There are two main types of faults
symmetric faults: system remains balanced; these faults are relatively rare, but are the easiest to analyze so we’ll consider them first.
unsymmetric faults: system is no longer balanced; very common, but more difficult to analyze
The most common type of fault on a three phase system by far is the single line-to-ground (SLG), followed by the line-to-line faults (LL), double line-to-ground (DLG) faults, and balanced three phase faults