45
table 5-4 Recommended specifications of AC circuit breaker
Inverter Model
Recommended rated voltage
Recommended rated current
SG285/320/333/
350HX
800 V 400 A
Multiple Inverters in Parallel Connection
When multiple inverters are connected to the grid in parallel, ensure that the maximum num-
ber of inverters connected in parallel to a single winding of the box-type substation is 15.
Otherwise, please contact SUNGROW for technical scheme.
MV Transformer
The MV transformer used together with the inverter should meet the following requirements:
• The transformer may be a distribution transformer, and it must be designed for the typical
cyclical loads of a PV system (load in the day and no load at night).
• The transformer may be of the liquid-immersed type or dry type, and shield winding is
not necessary.
• The line-to-line voltage on the LV side of the transformer should endure the output volt-
age of inverter. When the transformer is connected to the IT grid, to-ground withstanding
voltage of the LV winding of the transformer, the LV side AC cables, and the LV side sec-
ondary equipment (including the relay protection device, detection & measuring device,
and other related auxiliary devices) should not be lower than 1,500V.
• 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 con-
sistent with the grid voltage.
• At an ambient temperature of 30℃, the transformer can run in 1.1 times of load for long
time.
• A transformer with a rated capacity of 3200kVA and a short-circuit impedance equal to
7% (permissible tolerance: ±10%), or the one with a rated capacity of 4480kVA and a
short-circuit impedance equal to 8% (permissible tolerance: ± 10%) is recommended.
• 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 ac-
count. If more than 15 inverters are connected to the grid, contact SUNGROW.
• The transformer must be protected against overloading and short circuit.
• The transformer is an important part of grid-connected PV generation system. The fault
tolerance capacity of the transformer should be taken into account at all times. The fault
include: system short circuit, grounding fault, voltage drop, etc.
User Manual 5 Electrical Connection
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