SMA SC 500HE-20 - Manual (Page 25)

SMA Solar Technology AG 3 Product Description
Operating Manual SCxxxHE-20-BE-BEN111210 25
If the amount of voltage measured exceeds a certain threshold, the grounding of the PV array is
disconnected and the fault current is interrupted. This threshold can be set as a parameter.
If a soft grounding fault occurs, the inverter will stop operating. An electrically qualified person is
required to check and repair the insulation if necessary and reactivate the device by pressing the reset
button.
It is not possible to detect an insulation error on the grounded pole.
3.5.5 Insulation Monitoring Device
Depending on the order, an insulation monitoring device monitors the insulation resistance of the
PV plant in ungrounded networks.
In the "MPP load operation" operating state, the insulation resistance of the entire system will be
detected, from the PV modules to the medium-voltage transformer.
If the inverter is the "Grid monitoring" operating state, only the insulation resistance from the
PV modules to the inverter will be detected.
Figure 10: Insulation monitoring device in Sunny Central
A measuring circuit and a relay with a changeover contact are integrated in the insulation monitoring
device.
The insulation monitoring device is connected between the PV voltage and the protective conductor.
The contacts of the relay are placed on the customer's terminal strip and can be used by the customer
to trigger an signal light or horn. The specifications of the relay are indicated in the circuit diagram.
If the insulation resistance falls below the specified warning threshold ALARM2, the measuring circuit
closes and LED 2 on the insulation measuring device glows. An insulation warning is generated. In
parallel, the insulation monitoring device activates a relay that includes a changeover contact. This
relay is integrated in the inverter.
Object Description
A Display
B LEDs
C Control buttons