The fault changes the configuration of the PV array and causes
subsequent fault currents. After the fault, String 1 only has two
modules left operating, since the rest of modules (Module 3 ~
Module n) are short circuited by two ground points F and G. As
a result, String 1 is significantly mismatched with other normal
strings. Meanwhile, the operating voltage of the PV array might
be even larger than the open-circuit voltage of faulted String 1.
Therefore, instead of supplying power, String 1 may be forced
to work as a load in the 4th quadrant of its I-V curve (see Fig.
3). Now String 1 has a negative current backfeeding from other
normal strings. This current is often called backfed current
(I
back, or reverse current). I
back will flow into the fault point F and
become a part of I
g
. The other part of I
g
is I
1-, which is the current
coming from other (n-2) modules in String 1. Since Module
3 ~ Module n in String 1 are short-circuited by ground points,
I
1- will be equal to the short-circuit current of each PV module
(I
sc) under standard test conditions. Finally, the backfed current
(I
back) and the current from other modules(I
1-) will merge as the
ground-fault current (I
g
) at fault point F.