36
•
The voltage drop of the system cable should be 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 inverter 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 faults
include: system short circuit, grounding fault, voltage drop, etc.
•
Take ambient temperature, relative humidity, altitude, air quality, and other environmental
conditions into account when selecting and installing the transformer.
•
The overall technical requirements of the box-type LV cabinet are as follows:
–
The breaking capacity of the branch molded case circuit breaker (MCCB) and air cir-
cuit breaker (ACB) of the box-type LV cabinet should be greater than the short circuit
current at the LV side of the transformer. For example, the LV side short-circuit current
of a boost transformer with a rated capacity of 3150kVA and a short-circuit resistance
of 7% can be calculated in the following way: I=3150*1.1/0.8/1.732/0.07=35.73kA.
Thus the MCCB lcu of the LV cabinet branch circuit should be no less than 35.73kA
at 880Vac.
–
The temperature and altitude derating should be taken into account when a circuit
breaker is working, and a LV cabinet temperature rise test report is required.
–
When designing a LV cabinet, must pay attention to the impact of the diffused MCCB
electric arc on the cabinet and other branch circuit MCCBs, thus the interior of the
cabinet needs to be insulated. A third-party test report of the circuit-breaking perform-
ance of the whole machine in an event of a short-circuit on the LV side is also re-
quired. It is recommended to adopt graduated protection to ensure that in an event of
a single short-circuit fault on the LV side of the box, the corresponding branch MCCB
trips normally while the general ACB does not trip.
–
When PLC communication is adopted, the box-type LV power distribution room
needs to be equipped with a fuse switch disconnector or a circuit breaker. The recom-
mended specification of the cable connecting to the COM100A is 4mm
2
- 10mm
2
, the
cable voltage specification is 1.8/3kV, and the cable distance from the COM100A to
the box's LV bus should be no more than 30m.
•
When PID protection is enabled, the AC output common mode voltage of the inverter is
906Vac, and the following requirements should be met:
–
The effective to-ground withstanding voltage of the LV side winding of the transformer,
AC cables, and secondary devices (including protective relay, detection and meas-
urement instruments, and related auxiliary devices) should be no less than 906Vac.
–
If the LV side winding is in Y shape, neutral point grounding is prohibited.
User Manual
Summary of Contents for SG250HX-US
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