I would like to calculate the single phase-ground fault current, but have limited information from the utility. For example, we have information like the 3 phase fault from the transmission pole as well as from each terminal near the faulted transmission pole. From this can we calculate the single phase to ground fault current? If so how?

Line Voltage: 115kV

At the faulted transmission pole: 3IO Mag At Fault (Amps) 3356
3I0 Ang At Fault (Degrees) -53.4

From Terminal 1: 3IO Mag At Terminal 1(Amps) 2926 3I0 Ang At Terminal 1(Degrees) -53.9

From Terminal 2: 3IO Mag At Terminal 2 (Amps) 112 3I0 Ang At Terminal 2 (Degrees) -49.8

  • \$\begingroup\$ 3I0 suggests single-phase to ground fault. You may already have it in your hands. \$\endgroup\$ – relayman357 Oct 1 '19 at 14:05

I believe they gave you phase-ground fault current (which is 3I0) to begin with. But, to answer your question: No, you cannot calculate the phase-ground fault current if all you know is the system voltage and the three-phase fault current. You can guess, and assume the zero sequence Thevenin impedance equals the positive and negative, but that is guessing, not knowing.

  • \$\begingroup\$ Hold on, I thought 3IO means a bolted 3 phase fault? \$\endgroup\$ – stan_tj Oct 2 '19 at 15:05
  • \$\begingroup\$ No, it means 3 times zero sequence current (I0) in all cases i have ever seen. Plus, the fault angles they give you are little low. I would expect 115kV three-phase faults to be angles in the range -60 to -70. Don't have to be, just typical. All you have to do is ask them and they can tell you what they provided. Right? \$\endgroup\$ – relayman357 Oct 2 '19 at 17:30

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