. The line-to-ground voltages in per unit are shown in blue, and the currents in kA are in green.
Here are some examples to try:
Apply a fault to point 1, and view the voltage sags at different points with different transformer connections.
Use an ungrounded secondary connection on transformer 1, and apply a line-to-ground fault at point 2 (link). Note the currents and voltages. Now, change transformer 2 into a grounding transformer, and note what happens to the currents and voltages (link).
Use a delta – grounded-wye connection for transformer 1, and apply a line-to-ground fault at point 2 (link). Note the currents on the high side. Repeat for a line-to-line fault and a line-to-line-to-ground fault.
Use a delta – grounded-wye connection for transformer 1, and apply a line-to-ground fault at point 2. Change from a solidly grounded neutral to a 1-ohm reactor. Is it still effectively grounded? Look at the voltages on the unfaulted phases.
This model is a steady-state model. The transformers are “ideal” and do not include any magnetizing or saturation effects. The impedances also do not reflect winding configurations. The voltages and some of the transformer and line characteristics can be adjusted. Click the “Toggle more…” links to see extra inputs.
It is possible to input transformer connections that you really shouldn’t use (see the discussion in section 5.4.5) with a floating neutral. The bad effects won’t be apparent because of the idealized transformer models used.
OpenDSS is another tool that’s useful for this type of analysis if you want to do custom analyses.