GARD – Installation, Operation and Maintenance Manual
A l e n c o n S y s t e m s L L C - P a g e
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4.4.4.3
GFDI Principle
GFDI monitors the ground leak current in each of the GARD’s four channels. The GFDI measures
the input current on the PV positive and negative terminals and compares the values. If the current
difference exceeds a preset magnitude, the GFDI will disconnect the faulty channel both on the
positive and negative terminals. The FAULT flag is recorded into the GARD’s non-volatile memory
and the channel indicator turns from GREEN to RED. Faults can be cleared only by the operator
either by activating the RESET button on the GFDI face plate or by sending a RESET command
via MODBUS RTU. GFDI can be configured to detect a ground leak either for negatively grounded,
positively grounded or floating PV systems.
4.4.4.4
Arc Detection
The arc fault detector has been designed to work in conjunction with Alencon’s ground fault
detector and interrupter. The board has been designed and developed to detect an arc and provide
an interrupting signal to theground fault PCB. If an ARC signal is generated by the detector, the
GARD relays turn-off interrupting the current, thereby disconnecting the string.
Figure 6: AFD PCB
Arc fault detection is based on the arc noise signature analysis. The noise floor spectrum is not a
fixed waveform but a function of the power electronic equipment in-line, the operating conditions
and current transients. Detection schemes must be capable of handling the various peaks without
false tripping.
