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mounted/integrated at each PV module within the array. When the inverter
senses the loss of AC voltage by way of opening the PV system disconnect
switch, inverter circuit breaker or under loss of grid events, the transmitter
ceases sending the signal, and the MLPE devices go into rapid shutdown.
This rapid shutdown system has been tested and certified with APS RSD-S-
PLC/RSD-D products to meet NEC 2017/2020 rapid shutdown requirements.
Note: the negative fuses have been removed from this model in accordance
with 690.9(C).
2.7 Anti-Islanding Detection
The SCA25KTL-DO/US-208 3-Phase String Inverters include Unintentional
Islanding detection as required by UL 1741/IEEE 1547. The inverter will
continuously make bi-directional perturbations to the frequency of the output
current by injecting a small amount of reactive power to detect a possible
islanding condition. If the grid is stable, these small perturbations will have
negligible effects on the system voltage frequency. However, in an islanded
condition the changes in reactive power will force the frequency of the system
voltage to deviate significantly, which will trigger the inverter to cease
operation and disconnect from the grid.
2.8 DC Ground Fault Protection
The inverters include residual current detection GFCI as part of the DC ground
fault detection method required by UL 1741. If there is a ground fault in the
PV array, the ground fault detection circuitry will detect leakage current,
trigger an alarm, and the inverter will cease operation. See Chapter 5 for
further information regarding GFCI Static and Dynamic trip thresholds and
operation.
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