Reverse Current - Advanced Energy AE 3TL 600 Series Installation And Operation Manual

Advanced Energy
The inverter provides four LEDs and a display that are the primary indicators of the
system status.
When the FAULT LED is on:
1. Record the message on the display.
2. Turn the DC disconnect switch to the OFF position.

REVERSE CURRENT

The following provides background information on when reverse current may occur
and how fusing may be helpful.
The inverter is equipped with string fuses at both positive and negative terminals,
DC1 and DC2, to ensure that no dangerous reverse currents can occur in the event of
a short circuit.
Reverse currents are fault currents that only occur in PV systems that consist of
strings connected in parallel. Short circuits in individual modules or in cells of a
module, or a double ground fault can cause the open-circuit voltage of the affected
string to decrease to a degree that the intact strings connected in parallel force a
reverse current through the defective string. This can lead to excessive heating and
thus harm the string. The reverse current could also cause secondary damage.
To avoid damage to PV systems, appropriate precautions should be taken. There are
two possible situations that may create a reverse current:
• String sizing: Fusing is recommended when the PV array is sized such that the
total short-circuit currents from the non-faulted strings (n-1), is below the
maximum backfeed current for the modules.
• Fault event: A properly designed PV system ensures that reverse current during
a fault event does not exceed the harmful limit. Each string should be fused
individually using a series of connected fuses. If a fault occurs in this situation,
the array string with the fault will separate from the intact string, thus avoiding
damage to the string.
9‑2 Troubleshooting and Solar Energy Technical Support 570-1003552-05A