SMA SC 500CP-US-10 600V - Manual (Page 32)

3 Product Description SMA America, LLC
32 SCCP-US-BE-US_en-52 Operating Manual
3.6 Insulation and Ground Fault Monitoring
Types of insulation and ground fault monitoring are described in this section. The type of inverter insulation and ground
fault monitoring depends on the order option.
3.6.1 Operating Principles
The insulation and ground fault monitoring ensures plant protection. The type of monitoring depends on whether the
PV array is grounded or not.
In grounded PV arrays:
The ground fault monitoring is implemented by means of a residual-current monitoring device. If a ground fault occurs,
the residual currents will be detected and interrupted.
• Ground fault on the ungrounded terminal
If a ground fault occurs on the ungrounded pole of the PV array, the normally ungrounded pole of the PV array is
grounded non-specifically by the ground fault and a residual current flows to the grounded pole. This residual current
flows through the ground fault monitoring device, e.g. the GFDI, and triggers it.
• Ground fault on the grounded terminal
The GFDI is bypassed when a ground fault occurs on the grounded terminal of the PV array. The ground fault on the
grounded terminal cannot be reliably detected. A ground fault that occurs unnoticed on the grounded terminal poses
a safety risk. An additional ground fault on the ungrounded terminal leads to higher residual currents that cannot be
interrupted by the ground fault monitoring unit.
In ungrounded PV arrays:
An insulation monitoring device constantly determines the insulation resistance using an active measurement procedure.
As soon as the insulation resistance falls below the warning threshold specified in the insulation monitoring device, an
insulation warning will be given on the touch display. This allows preventative measures to be taken before faults occur
such as risk of injury to personnel due to leakage currents or plant failure. If the insulation resistance falls below the set
warning limiting value, the plant can switch off. The parameter IsoErrIgn can be used to activate or deactivate the
disconnection process under fault conditions.
Insulation check of the PV array using an insulation monitoring device
In order to ensure the residual current monitoring function in grounded systems, the PV array insulation must be
checked at regular intervals. It is therefore recommended to use an additional insulation monitoring device in
grounded systems. This will allow the insulation to be checked at regular intervals.