What are the different types of faults in power systems and their relative frequency?

Power system faults include: single line-to-ground (70-80% of faults, one phase contacts ground), line-to-line (15-20%, two phases short together), double line-to-ground (5-10%, two phases to ground), and three-phase (less than 5%, all three phases together). Three-phase faults are most severe but rarest. Single line-to-ground faults are most common, often caused by tree contact or insulation failure. Fault analysis uses symmetrical components to calculate currents.