6 Electrical Connection
User Manual
30
Medium-voltage Transformers
The following requirements must be observed when installing medium-voltage
transformers:
The transformer for the inverter can be a distribution transformer, however it
must be designed for the typical cyclical loads of a PV system(load in the day and
possibly no load at night).
The transformer can be of the liquid-immersed type or dry type. Shield winding is
not necessary.
The line-to-line voltage on the low-voltage side of the transformer must endure
the output voltage of inverter. When connecting to the IT grid, the withstanding
voltage of the low-voltage winding side of the transformer, the AC cables and the
secondary devices (including the relay protection, detection & measuring, and
other related auxiliary devices) to the ground should not be lower than 1000V.
The line-to-line voltage on the high-voltage side of medium-voltage transformer
should comply with the power grid voltage of installation site.
A transformer with a tap changer on the high-voltage side is recommended in
order to remain consistent with the grid voltage.
At an ambient temperature of 25
℃
, transformers should withstand 110% of total
load rating.
Transformer with a short-circuit impedance less than 6% is recommended.
For thermal rating, the load curve of the transformer and the ambient conditions
at the respective installation site must be taken into account.
The inverter apparent power is not permitted to exceed the transformer power.
The maximum nominal AC current of all connected inverters must be taken into
account. If the number of the grid-connected inverters exceed 40, please contact
Sungrow.
The transformer must be protected from overloading and short circuiting.
The transformer is an important part of grid-connected PV generation system.
The fault carrying capacity of the transformer should be taken into account at all
times. The fault types include: system short-circuit, grounding fault, voltage drop,
and etc...
Ambient temperature, relative humidity, altitude, air quality, and the relevant
indexes should be taken into account at all times.
