A line to ground fault is a fault where one of the three phases of a three-phase system is grounded. This type of fault produces the highest fault current because it provides the shortest path for the fault current to flow.
A three-phase to ground fault is a fault where all three phases of a three-phase system are grounded. This type of fault produces a lower fault current than a line to ground fault because the fault current has to flow through the ground resistance.
A line to line fault is a fault where two of the three phases of a three-phase system are connected together. This type of fault produces a lower fault current than a line to ground fault because the fault current has to flow through the line impedance.
Here is a table that summarizes the fault current for different types of faults:
Fault Type
Fault Current
Line to ground
Highest
Three-phase to ground
Lower
Line to line
Lowest
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I hope this helps! Let me know if you have any other questions.