Zero Sequence Impedance of the Grid Source

Corporate office carries out fault level calculation studies for entire power system for entire power system and provides 3-Ph and 1-Ph fault MVA values for every bus in the grid. Thus using reverse engineering and formula for 3-Ph fault level mentioned above one can write as

Then we can also write as

Knowing the value of X_1s and as we know that X_2s = X_1s above equation reduces to

After putting value of X_1s and 1-phase short circuit MVA at that bus in above equation we can find out X_0s

The method for calculation of 1-Ph fault level can be best understood after going through solved example. For example purpose we will consider same power system as discussed for 3-Ph fault calculations.