However, the current of each string inside the PV array is not
zero. For (n-1) normal strings, their operating point is at (VF,
other). Notice that the operating voltage VF is close to the knee of
their I-V characteristics. Therefore, each string is providing the
current close to I
sc. In other words, I
other is close to (n-1) I
sc. I
other
has no path to go but to backfeed into String 1. As a result, I
back
at String 1 becomes (n-1) I
sc, flowing into the ground-fault point F.
In summary, the worst-case current relationships of the PV array
under a ground-fault can be re-written in the following equations.
• At the positive busbar: I
pv+ = -Iback + (n-1) I
sc = 0
• At the negative busbar: I
pv- = n Isc
• At the ground-fault point F: I
g
= n Isc