5 Electrical Connection User Manual
Residual Current Monitoring Device
With an integrated universal current-sensitive residual current monitoring unit included, the
inverter will disconnect immediately from the mains power once a fault current with a value
exceeding the limit is detected.
However if an external residual current device (RCD) (type A is recommended) is mandatory,
the switch must be triggered at the residual current. RCD of other specifications can also be
used according to local standard. The recommended residual current is as follows.
Inverter Recommended Residual Current
SG125CX-P2 1250 mA
SG110CX-P2 1100 mA
SG75CX-P2 750 mA
Multiple Inverters in Parallel Connection
If multiple inverters are connected in parallel to the grid, ensure that the total number of parallel
inverters does not exceed 25.
MV Transformer
The MV transformer used together with the inverter should meet the following requirements:
• A distribution transformer can be used if it is designed for the typical cyclical loads of a PV
system (there is load in the day and no load at night).
• A liquid-immersed type transformer or a dry type transformer can be used, and the shield
winding is not a requisite.
• The line-to-line voltage on the LV side of the transformer should endure the output voltage
of inverter. When the transformer is connected to the IT grid, to-ground withstanding volt
age of the LV winding of the transformer, the LV side AC cables, and the LV side secondary
equipment (including the relay protection device, detection & measuring device, and other
related auxiliary devices) should not be lower than 1,100V.
• The line-to-line voltage on the HV side of the transformer should comply with the local
power grid voltage.
• A transformer with a tap changer on the HV side is recommended in order to keep the
voltage consistent with the grid voltage.
• The voltage drop of system cable is no more than 3%.
• The DC component that the transformer can withstand is 1% of the fundamental current
at rated power.
• For thermal rating, the load curve of the transformer and environment conditions should
be taken into account.
• The apparent power of the inverter should never exceed the power of the transformer. The
maximum AC current of all inverters connected in parallel must be taken into account. It is
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