The transformers considered are 3-phase units and the fault types treated are 3-phase line to ground, single-phase line to ground, line to line, and double line to ground. These are the standard fault types and are important because they are most likely to occur on actual systems. The transformer must be designed to withstand the worst of these fault types, or rather each coil must be designed to withstand the worst fault it can experience. In fact the terminals associated with all three phases of the faulted terminal or terminals are open before the fault occurs. After the fault, one or more terminals are grounded or connected, depending on the fault type. The currents are somewhat lower for the system not connected beyond the fault point compared with the currents for system connected beyond the fault point.